(Compiled from OSHA, CGA and Oklahoma State University)

There are several hazards associated with compressed gases, including oxygen displacement, fires, explosions, toxic effects from certain gases, as well as the physical hazards associated with pressurized systems. Special storage, use, and handling precautions are necessary in order to control these hazards.

Compressed-gas cylinders are designed to Department of Transportation (DOT) specifications. A standard 2-ksi+ (ksi=1000 psi) cylinder has 1.5 cubic feet of water volume and holds about 200 standard cubic feet of gas.

A standard cylinder has an outside diameter of 9 inches, but can vary in height-most being 50 inches tall. A compressed-gas cylinder should not be exposed to temperatures greater than 125° F.

Many industrial and laboratory operations require the use of compressed gases for a variety of different job tasks. Compressed gases present a unique hazard. Depending on the particular gas, there is a potential for simultaneous exposure to both mechanical and chemical hazards. Compressed gases can be:

Flammable or combustible - Gases are flammable if their flashpoints (temperature above which there is not sufficient vapors given off to ignite) are lower than room temperature. In these situations there is an ever present danger of fire or explosion.

Corrosive - A gas that causes visible destruction or permanent changes in skin tissue at the site of contact. Exposure to corrosive gas affects can be compounded due to the nature of the material.

Explosive Properties (Lower Explosive Limit and Upper Explosive Limit) - The lower limit of flammability of a gas or vapor at ordinary ambient temperatures expressed in percent of the gas or vapor in air by volume. This limit is assumed constant for temperatures up to 120 degrees C (250 degrees F). Above this, it should be decreased by a factor of 0.7 because explosiveness increases with higher temperatures. Below a certain concentration the gas or vapor is to lean to burn…conversely above a certain concentration the gas or vapor id too rich to burn.

Poisonous – Exposure to poisonous gases and vapors can go unnoticed for long periods of time. Dose is the all important measurement…as everything is poisonous if present in high enough concentrations.

Inert - An inert gas is a non-reactive gas and is usually a member of the noble gas family. Helium, neon and argon are the only true inert gases as they do not form any true compounds with other elements like the heavier noble gases. Examples include: helium, neon, argon, xenon, krypton, and radon.

IDLH - Immediately Dangerous to Life and Health is important terminology to understand. IDLH is an atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate danger to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere. Additional hazards of reactivity and toxicity of the gas, as well as asphyxiation, can be caused by high concentrations of even "harmless" gases such as nitrogen. Standardized safety procedures are important for handling; ?? All the various types of compressed gases, ?? the cylinders containing the compressed gases, ?? regulators or valves used to control gas glow, ?? and the piping used to confine or transfer gases during flow.

Identifying Contents:

Compressed gas cylinder contents must be clearly marked. Identification should be clearly visible on the cylinder, or a label affixed.

No compressed gas cylinder should be used that does not legibly identify its contents. If the labeling on a cylinder becomes worn or unreadable, or an attached tag is damaged to the extent where the contents cannot be identified, the cylinder should be marked accordingly such as, "contents unknown" or “contents unidentified”, and removed from service. Repairs to labels should be accomplished prior to the point where they become illegible. Cylinders where the contents cannot be identified should be taken out of service, stored in a safe manner and returned as soon as possible to the manufacturer.

Never make a determination as to contents by the color of the cylinder alone. Color coding is not reliable because cylinder colors can vary with a supplier. In addition, be aware that labels on caps have little value because caps are interchangeable.

Gas lines leading from a compressed gas supply station should be clearly marked as to the contents, area served, and the current emergency telephone numbers.

Labels should be color coded to distinguish hazardous gases (such as flammable, toxic, or corrosive substances) (e.g., a Red background and white letters).

Signs should be conspicuously posted in areas where flammable compressed gases are stored, identifying the substances and appropriate precautions that should be taken (e.g., HYDROGEN - FLAMMABLE GAS - NO SMOKING - NO OPEN FLAMES).

Cylinder Handling, Use and Storage:

Gas cylinders must be secured at all times to prevent them from falling over. Cylinders should be attached to a secure point, individually to the wall, placed in a holding cage, or have a non-tip base attached. Chains or sturdy straps should be used to secure them.

If a leaking cylinder is discovered, move it to a safe place (if it is safe to do so) and notify your emergency coordinator. You should also call the vendor as soon as possible.

Under no circumstances should any attempt be made to repair a cylinder or valve.

Cylinder valve outlet connections have been designed by the Compressed Gas Association (CGA) to prevent mixing of incompatible gases. Threads use varying diameters; some internally, some externally; some are right-handed, and some are left-handed. Generally, right-handed threads are used for non-fuel and water-pumped gases, and left-handed threads are used for fuel and oil-pump gases.

To minimize improper connections, only standard combinations of valves and fittings should be used in compressed gas installations. The threads on cylinder valves, regulators and other fittings should be examined prior to use.

Cylinders should be situated so the valve is accessible at all times. The main cylinder valve should be shut-off as soon as it is no longer in use (i.e., it should never be left open when the equipment is unattended or not operating). This can also prevent corrosion and contamination occurring from diffusion of air and moisture into the cylinder after it has been discharged.

