2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 22.1 General Safeguards For All Gases ................................................................................................. 2
2.3 Safeguards For Flammable Gases ................................................................................................. 32.3.1 Construction and Location .................................................................................................... 42.3.2 Occupancy ............................................................................................................................. 42.3.3 Protection .............................................................................................................................. 42.3.4 Ignition Source Control .......................................................................................................... 5
2.4 Safeguards for Acetylene ................................................................................................................ 52.4.1 Occupancy ............................................................................................................................. 5
2.5 Safeguards for Anhydrous Ammonia ............................................................................................... 52.5.1 Occupancy ............................................................................................................................. 5
2.6 Safeguards for Oxygen ................................................................................................................... 62.6.1 Occupancy ............................................................................................................................. 6
2.7 Safeguards for Poisonous and Irritating Gases .............................................................................. 62.7.1 Occupancy ............................................................................................................................. 6
2.8 Safeguards for Chemically Active Gases. ....................................................................................... 62.8.1 Occupancy ............................................................................................................................. 6
3.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................... 73.1 Compressed Gases ......................................................................................................................... 73.2 Cylinder Marking .............................................................................................................................. 73.3 Safety Devices ................................................................................................................................. 7
4.0 REFERENCES ..................................................................................................................................... 104.1 FM Global ...................................................................................................................................... 104.2 NFPA Standards ............................................................................................................................. 104.3 Others ............................................................................................................................................ 10
APPENDIX A GLOSSARY OF TERMS ..................................................................................................... 10APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 11
List of TablesTable 1. Sprinkler System Design and Water Supplies for Compressed Gases ......................................... 3Table 2. Cylinder Data for Industrial Gases .................................................................................................. 8
FM GlobalProperty Loss Prevention Data Sheets 7-50
This data sheet covers compressed gases in cylinders.
1.1 Changes
September 2002. Clarification was made to Table 2, Cylinder Data for Industrial Gases.
2.0 LOSS PREVENTION RECOMMENDATIONS
2.1 General Safeguards For All Gases
2.1.1 Occupancy
2.1.1.1 Protect cylinders against mechanical damage. Provide racks or other means to hold them securely.Keep valve caps in place except when cylinders are in use.
2.1.1.2 Use specially designed holders for moving cylinders by hoist, crane, or truck. Do not handle withelectromagnets, ropes, or slings. For manual handling, provide sturdy hand trucks mounting one or twocylinders.
2.1.1.3 Permit only authorized, trained personnel to have access to cylinders. Keep cylinder rooms and fencedareas locked to prevent tampering.
2.1.1.4 Post the names of the gases to be stored in cylinder storage areas.
2.1.1.5 Do not store cylinders where they will be exposed to temperatures above 125°F (52°C). Do not per-mit flames to contact the surface of a cylinder nor permit a cylinder to become part of an electric circuit. Donot store cylinders under refrigeration without the approval of the supplier. Many steels undergo decreasedductility at low temperatures.
2.1.1.6 In outdoor locations, keep cylinders off the ground on a raised concrete pad or noncombustible rack.Surround the area with a substantial wire fence, and eliminate dry grass, weeds, and all other combus-tibles. A noncombustible canopy to shield cylinders from the weather and direct rays of the sun is desirable.
2.1.1.7 Use piping and fittings suitable for the contained gas and pressure, installed in accordance withaccepted methods. Provide cylinder valves, regulators, and safety relief devices, and use only Approved mani-fold assemblies for connecting cylinders together.
2.1.1.8 Operate cylinder valves and regulators in accordance with the manufacturer’s instructions. Whenusing the gas, open valves slowly to the wide open position. Keep valve handles in place for quick emer-gency shutdown. Acetylene cylinder valves should be opened only 1-1⁄2 turns.
2.1.1.9 Maintain cylinders and accessories in good condition. Painting or repairs to cylinders, valves, andsafety relief devices should be done only by the owner or manufacturer of the cylinders.
2.1.1.10 If safety relief devices become defective, or if a cylinder leaks and the leak cannot be remediedby simply tightening a valve gland or packing nut, close the valve and move the leaking cylinder outdoorsto a well-ventilated location. Attach a suitable tag or warning sign and return the cylinder to the gas sup-plier or cylinder manufacturer for repairs.
2.1.1.11 Do not accept delivery from the gas supplier unless cylinders are clearly and legibly marked withthe name of the gas contained. Impress on plant personnel the importance of careful checking to ensure useof designated gas for specific processes. Connectors having special sizes and threads are recommendedto prevent connecting wrong cylinders.
