Well known process industry accidents:

1) LPG explosions and fire @ Mexico 1984 (500 death)

2) LPG tank farm fire @ Feyzin 1966 (18 death, 81 injuries)
3) Oil rig fire on Piper Alpha 1988 (167 death)
4) Oil rig fire on Guneshli 2015 (14 death, 16 missing)
5) Oil refinery fire @ Milford Haven 1994 (4 death)
6) Oil refinery explosion @Texas 2005 (15 death, 180 injuries)
7) Tianjin explosion 2015 (173 death)
8) Bhopal explosion (15000 death)
9) Ammonium Nitrate plant explosion @ Tolouse 2001 (31 death)
10) Chemical plant explosion @ Flixborough 1974 (28 death)

Hazards associated with fires and explosions include:

 Heat
 Smoke
 Blast wave/overpressure
 Missiles/flying debris
 Toxic combustion products
 Collapse of buildings
 Radiation
 CO2 emissions

What is ergonomics?
Ergonomics is the process of designing or arranging workplace, products, and systems user friendly, so that
they fit the people who use them (key words are user friendly and designing)

What is safety culture?

Safety culture is the collection of beliefs, perceptions and values that employees share in relation to risks
within an organization, such as a workplace or community (4 types: forced, protective, involved, integral)

Should be mental health issues be considered?

Definitely yes, because poor mental health and stress can negatively affect employees.

Difference between incident and accident?

Both happen unintentionally, accident is event that result in injury and harm.
incident not causing harm but has potential to harm, includes near-miss
What is near miss?
Near miss is unplanned event that did not result in any injury, illness or damage but had the
potential to do so.

Work ethics and staff morale

Work ethics is manners of work, set of values respecting other values, privacy or personal space
Staff morale is level of motivation at workplace.
What is “tragedy of Commons”?
It is economic problem of overconsumption under investment and ultimately depletion of common
pool resources, big example is overconsumption of planet

Micromanagement is managing of little tasks, sign of bad leadership

What are some of barriers to achieving sustainability?
Lack of seminar, mindset (bu suali deqiqleshdir)

Combustion Reactions
Combustion is a rapid, high temperature oxidation reaction, exothermic, the activation energy for
the reaction must be supplied before the reaction takes place to release heat. At higher
temperatures, more heat energy is available to contribute to this activation energy, so reaction
rate is higher. Catalysts lower activation energy. The relations between chemical reaction rate
constant, activation energy and T may be described by Arrhenius equation:
Ln(k)=Ln(A)-E/RT
K=rate constant
A=Arrhenius constant
E=Activation energy
R=universal gas constant
T=temperature with Kelvin
E azalsa, T artsa onda k artacaq.
Activation energy is the minimum quantity of energy which the reacting species must possess in
order to undergo a specified reaction.
The autoignition temperature or kindling point of a substance is the lowest temperature in which
it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a
flame or spark. For HC it ranges between 250-600C.
Highest T that can be attained when HC is burned in air is reached when the reagents are present
in stoichiometric proportion, which is when a complete reaction would leave neither fuel nor
oxygen behind.
Minimum concentration of fuel in air at which combustion is possible is lower or lean flammability
limit.
Maximum concentration of fuel in air at which combustion is possible is upper or rich flammability
limit.
A typical flammable range for
 HC is around 2:12 mole%,
 NH3 is around 16-25%,
 H is around 4.1-74 mole%,
 diethyl ether 1.9-48 mole%.
Flash point
Another fire risk related to volatile organic liquid is associated with its flash point.
A simple system of fire risk classification can be based on flash point:
- Combustible (>60 C)
- Flammable (32-60 C)
- Highly flammable (0-32 C)
- Extremely flammable (<0 C)

Effect of pre-mixing
In pre-mixed fires, fuel mixes with air before ignition and reaction rate is determined by kinetics.
With non-pre-mixed fires, fuel doesn’t mix with air before ignition and reaction rate is determined
by rate of mixing.
Pre-mixed fires tend to burn faster and rapidly.

