FM Global

Property Loss Prevention Data Sheets 7-52

January 2012
Page 1 of 8

OXYGEN

Table of Contents
Page

1.0 SCOPE ................................................................................................................................................... 2

1.1 Changes .......................................................................................................................................... 2
2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 2
2.1 Safeguards for Bulk Oxygen Storage ............................................................................................. 2
2.1.1 Construction and Location .................................................................................................... 2
2.2 Safeguards for Liquid-oxygen Cylinders ......................................................................................... 3
2.2.1 Construction and Location .................................................................................................... 3
2.2.2 Occupancy ............................................................................................................................. 3
2.3 Safeguards for Piping Systems ....................................................................................................... 3
2.3.1 Equipment and Processes .................................................................................................... 3
3.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................... 4
4.0 REFERENCES ....................................................................................................................................... 4
4.1 FM Global ........................................................................................................................................ 4
4.2 NFPA Standards .............................................................................................................................. 4
APPENDIX A GLOSSARY OF TERMS ....................................................................................................... 4
APPENDIX B DOCUMENT REVISION HISTORY ....................................................................................... 4
APPENDIX C SUPPLEMENTARY INFORMATION ..................................................................................... 4
C.1 General Information ........................................................................................................................ 4
C.1.1 Bulk Storage of Liquid Oxygen. ............................................................................................ 4
C.1.2 Bulk Storage of Gaseous Oxygen Gas ................................................................................ 5
C.1.3 Liquid Oxygen Cylinders ....................................................................................................... 5
C.1.3.1 Description ................................................................................................................ 6
C.1.3.2 Hazards ..................................................................................................................... 7
C.1.4 Piping Systems ..................................................................................................................... 8

List of Figures
Fig. 1. Liquid-oxygen storage system. ........................................................................................................... 5
Fig. 2. High-pressure oxygen-gas storage. Typical portable installation, above; typical fixed
installation, below. ............................................................................................................................... 6
Fig. 3. Typical cylinder for liquid oxygen, nitrogen, or argon. ........................................................................ 7
Fig. 4. Oxygen station outlets. ....................................................................................................................... 8

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7-52 Oxygen
Page 2 FM Global Property Loss Prevention Data Sheets

1.0 SCOPE
This data sheet address the hazards of liquid oxygen storage in large tanks or portable cylinders or large
high pressure gas systems. Protection for systems handling gaseous oxygen in portable cylinders is covered
in Data Sheet 7-50, Compressed Gases in Cylinders.

1.1 Changes
January 2012. Terminology related to ignitable liquids has been revised to provide increased clarity and
consistency with regard to FM Global’s loss prevention recommendations for ignitable liquid hazards.

2.0 LOSS PREVENTION RECOMMENDATIONS

2.1 Safeguards for Bulk Oxygen Storage

(For safeguards for portable cylinders of oxygen gas, see Data Sheet 7-50, Compressed Gases in Cylinders.)

2.1.1 Construction and Location

2.1.1.1 Locate bulk oxygen storage, including fixed or portable high-pressure bulk units and/or liquid-oxygen
equipment, out of doors or in a detached noncombustible structure used solely for this purpose and separated
as follows:
a) 75 ft (23 m) from:
Aboveground ignitable-liquid tanks of 1,000 gal (3.8 m3) or greater capacity.
Aboveground tanks of liquefied flammable gases of over 1,000 gal (3.8 m3) aggregate water capacity.
Low-pressure flammable-gas storage holders of 5,000 ft3 (140 m3) or greater capacity.
Unsprinklered combustible buildings.
Combustible yard storage.
Wood exterior walls.
b) 25 ft (7.6 m) from:
Aboveground ignitable-liquid tanks of less than 1,000 gal (3.8 m3) capacity.
Aboveground tanks of liquefied flammable gases of 1,000 gal (3.8 m3) or less aggregate water capacity.
Filling or vent connections to underground ignitable liquid tanks.
Low-pressure flammable-gas storage holders of less than 5,000 ft3 (140 m3) capacity.
Sprinklered buildings or buildings with both construction and occupancy noncombustible.
High-pressure bulk flammable-gas storage.
Ignitable-liquid unloading stations.
c) 5 ft (1.5 m) from:
Noncombustible construction having blank walls 10 ft (3 m) above and 10 ft (3 m) on each side of
the equipment.
2.1.1.2 Regulators and other control equipment may be located indoors in a noncombustible building
detached or cut off from main buildings or combustible storage. Cutoffs should have at least a 1 hour fire
resistance rating.
2.1.1.3 Outdoor oxygen-storage equipment should preferably be located on a base of crushed stone or
concrete. Keep the ground area within 15 ft (4.5 m) of the equipment free of high weeds and grass by frequent
mowing or the application of a herbicide.

