BP Process Safety Series

Hazards of
Nitrogen and
Catalyst Handling
A collection of booklets
describing hazards and
how to manage them
This booklet is intended as a safety supplement to operator training courses, operating
manuals, and operating procedures. It is provided to help the reader better understand
the ‘why’ of safe operating practices and procedures in our plants. Important engineering
design features are included. However, technical advances and other changes made
after its publication, while generally not affecting principles, could affect some
suggestions made herein. The reader is encouraged to examine such advances and
changes when selecting and implementing practices and procedures at his/her facility.

While the information in this booklet is intended to increase the store-house of knowledge
in safe operations, it is important for the reader to recognize that this material is generic in
nature, that it is not unit specific, and, accordingly, that its contents may not be subject to
literal application. Instead, as noted above, it is supplemental information for use in
already established training programmes; and it should not be treated as a substitute for
otherwise applicable operator training courses, operating manuals or operating
procedures. The advice in this booklet is a matter of opinion only and should not be
construed as a representation or statement of any kind as to the effect of following such
advice and no responsibility for the use of it can be assumed by BP.

This disclaimer shall have effect only to the extent permitted by any applicable law.

Queries and suggestions regarding the technical content of this booklet should be
addressed to Frédéric Gil, BP, Chertsey Road, Sunbury on Thames, TW16 7LN, UK.
E-mail: gilf@bp.com

All rights reserved. No part of this publication may be reproduced, stored in a retrieval
system, or transmitted, in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, without the prior permission of the publisher.

Published by
Institution of Chemical Engineers (IChemE)
Davis Building
165–189 Railway Terrace
Rugby, CV21 3HQ, UK

IChemE is a Registered Charity in England and Wales and a charity registered in Scotland
(SC 039661)
Offices in Rugby (UK), London (UK), Melbourne (Australia) and Kuala Lumpar (Malaysia)

© 2009 BP International Limited

ISBN 978 0 85295 540 6

First edition 2002; Second edition 2003; Third edition March 2004;
Fourth edition September 2004; Fifth edition 2006; Sixth edition 2009

Typeset by Techset Composition Limited, Salisbury, UK

Printed by Henry Ling, Dorchester, UK
 Foreword

Nitrogen is very often used in the chemical or oil industries as a ‘safety’ tool.
However, nitrogen has proved that it can be as deadly as any other gas handled
in our plants. In this booklet you will find various descriptions of serious
incidents involving nitrogen.
This booklet was created to help share knowledge and improve the
understanding on the basic principles for safe use of nitrogen. Due to the
serious nature of the incidents along with the widespread use of nitrogen in our
industry, BP published a comprehensive ‘nitrogen information pack’ to
complement this booklet.
I strongly recommend you take the time to read this book carefully. The
usefulness of this booklet is not limited to operating people; there are many
useful applications for the maintenance, design and construction of facilities.
Please feel free to share your experience with others since this is one of the
most effective means of communicating lessons learned and avoiding safety
incidents in the future.

Frederic Gil, Process Safety and Fire Engineering Advisor

iii
 Contents

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
1 Safe use of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Properties of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Uses and hazards of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Hazards of open manholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.5 Hazards of temporary confined spaces . . . . . . . . . . . . . . . . . . . . . . 10
1.6 Hazards of piping under nitrogen purge . . . . . . . . . . . . . . . . . . . . . . 13
1.7 Hazards of inerting equipment leaving a site . . . . . . . . . . . . . . . . . . 14
1.8 Hazards of confusing nitrogen with air . . . . . . . . . . . . . . . . . . . . . . . 15
1.9 Hazards of trapped pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.10 Hazards of liquid nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.11 Hazards of explosimeter use in nitrogen atmospheres . . . . . . . . . . 24
1.12 Hazards of contaminated nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.13 General advice and safe practices . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2 Safe handling of catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.1 Properties of catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.2 Fire hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3 Health hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.4 Spent catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.5 Nickel carbonyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.6 Crushing hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.7 Other hazards associated with catalyst handling . . . . . . . . . . . . . . . 38
2.8 Catalyst unloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.9 Catalyst labelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.10 Catalyst disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.11 Respiratory and protective equipment requirements . . . . . . . . . . . . 43
2.12 Catalyst specialist contractors for inert gas/nitrogen reactors . . . . . 48

3 Some points to remember . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

4 Test yourself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

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1
Safe use of nitrogen

1.1 Introduction
The atmosphere we live in, the air we breathe every day consists of 79%
nitrogen, 21% oxygen and traces of other gases. But only oxygen is vital and
essential to human beings for respiration/survival. Without sufficient oxygen,
i.e. if oxygen level falls below 16%, we will die of asphyxiation.
Nitrogen gas behaves somewhat like a diluent or buffer gas in the atmosphere.
Nitrogen in itself is inert, stable, non-reactive and non-toxic, but too much nitrogen
reduces the oxygen content in the atmosphere, creating an invisible condition
that can kill. If the earth was without nitrogen but filled with just oxygen, then
fires would burn out of control and steel structures would quickly rust away!
Therefore, nitrogen is an effective diluent or buffer gas that we can’t live without,
yet too much of it would deprive us of vital oxygen, which can lead to asphyxiation
and even death within seconds.
Nitrogen is widely used for various purposes in refineries and petrochemical
plants, for example, to provide an inert atmosphere, to purge a vessel of
hydrocarbons, for blanketing and padding storage tanks in order to prevent
explosions and fires.
Nitrogen is odourless and colourless. It can kill without warning. Therefore, it is
known as the invisible killer that has caused many fatalities in the refineries
worldwide.
It is one of the most dangerous gases found in refineries and chemical plants.

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1.2 Properties of nitrogen

Nitrogen is not toxic since about 79% of the air we breathe is this gas. The
mechanism of nitrogen gassing is different to that of hydrogen sulphide (H2S).
Whilst H2S has a direct toxic effect which is well documented, nitrogen rich
atmospheres will asphyxiate due to a reduction in the oxygen content of the
inhaled gases. The typical physiological effects of varying degrees of oxygen
deficiency are also well documented:

Oxygen (%vol) Effects & Symptoms

23.5 Maximum ‘safe level’ (23% is often the high level alarm of
most O2 detectors)
21 Typical O2 concentration in air
19.5 Minimum ‘safe level’ (19% is often the low level alarm of
most O2 detectors)
15–19 First sign of hypoxia. Decreased ability to work strenuously.
May induce early symptoms in persons with coronary,
pulmonary or circulatory problems
12–14 Respiration increases with exertion, pulse up, impaired
muscular coordination, perception and judgment
10–12 Respiration further increases in rate and depth, poor
judgment, blue lips
8–10 Mental failure, fainting, unconsciousness, ashen face,
blueness of lips, nausea, vomiting, inability to move freely
6–8 6 minutes—50% probability of death
8 minutes—100% probability of death
4–6 Coma in 40 seconds, convulsions, respiration ceases, death

When a person enters an oxygen-deprived atmosphere, the oxygen level in the

arterial blood drops to a low level within 5 to 7 seconds. Loss of consciousness
follows in 10–12 seconds and if the person does not receive any oxygen within
2–4 minutes, heart failure and death follow.
In its case study of fatal incidents (see Bibliography at the end of this book), the
US Chemical Safety Board details how nitrogen acts: ‘Equipment containing
concentrated nitrogen purge gas (oxygen content less than about 10 percent)
quickly overcomes the victim without warning (see table above). After only one
or two breaths the oxygen concentration in the blood drops dangerously low,
and the victim is likely to lose consciousness in less than 60 seconds. Death
occurs within a few minutes.
Both the rescuer’s attempt to help his coworker, and the possible intentional
reactor entry by the first victim, suggest that some workers may believe that
they can hold their breath long enough to enter an oxygen-deficient atmosphere
and return to safety before being overcome. Workers might mistakenly conclude
that they can hold their breath while inside the reactor, similar to their ability to
hold their breath when they swim underwater.

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Swimmers are acutely aware that inhaling water causes sudden, uncontrollable
coughing. This is a powerful stimulus that helps a swimmer resist the body’s
breathing reflex even after being submerged for a long time. But nitrogen, which
is odourless, tasteless, and colourless, provides no stimulus to voluntarily resist
the breathing reflex. In a highly emotional and physically demanding
emergency, it is extremely unlikely that a person would hold their breath.
Furthermore, workers may be unaware of another dangerous complication—
inhaling nitrogen or other inert gas suppresses the brain’s breathing reflex
response. The breathing reflex is controlled primarily by the amount of carbon
dioxide in the blood rather than the shortage of oxygen.
Normally, the ability to voluntarily hold one’s breath is eventually overwhelmed
by the brain’s respiratory control centre, which is triggered by the increased
carbon dioxide concentration in the blood, combined with a drop in the blood’s
pH (acidity). If high-purity nitrogen or other inert gas is inhaled, the body may
simply stop breathing, as carbon dioxide accumulation in the blood is
insufficient to stimulate the breathing reflex.’

Moving affected and unconscious persons from a N2 atmosphere

into fresh air is not enough to promote recovery, the patient has to
be physically resuscitated in order to restore the oxygen supply
to the brain.