2.1.2 Protection
2.1.2.1 Provide automatic sprinkler protection if building construction or occupancy is combustible. Sprin-kler system design and water supplies should be in accordance with Table 1, unless other occupancy in thevicinity requires a greater degree of protection.
7-50 Compressed Gases in CylindersPage 2 FM Global Property Loss Prevention Data Sheets
2.2.1.1 Cylinders of liquefied gases are charged by weight; the liquid portion should not completely fill thecylinder at temperatures below 130°F (54°C).
2.2.1.2 Nonliquefied gases and gases in solution are charged by pressure, which should not exceed thedesign service pressure of the cylinder at 70°F (21°C).
2.2.1.3 Use appropriate cylinder valve outlet and inlet connection. Cylinder valve outlet and inlet connec-tions are standardized in American and Canadian Standard Compressed Gas Cylinder Valve Inlet and OutletConnections (ASA-B57.1 and CSA-B96) to avoid improperly connecting a cylinder of one class of com-pressed gas to a piping system or charging device containing another noncompatible class of gases.
2.3 Safeguards For Flammable Gases
Escape of flammable compressed gases due to failure of equipment, human failure, premature operationof safety relief devices, or rupture of cylinders exposed to fires in other materials has caused many severegas fires and explosions. The locating of cylinder storage and manifold facilities in plant yards or detachedbuildings is recommended. Limited numbers of cylinders are acceptable in cut-off rooms or main areas ofbuildings, depending on the density of the gas, building construction, protection, and other factors.
Automatic sprinklers provide effective control of fires involving flammable-gas cylinders by cooling andpreventing gas discharge caused by melting of fusible plugs, or released by relief valves of exposed cylinders.
Table 1. Sprinkler System Design and Water Supplies for Compressed Gases
A. Nonflammable gases or flammable gases up to 3000 cu ft (90 m3).Occupancy
ClassSprinkler
TemperatureRating
TypeSystem
Density of Sprinkler Discharge Area of Operation
gpm/ft2 (mm/min) ft2 (m2)OrdinaryHazard
Any Wet 0.15 (6) 2500 (225)Dry 0.15 (6) 3500 (315)
2.3.1 Locate outdoor cylinder storage facilities of over 6000 cu ft (180 m3) total capacity at least 25 ft (7.5m)from any unprotected wall opening in any important building. Where the capacity can exceed 15,000 cu ft(450 m3) of a heavier-than-air gas, storage should be at least 50 ft (15 m) from any unprotected opening.
2.3.1.2 Detached buildings for flammable-gas cylinders should preferably be located at least 50 ft (15 m) fromimportant buildings and equipment. Use light noncombustible construction on steel framing except within50 ft (15 m) of important buildings that are combustible or have unprotected openings; these walls shouldbe of substantial, fire-resistive construction.
2.3.1.3 Cut-off rooms or enclosures at exterior walls of important buildings are acceptable for storage oflighter-than-air flammable gases in cylinders. Construction should be of 2 in. (50 mm) cement plaster andmetal lath on steel framing or other material having at least equal fire and explosion resistance. Entranceshould be from outside the main building, with no interior doorways or other openings to manufacturing areas.
2.3.1.4 Explosion venting should be provided in detached buildings, cut-off rooms, and enclosures hous-ing flammable-gas cylinders, in the ratio of at least 1 ft2 of vent area per 15 ft3 (1 m2/4.5 m3) of room vol-ume. Corrugated metal, corrugated asbestos, and lightweight insulated metal panels, arranged to releasewhen subjected to a 20 psf (1 kPa) internal pressure, or Approved explosion-venting windows are accept-able. Explosion venting may be omitted from detached buildings having less than 400 ft2 (36 m2) of floorarea.
2.3.2 Occupancy
2.3.2.1 Storage of lighter-than-air gases should conform to the following standards:
a) In main areas of buildings, limit the amount of gas to 3000 ft3 (90 m3) of cylinder capacity.
b) In cut-off rooms with automatic sprinkler protection, limit the amount of gas to 15,000 ft3 (450 m3) ofcylinder capacity.
c) In cut-off rooms without automatic sprinkler protection limit the amount of gas to 6000 ft3 (180 m3) ofcylinder capacity.
d) For acetylene and ammonia, also see special safeguards below.
