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Working Safely With Compressed Gas

All compressed gases have the pressure hazard, but a gas may also have more hazards such as they may be toxic, corrosive, flammable, asphyxiating, oxidizing, pyrophoric and/or reactive. All may impact the design of the system and how the gases are used. Beware of oxygen deficiency hazard (ODH) situations.

General

Never Become Complacent When Using a Compressed Gas

Below are specific Do's and Don'ts for compressed gases, as well safety reminders and recommendations. For additional information, contact your ESH Coordinator, the Safety and Health Representative, Safety Engineering, or Industrial Hygiene Group leaders.

Do:

  • Implement appropriate controls for the long-term safety of the operation.
  • Use compressed gas system components in accordance with the limits and specifications of the cylinder, system, and component manufacturer or designer.
  • Wear safety glasses when pressurizing or working on compressed gas systems.
  • Shut off cylinders that are not in use and place a cylinder cap on any cylinder that is in storage or is not in use.
  • Keep outlet caps on the valve outlets at all times except when connected to dispensing equipment, if such devices are provided.
  • Isolate any system (piping, manifolds, containers, etc.) you are pressurizing whenever practicable. It is the user's responsibility to see that their system has proper pressure relief device(s) built into it. The relief device on the compressed gas cylinder's regulator is not designed to protect downstream systems. Pressure relief discharge points should consider venting to safe locations (not directed towards people or routed to safe locations for hazardous gases).
  • Use a suitable pressure-regulating device where gas is admitted to a system of lower pressure rating than the supply pressure, and where, due to the gas capacity of the supply source, the system rating may be exceeded. A pressure regulator is required regardless of the existence of a pressure relief device protecting the lower pressure system.
  • Ensure the area has proper ventilation or has had an oxygen deficiency hazard (ODH) analysis performed.

WARNING: EXPOSURE TO AN ATMOSPHERE WHICH HAS 12% OR LESS OXYGEN WILL BRING ABOUT UNCONSCIOUSNESS WITHOUT WARNING AND SO QUICKLY THAT THE INDIVIDUALS CANNOT HELP OR PROTECT THEMSELVES.

Don't:

  • Don't refill gas back into a cylinder or use a cylinder for storing any material. If material is accidentally forced back or sucked back into a cylinder, mark the cylinder well and inform your gas supplier. Almost all recent deaths involving compressed gas cylinders involved fillers at the compressed gas plants or users trying to put materials back into cylinders.
  • Don't rely on the color of the cylinder to identify the contents. If there is any conflict or doubt about the contents, do not use the cylinder. Return it to your vendor.
  • Don't allow cylinders to become part of an electrical circuit.

Regulators

Regulator Requirements

Use the appropriate regulator for the service.

  • Use a regulator to control pressure and flow from lecture bottles. The cylinder valve is never used as the primary control for flow or pressure.
  • Do not modify regulators. Never replace the CGA connection the regulator manufacturer has put on a regulator with one for a different gas service. Only the regulator manufacturer or a trained service representative can properly re-clean the regulator and knows the gas compatibility of the regulator's internal design.

NEVER USE AN ADAPTER BETWEEN A CYLINDER AND A PRESSURE REDUCING REGULATOR.

  • Check that the CGA connection(s) on the cylinder and the pressure reducing regulator fit together properly without being too loose or too tight. Proper connections will go together smoothly. Never use excessive force to connect a CGA connection.

NEVER USE AN AID (such as pipe dope or Teflon tape) TO CONNECT A REGULATOR TO A CYLINDER.

  • Two-stage regulator deliver a constant pressure as supply (cylinder) pressure changes.
  • Single stage regulators output pressure needs to be monitored and adjust pressure as supply (cylinder) pressure changes
  • Special regulators are required for gases such as propane, acetylene, LPG, ammonia, and CO. Liquefied gases also take special regulators. Discuss other exceptions with the ESH Coordinator.
  • Use gauges at 75% of the gauge's maximum face reading. For example, a 3,000-psi system should use at least 4,000-psi gauge. If your system can see a maximum pressure of 75 psi, the gauge monitoring the system should be at least 100 psi. (Immediately replace any gauge whose pointer does not go back to its zero point when pressure is removed.)
  • Confirm that the valve on the compressed gas cylinder and the pressure reducing regulator have the proper CGA connections for the pure gas (CGA V-1) or gas mixture (CGA V-7) you are using. All compressed gas cylinder connections can be found listed with their recommended gases and the maximum allowed pressures in CGA/ANSI V-1 (Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections).