Types of fires
Jet fires – gas leaves pipe or vessel in some velocity and burns as it mixes with air (flare stacks)
Pool fires – a pool of liquid ignites and as it burns, it evaporates, leading to burn vapour more
rapidly.
Flash fires – when flammable gas mixes with air and find ignition source to combust, can cause
asphyxiation (absorbing oxygen from air)
Fireballs – occur when there is catastrophic failure of vessel or equipment, releasing a cloud of
flammable gas which ignites rapidly.

Fire Extinguishing Media

Fire extinguishers are used to cool area and exclude oxygen from air.
Main fire extinguishers are Water, dry powder, foam spray and CO2.

Wood, paper, Flammable

Electrical fires Metal fires
textiles liquids

Water + - - -
Dry powder
+ + + +
Foam spray + + - -
Hold horn
CO2 - + + - when
operating

Asphyxiant gas – removes oxygen from air and leaves no oxygen to start combustion. It can be CO2
or nitrogen.
Halon extinguisher is used till 1987 as it forms free oxygen radicals and damage ozone layer.
Ternary eutectic chloride (TEC) is a mixture of sodium, potassium and barium and used in metal
fires in order to exclude oxygen.
Buckets of sand is simple and effective fire extinguisher media for small fires.

What should we do if we discover fire:

- Sound alarm
- Close all windows and doors
- Leave building by nearest available exit and report to assembly point.
If we hear alarm:
- Close all windows and doors
- Leave building and report to assembly point
- Don’t use elevator
- Don’t try to fight fire, don’t take risks

Fire protection strategy

- Fire prevention;
- Fire mitigation;
- Fire protection;
- Fire control;
- Active and passive systems.

Fire prevention
To initiate fire, we need fire triangle:
Oxygen
Heat represents ignition source. Fuel

Possible ignition sources can be:

-Electrical arcing
- mechanical sparks Heat
- static change
- heat surfaces
- welding
- smoking
- open flames
- infra-red radiation
Good housekeeping – maintaining workplace in a clean and tidy condition – is necessary for fire
prevention.

Common reasons for occurring fire accidents:

- Lack of training
- Inadequate training
- Failure or malfunction of equipment
 - Inadequate installation and operation
- Overheating flammable liquids
- Procedural errors
- Inadequate control of ignition source
- Dismantling or disposal of plant and equipment
- Hot work (svarka) on or close to flammable liquid
- Exposure to heat from nearby fire
- Incorrect use of solvents and cleaning
- Misuse of flammable liquids.
What is DSEAR?
DSEAR=Dangerous Substance and Explosive Atmospheres Regulations, it explains what employers
may need to do to protect their employees from fire and explosion risks

What is dangerous substance?

Dangerous substances are any substances used or present at workplace that could, if not properly
controlled, cause harm to people as a result of fire, explosion or similar incident, such as an
uncontrolled chemical reaction. Dangerous substance includes solvents, paints, varnishes,
flammable gas, liquified petroleum gas, dusts from machining and sanding operations, dusts from
foodstuffs.
What is an explosive atmosphere?
An explosive atmosphere is mixture of dangerous substance or substances with air which has the
potential to catch fire or explode. An explosive atmosphere does not always result in explosion, but
if it does catch fire, the flames travel quickly. If it happens in closed space, the rapid spread of
flames or rise in pressure can also cause an explosion.

Risk assessments under DSEAR includes five steps:

1. Identify the fire and explosion hazards and hazards from similar energetic events
2. Decide who might be harmed and how
3. Evaluate the risks and decide on precautions
4. Record your findings and implement control measures
5. Review your risk assessment and update if necessary
DSEAR requires a hierarchical approach for the elimination or reduction of the risks from
dangerous substances
Review of topic 1

Topic 1
Hazards associated with fire and explosions include:
 Heat.
 Smoke.
 Blast wave / overpressure.

 Missiles / flying debris.