2.3.2.2 Safeguard heavier-than-air gases, as follows:
a) Permit only one cylinder at a time to be used indoors in a main area and move the cylinder outdoorswhen not in use. If more than one cylinder is required for a process, locate all out of doors and pipe thegas to the point of use.
b) Natural ventilation will normally be adequate in large areas having high roofs or ceilings. Positive ven-tilation should be provided in pits, basements, or other below-grade spaces to which the gas may flow.
c) Do not locate cylinders in basements or other low spaces or where escaping gas can penetrate to suchspaces.
d) If cylinders are manifolded, provide hydraulic flame arresters on the discharge side of fuel-gas-pressureregulators where an oxygen or air mixture may form in the supply line and there is a possible ignitionsource, or where oxygen or air may back up in the supply line.
2.3.2.3 Provide natural ventilation through permanent louvered openings near floor and ceiling.
2.3.2.4 Keep stored cylinders well away from combustible materials, open flames, or other sources of ignition.So far as practical, this also applies to cylinders in use.
2.3.3 Protection
2.3.3.1 Buildings of noncombustible construction containing lighter-than-air flammable-gas cylinders withtotal capacity below 6000 ft3 (180 m3) do not require sprinkler protection. However, if there is combustibleoccupancy, heavier-than-air flammable-gas cylinders or if the cylinders are an exposure hazard to personnel,other buildings, or important equipment, automatic sprinklers should be installed over the cylinders and for20 ft (6 m) beyond in all directions in accordance with Table 1.
7-50 Compressed Gases in CylindersPage 4 FM Global Property Loss Prevention Data Sheets
2.3.4.1 Install electrical equipment in cylinder rooms as specified in the National Electrical Code for Class I,Division 2 locations.
2.3.4.2 Heat cylinder buildings and rooms by steam or hot water.
2.4 Safeguards for Acetylene
Special cylinders used for acetylene contain a porous material and acetone, in which the gas dissolves andbecomes practically stable. The porous filler absorbs the acetone and eliminates large voids in which decom-position might occur.
Cylinders are commonly manifolded to furnish larger amounts of acetylene where generators are not avail-able. This involves the handling of gas at approximately 250 psi (1.75 MPa), at which pressure explosivedecomposition may occur if the gas is subjected to heat or shock. The parts of Approved manifolds that areexposed to cylinder pressure are designed to withstand high pressures and prevent a decomposition explo-sion from passing into the cylinders or piping. A regulator should be located on the manifold discharge. AnApproved medium-pressure hydraulic flash arrester, with relief valve set at 15-20 psi (105-140 kPa) shouldbe installed between the regulator and distribution piping.
2.4.1 Occupancy
2.4.1.1 Do not handle cylinders roughly, subject them to hydrostatic test, or take any other action that cancreate large voids in the mineral filler.
2.4.1.2 Provide separate storage locations for acetylene and oxygen or chlorine cylinders. A gas-tightnoncombustible partition will serve to separate a detached building or cut-off room for this purpose.
2.4.1.3 Store and use cylinders in an upright position to prevent loss of acetone.
2.4.1.4 Do not withdraw acetylene from a cylinder or manifold at a rate in excess of one-seventh of the totalcylinder capacity per hour. Provide additional cylinders or portable manifolds if needed to supply higherdemand without exceeding this rate.
2.4.1.5 On indoor manifolds, limit the amount of gas connected to 3000 ft3 (90 m3). Limit the amount ofacetylene cylinder storage indoors, not in use or connected to manifolds, to 2000 ft3 (60 m3).
2.4.1.6 Use a pressure regulator at the discharge of an individual cylinder or manifold to reduce the gaspressure to 15 psi (105 kPa) or less.
2.4.1.7 Keep acetylene cylinder valves closed when gas is not being used, and open the valves only 1-1⁄2 turnswhen in use.
2.5 Safeguards for Anhydrous Ammonia
(See also Data Sheet 7-13, Mechanical Refrigeration.)
Although designated a green label gas by the DOT, anhydrous ammonia has an explosive range of 15 to28 per cent by volume in air, and will burn or explode under favorable conditions of temperature, pressure,or contamination. It starts to decompose into nitrogen and hydrogen at 840 to 930°F (450-500°C), and com-bines with silver oxide and mercury to form explosive fulminating compounds. Moist ammonia reacts with zinc,copper, silver, tin, and their alloys, causing rapid corrosion.
2.5.1 Occupancy
The following special safeguards are in addition to the general safeguards for flammable gases, althoughgreater quantities of ammonia in cylinders may be accepted indoors under favorable conditions:
2.5.1.1 Limit the amount of anhydrous ammonia in main plant areas to two 10-cylinder banks of 160-lb (72-kg)cylinders, or the minimum required for a 24-hr supply, whichever is smaller. Where larger quantities areneeded, locate the cylinders outdoors or in a detached building or cut-off room.