NOTE: There is also a risk of suffocation with all compressed gases (for
example—argon, CO2, helium, etc.), which either replaces the oxygen or con-
sumes it. This risk also exists in situations where there is a large consumption of
oxygen (fires, and rusting in ballast tanks of a ship or water tanks, etc.).

INCIDENT Four fatalities occurred at a construction site during the

welding of a stainless steel 54-inch (1.4m) diameter pipe. A grinder entered
the pipe (a confined space) without authority for some unknown reason and
was overcome by accumulated argon (welding shielding gas). Three additional
fatalities occurred when others entered the pipe to rescue the first casualty.

Nitrogen (N2) is a very common and extremely dangerous gas that you
may be exposed to at a refinery or chemical plant. You must always be
on your guard.

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1.3 Uses and hazards of nitrogen

Most useful or most dangerous gas???

What is nitrogen used for?

Nitrogen has numerous safety applications in plants:
As a gas:
• for inerting equipment to prevent flammable atmospheres;
• for preparing equipment for maintenance by purging out hydrocarbons;
• for removal of air / oxygen in equipment before start-up;
• for blanketing tanks to prevent the ingress of air;
• for specific welding operations;
• for ‘mothballing’ equipment to avoid the rusting process;
• for use as fire-fighting agent as it removes air.
Some sites may also have a practice of using nitrogen to back-up the
instrument air system in case of instrument air supply failure—this is discussed
in section 1.8.
As a liquid:
• for cooling purposes in the laboratory, freezing a pipeline, etc.
• for storage and transportation of nitrogen in large quantities.

Removal of hydrocarbon vapour

prevents possibility of a flamma-
ble atmosphere in preparation
for maintenance.

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What are the hazards of nitrogen?

Nitrogen is not toxic since about 79% of the air we breathe contains this gas.
However, it is not harmless and it has no smell.
As a gas:
• It can cause suffocation by replacing the oxygen in a confined area.
• Its presence will give false readings when using explosimeters or flammable
gas detectors.
• Like other compressed gases, there are the risks related to its pressurised
containment when it is stored in high pressure cylinders.
When using nitrogen for inerting purposes, it is important to be aware that it
does not ‘wet’ pyrophoric iron sulphide deposits like steam or water do. For
more information on pyrophoric materials, refer to BP Process Safety Booklet
Safe Ups and Downs for Process Units.
As a liquid:

• The same as the gas, when it evaporates.

• By creating an intense coldness (⫺196°C / ⫺312°F) that can cause frostbite,
crack steel equipment and explode tyres.
• It boils at a colder temperature than oxygen thereby condensing the oxygen
in the air (which can then form explosive mixtures with other vapours or
cause a violent reaction in contact with organic substances).

What is an asphyxiant?
A chemical (gas or vapour) that can cause death or unconsciousness by
suffocation. Simple aphyxiants such as nitrogen, displace oxygen in air.
They become especially dangerous in confined or enclosed spaces.
Chemical asphyxiants, such as carbon monoxide and hydrogen sulphide,
interfere with the body’s ability to absorb or transport oxygen to the tissues.

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1.4 Hazards of open manholes

The invisible killer: a danger commonly found in refineries

Previous incidents with open vessels under nitrogen include:

• sampling a nitrogen atmosphere for hydrocarbons in the reactor without

wearing breathing apparatus;
• attempting to rescue inert entry technicians without suitable breathing
apparatus and rescue plan;
• recovering entangled rope or equipment from inside a reactor;
• helping inert entry technicians to move ladder from the outside;
• performing work activities outside reactor e.g. cleaning reactor interior from
outside adjacent to open manhole;
• installing blinds nearby an open manhole during catalyst unloading, whilst is
adequately protected from nitrogen and catalyst dust;
• opening the top manhole of a vessel under nitrogen purge with unprotected
workers located in an oxygen deficient atmosphere.

Oxygen Deficient Atmosphere: An atmosphere with an oxygen content

below 19.5% by volume. (OSHA Definition)

CAN YOU SEE OR SMELL THE INVISIBLE KILLER?!!

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No! And how are you sure it is safe to

enter? What are your precautionary
measures before entry? Do you carry
a portable gas detector that beeps if
oxygen falls below 19%? Do you have
a standby attendant?
Do you know that you can be over-
come by N2 by just looking into the
manhole without wearing breathing
apparatus?

ACCIDENT While in the process of taking a sample of the atmosphere

from a reactor under nitrogen purge, a process operator became asphyxiated
and fell to his death through this open manhole. He was found on the second
tray approximately 20 ft (6m) below the manhole.
It should also be noted that instruction manuals/handbooks on gas-testing,
confined space entry, etc . . . must raise awareness on the risk to the operator
of doing a gas test or taking a sample from the outside of a vessel. Pictures
below are typical illustrations of poor practices.

Initial gas testing should be performed from outside the space by inserting a
probe or piece of flexible tubing. However, ensure that the contractor or
employee performing gas testing is adequately protected with breathing
apparatus and accompanied by a second person.

ACCIDENT A subcontractor
employee (not wearing breathing
apparatus or safety harness) entered
the barricaded area atop a reactor to
assist a confined space entry
attendant in lifting the internal access
ladder. He was overcome by an
oxygen deficient atmosphere around
the manhole and fell into the reactor.
Without the vital oxygen to sustain
respiration, it is very unlikely that
anyone could exit the reactor alive!
continued…

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Nitrogen can create an oxygen

deficient atmosphere outside
the vessel/piping that is being
purged with this medium

You are asphyxiated with only

your head inside an oxygen
deficient atmosphere – not
your whole body.

INCIDENT Two workers perished in an incident while working to

re-attach piping near the open manway of a hydrocracker reactor that was under
nitrogen purge to prevent moisture from reaching the catalyst.
It appears that one of the two contractors likely became disoriented, passed
out, and fell into the vessel after he breathed nitrogen near the manway
opening on top of the vessel. Upon seeing his colleague fall into the vessel,
the second contractor employee then entered it, probably in an attempt to save
his coworker. Both men died quickly from nitrogen asphyxiation.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

KEEP TECHNICIANS AWAY FROM AREAS OUTSIDE MANHOLES

THAT COULD BE DEFICIENT IN O2 (UNLESS AUTHORISED THROUGH
A CONFINED SPACE ENTRY PERMIT).

ACCIDENT A fixed bed reactor was filled with catalyst under a nitrogen
blanket. At the start of a new shift the operator went to inspect the reactor top
alone. When he failed to return, a colleague went to look for him and
eventually saw him lying on top of the catalyst in one of the reactors. He put
his head inside an oxygen deficient atmosphere, knowing all the hazards, but
for a moment ignored them.

Good practice
A device was developed for placing across manholes and other openings to
confined spaces which may contain an oxygen deficient atmosphere. The
device can be locked into place to prevent unauthorized removal and physically
prevents access. Removal would only be allowed as a condition of a confined-
space entry permit.

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1.5 Hazards of temporary confined spaces

Outside areas can be

deficient in oxygen which
are exacerbated by any
form of closure or tent.

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ACCIDENT A process column had been taken out of service for

maintenance for several weeks. The column had been cleaned, several
manholes were open, and a nitrogen purge was on the column. Two
experienced workers were examining the flange surface of a remote manhole
for stress cracks. They sprayed dye on the flanges and used a black light to
identify the suspect areas. The weather conditions were sunny, windy and mild.
A tarpaulin was draped over the flange but it is unclear whether this was to
block the wind while they were using dye penetrant or to facilitate using the
black light, or both. The confined space created by the tarpaulin was soon
filled with nitrogen which asphyxiated both men. One man died as a result of
the exposure and the other survived because he collapsed face down on the
expanded metal grating, which allowed sufficient oxygen to sustain his life.
The immediate cause of the accident was the inadvertent creation of a
confined space environment around an open manhole that was being purged
with nitrogen. The basic causes were the failure to recognise a confined
space and the risk of asphyxiation from nitrogen coming out of the manhole,
and inadequate control of work on a column that was being nitrogen purged.

NOTE: The nitrogen

injection points were a
considerable distance
from the location where
the nitrogen gas was
being emitted through
the opening.

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ACCIDENT A technician was overcome by an oxygen deficient atmo-

sphere while connecting up a motor. The catalyst had been removed and the
reactor was floating on nitrogen. The pump seal on the reactor was leaking,
allowing nitrogen to enter the reactor skirt. The supervisor assumed that the
reactor seal was tight and there was no requirement for either:

• air-line breathing apparatus;

• air movers;
• continuous oxygen monitoring with alarm.
Skirts surrounding the bottom of vessels must be considered a Permit-
Required Confined Space.

Sketch of situation when technician was semi-asphyxiated

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1.6 Hazards of piping under nitrogen purge

Beware of changing fittings on piping being purged with nitrogen:

• changing a valve;
• replacing a section of pipe;
• turning a spectacle plate;
• installing or removing full face blinds.

ACCIDENT A technician collapsed during reinstallation of valve and

section of pipe shown by dotted line.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Good practice
• Breathing apparatus must be worn where there is risk of exposure to a level
of nitrogen that could cause oxygen deficiency in the local surrounding
atmosphere.
• All persons, and in particular supervisors, must be made aware of the risks
associated with nitrogen to ensure that suitable precautionary measures are
taken when vessels and pipelines are being purged with nitrogen.

