Compressed Gas Cylinder Safety

COMPRESSED GAS CYLINDER SAFETY

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Compressed gases present a unique hazard. Depending on the particular gas, there is a potential for simultaneous exposure to both mechanical and chemical hazards. Gases may be:

Flammable or combustible
Explosive
Corrosive
Poisonous
Inert
or a combination of hazards

If the gas is flammable, flash points lower than room temperature compounded by high rates of diffusion present a danger of fire or explosion. 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.

Since the gases are contained in heavy, highly pressurized metal containers, the large amount of potential energy resulting from compression of the gas makes the cylinder a potential rocket or fragmentation bomb (See "The One That Got Away").

Careful procedures are necessary for handling the various compressed gases, the cylinders containing the compressed gases, regulators or valves used to control gas flow, and the piping used to confine gases during flow.

Identification

The contents of any compressed gas cylinder must be clearly identified.

Such identification should be stenciled or stamped on the cylinder or a label. Commercially available three-part tag systems may also be used for identification and inventory.

No compressed gas cylinder should be accepted for use that does not legibly identify its contents by name. If the labeling on a cylinder becomes unclear or an attached tag is defaced to the point the contents cannot be identified, the cylinder should be marked "contents unknown" and returned directly to the manufacturer.

Always read the label!!

Never rely on the color of the cylinder for identification. Color coding is not reliable because cylinder colors may vary with the supplier. Additionally, labels on caps have little value because caps are interchangeable.

The labels should be color coded to distinguish hazardous gases (such as flammable, toxic, or corrosive substances) (e.g., a yellow background and black letters).

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

The One that Got Away

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The anchoring of compressed gas cylinders, to keep them from being knocked over with the accompanying possibility of breaking off the valve, is an accepted safe practice. However there has been some skepticism as to what would happen if a cylinder valve was knocked off.

While it wasn't asked for, we now have first-hand knowledge as to what happened in one case, thanks to a compressed gas cylinder (CO2) that caused a few moments of frenzied activity in a building under construction.

Six 220-cubic foot cylinders, part of a fire extinguishment system, had been moved away from their wall supports to allow painters to complete the painting of the area. While moving them back into position, it was noticed that one cylinder was leaking. The painter had the cylinder leaning against his shoulder, and was attempting to scoot it across the floor. At this time, the valve separated from the cylinder and was projected backward hitting the side of a stainless steel cabinet.

The man suddenly found himself with a jet-propelled 215 pound piece of steel. He wrestled it to the floor, but was unable to hold it. The cylinder scooted across the floor hitting another cylinder, knocking it over and bending its valve. The cylinder then turned 90 degrees to the right and traveled 20 feet where it struck a painters scaffold causing a painter to fall 7 feet to the floor. After spinning around several times, it traveled back to its approximate starting point, where it struck a wall.

At this point, the cylinder turned 90 degrees to the left and took off lengthwise of the room chasing an electrician in front of it. It crashed into the end wall 40 feet away breaking four concrete blocks. It turned again 90 degrees to the right, scooted through a door opening, still chasing the electrician. The electrician ducked into the next door opening, but the cylinder continued its travel in a straight line for another 60 feet, where it fell into a truck well striking the truck well door. The balance of the cylinder pressure was released as the cylinder spun harmlessly around in the truck well area.

The painter who fell from the scaffold received multiple fractures of his leg.

It is surmized that the cylinder valve had obtained previous damage, and it was a matter of chance that it separated from the cylinder at this particular time.

This incident illustrates what can happen when a valve is separated from a compressed gas cylinder. The one contained pressure of about 900 pounds per square inch, but many cylinders are pressurized to 2200 pounds per square inch. If you have any doubts about the need for anchoring compressed gas cylinders, you might think about the 2200 pounds per square inch and ask yourself, "what if....?"

In preventing the accidental release of compressed gases, all precautions must be taken to avoid dropping, knocking over, rolling or dragging cylinders as well as striking cylinders against each other. This means that it is imperative that all cylinders be stabilized in storage, transportation, and in use.

Handling & Use

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The following video is a supplement to the training session.

Compressed Gas in Quicktime Movie
RunningTime: 6 minutes

When transporting gas cylinders, use an appropriate hand truck and strap the cylinder down. Never drag or roll cylinders. Leave the valve cover cap on until the cylinder is secured in its area of intended use.