Regulator Best Practices

Do not use a compressed gas cylinder without a pressure reducing regulator or device that will safely reduce the cylinder pressure to the pressure of your system. Whenever possible, use regulators that have both a high pressure gauge and a low pressure gauge—this allows you to monitor both the pressure in the compressed gas cylinder and the pressure in the system. After attaching a pressure reducing regulator to a compressed gas cylinder

  • Turn the regulator's adjustment screw out [counterclockwise] until it feels loose.
  • Stand behind the cylinder with the valve outlet facing away from you. Observe the high pressure gauge on the regulator from an angle - do not pressurize a gauge while looking directly at the glass or plastic face plate.
  • Then open the valve handle on the compressed gas cylinder S-L-O-W-L-Y until you hear the space between the cylinder valve gently fill the gas. You can also watch the pressure rise on the high pressure gauge. If you turned the regulator's adjustment screw back properly, there should be no gas flow out of the regulator or pressure rise on the low pressure gauge.
  • If you are using a non-toxic, non-flammable gas you can insure purity by shutting off the cylinder valve and gently cracking the CGA connection at the cylinder valve. (Generally three pressurizations with venting will insure the interior of the connection has a clean representative sample of the gas in the compressed gas cylinder. For toxic or flammable gases you can purchase special venting regulators which can be safely vented to a hood or gas cabinet.) NOTE: Low pressure cylinder valves (acetylene) should be opened the minimum amount required to deliver acceptable flow so that it can be closed as quickly as possible in an emergency situation. One and one half turns is usually sufficient to provide adequate flow.
  • When you are ready to use the compressed gas cylinder (containing non-toxic, non-flammable or non-combustible gas), fully open the cylinder valve until you feel it stop, then close it ¼ turn. (A fully open valve that has no play in it can confuse a person who is checking to see if it is open.) NOTE: Some high pressure valves seal (the stem) when they are fully opened. Care must be taken when turning the valve back to a closed position to avoid causing a leaky valve stem. Many accidents have been recorded by people trying to open a previously fully opened valve by using a large wrench. This could be a problem when using a toxic or flammable gas. Low pressure cylinder valves (i.e., acetylene) valves should be opened the minimum amount required to deliver acceptable flow so that it can be closed as quickly as possible in an emergency situation. One and one half turns is usually sufficient to provide adequate flow.

When turning on the gas:

  • "Back out" the regulator pressure control.
  • Slowly open the cylinder valve, standing away from the regulator body in case of diaphragm failure.
  • Slowly turn the regulator pressure control to achieve the desired pressure.

Never attempt to modify or repair a regulator yourself. Dispose of damaged regulators, or send them to the manufacturer or to a manufacturer-approved location for repair.

Tubing/Piping

  • Use "hard" piping (such as copper and stainless steel tubing) whenever possible (as opposed to flexible or plastic tubing). Never use cast iron pipe or fittings.
  • When flexible tubing must be used, select tubing compatible with the chemical and pressure properties of the gas being used in the system. Do not use flexible tubing for highly toxic gases. Flexible tubing should only be used within "line of sight." Do not run flexible tubing through walls, ceiling spaces, doorways, or other non-visible pathways if chafing is likely to occur.
  • Always clamp flexible tubing connections. Use a clamp approved for the maximum allowable pressure that the connection is subject to. Never use wire, which may cut the flexible tubing.
  • Most flexible tubing deteriorates with age or exposure to chemicals or UV light. Replace old flexible tubing before it deteriorates.
  • Always leak-check tubing or piping connections when using hazardous gases.
  • Secure and support tubing or piping to keep it in place and to prevent "whipping" if a connection fails under pressure.
  • Appropriately rated flexible lines are suitable for manifold/cylinder connections.

Considerations for Use by Type

This is information to consider in planning for the use of compressed gases. The gas or gases you use may have gas-specific hazards and use requirements. Contact your ESH Coordinator or Safety Engineering to determine if the gases you use have special requirements.