1.7 Hazards of inerting equipment leaving a site

ACCIDENT Railcars were used to move Decene (C10 hydrocarbon) to
and from a chemical site. A railcar was identified as having a problem with a
leak on a vent valve on the top of the railcar and was subsequently notified for
repair. A few days later, after being moved to a repair workshop, a worker was
found unconscious inside the railcar and was pronounced dead at the scene.
A few months earlier, it had been decided to inert the railcars to solve reliability
problems. The Management of Change process only covered the engineering
requirements, not the safety aspects, and the railcar sent for repair had no
sticker or documentation attached that mentioned the hazard of an inert atmo-
sphere.

Valve which
was due for
repairs.

Good practice
• Provide a visible and overt warning of the hazardous atmosphere present in
equipment leaving facilities.
• Rigorous discipline on documenting communications should be practised.
• Fully comprehend safety practices of contractors and subcontractors and the
consequences through the Management of Change (MOC) process when
procedures/practices change.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

• Do not assume that personnel outside your facility understand safety

practices necessary to safely manage hazards with which you may be
intimately familiar.
• Implementation plans and training materials need to be provided when new
procedures or practices are installed.

1.8 Hazards of confusing nitrogen with air

Previous incidents of confusing nitrogen with air include:

• no unique bayonet fittings for breathing air supply;

• air-line system was not checked or verified prior to connection;
• air-line system isolated and used as a nitrogen header, but the operator was
not aware of the change after returning from his rest days.

ACCIDENT An incident occurred on a Monday when the foreman

instructed the technician to connect up the breathing air supply to the air
receivers of the plant’s instrument air system, as he had done the previous
Friday. Instead the technician connected the hoses to a regeneration air
manifold which had been blinded / blanked from the air system and was being
used as a nitrogen header. No reason for this change was established other
than it may have been ‘more convenient’. The ‘Management of Change’
procedure had not been initiated prior to making this temporary modification.

Good practice
• Never use nitrogen instead of compressed air (for instance with pneumatic
tools).
• Use different couplings. Although special couplings for nitrogen connections
are a good practice, they should not be relied upon during turnarounds. The
valve should be kept chain-locked as contractors have all kind of couplings
to defeat the system. Locking of the isolation valves should be mandatory

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on utility stations for nitrogen to prevent misuse by contractors and control

usage through the Lockout-Tagout Procedure.
• Never store bottles of compressed nitrogen in confined unventilated areas
(a 50-litre [13 US gallons] bottle at 200 bars can cause the oxygen level in an
average 9 sq. metre [97 ft2] room to drop to 12%).
• Never use nitrogen to back-up an air system without a formal risk
assessment.

Do not confuse N2 with air!

Good utility station:

• colour coding;
• signage and labels;
• specific fool-proof couplings;
• check valves;
• all piping and accessories welded on
nitrogen to prevent dismantling;
• non-threaded vents/drains on nitrogen to
prevent connection of different couplings;
• nitrogen valve locked close when not in
use and key delivery controlled.

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Always use dedicated breathing air supply

A mobile, self-contained, high pressure cylinder storage system undoubtedly
provides the highest integrity, freedom of operation and safety when using
air-line breathing apparatus. Most sites prefer to either use bottled air,
supplied from a trolley set (wheeled trolley with air bottles on it) or from a
bank of dedicated air bottles located on the plant. There is a requirement to
ensure that the quality of air in supply bottles is correct, whether they are
refinery filled or otherwise by a respectable external company.

ACCIDENT Following
a total power blackout at
the process site, an
instrument technician was
found unconscious in an
analyser house. He was
rushed to a local hospital
but pronounced dead on
arrival. During the power
failure, instrument air was
replaced with nitrogen. It
was suspected that a
nitrogen leak was the
cause of the fatality.

Analyser house with

atmosphere warning
signs.

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1.9 Hazards of trapped pressure

ACCIDENT A contract employee was fatally injured while removing
catalyst from a Hydrodesulphurisation (HDS) Reactor.
After shutdown and a nitrogen purge, the reactor inlets and outlets were
blinded, and a nitrogen hookup provided to supply a continuous purge for
use by the catalyst unloading contractor. The atmosphere at the reactor top
opening was checked for oxygen, flammable material and hydrogen sulphide
and found to be satisfactory. Wearing respiratory equipment suitable for inert
gas entry work, the worker went inside the top of the reactor to remove the
internal structure.
There was a crusted layer on top of the catalyst bed below the distribution
tray in the top of the reactor. What was unknown to everyone was the build-up
of nitrogen pressure under the crusted layer. When the worker inside the
reactor chipped the crust, the sudden release of pressure killed him. His
equipment and part of the reactor contents were expelled upwards through a
22 feet (0.6 m) diameter manhole.

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Precautions
Nitrogen injection pressure should be lowered to less than 0.7 psig (50 mbar), or
strict formal checking procedures enforced. An example of a pressure regulating
system with simple pressure relief device is given below:

NOTE: Remember that nitrogen (or any other gas) should never be used for
strength testing of pressure vessels except in very special circumstances
following a risk assessment and approval process.

ACCIDENT A mechanical plug installed inside a pipe to isolate hot work

from process fluids released suddenly striking and killing the welder. The
work in this incident involved a welding operation on a 28-inch (71 cm) water
line that had residual water and hydrocarbons in it. A non-pressure
containing mechanical plug (also known as ‘plumber’s plug’) had been
installed about 12-inch (30 cm) inside the pipe as a barrier against process
fluids. The pipe area behind the plug was blinded at both ends, and was
being purged with plant nitrogen to carry away potential hydrocarbon
vapours. Nitrogen at 30 psig (2.07 barg) was introduced by a 3⁄4-inch (2 cm)
hose through a connection at the centre of the plug, and was being vented by
a separate 3⁄4-inch (2 cm) hose coming from the top of the pipe. The vent line
ran out of the module through a door, to prevent the build-up of nitrogen in the
atmosphere inside the module. The nitrogen absorbed residual water in the
pipe and the water condensed and froze inside the nitrogen vent line when
exposed to the cold temperatures outside, approximately 0°F (⫺18°C). The
frozen water blocked the nitrogen vent line, causing pressure to build behind
the 63 lb (29 kg) plug and blew it off. continued…

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Module layout

A Job Safety Analysis (JSA) recognised the potential hazard of the purge line
freezing. To mitigate the risk, the line was checked periodically for flow by
placing a hand at the end of the vent hose, which proved to be inadequate.
There was no pressure gauge, regulator, or secondary relief on the purge to
allow pressure to be checked or to prevent pressure build-up.

View of the 28-inch (71-cm) Pipe View of Mechanical Plug

When purging systems using such plugs, procedures should address the size
of inlet and vent hoses, placement of vent hoses, use of regulators to control
flow, use of secondary pressure relief to prevent overpressure, positioning of
workers away from the plug, and work crew training and hazard awareness.

Where possible, the best option is to design tie-ins so that isolation plugs
between hot work and hydrocarbons are not needed. Alternatively, evaluate
the use of better plug types, including double-sealing hydraulic plugs (Car-Ber
type) and pressure rated plugs (Thaxton) that have the potential to be used
with or without purging.

For more details on the hazards of trapped pressure, refer to the BP Process
Safety Booklet Hazards of Trapped Pressure and Vacuum.

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1.10 Hazards of liquid nitrogen

ACCIDENT A 30 ft. (9 m) section of a 2 inch (0.05 m) carbon
steel nitrogen transfer line at a refinery failed as a result of brief low
temperature embrittlement arising from the malfunction of a
solenoid valve. The failure was potentially serious and one witness
described the noise as an explosion and saw the line lift 6 ft (1.8 m)
into the air before disintegrating. At the time of the fracture part of
the pipe was covered by a layer of frost about 1/8-inch (0.003 m)
thick. Hazardous bulk nitrogen systems at four different sites were
modified by fitting a low temperature sensor connected to magnetic
or air-operated shut-off valves.

ACCIDENT When a High Pressure Lube Oil Hydrogenation Unit

(HPH) was being decommissioned and cooled down for a statutory
overhaul, liquid nitrogen from the associated nitrogen vaporizer was
inadvertently discharged into three reactors via temporarily installed
hoses. The initial cooling rates for the reactor were found to be too
low so the decision was taken to abandon the normal decom-
missioning procedure and instead supply nitrogen using hoses from
a nitrogen vaporizer. This new procedure represented a major
departure from the existing one and no hazard analysis was
undertaken as part of a Management of Change procedure prior to
making the change. The injection of liquid nitrogen caused damage
to the vessel. Magnetic crack detection and dye penetrant methods
carried out detected several cracks in the weld metals. Three
thermowell nozzles on the top of the reactor were severely damaged
through excessive shrinkage caused by thermal shock. The cracks,
which were as long as 40 mm (1.6 inch), were grinded out and made
good by rewelding. Repair costs were significant.

Safe handling of liquid nitrogen in laboratories

Liquid nitrogen is frequently used in chemical research laboratories for the
purpose of cooling. Liquid nitrogen is a valuable coolant because of its low

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boiling point of –196ºC / –321ºF, inexpensive price, and low toxicity. In

comparison to liquid air, which was previously used as a popular coolant, liquid
nitrogen has the advantage that it does not support combustion.