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FM Global Property Loss Prevention Data Sheets Page 3

2.2 Safeguards for Liquid-oxygen Cylinders

2.2.1 Construction and Location

2.2.1.1 General safeguards for gaseous-oxygen cylinders are applicable to liquid-oxygen. (See Data Sheet
7-50, Compressed Gases in Cylinders.)
2.2.1.2 Locate cylinders and manifolds out of doors in detached buildings or in cut-off rooms of
noncombustible construction. Where floor or pad drainage is needed, use wall scuppers or exterior doorways
and pitch the pad to the outer edge. Do not use floor drains, trenches, or other drainage arrangement
involving essentially enclosed, below-grade, or floor-level drainage-system elements. Ramp, curb, or pitch
floors at interior doorways of cutoff rooms to prevent passage of liquids into or out of the room.
2.2.1.3 Limit quantities in cut-off rooms to eight cylinders or less. Locate larger quantities out of doors or
in detached structures as outlined in the previous section on bulk storage.

2.2.2 Occupancy
2.2.2.1 Enclosed structures should be well ventilated. Positive mechanical ventilation of at least 0.25 cfm/ft2
(0.08 m3/min/m2) of floor area or natural ventilation of 1 ft2 (0.1 m2) each of free inlet and outlet openings
per 500 ft2 (46.4 m2) of floor area is recommended.
2.2.2.2 Install and handle liquid-oxygen cylinders in accordance with the manufacturer’s recommendations.
2.2.2.3 Use equipment such as manifolds and cylinder leads specifically approved for service with these
cylinders. When standard gas cylinders are used for standby, manifold equipment should be a high pressure
type arranged and connected to the distribution system in accordance with the manufacturer’s instructions.
2.2.2.4 Handle cylinders in an upright position only.

2.3 Safeguards for Piping Systems

2.3.1 Equipment and Processes

2.3.1.1 Use extra-heavy steel or nonferrous pipe and fittings if the oxygen pressure is over 150 psi (10 b)
(1 MPa). For lower pressures, standard-weight pipe and fittings are satisfactory. Cast-iron fittings should not
be used.
In medical oxygen gas systems, Type K or L (ASTM B-88) copper tubing may be used. Brazed fittings should
be used for 3⁄4-inch (19-mm) and larger tubing. Flared-type tubing fittings may be used in smaller sizes where
the fitting is visible in the room.
2.3.1.2 Provide a relief valve in the piping system downstream of the main regulator. The start-to-discharge
setting of the valve should be no higher than 125 % of the normal working pressure of the piping system.
Pipe the discharge of the valve to outdoors.
2.3.1.3 Use only approved valves, separators, and station-outlet regulators. Make all connections for station
outlets from the top of the branch supply line. Provide traps at low points in the piping to permit removal
of condensed water.
2.3.1.4 Use welded joints whenever possible. If threaded joints are necessary, they should be carefully made
up, using litharge and glycerin or proprietary materials compounded for oxygen service. Compounds
containing oils should not be used. Gaskets should be entirely of noncombustible materials.
2.3.1.5 Overhead piping should be rigidly supported well above floor level and located where not exposed
to excessive heat, vibration, or physical damage.
2.3.1.6 Protect piping against corrosion.
2.3.1.7 Do not install oxygen piping in the same trench or duct with ignitable-liquid piping.
2.3.1.8 Before piping is installed, hammer all fittings and pipe lengths to dislodge dirt and loose scale and
then blow them out by compressed air or steam. Wash with a hot solution of sodium carbonate or trisodium
phosphate to remove all grease and oil.
2.3.1.9 Pressure-test new piping at 1.5 times the working pressure.