Sections

Hazard Classification Criteria Distribution Equipment Considerations Use/Storage Location Considerations
Non-Controlled Compressed Gas
(General category: All conditions are applicable in all other categories.)
A gas, other than in solution, packaged under the charged pressure is entirely gaseous at a temperature of 68°F (20°C) and has a LC 50 > 2000 PPM
  • Secure fitting.
  • Pressure rated for tank.
  • Gases can be asphyxiants.
  • Pressure hazard.
Corrosive Compressed Gas Halogens, halogenated gases or other gases that form strong acids or alkalines upon exposure to water.
  • Corrosion resistant system, (e.g., CGA Valve/Regulator, piping). Stainless steel is the only compatible metal for all cases, but will corrode if water is present, even from brief exposures of plumbing surfaces to the atmosphere.
  • A pump/ purge regulator manifold is strongly recommended.
  • Minimize moisture or humidity penetration into the system.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Emergency showers and eyewash stations are required.
  • Address safe shut down and emergency response in the facility’s Local Emergency Plan.
  • Follow inventory limits established in work planning.
Flammable Compressed Gas A gas that is flammable at atmospheric temperature and pressure.
  • Backflow/flash arrestor equipment when using with oxidizers.
  • System components are suitable for the gas.
  • Materials conform to ASME B31.3 Process Piping.
  • All lines and equipment are bonded and grounded.
  • 20-ft distance or ½-hour fire barrier separation from oxidizers.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Address safe shut down and emergency response in the facility’s Local Emergency Plan.
  • Follow inventory limits established in work planning.
Toxic Compressed Gas A gas with an LC50 between 200 PPM and 2000 PPM
  • Perform bubble leak test
  • No compression fittings (e.g.,swagelok or VCO) allowed
  • A pump/purge regulator manifold is recommended
  • Ensure quantity is in compliance with NYS Fire Code.
  • Monitor at point of use, during initial usage.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Address safe shut down and emergency response in the facility's Local Emergency Plan.
  • Follow inventory limits established in work planning.
Highly Toxic Compressed Gas A gas or vapor with an LC50 < 200 PPM or 2 mg/l or less of mist, fume, or dust, when administered by continuous inhalation for one hour.
  • Distribution lines must be assembled from all welded tubing.
  • Tees prohibited.
  • Helium leak test of 150% of use pressure.
  • Metal face seal fittings.
  • A pump/purge regulator manifold is required.
  • Ensure quantity is in compliance with NYS Fire Code.
    • Total quantities are kept as small as practical;
    • Follow inventory limits established in work planning;
    • Do not store near air inlets.
  • Special requirements for outside storage may be necessary.
  • Ventilated and sprinkled cabinet.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Total quantities are kept as small as practical.
  • Address safe shut down and emergency response in the facility's Local Emergency Plan.
  • Follow inventory limits established in work planning.
  • Leak Detection/in-line or hand held monitoring at the point of use
  • Emergency Response Plan.
Oxidizing Compressed Gas A gas that contains >21% oxygen or can react to release oxygen at >21% concentration, or can support and vigorously accelerate combustion in the presence of an ignition source and a fuel.
  • Hydrocarbon free distribution system
  • Materials are suitable for oxygen or oxidizer service, as applicable.
  • 20-ft distance or fire barrier (see definition) separation from flammables.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Address safe shut down and emergency response in the facility's Local Emergency Plan.
  • Follow inventory limits established in work planning.
  • Cleaned with oxygen-compatible materials, free of oils, greases, and other contaminates.
Pyrophoric Compressed Gas A gas capable of spontaneous combustion.
  • Purge with inert gas
  • Consider using flow check/back flow preventer valve.
  • A pump/purge regulator manifold is required
  • Special requirements for outside storage may be necessary.
  • Exhaust gas treatment may be necessary.
  • Building Manager or Local Emergency Coordinator identifies hazard to Fire Rescue in the Pre-Fire Response Plan.
  • Total quantities are kept as small as practical.
  • Address safe shut down and emergency response in the facility’s Local Emergency Plan.
  • Follow inventory limits established in work planning.

Information about Oxygen, Acetylene, Hydrogen and LPG Gases

The following provides some information specifically related to the storage, handling and use liquefied petroleum gases (LPG), hydrogen, acetylene, and oxygen. It is provided as an example of the types of gas-specific information that apply to these four common gases. The specific gas or gases use may have gas-specific hazards and use requirements. Contact your ESH Coordinator or Safety Representative to determine if the gases you use have special requirements.

WARNING: Oxygen cylinders must be stored separated from fuel gas cylinders by a minimum distance of 6 m (20 ft), or by a noncombustible barrier at least 1.5 m (5 ft) high, having a fire resistance rating of at least ½ hour.

CAUTION: Non-sparking tools must be used when working with or on flammable compressed cylinders and systems.


Sections

Oxygen

Oxygen is nonflammable. However, many materials that will not burn in air may burn in an oxygen-enriched atmosphere. Materials that burn in air will burn more vigorously in an oxygen-enriched atmosphere. Some combustibles, such as oil, will burn with near explosive violence in oxygen.