Cold traps cooled with liquid nitrogen

A common use of liquid nitrogen is as a coolant for cold traps incorporated in
vacuum lines. A cold trap is used in vacuum lines to collect organic/toxic vapour
specimens by cooling and condensation. In addition, a cold trap helps the
system to achieve a better vacuum with a smaller vacuum pump.
Care must be employed when using liquid nitrogen as a cold trap coolant.
Systems including liquid nitrogen traps must never be opened to the
atmosphere until the trap is removed from the coolant. This is because oxygen
has a higher boiling point (–183ºC / –283ºF) than nitrogen (–196ºC / –321ºF)
and will condense out of the atmosphere and collect in a liquid-nitrogen cooled
vessel open to the air.

ACCIDENT This phenomenon was confirmed during an experiment

reported by a research engineer at a laboratory. He reported that after leaving
an open cold vent, with the liquid nitrogen still in the dewar, in the hood, for
about five minutes, it was later found full of liquid.
He suspected that the incident was caused by a very small leak in the vacuum
system such that air got into the line downstream of the glassware apparatus.
The oxygen in the air then condensed inside the cold trap, together with other
chemical vapours. This would have caused a highly flammable (explosive)
mixture. Upon ignition this would cause serious injuries to laboratory personnel.

ACCIDENT A similar incident was reported in the food industry by the

Loss Prevention Bulletin (no. 191): Finely ground baked pork rinds were
cooled with liquid nitrogen to make them brittle, before being processed
through a grinder. On the day of the incident, pork rinks were left in nitrogen
over a meal break. When the grinder was started, an explosion occurred
because the rinds became oxygen-enriched to the point where the energy
generated by the rotating blades of the grinder was sufficient to cause the
grease in the rinds to detonate.

Liquid oxygen may also be mistaken for water by laboratory personnel, and
direct contact with unprotected skin will cause serious cold burns. If the liquid
oxygen is disposed of as water, it may react violently with some organic
materials and explode.

Recommendations
• Prepare an inspection and maintenance program to check for any leakage
in the vacuum system and other associated systems.
• If you suspect liquid oxygen has condensed in a cold trap, then shield the
trap (with an explosion shield, closed hood window, etc.), post a sign

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indicating the danger, and allow the trap (vented to the atmosphere) to slowly
warm to room temperature.
Other recommendations regarding use of liquid nitrogen:
• Cryogenic liquids such as liquid nitrogen can cause very severe burns upon eye
or skin contact. Splashes are common when handling liquid nitrogen, so safety
goggles must therefore be worn at all times when working with this material.
• In addition, protective gloves that can easily be removed in the event of a
spill should be worn when handling liquid nitrogen (alternatively, potholders
may sometimes be more convenient for handling small containers of
cryogenic materials).
• Particular care must be taken to prevent uninsulated vessels containing
liquid nitrogen from coming into contact with unprotected parts of the body,
since extremely cold materials can become firmly bonded to the skin such
that separation is not possible without serious injury.
• Contact of the skin with liquid nitrogen can cause severe cryogenic burns.
The tissue damage that results is similar to that caused by frostbite or
thermal burns. Since small amounts of liquid nitrogen quickly evaporate
from the surface of exposed skin, some inexperienced employees may
mistakenly underestimate the risk of cryogenic burns when working with this
material. In fact, it is not unusual for spills and splashes of liquid nitrogen to
become trapped under rings, bracelets, watchbands, or inside gloves, and
this can result in serious and painful burns.

Containers for liquid nitrogen

• The properties of some materials (including metals) change drastically when
exposed to cryogenic liquids such as liquid nitrogen. Containers for such
liquids must therefore be selected carefully to ensure that they can withstand
the temperatures and pressures they may be exposed to. Liquid nitrogen is
commonly stored in Dewar flasks which should be taped to minimize the
hazard in the event of an implosion.
• A Dewar flask is a container after which the common thermos bottle is patterned.
It consists of two flasks, one placed inside the other, with a vacuum in between.
The vacuum prevents the conduction of heat from one flask to the other. For
greater efficiency the flasks are silvered to reflect heat. The substance to be
kept hot or cold, such as liquid nitrogen, is contained in the inner flask.

Liquid nitrogen and condensed argon

Argon, a gas commonly employed as an ‘inert atmosphere’ for chemical
reactions, distillations, and other laboratory operations, also has a boiling point
(–186ºC / –303ºF) which is higher than that of nitrogen. Consequently, liquid
argon will condense in a reaction vessel under an argon atmosphere which is
cooled with liquid nitrogen. This creates an extremely hazardous situation, since
if the vessel is then removed from the coolant, the liquid argon will instantly
vaporize, expanding in volume by a factor of 847! Even if the vessel is vented (to
an inert gas line, for example), an explosion is very likely due to the rapid increase
in pressure in the vessel. Consequently, never cool an apparatus that is under an
argon atmosphere using liquid nitrogen.

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1.11 Hazards of explosimeter use

in nitrogen atmospheres
Explosimeters (flammable gas detectors) do not tell the truth in nitrogen
atmospheres:

• Explosimeters or gas detectors give false readings in an oxygen deficient

atmosphere.
• The types of portable flammable gas detectors in use in refineries usually
operate by the catalytic combustion of a flammable gas on a heated filament
(usually platinum), to give a reading of the %LEL*/LFL*. Accordingly, there
must be approximately 21% oxygen in the sample to give an accurate reading.
If the atmosphere being tested is deficient in oxygen, for example when
purging with nitrogen, it is not possible to use a standard type of flammable
gas detector in its normal mode of operation to detect hydrocarbon vapours.
• A standard catalytic gas detector, therefore, can only be used to give a
reading of flammable gas in an inert atmosphere by using special
techniques involving air dilution attachments. The interpretation of results is
difficult, and hence is not recommended for day-to-day plant use.
• A review of operating and commissioning procedures highlighted a common
practice of purging equipment and plant free of hydrocarbon vapours with
nitrogen using hydrocarbon / air flammable gas detectors at sample points to
determine the presence of hydrocarbon gas. The use of a standard
flammable gas detector is not suitable for this purpose.
• Portable instruments are currently available that can be used in hazardous
areas and which can give true indication of the level of flammable gas in a
nitrogen atmosphere. These include infrared sensors and ‘Tankscope’ gas
indicators used on ships.

Always check the oxygen level first before carrying out a flammable
gas test using an explosimeter in preparation for hot work or
confined space entry.

* LEL ⫽Lower Explosive Level

* LFL ⫽Lower Flammable Level

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Controlled combustion takes place here:

Oxygen ⫹ Flammable gases ⇒ CO2 ⫹ H2O ⫹ Heat.
Working Principle of an Catalytic Explosimeter

1.12 Hazards of contaminated nitrogen

Contamination of nitrogen presents two hazards:

• toxics or flammables may be carried to another part of the plant;

• nitrogen that is used for inerting equipment to prevent flammable atmospheres
may not be inert anymore if enough air has entered the nitrogen supply.

ACCIDENT Flammable gas was detected at various locations on the

nitrogen network of a refinery. A chromatograph in a laboratory caught fire.
All N2 flexible hoses connected to process equipment were immediately
removed and the N2 network purged. Within an hour all the LPG within the
nitrogen system had been eliminated.
Investigation
The contaminant was butadiene that had entered the nitrogen stream at a pig
receiver station during a pigging operation. The isolation and check/non-return
valves on the fixed 6 barg (87 psig) N2 supply line to the pig receiver were
passing/leaking. The butadiene was at a higher pressure (10 barg/145 psig)
which allowed it to back flow through the permanent N2 connection since it
was not positively isolated.
continued…

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Lessons learned
• Permanently connected utility systems must be isolated (with a full face
blind/blank or disconnected) when not in use.
• A single check/non-return valve and/or isolation valve does not provide a
positive isolation.
• Pig traps and their associated operating procedure must undergo a
HAZOP.

Nitrogen connections to process equipment containing liquid or gaseous

hydrocarbon streams which are not required for safety or process reasons,
must be disconnected or blinded when not in use to prevent potential
contamination of the nitrogen system.
Utility stations on a nitrogen distribution system must also have a non-return
device (for example, check valve), must be clearly identified and use special
connectors and hoses which are not common to any other system. Other good
practices on these utility stations to avoid unauthorised use are to:
• lock the valves;
• weld the nitrogen specific connectors.

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Permanent nitrogen connections required for safety or process reasons must

include a non-return device (for example, check valve) to prevent potential
contamination of the nitrogen system.

ACCIDENT A pressure vessel (not designed, constructed or modified to

internationally accepted standards for pressure vessels) was one of two
(vessels 6 and 7) that received molten polyethylene wax for processing (see
figure below). It contained steam piping in order to maintain the temperature
of the molten wax at 149°C (300°F). Nitrogen was used to pressurise / force
the liquid wax to the feed pump for the wax refining process.
The flow from the N2 generator was sometimes insufficient to maintain the
required throughput of wax. As a result, a temporary hose was connected up
to bypass the N2 generator with air to make up the reduced pressure. Later,
this temporary modification was replaced by permanent piping. Operators
pressurised the vessel with N2 containing 18% O2, more than enough to
sustain combustion.
Sparks generated from a ruptured patch plate probably ignited the wax and
hydrocarbon vapours (the wax had a flashpoint of 110°C / 230°F).
An internal deflagration blew the vessel head into multiple fragments. The
blast ignited large fires that burned for several hours, and two firefighters were
injured during the emergency response.