 Toxic combustion products.

 Collapse of buildings.

Combustion – rapid, high T oxidation reaction.

Autoignition – above certain temperature, the reaction rate is high enough for the
heat produced to cause a localized temperature to rise which increase reaction rate
still further. The reaction becomes self-sustaining and there is a sudden increase in
temperature and thus the hydrocarbon ‘catches fire’. The lowest temperature at
which reaction with oxygen becomes self-sustaining is called auto ignition
temperature. For hydrocarbons, autoignition temperature range is 250 – 600Celcius.
No ignition source is required at autoignition temperature.

Highest temperature (max T rise) – to achieve it, reagents should be in

stoichiometric proportion. Since unreacted substances left in gas phase, they (gas)
absorb product heat, but will not produce the heat. Therefore, this leads to barriers
to achieve the highest temperature.

Flammability limit – minimum concentration of fuel in air at which combustion is

possible is lean or lower flammability limit. Maximum fuel concentration – rich or
upper flammability limit. For hydrocarbons flammable range is between 2 – 12
moles %.
Flash point – is the temperature at which liquid is sufficiently volatile to form a
flammable mixture with air in vapour phase above liquid level. For a fire to start at
flash point, ignition source is required (unlike autoignition temperature). Liquid
with high vapour pressure tend to have low flash points and vice versa.
Flash point classification:
• Combustible – FP > 60 C
• Flammable – FP 32 – 60 C
• Highly flammable – FP 0 – 32 C
• Extremely flammable – FP < 0 C

Hydrocarbon fires are divided into two types:

Pre-mixed – fuel mixes with air before fining ignition source. Reaction rare is
determined by kinetics. Pre-mixed fires burn hotter and rapidly.
Non-pre-mixed - fuel does not mix with air before finding ignition source. Reaction
rate is determined by rate of mixing.

Types of fire:
• Jet fire – it occurs when gas leaves a pipe or vessel with velocity and burns as
it mixes with air. Jet fires are directional fires with turbulent flow. Main hazard is that
they can cause fire escalation (considerable heating) as they affect certain point
causing equipment failure.
• Pool fire – it is burning of liquid as pool form. It occurs when a pool of
flammable liquid ignites and evaporates to feed the flames. There is less pre-mixing
than jet fires. This type fire can flow from one point to another. If they are contained
in bunds, they will heat the vessel till the failure point.
• Flash fire – it occurs when flammable gas mixes with air and then finds an
ignition source. These fire flames move rapidly and cause asphyxiation since flames
consume available oxygen.
• Fireballs – it occurs when there is a catastrophic failure of a process plant,
releasing a flammable gas cloud which ignites in a brief but intense burst of flame.

Fire Extinguishing Media:

• Water – it is one of the most common and useful fire extinguishing media,
being relatively cheap and abundant on most process plants. It has a high heat
capacity and a high latent heat of vaporisation which plays roles as cooling and
preventing the fire. They are used in organic fires such as wood or paper. They leave
residue dump and prevent re-ignition. They are not used in electrical fires due to risk
of electrocution, and not in hydrocarbon fires due to its high density compared to
them (fuel can float on the top of water). Water foam is used in hydrocarbon fires.
• Chemical foam – produce by mixing water with surfactant and aspirating with
air. It has density. It can be used to tackle hydrocarbon pool fires.
• Carbon dioxide – it cools and exclude oxygen from the area where it is
applied. It is asphyxiant gas and is no used in populated areas. It is not suitable for
metal fires since some metals can react with CO2 violently. It is suitable for electrical
fire & small fires inside buildings.
• Dry powder – it consists of sodium carbonate, potassium carbonate or
ammonia phosphate which slows down combustion to extinguish a fire. It forms a
white fog after usage which reduces the visibility and leaves area with dry white
powder which is hard to clean.
• Nitrogen – it displaces and dilutes the oxygen. It is asphyxiant gas, so could
not be used in populated areas. No personnel present.
• Halon extinguishers – they are based on vaporizing hydrocarbons, which
interfere with combustion to form free radicals to terminate the oxidation reaction.
• Thermal eutectic chloride (TEC) – a mixture of sodium, potassium and barium
chlorides. It is used in metal fires. It forms a layer to exclude oxygen.
• Sand – buckets of sand are a simple and effective fire extinguisher for small
fires.