2.5.1.2 Natural draft ventilation is acceptable. Ordinary fixed lighting fixtures may be used.
Compressed Gases in Cylinders 7-50FM Global Property Loss Prevention Data Sheets Page 5
2.5.1.3 Do not use galvanized materials, brass or copper pipe, or soldered joints for ammonia distribution.Do not use cast-iron fittings or other cast-iron components. Use extra-heavy steel pipe and fittings where linepressure exceeds 125 psi (875 kPa).
2.5.1.4 Cylinders may be arranged to discharge either liquid or gaseous ammonia. Manifolded cylindersarranged for withdrawal of liquid ammonia introduce a hazard under certain conditions. A cylinder may becomecompletely full of liquid ammonia from other cylinders, and if the valves are closed, cylinder rupture is pos-sible. When it is necessary to connect together two or more cylinders for liquid discharge, install a checkvalve in the discharge line at each cylinder.
2.5.1.5 Wherever practical, arrange manifolded cylinders to discharge gaseous ammonia.
2.6 Safeguards for Oxygen
Standard cylinders are usually charged to 2200 psi (15 MPa) pressure, and contain about 20 lb (9 kg) ofoxygen. Bursting disks designed for operation at 2,600 to 3,000 psi (18-21 MPa) are provided on the cylin-der valve. The outlet connection has a special thread to prevent accidental connections with the wrongapparatus.
Approved manifolds are constructed of nonferrous metal with welded, soldered, or screwed joints, designedto withstand high pressure and connected to a single regulator. The manifold is commonly divided that oxygenis used from half the cylinders at a time and empty cylinders can then be replaced without interrupting thesupply.
2.6.1 Occupancy
2.6.1.1 Separate oxygen cylinders from acetylene generators, from cylinders or manifolds containing flam-mable gases, and from other combustible materials. Gas-tight fire partitions having at least 1⁄2-hr fire-resistance rating are suitable as cutoffs.
2.6.1.2 Locate oxygen cylinders and manifolds outdoors, in detached buildings, or in a cut-off room ofnoncombustible construction.
2.6.1.3 Do not use oil or grease for lubricating valves, gauge connections, or other parts of the oxygen system.
2.7 Safeguards for Poisonous and Irritating Gases
Gases such as chlorine and sulfur dioxide present little fire hazard, but if released in a fire may interfereseriously with fire fighting.
2.7.1 Occupancy
2.7.1.1 Permit only one cylinder at a time in main indoor areas.
2.7.1.2 If two or more cylinders are required, provide a small detached building of noncombustible construc-tion, or a room or enclosure cut off from main areas by a blank gas-tight wall. Provide a remotely con-trolled valve or other accessible means for shutting off the gas in an emergency.
2.7.1.3 Keep the cylinder location completely free of combustibles, including flammable gases.
2.7.1.4 Main indoor areas should have positive exhaust ventilation.
2.8 Safeguards for Chemically Active Gases.
Certain combinations of gases will react chemically to produce heat or cause a fire or an explosion. (SeeData Sheet 7-46/17-11, Chemical Reactors and Reactions.)
2.8.1 Occupancy
2.8.1.1 Cylinders of chlorine and acetylene should not be stored in the same area.
2.8.1.2 Combinations of gases that will react to produce flame should not be released or stored in the samearea.
7-50 Compressed Gases in CylindersPage 6 FM Global Property Loss Prevention Data Sheets
A great variety and quantity of compressed gases in cylinders are stored and handled at industrial proper-ties for cutting and welding, furnace atmospheres, fuel, chemical processes, and other purposes. Their useintroduces hazards of fire and explosion, increased rates of combustion, exothermic chemical reactions, orserious interference with manual firefighting efforts, depending on the characteristics and properties of thespecific gases. Properties and cylinder data for a number of industrial gases are listed in Table 2. For safe-guards for LP-gas cylinders, see Data Sheet 7-55/12-28, Liquefied Petroleum Gas.
3.2 Cylinder Marking
Only cylinders designed and safeguarded in accordance with DOT regulations for interstate shipment shouldbe used for compressed gases. They are marked with the DOT specification number, and usually with thedesign service pressure of the particular cylinder. In Canada, applicable regulations are those of the Board ofTransport Commissioners for Canada.