Gas cylinders must be secured at all times to prevent tipping.

Cylinders may be attached to a bench top, individually to the wall, placed in a holding cage, or have a non-tip base attached. Chains or sturdy straps may be used to secure them.

Always read the label!!

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

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

Standard cylinder-valve outlet connections have been devised by the Compressed Gas Association (CGA) to prevent mixing of incompatible gases. In general, right-handed threads are used for non-fuel and water-pumped gases, while left-handed threads are used for fuel and oil-pump gases. To minimize undesirable connections, only CGA standard combinations of valves and fittings should be used in compressed gas installations; the assembly of miscellaneous parts should be avoided. The threads on cylinder valves, regulators and other fittings should be examined to ensure they correspond and are undamaged.

Cylinders are equipped with either a hand wheel or stem valve. For cylinders equipped with a stem valve, the valve spindle key should remain on the stem while the cylinder is in service. Only wrenches or tools provided by the cylinder supplier should be used to open or close a valve. At no time should pliers be used to open a cylinder valve. Some valves may require washers; this should be checked before the regulator is fitted.

Cylinder valves should be opened slowly. Oxygen cylinder valves should be opened all the way. 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. Oxygen cylinders must have the valve opened up all the way because of the high pressure in the cylinder. There is a back-seating valve on the oxygen cylinder. This prevents the high-pressure gas from leaking out through the threaded stem.

When opening the valve on a cylinder containing an irritating or toxic gas, the user should position the cylinder with the valve pointing away from them and warn those working nearby.

Cylinders containing flammable gases such as hydrogen or acetylene must not be stored in close proximity to open flames, areas where electrical sparks are generated, or where other sources of ignition may be present.

Cylinders containing acetylene shall never be stored on their side.

An open flame shall never be used to detect leaks of flammable gases. Hydrogen flame is invisible, so "feel" for heat. One common practice is to use a natural bristle broom to "sweep" the air in front of you. All cylinders containing flammable gases should be stored in a well-ventilated area.

Oxygen cylinders, full or empty, shall not be stored in the same vicinity as flammable gases. The proper storage for oxygen cylinders requires that a minimum of 20 feet be maintained between flammable gas cylinders and oxygen cylinders or the storage areas be separated, at a minimum, by a fire wall five feet high with a fire rating of 0.5 hours. Greasy and oily materials shall never be stored around oxygen; nor should oil or grease be applied to fittings.

Regulators are gas specific and not necessarily interchangeable!

Always make sure that the regulator and valve fittings are compatible.

If there is any question as to the suitability of a regulator for a particular gas, 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.

The following rules should always be followed in regards to piping:

Copper piping shall not be used for acetylene.
Plastic piping shall 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 can build up and cause an accident.
Distribution lines and their outlets should be clearly labeled as to the type of gas contained.
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 possible, the lines bled.

Empty and full cylinders should be stored in separate areas.

Where the possibility of flow reversal exists, the cylinder discharge lines should be equipped with approved check valves to prevent inadvertent contamination of cylinders connected to a closed system. "Sucking back" is particularly troublesome 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 so labeled and returned to the supplier.

Liquid bulk cylinders may be 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. All valves should be clearly marked as to their function. These cylinders will also vent their contents when a preset internal pressure is reached, therefore, they should be stored or placed in service 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, including lecture-size cylinders, must be returned to the supplier when empty or no longer in use.

Compressed Gas Cylinder Quiz

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First Name: Last Name:
Student/Staff ID:
Supervisor:

Cylinders must be used in an upright and secured position
		True
		False

The cap must be left on the valve when the cylinder is not in use.
		True
		False

Mismatched threads may be used if they don’t leak.
		True
		False

Valves must be opened slowly.
		True
		False

Regulators valves are an option, not a necessity
		True
		False

If a leak occurs, just tighten all the fittings until the leak stops
		True
		False

Any regulators valve works with any gas.
		True
		False

If a leak occurs the cylinder should be taken outside, tagged, and the proper authorities notified..
		True
		False

Oxygen may be substituted for compressed air
		True
		False

Before removing a regulator valve, the cylinder valve must be closed and the regulator valve opened to release any pressure.
		True
		False

NOTE When finished, print out a copy and return it to your Safety Officer. Or...

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Last Modified: 10/07/2008