Fire Mitigation – it aims to reduce the risk from accidental fires in process
equipment. For example, automatic shutdown system, pressure relief system,
emergency valves.
Fire Protection – it aims to reduce fire escalation (escalation - tendency of a fire that
starts in one point of a plant to spread to other areas).
Protection from IR may be achieved by:
✓ Intumescent paint – passive protection system which consist of a layer of paint
on the outer vessel surface which expands on heating to form a char with low
thermal conductivity.
✓ Sprinkler or water deluge system – active protection. It consists of water jets
which cool the vessel surface and prevent the contents from overheating. It is useful
protection against BLEVE, but only limited protection.
Fire Control – it aims to contain the fire within restricted zone to prevent escalation.
Techniques for containment:
• • Water spray or stream curtains (active) – absorbs IR radiation, reducing the
heat transmitted from the affected area.
• • Fire walls (passive) – made of reinforced concrete. It not only reduces IR
radiation spread, but also give some protection against missiles such as flying debris.
• • Foam and carbon dioxide system (active) – automatic release of
extinguishing chemicals to suppress fire before it spreads.
• • Bunding (passive) – a low wall which surrounds a process vessel to catch any
liquid which spills from leaking tanks / pipes. It is used to contain leaks of flammable
or toxic materials to prevent entering drains. It must be designed to contain 105% of
vessel volume.

Fire Triangle:
All 3 components must be present to start a fire.
Heat represents ignition source.
Fire prevention – preventing fire at first place.
Fire prevention methods:
• Fuel must be isolated from open air, not to let it
find ignition source. Combustible dust should not
be let accumulated on open surface (good
housekeeping).
• O2 cannot be eliminate from open air or from areas where people are working. It
can and should be removed from sealed areas that are unpopulated (such as remote
computer rooms). At least, oxygen concentration can be decreased by inerting with
N2. Nitrogen blanketing is used in tanks and vessels to remove oxygen.
• Ignition sources are difficult to eliminate but can be controlled.

Possible ignition sources:

1. Mechanical sparks.
2. Static electricity.
3. Electrical sparks from switches etc.
4. Hot surfaces.
5. Infra-red (IR) radiation.

Active – foam or CO2 systems, water deluge system.

Passive – paint, bunding.
It is better to combine both systems to achieve the highest effectiveness.

Burn-down rate – it directly related to type of liquid (liquid volatility), ambient

temperature, air movement (speed), and inversely related to pool diameter.
Threshold radiation of human body – we are exposed to 1.2 kW/m2 radiation on
sunny days. At 1.5 kW/m2 and higher radiation, human body is affected.

Explosions – it is sudden and violent release of energy which produces localized

overpressure. It has two types:
1. Detonation – explosion or burning of a material induced by a shock wave. It
travels at sonic wave (2000 – 3000 m/s). Overpressure can reach 20 bar.
2. Deflagration – simple burning of a material induced by heat transfer. It travels at
sub-sonic wave (1 m/s). Overpressure should not exceed 8 bar.
Vapour Cloud Explosion (VCE) – VCE occurs when gaseous fuel/air mixture finds an
ignition source in an open air and explodes. Violence of VCE is affected by
turbulence. For example, if there is a process vessel as a barrier, VCE is more likely to
occur.
Boiling Liquid Expanding Vapour Explosion (BLEVE) – BLEVE occurs when a pressure
vessel containing liquid is exposed to fire and become hot. Increasing pressure leads
to vapor pressure rise inside of vessel and walls of vessel becomes less strong. After
failure, fireball occurs. Personnel can get injuries by flying missiles. Fire escalation
can occur. Bund can increase BLEVE occurrence but prevents fire escalation.