Assurance must be provided that supplied nitrogen, as it enters the site, is not
contaminated with oxygen, whether via pipeline or vaporisation into the plant
distribution system. This assurance can be provided in a variety of ways, (e.g.,
process analyser, regular laboratory testing, supplier QA/QC procedures, etc.).
Consideration should be given to additional monitoring at individual units or at
other key locations in a nitrogen distribution system to ensure non-contamination.

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1.13 General advice and safe practices

Communication / Work Permit / Lockout-Tagout procedure
• Enhance the communication and exchange of information between shifts by
mandatory formal review of isolation certificates and work permits.
• Ensure all operators are competent in the requirements of the Lockout-
Tagout Procedure and Work Permit Regulations through training
programs.
• Identical work carried out on different days (even if it is a matter of one day)
must be re-assessed and re-confirmed with newly issued or endorsed work
instructions / work permit to cover changes or modifications.
• Ensure training programs for employees and safety orientation for
contractors clearly communicate the hazards and symptoms of exposure to
nitrogen and other asphyxiants.
• Ensure that a specific work procedure is provided for inert gas entry. (Refer
to pages 48 and 49 for details).
• Suitable signage should be placed at the entrance to open vessels having an
oxygen deficient / toxic atmosphere to warn personnel of asphyxia hazards.
The manhole area should be barricaded and cordoned off.

Cold Work Pemit Confined Space Entry Permit

• All personnel required to wear breathing apparatus must be properly trained

and ‘refresher courses’ incorporated into the annual training program.

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• Evaluate the use of portable gas detectors that will give off alarms when the
oxygen concentration in the vicinity of the vessel drops below a critical level.
Typically, normal oxygen level is 21%, and alarm levels on gas detectors are
19.5% (low O2 alarm) and 23.5% (high O2 alarm).
• If the oxygen content ever goes above 21%, there is something wrong like a
leaking oxygen cylinder. Investigate the situation first before allowing
personnel in the confined space.

If you see someone lying unconscious on the ground or through the opening
of a tank or pipe:

• Call the fire department / rescue team

NEVER ENTER A CONFINED SPACE OR
AREA ALONE TO GIVE HELP. CALL FOR ASSISTANCE

For more details on permit to work and confined space entry, refer to BP
Process Safety Booklets Control of Work and Confined Space Entry.

Unacceptable behaviour
• Peeking into a reactor without respiratory protection.
• Working near open manholes of a vessel under nitrogen without wearing
adequate breathing apparatus (cartridge or dust masks are unacceptable).

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2
Safe handling of
catalyst
2.1 Properties of catalysts
Catalysts are substances that increase the rate of reaction in certain pro-
cesses. Catalysts are available in many forms (e.g. cylinders, tubes, balls,
granules, powder) and colours. They are used in a number of processes at
refineries that include naphtha hydrotreatment, hydrocracking, resin hydropro-
cessing, alkylation, fluidized catalytic cracking, sulphur recovery, chloride
removal and in absorbers and dryers.

Some common catalysts used in the refinery and petrochemical plants.

Some catalysts must be handled under a nitrogen atmosphere due to their

pyrophoric and self-heating characteristics. Two types of substances
distinguished by their spontaneous combustion properties are:
Pyrophoric substances: even in small quantities will ignite within five minutes
of coming in contact with air and are liable to spontaneous combustion.
Self-heating substances: substances in contact with air, without energy supply
are liable to self-heating; ignite only when in large amounts (kg) and after long
periods of time (hours or days) e.g. presulphided new catalyst or used catalysts.
The increasing use of nitrogen in catalyst charging and changeout has no
doubt increased the number of fatal nitrogen gassing incidents in the industry
reported over recent years. Today, nitrogen is becoming as serious a gassing
hazard as H2S. Therefore, it is vital to fully understand the hazards of catalyst
charging and changeout and how it can be carried out safely.

Unregenerated catalyst is normally a self-heating substance and

often pyrophoric. On exposure to air, it can rapidly catch fire.

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2.2 Fire hazards

• Caused by reaction of catalyst with oxygen (in
the air) if the heat developed is not conducted
HOW???? away rapidly enough to the surroundings.
• Spontaneous combustion occurs when rate of
heat production exceeds the rate of heat loss.
HOW???? • When the auto-ignition temperature is
reached.

Good practice
• Storage and transport of self-heating catalyst carried out in accordance with
UN/IMO regulations.
• Always securely seal prescribed containers to prevent contact with air.
• Certain conventional methods include storage and transport of catalyst
under oil / water cover or nitrogen blanket.
• In case of fire, fire-fighters should wear self-contained breathing apparatus.
• Water is the best extinguishing media, but CO2, powder or foam can also be
used (refer to the MSDS for each catalyst).
• Safety showers should be available near catalyst unloading manholes to
allow total removal of catalyst dust from the surface of protective clothing
that could potentially ignite when in contact with the air.
• For extremely pyrophoric catalyst, fire resistant throw-away coveralls should
be provided to catalyst handling personnel.

Poor practice
• Never store presulphided new catalyst in bags (except for a very short period
of time such as for loading the reactor). Use metallic drums or containers.

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Fire from presulphided

new catalyst stored in
large cardboard boxes.

Metallic containers
and UN/IMO drums
for the transport and
storage of preacti-
vated new catalyst or
spent catalysts.
Reloading of a reactor using Do not reuse the
‘big bags’ drums.

Wear the correct personal protective equipment and use the

correct storage containers when handling catalyst.

INCIDENT While dumping catalyst from an isomerization reactor (via the

bottom dump valve) an uncontrolled release of catalyst occurred and caught
fire. The reactor was being dumped under a nitrogen purge. The catalyst
contractor had two employees, wearing fall protection and supplied breathing
air equipment, stationed on a small scaffold to operate the dump valve, the
unloading shoot, and the catalyst bin.
The catalyst contractor’s plan identified the bottom dump valve as the reactor
nitrogen purge vent to avoid excessive pressure buildup within the reactor.
Just prior to the release of catalyst, the employee at the bin told his foreman
there was excessive nitrogen blowing past the closed dump valve and to
reduce the nitrogen flow into the reactor. However before the nitrogen flow to
the reactor was reduced the other employee began opening the dump valve.
A pressurized cloud of catalyst dust and catalyst blew out and overflowed the
bin. Both employees moved quickly to a safe location. After a few minutes the
catalyst pile ignited. The refinery fire department secured the slide valve, and
extinguished the fire, with some difficulty using foam.
The investigation report recommended to:
• install a regulator on the nitrogen supply;
• install a low range pressure gauge on the reactor;
• install a vent and relief system on the reactor.”

Exothermic reactions
• The risk of an exothermic reaction usually occurs during plant operations
(not during loading or unloading of catalyst).

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• When catalyst is exposed to abnormal chemicals, water or abnormal

temperature/pressure conditions (such as during start-up or shutdown),
exothermic reactions may develop.
• Kinetics of reaction may be very fast, with risk of metal overheating and
over pressuring.

ACCIDENT CoMo catalyst in its oxide form, not in its sulphided form, was
loaded into the hydrodesulphurization (HDS) reactor. Due to the incorrect
catalyst used in the reactor, a runaway temperature reaction (hydrocracking)
took place and deformed/bulged the bottom head of the HDS reactor and the
top head of a downstream vessel, indicating direct exposure to operating
temperatures over 620°C. The HDS reactor also suffered a leak on a flanged
joint at the reactor outlet. The resultant fire at the flange damaged instrument
cabling in the vicinity of the reactor, causing an emergency shutdown of the unit.

The deformed / bulged section of the overheated reactor from a runaway reaction.

Reaction with water

Catalysts may react violently with water, where penetration into the catalyst
pores causes an exothermic process. This may lead to violent expulsion of both
the boiling water and catalyst. The smaller the pores, the more exothermic the
reaction, particularly with catalysts used in dryers as desiccants or adsorbents.

Good practice
• Adequate start-up procedures, planning, control and supervision during
commissioning of catalyst loaded reactors.
• Process Hazards Analysis (PHA) must cover the potential failure of critical
operating systems, such as temperature indicators and emergency
operating systems.
• Backup systems should be available so that reactors can be operated safely
in cases of instrument malfunction especially during a temperature runaway.
Instrumentation should maintain equipment integrity and discontinue
operation if conditions go outside the stipulated safe operating envelope.
Critical safety devices should be tested regularly.
• Operators should receive regular training on unit process operations and
chemistry (including reaction kinetics and the causes and control of tem-
perature excursions). Operators must be familiar with the use of emergency
procedures when required. Emergency drills should be practiced regularly.

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ACCIDENT Natural gas liquids are passed through molecular sieves in a

dryer vessel to remove water prior to a cryogenic process. After 3–4 years
the adsorbent is used up and has to be replaced. The renewal process
involves purging of the molecular sieve with hot residue gas (containing
approximately 830 ppm H2S), followed by cooling with nitrogen. For disposal,
the adsorbent material is removed from the dryer into a high-sided tipper
truck via a chute. The spent adsorbent is kept wetted in the truck to avoid
pyrophoric activity and generation of dust.
On this occasion, a mound of spent adsorbent was formed at one end of the
truck. A contract employee climbed into the truck to level the mound using
a shovel. He was later assisted by two additional contract employees. Ten
minutes later, all three became unconscious and died. The spent adsorbent
contained adsorbed and trapped H2S that was released to atmosphere into the
semi-confined space provided by the high-sided truck. The spent adsorbent
had a far greater affinity for water than for H2S. H2S is only slightly soluble in
water and was released into the semi-confined space killing the contractors.