Avoid fire hazards by not doing the following:

  • Do not place oxygen cylinders near flammable material, especially oil, grease, or other readily combustible substances.
  • Do not store oxygen cylinders where oil can drip onto the cylinder, the valve, or other attachments using oxygen as a substitute for compressed air.
  • Do not lubricate oxygen valves, regulators, gauges, or fittings with oil or any other combustible substance.

Liquefied Petroleum Gases (LPG)

Almost all LPG sold commercially is treated with a distinctive odor to enable people to detect leaking gas at a concentration in air of not over 1/5 the lower limit of flammability. Some work requires LPG without the odor.

Failure to store and use portable LPG containers in the orientation as designed can be hazardous. Spring-loaded pressure relief valves (SRVs) are designed to operate in the vapor phase. If a cylinder is out of orientation (horizontal as opposed to vertical), then the relief valve may fail to operate properly when needed.

An unacceptable hazard may be created by keeping LPG inside structures and enclosures. The ESH Coordinator and/or Building Manager can provide guidance. (Cylinders of 1 pound or less are exempted.)

LPG installations are governed by numerous codes and standards. Your ESH Coordinator can provide assistance in planning any installation.

Only qualified vendors or staff who have received required training are allowed to refill LPG containers.

Acetylene

To allow safe handling of acetylene in cylinders, suppliers use specially made cylinders containing a porous packing material saturated with acetone in which acetylene is dissolved.

Acetylene cylinders are equipped with fusible plugs that melt at 100°C. (212°F). When the fusible plug is activated, the entire contents of the cylinder are allowed to escape.

Steel or wrought iron pipe are the safest materials to use with acetylene. Under certain conditions, acetylene readily forms explosive compounds with copper, silver, and mercury.

Acetylene has a wide flammability range (2.5% to 82% in air) and is extremely unstable. Under pressure and certain conditions acetylene can decompose with explosive force. A regulator set at 15 psig or less should be used to discharge acetylene from its cylinder. Acetylene should be discharged from a cylinder through a regulator at no higher than 15 psig.

Unsafe and unplanned discharge of acetone may occur unless acetylene cylinders are stored, used, and handled in the upright position.

To allow quick closing of the valve in the event of an emergency, the following practices must be used:

  • Open acetylene cylinder valves no more than 1½ turns.
  • Leave the wrench on the valve spindle when the cylinder is being used if the acetylene cylinder has a T-wrench instead of a hand wheel valve.

Hydrogen

Hydrogen has a very wide flammability range of 4% to 74% in air and it burns with an almost invisible flame. It has a very low ignition energy (0.02 millijoules), which is an order of magnitude less than for hydrocarbons.

  • It can be ignited by an almost imperceptible spark or by static electricity.
  • It heats when expanded and may self-ignite.

Because of its small molecular size, hydrogen diffuses rapidly through porous materials.

  • It also dissolves in and diffuses through metals slowly at ambient temperatures and more readily at elevated temperatures.
  • It may leak out of a system that is gas-tight for air or other gases at equivalent pressures.
  • It is noncorrosive and is considered nonreactive, but hydrogen service may degrade the mechanical properties of some metals by the process of embrittlement.

Leakage may occur if the piping, tubing, and fittings are not specifically suitable for hydrogen service, as well as for the pressures and temperatures involved. Cast iron pipe and fittings are not suitable. To prevent leakage after installation, all piping, tubing, and fittings must be tested and proved hydrogen-gas-tight at maximum operating pressure.

Leaking hydrogen may accumulate in high spots if ventilation is not adequate.

Hydrogen is colorless, odorless, and tasteless. Hydrogen is nontoxic and has been used in scuba diving mixtures. However, hydrogen can act as an asphyxiant by displacing oxygen in air.

Hydrogen cylinders (standard-sized DOT cylinders) are equipped with pressure relief valves (PRVs) that release the gas if the cylinder is subjected to abnormally high temperatures, as in a fire. The PRVs are a frangible disk and thermal fuse designed to burst under high temperature and/or excessive pressure.

The following activities are hazardous:

  • Attempting to mix gases in a hydrogen cylinder;
  • Transferring hydrogen from one cylinder to another;
  • "Cracking" a hydrogen cylinder valve to remove dirt or dust from the fittings before connecting to a regulator or manifold; self-ignition may occur;
  • Using hydrogen from a cylinder without reducing the pressure through a suitable regulator at the cylinder.

There are a variety of space and location requirements for hydrogen systems of the various sizes.