Dust Explosions – it occurs when finely divided combustible powder finds an ignition
source and reacts rapidly to produce overpressure. It is dangerous because, as
components are finely divided, surface area increases which leads to high oxygen &
fuel contact. Dust explosion probability depends on dust concentration in air, local
oxygen concentration, ambient temperature, energy amount from ignition source.
Good housekeeping can help to prevent formation of combustible powder on
surface. (The West Pharmaceutical polyethylene, The Imperial Sugar dust
explosions).

Bunce field (UK, 2005, VCE accident) – it lasted 4 – 5 days with black smoke
spreading over the region. No one was killed, but there were 43 injured people.
Pollutants from fuel & firefighting entered the groundwater after accident.
→ Petrol started to be pumped in tank 912 in bund A at 7 PM. After some time,
liquid gauge level showed no change in liquid level, showing 75% full.
→ Petrol started to overflow from the top of the tank into the bund.
→ Vapour cloud began to from which was visible on CCTV. It flowed out from the
bund in all directions.
→ First explosion took place, followed by 2 more.
→ Pool fire also took place.

Causes:
• The level indicator and high-level switch were malfunctioning. There were lack
of communication between switch suppliers and maintenance staff since high-level
switch was installed incorrectly, and not enough attention to regular safety testing
(hidden failure).
• Fire-fighting facility was not operable since pumphouse was destroyed.
• Bund failed to prevent spreading since it could not contain all the vapour
formed.

Feyzin (France, 1996, BLEVE) – it initiated at the LPG storage are with propane &
butane storage spheres of 1200 m3 & 2000 m3. Each sphere was equipped with
water sprays.
Operator, fireman and lab technician were to take LPG samples from the tanks.
Sample was taken from propane sphere.
Operator opened valves in incorrect order >>> some caustic soda & gas released.
Operator closed the drain valve and opened it again slightly to remove the last traces
of water. Nothing happened, he opened the valve fully.
Initially, sphere did not explode, and it would though. As the temperature increased
due to fires, sphere burst.
Possible causes:
• Lack of awareness about BLEVE type explosions.
• Reliability on PRV, while they were inadequate for explosions.
• Human error >>> incorrect order of valve opening.

Zoning – categorizing area on a plant where flammable vapours may be present.

• Zone 0 – explosive atmosphere with flammable gas, vapour or mist is present
continuously or for a long period of time. For example, surface of ambient
pressure vented storage tank.
• Zone 1 - explosive atmosphere with flammable gas, vapour or mist is present
at normal operation occasionally. For example, breaking connections to hoses
that have carried flammable liquid.
• Zone 2 - explosive atmosphere with flammable gas, vapour or mist is not likely
to occur at normal operation. For example, use of faced ventilation.

Zoning depends on physical layout of the site and ventilation availability. Ventilation
can help switching to a lower risk zone.
Pressure Relief Valve (PRV) – it is used to prevent slight overpressure by ventilation.
It is not a protection method against explosions since they can not deal with abrupt
overpressure.
Explosion Mitigation:
• Explosion relief panels – they are fitted to sections of vessel wall and designed
to break free at a certain vessel pressure, opening a large area for venting. It should
be taken into account that panels don not fly off to damage people or plant.
• Bursting discs – they are circular metal or plastic plates, fitted into a pipe
flange which are designed to break off at a pre-set pressure. This opens up
practically entire pipe dimeter for venting. It is better to used PRV and bursting discs
together.

Domino Effects – incident at one process site causes damage to another site beyond
the boundary. It has 2 types:
1) Direct – when domino vector causes fire or loss of containment at another site.
Vector can include:
 Fire spreading.
 IR radiation.
 Missiles.
 Explosion overpressure.
2) Indirect – when domino vector does not necessarily cause physical damage to
nearby plant, but affects control systems, utilities, personnel so on.