2.3 Health hazards

• Health hazards are mainly associated with metallic dusts that are toxic when
inhaled.
• Exposure occurs during the handling of catalyst at site during loading and
unloading of reactors.
• Catalysts can enter the body by a number of routes including skin
absorption. Long-term exposures to low concentrations can cause serious
chronic illnesses.

Catalyst dusts are a hazard to health—wear the stipulated respirator

that provides the appropriate level of protection.

2.4 Spent catalyst

• Spent catalyst exhibits the same hazards as new catalysts as well as other
hazards associated with the products they come into contact with. For
example, steam cracker gasoline hydrogenation catalysts may contain high

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concentrations of benzene. Therefore, more extensive precautions should

be exercised when handling spent catalysts.
• Typical catalyst used in hydrogenation units contains between 4 to 21%
carbon and 5 to 10% sulphur. Reprocessed or regenerated catalyst is
considered spent catalyst and not new catalyst, as trapped products may be
released during handling. Beware that hydrocarbon vapours can be
released in very high concentrations when handling the spent catalyst.

Example of protecting workers at bottom of reactor

from catalyst dust using full life support system that is
designed for entry into inert gas atmosphere.

Another good example is to use hoods pressurised

with a fresh air supply (not a dust mask).

ACCIDENT Reprocessed catalyst was being loaded into a reactor. After

each bed loading, an inspector went in to check the partition of the catalyst. He
was protected only by a dust mask, and was overcome by hydrocarbon vapours
and collapsed. Fortunately, he was quickly rescued and fully recovered.
When stipulating precautionary measures, the hazards to be considered are
not limited to skin absorption of catalyst but must include the flammability,
reactivity, corrosiveness and toxicity of the hydrocarbons present.

Good practice
• An occupational health risk assessment must be undertaken using MSDS
and other information available from the suppliers / manufacturers of the
catalyst and licensor of the process technology to prevent harmful effects.
• Undertake airborne monitoring of the atmosphere and regularly carry out a
medical evaluation of the technicians.
• Clean full-body clothing should be provided at the beginning of each shift
and removed prior to breaks/meals.
• Contaminated clothing must not be taken home. It must be discarded into
properly labelled drums for disposal or laundered on site under special
instructions.
• A person entering the exclusion zone must wear the appropriate approved
respirators.
• All personnel wearing respiratory protection must conform with the site’s
safety requirements and be instructed in its proper use and limitations as
part of any statutory written program on respirators.
• Personnel entering vessels must conform with the minimum precautionary
measures stipulated under the site’s safety standards.
• All personnel should be trained on the hazards of the dust and operations
according to the local statutory hazard communication standard.
• If in doubt, overprotect the workers, for example, use air-line respirators that
provide a higher protection factor than air purifying respirators.

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2.5 Nickel carbonyl

Nickel carbonyl [Ni(CO)4] is used as a catalyst in some plastic, rubber and
petroleum industries. Nickel carbonyl vapour may also be formed inadvertently
in refining cracking processes that use nickel as a catalyst. Nickel carbonyl is
highly irritating to the lungs and can produce asphyxia by decomposing to liberate
carbon monoxide. Lethal human exposures have been estimated as 30 ppm for
30 minutes inhalation, and 50 to 500 mg/kg if ingested. Initial symptoms include
headache, dizziness, nausea and vomiting, which disappear when exposure
ends. Vapour also irritates the eyes, nose and throat. Nickel contact dermatitis
is the most common skin reaction to nickel carbonyl, often referred to as ‘nickel
itch.’ It is also a suspected carcinogen (cancer-causing agent).

Carry out an occupational health risk assessment before undertaking

any work associated with the handling of catalysts.

2.6 Crushing hazards

When digging through catalyst, specialist contractors must take care that no
high ‘wall’ of catalyst is left in place, ready to cave in if disturbed.
A recommended maximum height is 0.8 to 1.0 m (2.6–3.3 ft).

• Entry personnel should be properly trained on this issue and a good control
of the work by both the specialist contractor and the refinery team is
essential.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

• Specialist contractors are responsible for the rescue of personnel from a

confined space that is knowingly under 100% nitrogen.
• The specialist contractor’s emergency response team must always be well
equipped and ready to enter the reactor in case of an incident.

ACCIDENT A nitrogen entry specialist contractor was buried under hot

catalyst while carrying out catalyst unloading work in a nitrogen purged reactor
at a refinery. This work was carried out despite a clear recommendation on the
permit that any ‘inert entry diver must never come under the catalyst level’.

The worker was successfully rescued by his partner who was fully equipped,
suited and on stand-by. The victim suffered burns to his neck. Local catalyst
self ignition was made possible because of air leakage from a damaged
supply hose (and also maybe because of the atmosphere disturbance when
the catalyst wall fell). This successful rescue was possible due to a recent
change of procedure requiring a stand-by person to be available at all times
and prepared during any vessel entry under nitrogen purge.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

2.7 Other hazards associated with

catalyst handling
It is worth noting that other ‘more conventional’ incidents frequently occur during
catalyst loading and unloading operations, for example:

• A fork-lift truck overturned and crushed the operator while transporting

catalyst on pallets.
• An operator fell while handling catalyst at height (the use of a rope ladder in
a 30-metre (100 ft) high reactor is unacceptable).
• The weak internal structure of a reactor collapsed under the weight of an
operator.

• Dropped object during lifting of equipment of catalyst (in containers or big

bags).

Provide an exclusion zone around catalyst handling areas. Conditions

for entry shall be stipulated on work permit and procedures.

ACCIDENT A forklift truck was moving catalyst drums to the hydrofiner

loading area. It collided with a lamp-post and knocked it down. The driver was
thrown out and the vehicle overturned trapping him underneath. The driver
died from the injuries he received during this incident.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

ACCIDENT During the loading phase under air of a catalyst change out of
hydrodesulfurizer (3 beds) reactor, a technician entered the reactor to
commence sock loading of catalyst in the bottom bed. Loading of the required
layers of ceramic balls had previously been completed and the target was to
load 4 m3 (141 cu ft) of catalyst to bring the level up to the first thermocouple.
A short time after loading of the catalyst was underway the flexible loading
sock that was being used to convey the catalyst from the loading hopper to the
bottom of the third bed became detached from the loading hopper. The loading
sock had become overfilled with catalyst and a large portion of it fell to the
bottom of bed number three where the technician was working. The loading
sock struck the technician on the back of his neck. Whilst being restrained by
his umbilical line and unable to roll with the blow, the force of the loading sock
broke his neck resulting in a fatal injury.
The catalyst sock (approximately 37m (120 ft) in length) far exceeded the
recommended maximum length and was unable to support the weight of the
catalyst.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

ACCIDENT A similar incident occurred in another refinery whilst the catalyst

loading was being performed under nitrogen atmosphere. Two contractors were
hit by a catalyst loading sock that separated from the loading hopper, right above
the reactor top flange. There was the potential for two fatalities, if dropping of the
sock had damaged the air supply of the two contractors working in the vessel
under inert entry, or potential for serious physical injury due to the 320 kg (700 lb)
weight of the catalyst sock (appx. 30m (98ft) long).

The risk analysis for these operations should consider the following issues:

• Is there a real need to load catalyst under inert atmosphere? Could it be

done under air (using a different catalyst or using filtering masks)?
• Do the workers need to be in the vessel every time a big bag is emptied?
Could they enter only after the big bag is emptied?
• Are the air hoses protected and entering by another manhole? What if the
big bag is dropped on the funnel, jamming the manhole and severing the air
hoses?

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

2.8 Catalyst unloading

Typical discharge of unregenerated catalyst to prevent pyrophoric activity.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

2.9 Catalyst labelling

Drums of spent or unregenerated catalyst must be properly labelled. For
example:
Danger – contains nickel
– pyrophoric; will catch fire on exposure to air
– avoid dust inhalation and skin contact
– cancer suspect agent

2.10 Catalyst disposal

The final word is for the protection of the environment. Unregenerated catalysts
and used catalysts must be sent to an approved recovery plant through a
reputable contractor meeting all statutory requirements for shipment and
handling.

Wrong way to dispose Melted metals recovered

of spent catalyst from used catalysts

Unregenerated catalysts shall only be sent off site in

high integrity containers correctly labelled to
approved reprocessing plants.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

2.11 Respiratory and protective equipment

requirements

Guide to respirator selection *(IDLH ⫽Immediately Dangerous to Life & Health)

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Air-purifying Respirators Combination Respirators Air-line Respirators

have filters, cartridges, Continuous flow air-line/ supply clean air directly
or canisters that remove air-purifying respirator to the user from a source
contaminants from the air with full facepiece. Filters other than the air
by passing the ambient are facepiece-mounted. surrounding the user.
air through the air- E.g. air-line respirator,
purifying element before self-contained breathing
it reaches the user. E.g. apparatus (SCBA).
dust mask, gas mask.