Cylinders under DOT control carry a red label for flammable gases, a green label for nonflammable gases,a white label for poison gases, or a corrosive or flammable liquid label. Absence of a label does not guar-antee that the gas is non-hazardous; it may indicate only that the cylinder is not subject to DOT regula-tions or is shipped at a pressure below that which requires a label. Similarly, the presence of a green label doesnot necessarily guarantee that the gas offers no fire or explosion hazard. Anhydrous ammonia, for example,is classed as a green label gas but forms explosive mixtures with air.
Cylinders should be further identified in accordance with ANSI Z48.1 entitled American Standard Method ofMarking Portable Compressed Gas Containers to Identify the Material Contained, which applies to gas con-tainers having a maximum water capacity of 1,000 lb (450 kg) by weight or 120 gal (0.45m3) by volume, andwhich requires legible marking by stenciling, stamping, or labeling with at least the chemical or commonlyaccepted name of the gas. Dependence on color coding alone as a means of identification of compressed-gas cylinders is not recommended. Color coding is acceptable for such purposes as ownership identifica-tion, manufacturer’s segregation, housekeeping, and maintenance.
3.3 Safety Devices
Most DOT cylinders are required to be equipped with an Approved safety device to prevent explosion of nor-mally charged cylinders when involved in fire. Exceptions include certain small cylinders, those containingnonliquefied gas at 300 psi (2.1 MPa) or less pressure at 70°F (21°C) and those containing poison gas or cer-tain other toxic or irritating gases.
Approved devices constructed in accordance with the Safety Relief Device Standards of the CompressedGas Association include frangible disks, fusible plugs, relief valves, and combinations. Frangible-disk rat-ings do not exceed the minimum required test pressure of the cylinders with which they are used. Whentested, frangible disks burst at between 90 and 100 per cent of their rated bursting pressure. Fusible plugsare available in two common types: CG-2, which melts at 157 to 170°F (70-77°C) and CG-3, which melts at208 to 220°F (97-104°C). Combination devices have fusible metal on the discharge side of the frangibledisk to prevent bursting of the disk at ordinary temperatures.
Relief valves have flow-rating pressures that do not exceed the minimum required test pressures of therespective cylinders. The start-to-discharge pressure is 75 to 100 per cent of the cylinder test pressure, andthe reseating pressure is not less than the pressure in a normally charged cylinder at 130°F (54°C). Com-bination relief-valve thermal devices open at a predetermined temperature and pressure, and reseat at apredetermined pressure.
Compressed Gases in Cylinders 7-50FM Global Property Loss Prevention Data Sheets Page 7
Trimethylamine (CH3)3N 20(140) 600 (18) 100(45) 2.03 Flammable gas Severe
Vinyl chloride C2H3Cl 30(210) 850(25.5) 150(68) 2.15 Flammable gas Severe
Vinyl methyl ether C3H6O 28(195) 310(9.3) 50(22.5) 2.00 Flammable gas Severe
Xenon Xe 100(700) 4.53 Nonflammablegas
None
*From manufacturer’s literature, or calculated from the following formula to obtain a rough approximation:
Cylinder capacity (cu ft) = cylinder contents (lb) × 12.4calculated density (from table)
4.0 REFERENCES
4.1 FM Global
Data Sheet 7-13, Mechanical Refrigeration.Data Sheet 7-46/17-11, Chemical Reactors and Reactions.Data Sheet 7-55/12-28, Liquefied Petroleum Gas.
4.2 NFPA Standards
NFPA 50A, Gaseous Hydrogen Systems at Consumer Sites.NFPA 51, Oxygen-Fuel Gas Systems for Welding and Cutting.NFPA 56F, Nonflammable Medical Gas Systems.
There are no conflicts with these NFPA standards.
4.3 Others
ASA-B57.1 and C5A-B96, American and Canadian Compressed Gas Cylinder Valve Inlet and OutletConnectors.
ANSI 248.1, American Standard Method of Marking Portable Compressed Gas Containers to Identify theMaterial Contained.
APPENDIX A GLOSSARY OF TERMS
Compressed gases: are defined by the Department of Transportation as any material or mixture in containershaving an absolute pressure in excess of 40 psi (280 kPa) at 70°F (21°C) or in excess of 104 psi (720 kPa)at 130°F (54°C) or any liquid flammable material having a Reid vapor pressure exceeding 40 psia (280 kPa)at 100°F (38°C). Other gases that do not fall within this definition may also be hazardous and require simi-lar safeguards.
7-50 Compressed Gases in CylindersPage 10 FM Global Property Loss Prevention Data Sheets