Cylinders have either a hand wheel or stem valve. For stem valve cylinders, the valve spindle key should remain attached while the cylinder is in service. Only tools conforming to the recommendations made by the cylinder supplier should be used to open or close a valve. Pliers should not be used to open a cylinder valve. Some valves may require washers (e.g., air bottles); this should be checked before the regulator is fitted.

When opening the valve on a irritating or toxic gas cylinder, the cylinder should be positioned with the valve pointing away from them.

Open cylinder valves slowly. Open up the oxygen cylinder valve stem just a crack. Once the needle on the high pressure gauge has stopped, open up the valve all the way. This back-seats the valve, preventing the high-pressure gas from leaking out through the threaded stem.

Flammable Gases:

Flammable gases such as hydrogen or acetylene must not be stored close to open flames, where electrical sparks are generated, or where other sources of ignition may be present.

Acetylene cylinders should never be stored on their side.

Oxygen cylinders, regardless of being full or empty, should not be stored in the vicinity of flammable gases. Storage of oxygen cylinders requires that a minimum of 20 feet be maintained between them and flammable gas cylinders or the storage areas be separated, at a minimum, by a fire wall five feet high with a fire rating of 1/2 hours. Grease, solvents or oily materials should never be stored near oxygen; also oil or grease should not be applied to fittings.

As stated previously, Regulators are gas specific and not necessarily interchangeable. Always make sure that the regulator and valve fittings are compatible.

If there is a question as to the suitability of a regulator for a particular gas, check with your supervisor or call your vendor for advice. After the regulator is attached, the cylinder valve should be opened just enough to indicate pressure on the regulator gauge (no more than one full turn) and all the connections checked with a soap solution for leaks. Never use oil or grease on the regulator of a cylinder valve.

PIPING SYSTEMS

The following rules apply to piping systems:
• Copper piping should not be used for acetylene gas.
• Plastic piping should not be used for any portion of a high-pressure system.
• Do not use cast iron pipe for chlorine.
• Do not conceal distribution lines where a high concentration of a leaking hazardous gas could build up.
• Distribution lines and their outlets should be clearly labeled as to the type of gas they contain.
• Piping systems should be inspected for leaks on a regular basis.
• Special attention should be given to fittings as well as possible cracks that may have developed.

A cylinder should never be emptied to a pressure lower than 172 kPa (25 psi/in2) (the residual contents may become contaminated if the valve is left open). When work involving a compressed gas is completed, the cylinder must be turned off, and if feasible, the lines bled.

When the cylinder needs to be removed or is empty, all valves shall be closed, the system bled, and the regulator removed. The valve cap shall be replaced, the cylinder clearly marked as "empty," and returned to a storage area for pickup by the supplier.

Empty cylinders should be stored separately from full cylinders.

If the possibility of flow reversal exists, cylinder discharge lines should be equipped with approved check valves to prevent contamination of cylinders connected to a closed system. "Back pressure" is particularly dangerous where gases are used as reactants in a closed system. A cylinder in such a system should be shut off and removed from the system when the pressure remaining in the cylinder is at least 172 kPa (25 psi/in2). If there is a possibility that the container has been contaminated, it should be labeled and returned to the supplier/distributor.

Liquid bulk cylinders are generally used in laboratories where a high volume of gas is needed. These cylinders usually have a number of valves on the top of the cylinder. Valves should be clearly marked as to their function. These cylinders are designed to vent their contents when a preset internal pressure is reached, therefore, they should be stored or placed where there is adequate ventilation.

Always use safety glasses (preferably with a face shield) when handling and using compressed gases, especially when connecting and disconnecting compressed gas regulators and lines.

All compressed gas cylinders should be returned to the supplier when empty or no longer in service.

TRANSPORTING CYLINDERS

When moving or transporting a compressed-gas cylinder, make sure the regulator is off and a cap is attached to protect the valve. Never lift a cylinder by the protective cap as it can come off unexpectedly causing you to drop the cylinder.

Cylinders must always be adequately secured whether transporting, handling, or in use. When transporting cylinders horizontally on a wooden pallet, secure them with double bands and wooden blocks between the cylinders.

The cylinders that contain compressed gases are shipping containers and should not be subjected to rough handling. Rough handling can weaken a cylinder and render it unsafe for use. To protect the valve during transportation, the cover cap should be screwed on hand tight and remain until the cylinder is in place and ready for use.

1. Cylinders should not be rolled or dragged.
2. When moving large cylinders, they should be strapped to a properly designed wheeled cart to ensure stability.
3. Only one cylinder should be moved at a time.

References

OSHA Topics: Pressure Vessels
1926.57 Ventilation.
1926.60 Methylenedianiline.
1926.65 Hazardous waste operations and emergency response.
1926.103 Respiratory protection.
1926.153 Liquefied petroleum gas (LP-Gas).
1926.350 Gas welding and cutting. .
1926.801 Caissons (Underground Construction, Caissons, Cofferdams, and Compressed Air).
1926.803 Compressed air (Underground Construction, Caissons, Cofferdams, and Compressed Air).
1926.913 Blasting in excavation work under compressed air.

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