Respirator assigned protection factor Highest
Life Support

Protection System
The assigned protection factor of a respirator
reflects the minimum level of protection that
a properly functioning respirator would be
expected to provide to a properly fitted and
trained user. For example, a protection factor
of 10 for a respirator means that a user could
expect to inhale no more than one tenth of
Lowest
Dust mask
the airborne contaminant present. Protection

Permitted maximum Maximum

airborne concentration Protection Factor permissible exposure
of catalyst dust around ⬍ of Respirator* ⫻ limit for the
technicians particulate/
contaminant*
Note: 
Less Than

* Refer to manufacturers literature, national standards and NIOSH Pocket

Guide to Chemical Hazards for further information. Visit NIOSH web pages
http://www.cdc.gov/niosh/homepage.html for details.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Respirator selection for various tasks involving use of nitrogen and catalyst handling.

Besides wearing the correct respirator when handling catalyst, it is also

important to avoid skin contact with the catalyst by wearing appropriate dust
proof coveralls. Ensure that coveralls are removed and properly disposed of at
the end of each shift /work period.

Ensure that workers are informed of the risks of not wearing the correct
personal protective equipment (PPE) and are trained in the proper use
(including ‘fit test’) of the appropriate respirator.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

ACCIDENT A contract labourer was asphyxiated as a result of working in

an oxygen deficient atmosphere whilst wearing a dust mask. Prompt action by
operating staff in rescue and resuscitation saved this man’s life. A ‘Confined
Space Entry Permit’ was issued to allow entry to the reactor, which clearly
stated that the vessel was: (a) under a nitrogen purge; (b) deficient in oxygen;
and (c) that breathing apparatus must be worn. However, conditions were not
explained to the person in charge of the job, and the man carrying out the
work was not informed that the vessel was under a nitrogen purge and the at-
mosphere was deficient in oxygen. Previously the workman had worked
inside a similar vessel near the one where the incident occurred. The
previous vessel had been gas freed and its oxygen content was acceptable
so the men assumed that the conditions were the same and worked inside
wearing only dust masks.

Good practice
• Personnel must be trained to realise that each vessel entry is a separate job
covered by a separate confined space entry permit with different conditions
and precautionary measures. Working conditions differ from vessel to vessel
and from day to day.

Air-line respirators
Air-line respirators are available in many types of configuration. Each type has
specific limitations that must be considered. One major advantage is that air-line
respirators can protect against both gases and dusts, and its use is not limited
by filter loading or cartridge capabilities (except for combination air-purifying and
air-line respirators). These devices tend to consist of more components than
air-purifying respirators, perhaps making them more complex. Care must be
taken to provide the following:

• Good quality air for breathing to a recognized standard.

• Sufficient quantity of air to meet the respirator’s operating requirements (as
indicated on the approval label) and use duration.
• A vortex fitted to the air supply to provide cool air to prevent heat stress in
hot climates. This requires a much bigger air flow rate. The cool air must not
be so cold that condensation occurs on the mask and impairs vision.
Air-line respirator and SCBA are not life support systems suitable for work
inside a nitrogen atmosphere.

Continuous flow air-line respirator with

vortex for airflow control valve. Vortex pro-
vides cooler air to worker. Note the filter
and regulator panel in upper right-hand
corner.
NOTE: This is not a full life support system

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Schematic diagram of
a typical air-line res-
pirator with auxiliary
escape air supply
worn on the waist.

ACCIDENT Two men were found dead inside the CO converter in an

ammonia plant during the removal of catalyst from the converter under
nitrogen cover. One operator was working inside the CO converter which was
under a nitrogen blanket wearing conventional compressed air breathing
apparatus; the air was supplied from bottles situated outside the vessel. He
was also equipped with a separate emergency air supply from a small bottle
attached to his waist but he had made no attempt to switch it on. The other
man remained outside the vessel to act as a ‘safety look out’.
Investigations concluded that the man working inside the vessel had a poor
seal around the face mask with a faulty air-line and was unaware that the air
he was breathing was slowly becoming deficient in oxygen (the symptoms of
asphyxiation in the early stages can be loss of judgment and loss of ability to
think clearly). The ‘look out’ man was found inside the vessel without
breathing apparatus and it was assumed that he must have gone inside the
vessel to rescue his fellow worker.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Poor face seal

(see respirator
selection matrix
in section 2.11).

SPECIALIST LIFE SUPPORT SYSTEM

Unlike the Specialist Life Support
System, breathing apparatus normally
available at refineries and chemical
plants does not provide an adequate
safeguard to cover the risks associated
with work in an inert gas or nitrogen
Lockable helmet connected to atmosphere. This work can only be
Specialist Full Life Support carried out by specialist contractors.
System (refer to figures at the
end of this section for details)

The precautions for work in an inert atmosphere must reflect the possibility and
seriousness of an incident occurring and therefore requires the use of very
sophisticated equipment and experienced personnel not normally available at
refineries. This equipment and the expertise that goes with it is only available
from outside specialist contractors.

2.12 Catalyst specialist contractors for

inert gas/nitrogen reactors
Management must thoroughly scrutinize the management systems and
associated procedures employed by inert gas ‘specialist’ contractors prior to
the award of contract.
In view of the restricted space inside reactors and the limited time available to
save an ‘unprotected’ operative inside an nitrogen atmosphere, ‘specialist’
contractors must prove that they have the required back-up respiratory
and other emergency/rescue equipment to handle the range of potential
failures.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Due to the hazards of working in nitrogen atmospheres, alternative

processes not requiring entry into an inert atmosphere must be
considered and, when appropriate, become the preferred alternative.

Pre-contractual arrangements
• Prior discussions involving site safety
advisor, maintenance and operations
personnel, specialist contractor’s pro-
ject leader. Final approval of procedures
by Site Manager.
• Precautionary measures must be
agreed and responsibilities assigned.
• Emergency response/egress proce-
dures to be agreed. Trial rescue must
be carried out before work commences.
• Visit a site to witness similar work being carried out by proposed specialist
contractor.
• Formal appointment of site representative to manage the project.

Pre-requisite for specialist contractors

• Effective safety management system including a drug / alcohol abuse policy.
• Certified life support equipment.
• Safety and operations manual covering procedures to undertake such
hazardous work.
• Inert gas confined space training document / certificate for each potential
entrant.
• Proven medical fitness of personnel (current certificate).
• Detailed emergency rescue plan.
• Written reports of past similar works undertaken.

Typical specialist contractor’s equipment

• Proven certified safety helmets that are lockable providing head protection,
primary and secondary regulators and communication system.
• Certified compressed air breathing cylinders.
• Emergency Air Egress bottles connected to each contractor providing an
individual independent emergency escape supply.
• An independent backup emergency supply of air available inside the
reactor.
• A monitoring station equipped with the following and positioned close to
job site:

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

• a primary air pressure monitor for each individual wearing helmet with audible
and visual alarms to indicate low primary supply and regulated pressure;
• a secondary air pressure monitor for each individual wearing a helmet,
including an alarm indicating the cut-in of the secondary supply to any of
the helmets and to alarm to indicate a low supply pressure;
• a battery-fed power supply to cut in automatically on failure of the
electrical supply to the monitoring station;
• an open line communications link between entry personnel and persons
supervising the entry. A communications link should also be established
between those supervising the entry and emergency standby personnel;
• communication system between entry person, supervisor and emergency
standby attendant.

• Armored umbilical cords for each entry man.

• Safety harnesses should be of the parachute type.
• Sufficient instruments to continuously monitor O2 level together and other
contaminants.
• Portable O2 meter for the outside atmosphere.
• Winch for swift removal of personnel from reactor.
• O2 resuscitator and at least one entry-monitoring team certified for cardio-
pulmonary resuscitation.

Typical procedures
A detailed written procedure to include the following:

• a vessel diagram showing:

䉬 isolation points 䉬 N2 purging inlets

䉬 O2 monitoring points
䉬 entry point 䉬 internal fittings
• safety / procedure check list;
• all remaining potential hazards;
• details of equipment to be used;
• all precautionary measures;
• details of type of Work Permit required for each stage of the operation;
• emergency Rescue Plan for the specific vessel;
• briefing of site personnel on the above requirements prior to commencement
of work.

Specialist contractors including their safety management system,

equipment, working methods and previous work experience must be
thoroughly reviewed before being awarded a contract to remove
catalyst from an IDLH atmosphere.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

Areas of responsibilities (should be clearly defined in writing)

Site Owner / Representative Specialist Contractor

• Specify all hazards to contractors • Responsible for the safety

and own staff of personnel
• Enforce Permit to Work System • Compliance to agreed protective
and agreed procedures equipment requirements.
• Isolate equipment for entry • Ensure adequate number of
• Minimise presence of other qualified, experienced and
contaminants during the shutdown properly equipped personnel
and purging operations • Brief employees of any
• Provide reliable N2 supply, if additional hazards and
supplied by site take appropriate measures
• Provide safe access to place • Monitor local working
of work environment and arrange
precautions if additional
• Prevent unauthorized access to necessary e.g. oxygen and
the area flammable gas detectors.
• Provide continuous supervision • Ensure Emergency
of work; monitor N2 purge and Response / Egress Plan in
provide standby fireman place and ready
• Provide FM radio sets for • Comply to site safety rules
communication between site and procedures
representative and contractor’s • Ensure any change to agreed
supervisor procedures is authorized
• Monitor outside barricaded area through the site’s Management
for O2, toxics and flammables. of Change procedure

Joint Responsibilities

• To ensure O2 level is kept down to a safe level (below 2 % v/v) inside

reactor
• Number of N2 injection points
• Purge position and monitoring of N2 supply
• Number and position of sampling heads for O2 meters/alarms and person
to calibrate and monitor this equipment. Both inside and outside reactor.
• Minimum N2 flow and daily consumption
• Continuous temperature monitoring within the vessel

To read more on work in inert atmospheres, refer to API Publication 2217A

Guidelines for Work in Inert Confined Spaces in the Petroleum Industry.