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7-52 Oxygen
Page 4 FM Global Property Loss Prevention Data Sheets

2.3.1.10 Inspect piping at regularly scheduled intervals, and repair any leaks immediately.

3.0 SUPPORT FOR RECOMMENDATIONS

Oxygen is a colorless, odorless gas about 1.1 times as heavy as air. It constitutes about 21 % by volume
of the earth’s atmosphere. It is used in large amounts for oxyacetylene cutting and welding, chemical
processes, steel-plant furnaces, and other applications.
Oxygen itself is neither combustible nor explosive. However, the intensity of any ordinary fire or explosion
increases as the amount of oxygen in the surrounding air increases. Some materials, such as greases and
oils, which produce intense fires with air, burn in an atmosphere of oxygen with explosive violence.
Explosions have occurred in oxygenpressure gages when they were placed in service after being tested on
common oil-filled gage testers. Oxygen at atmospheric pressure in a closed system can combine explosively
with motor-lubricating oil at temperatures as low as 340°F (170°C).
Metals such as iron, which are noncombustible in air, will burn if raised to a high temperature in an oxygen
atmosphere. The ignition temperatures of materials are lowered as the pressure of the oxygen atmosphere
is increased.

4.0 REFERENCES

4.1 FM Global
Data Sheet 7-35, Air Separation Processes.
Data Sheet 7-50, Compressed Gases in Cylinders.

4.2 NFPA Standards

NFPA 50, Bulk Oxygen Systems at Consumer Sites.
NFPA 51, Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting and Allied Processes.
NFPA 55, Compressed and Liquified Gases in Portable Cylinders.
NFPA 99, Health Care Facilities.
NFPA 99B, Hypobaric Facilities

APPENDIX A GLOSSARY OF TERMS

Ignitable Liquid: Any liquid or liquid mixture that is capable of fueling a fire, including flammable liquids,
combustible liquids, inflammable liquids, or any other reference to a liquid that will burn. An ignitable liquid
must have a fire point.

APPENDIX B DOCUMENT REVISION HISTORY

January 2012. Terminology related to ignitable liquids has been revised to provide increased clarity and
consistency with regard to FM Global’s loss prevention recommendations for ignitable liquid hazards.
January 2000. This revision of the document has been reorganized to provide a consistent format and
information on air liquefaction processes, previously relocated to Data Sheet 7-35, Air Separation Processes,
has been deleted.
February 1975. Document was updated from information in the Handbook of Industrial Loss Prevention.
April 1994. Information on air liquefaction process relocated to Data Sheet 7-35, Air Separation Processes.

APPENDIX C SUPPLEMENTARY INFORMATION

C.1 General Information

The principal hazard of oxygen storage is exposure by other combustibles. If overheated by an exposure
fire, oxygen tanks or cylinders may rupture. An intense fire involving the containers and associated equipment
can occur in the oxygen-rich atmosphere near any breaks or leaks.

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Oxygen 7-52
FM Global Property Loss Prevention Data Sheets Page 5

C.1.1 Bulk Storage of Liquid Oxygen.

Where large quantities of oxygen are used, liquid-oxygen storage equipment is frequently installed. The
equipment usually is owned and maintained by the oxygen supplier. The volume-expansion ratio from
saturated liquid at one atmosphere to gas at atmospheric pressure is about 1:862.
Liquid-oxygen equipment consists of one or more specially designed and well-insulated storage containers,
a hot-water or steam-heated vaporizer, pressure regulators, relief valves, and flow controls (Fig. 1).
Liquid-storage containers are constructed of stainless steel or other metal with suitable properties for
low-temperature service in accordance with American Society of Mechanical Engineers (ASME) codes. A
gastight carbon steel jacket encloses the container, and the space between is filled with insulation. A high
vacuum is usually maintained in the space.

Fig. 1. Liquid-oxygen storage system.

Liquid-oxygen storage containers are usually located out of doors on steel supports or are housed in a
noncombustible building, with the auxiliary equipment located either below the container or in a separate
noncombustible building. The system is filled from similar containers mounted on trucks or railroad cars.

C.1.2 Bulk Storage of Gaseous Oxygen Gas

High-pressure [2,200 psi (150 b)(15 MP)] bulk storage usually is provided by storage receivers or banks of
various types and sizes of fixed or portable cylinders (Fig. 2). Fixed cylinders may be installed horizontally
or vertically and may be in a sheet metal enclosure or outdoors. They are filled by a compressor supplied with
gaseous oxygen from a low-pressure gasholder, fixed oxygen converter, or a transport liquid-oxygen unit.
Portable systems consist of a number of cylinders mounted in a steel cradle or cabinet or on a trailer or
semitrailer in either horizontal or vertical positions. Usually provision is made for several units so that empty
units can be replaced without interruption of the gas supply. A regulator may be provided for each cylinder

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7-52 Oxygen
Page 6 FM Global Property Loss Prevention Data Sheets

Fig. 2. High-pressure oxygen-gas storage. Typical portable installation, above; typical fixed installation, below.

bank, or all the cylinder banks may be connected to a single regulator. The piping is so arranged that
changeover from one bank of cylinders to another may be readily accomplished either automatically or
manually.

C.1.3 Liquid Oxygen Cylinders

Liquid-oxygen cylinders with integral provision for withdrawal of the oxygen as a gas are intended to fill the
quantity-demand gap between conventional gas-cylinder systems and large bulk-liquid systems. Usually,
no more than four cylinders are used in a single system.
The cylinders are combination storage vessels and vaporizers. They are jacketed, insulated containers, quite
similar to the arrangement of bulk liquid-oxygen code containers. The oxygen is at low pressure as in bulk
systems.
As compared with high-pressure gas cylinders, liquid-oxygen cylinders require different types of equipment,
installation, and method of handling.

C.1.3.1 Description
Cylinders are constructed in accordance with U. S. Department of Transportation (D.O.T.) regulations (Fig. 3).
They have a capacity of 248 lb (112 kg) or about 3.5 ft3 (100 dm3) of liquid oxygen, which is equivalent to
about 3,000 ft3 (85 m3) of gaseous oxygen at normal room temperature and room pressure. One cylinder has
the capacity of about 12 standard (245 ft3)(7 m3) gas-oxygen cylinders.
Liquid vaporization is continuous in spite of very efficient insulation and, if gas is not withdrawn, the internal
cylinder pressure will rise until the relief valve operates. In an upright cylinder with insulating vacuum intact
this will normally occur in three to six days, depending upon the amount of liquid in the cylinder. A full cylinder
takes a longer time. Under these conditions between 2 and 3 standard cubic feet per hour (57 to 85 dm3/hr)
of gaseous oxygen will be vented. Complete loss of vacuum could increase the discharge to about 50
standard cubic feet per hour (1.4 m3/hr).
Placement of cylinders in a horizontal position increases the vaporization rate because liquid is then in contact
with the uninsulated inner container neck. This reduces the hold time for full cylinders to as little as 4 hr. It
also increases the relief-valve discharge rate to about 300 standard cubic feet per hour (8.5 m3/hr) until the
liquid level drops below the neck of the inner container, usually in about 5 hr.

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Oxygen 7-52
FM Global Property Loss Prevention Data Sheets Page 7

Fig. 3. Typical cylinder for liquid oxygen, nitrogen, or argon.

Maximum continuous withdrawal rate from a cylinder is 300 standard cubic feet per hour (8.5 m3/hr) at 75
psi (5.2 b) (520 kPa). Rates up to 1,000 standard cubic feet per hour (28 m3/hr) can be obtained for intermittent
periods of about 5 min duration, interposed with 10-min recovery periods.
Cylinders can be manifolded using equipment specifically designed for service with these low-pressure liquid
cylinders. Standard gas cylinders may be connected to the distribution system as a standby supply.

C.1.3.2 Hazards
Liquid-oxygen cylinders are considered comparable to gas cylinders in overall hazard with the exception
that gaseous-oxygen discharge cannot be prevented if the hold time is exceeded. In most situations, as
indicated in extensive tests by the manufacturer, the hazard is that of escaping gaseous oxygen, which
intensifies any ordinary fire in the area. However, the possibility of liquid-oxygen escape is present and must
be considered in safeguarding an installation.

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7-52 Oxygen
Page 8 FM Global Property Loss Prevention Data Sheets

When liquid-oxygen cylinders are exposed to fire, the cylinder relief valve operates and the vaporizer coil
may rupture from fire temperatures as the metal weakens and interior pressure increases. In both cases,
discharge is gaseous oxygen.
When subjected to severe mechanical shock, the inner container may fail by breaking away at the neck. If
this occurs, oxygen enters the vacuum space and escapes to atmosphere as a gas through the bursting disk
of the outer container.

C.1.4 Piping Systems

Oxygen-distribution pipelines are supplied from a bulk storage system or cylinder manifold. Pressures vary
with individual installations and are usually about 150 psi (10 b) (1 MPa). At each point of use a station outlet
(Fig. 4) is provided consisting of a drop pipe, a shutoff valve, a station pressure regulator, and usually a drip
leg or an oxygen-line filter.

Fig. 4. Oxygen station outlets.

Properly installed and well-maintained oxygen-distribution systems present less fire hazard than portable
cylinders. Fires and explosions have occurred where flammable gases and ignitable liquids were allowed to enter the
oxygen system or where combustible materials were used for valve disks and packing.

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