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52

H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G
Example of a high integrity life support system used by a specialist contractor
 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G
Typical personnel arrangements at top of reactor
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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

3
Some points to remember

1. Moving affected and unconscious persons from

a nitrogen atmosphere into fresh air is not
enough to promote recovery. The patient has to
be physically resuscitated in order to restore the
oxygen supply to the brain.

2. Nitrogen (N2) is a very common and extremely

dangerous gas that you may be exposed to at a
refinery or chemical plant. You must always be on
your guard.

3. Most useful or most dangerous

gas???

4. An asphyxiant is a chemical (gas or vapour)

that can cause death or unconsciousness by
suffocation. Simple aphyxiants such as nitrogen,
displace oxygen in air. They become especially
dangerous in confined or enclosed spaces.
Chemical asphyxiants, such as carbon monoxide
and hydrogen sulphide, interfere with the body’s
ability to absorb or transport
oxygen to the tissues.

5. An Oxygen Deficient Atmosphere is an atmosphere with

oxygen content below 19.5% by volume. (OSHA
Definition)

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

6. Nitrogen can create an oxygen deficient

atmosphere outside the vessel/piping that is
being purged with this medium.

7. You are asphyxiated with only your

head inside an oxygen deficient
atmosphere—not your whole body.

8. Keep technicians away from

areas outside manholes that
could be deficient in oxygen
(unless authorized through a
Confined Space Entry
Permit).

9. Do not confuse N2 with air !!!

10. A mobile, self-contained, high pressure

cylinder storage system undoubtedly
provides the highest integrity, freedom of
operation and safety when using air-line
breathing apparatus. Most sites prefer to
either use bottled air, supplied from a trolley
set (wheeled trolley with air bottles on it) or
from a bank of dedicated air bottles
located on the plant. There is a
requirement to ensure that the quality of air
in supply bottles is correct, whether they
are refinery filled or otherwise by a
respectable external company.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

11. Always check the oxygen level first before

carrying out a flammable gas test using an
explosimeter in preparation for hot work or
confined space entry.

12. If you see someone lying unconscious on the ground

or through the opening of a tank or pipe. Call the fire
department / rescue team. Never enter a confined
space or area alone to give help. Call for assistance.

13. Unregenerated catalyst is normally

a self-heating substance and often
pyrophoric. On exposure to air, it can
rapidly catch fire.

14. Wear the correct personal pro-

tective equipment and use the
correct storage containers when
handling catalyst.

15. Catalyst dusts are a hazard

to heath–wear the stipulated
respirator that provides the
appropriate level of protection.

16. Provide an exclusion zone

around catalyst handling
areas. Conditions for entry
shall be stipulated on work
permit and procedures.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

17. Carry out an occupational health risk assessment

before undertaking any work associated with the
handling of catalysts.

18. Unregenerated catalysts shall only be sent

off site in high integrity containers correctly
labelled to approved reprocessing plants.

19. Provide adequate

engineering
controls to prevent
emission of dust to
atmosphere.

20. Specialist contractors including their safety

management system, equipment, working
methods and previous work experience
must be thoroughly reviewed before being
awarded a contract to remove catalyst from
an IDLH atmosphere.

21. Unlike the Specialist Life Support

System, breathing apparatus normally
available at refineries and chemical
plants does not provide an adequate
safeguard to cover the risks associated
with work in an inert gas or nitrogen
atmosphere.

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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

22. Preference should always be

given to the dumping of
catalyst that is wetted with
special additives i.e. will not
cause a dust hazard and as
such is encapsulated to
prevent pyrophoric activity. This
would allow workers to enter
reactors not deficient in oxygen
since it would not require the
presence of an inert gas or
nitrogen filled atmosphere.

23. Due to the hazards of working

in nitrogen atmospheres, alter-
native processes not requiring
entry into an inert atmosphere
must be considered and, when
appropriate, become the
preferred alternative.

If you have any doubts,

please consult the safety procedures,
Do not hesitate to ask your Safety Department
for more information.

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 H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

4
Test yourself!

1. Whatever its state, the only risk related to nitrogen is suffocation.

True
·
2. The smell of nitrogen immediately identifies an oxygen deficient
environment.
False
·
True
·
3. Testing for flammable gases in pipes purged with nitrogen does not
pose any problems with explosimeters.
False
·
True
·
4. There is no risk in leaving a bottle of nitrogen in a small room.
False
·
True
·
5. An air-purifying respirator will adequately protect me in an oxygen
deficient atmosphere.
False
·
True
·
6. It is safe to pour liquid nitrogen on myself.
False
·
True
·
7. Even if I inhale pure nitrogen, I will be safe for a few minutes thanks to
the oxygen stored in my blood.
False
·
True
·
8. Nitrogen is not the only gas that can cause suffocation.
False
·
True
·
9. Nitrogen is only used on the site for preparing equipment for
maintenance (never for other purposes or in the tank farms)
False
·
True
·
10. Unregenerated catalyst can be pyrophoric.
False
·
True
·
11. Handling, unloading, storage and shipment of unregenerated catalysts
is normally carried out under nitrogen cover.
False
·
True
· False
·
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H A Z A R D S O F N I T R O G E N A N D C AT A LY S T H A N D L I N G

12. Catalyst dust is not a threat to our health and therefore air-line
respirators are not required.
True
·
13. Dust masks always provide adequate protection to prevent inhalation
of catalyst particles.
False
·
True
·
14. Specialist contractors for inert gas confined space entry projects use
conventional SCBA because they are trained underwater divers.
False
·
True
·
15. Providing the atmosphere is between 19.5% and 23.5% oxygen, it is
always safe to enter the confined space.
False
·
True
·
16. Open manholes are dangerous because technicians are likely to put
their heads inside.
False
·
True
·
17. Oxygen deficient atmospheres can be created outside a confined
space.
False
·
True
·
18. An occupational health risk assessment is required prior to any
possible exposure to catalyst, to protect the technicians and the
False
·
environment from harmful effects.
True
·
19. Conventional breathing apparatus normally found in refineries
provides adequate protection for working in an inert / nitrogen-filled
False
·
confined space.
True
·
20. All air compressors provide the quality of air necessary for breathing
apparatus.
False
·
True
· False
·
16T / 17T / 18T / 19F / 20F
11T / 12F / 13F / 14F / 15F
6F / 7F / 8T / 9F / 10T
1F / 2F / 3F / 4F / 5F

ANSWERS

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5
Bibliography

American National Standard Institute (ANSI) / American Society of Safety

Engineers (ASSE), 2003. Safety Requirements for Confined Spaces,
ANSI/ASSE Z117.1-2003.
American Petroleum Institute (API) Publication 2217A Guidelines for Work in
Inert Confined Spaces in the Petroleum Industry.
US Occupational Safety & Health Administration Standard Permit-Required
Confined Spaces, 29 CFR 1910.146.
UK Health and Safety Executive:

• Safe work in confined spaces leaflet INDG258.

• Safe work in confined spaces. Confined Spaces Regulations 1997, ISBN
978 0 71766 233 3.
• Cleaning and gas freeing of tanks containing flammable residues, ISBN
0 71761 365 8.

US Chemical Safety Board:

• Union Carbide Corp. Nitrogen Asphyxiation Incident Hahnville, LA, March

27, 1998; Report No. 98-05-I-LA.
• Valero Refinery Asphyxiation Incident Delaware City, DE, November 5, 2005;
case study No. 2006-02-I-DE and video animation on CSB website.
• Safety Bulletin: Hazards of Nitrogen Asphyxiation, No. 2003-10-B, June
2003.

US Compressed Gas Association, Inc.:

• Safety Bulletin, Oxygen-Deficient Atmospheres, SB-2, 2007.

• Safety Alert, Hazards of Nitrogen/Inert gas creating an oxygen-deficient
atmosphere, SA-17, 2008.

BP Process Safety booklets:

• Control of Work, ISBN 978 0 85295 514 7.

• Confined Space Entry, ISBN 978 0 85295 479 4.

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Your notes

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Acknowledgements

The co-operation of the following in providing data and illustrations for this
edition is gratefully acknowledged:

• ABS Consulting Singapore Office

• American Industrial Hygiene Association
• BP Refining Process Safety Network
• BUCHEN ICS
• CAT TECH
• EURECAT France
• SGAE
• TOTAL Antwerp
• John Bond, IChemE Loss Prevention Panel member
Note: BP also published:
• in 2003 a comprehensive ‘Nitrogen Information Package’ (including video,
CDrom, slides, quiz, leaflet, poster, good practice documents). Some pictures
from this video have been included to illustrate incidents described in this
booklet.
• and in 2005 a specific Computer Based Training module.

iv