Compressed and Liquefied Gases

Compressed gases in the laboratory expose lab personnel to a variety of risks and hazards. Most notable are the risks associated with the chemical material contained in the cylinder and physical hazard represented by the steel cylinder maintained under high pressure.

The chemical properties must always be noted - flammable materials are capable of ignition and explosion, toxic gases may cause injury or death upon exposure, and even non-toxic materials are capable of injury or death if the gaseous concentration displaces enough oxygen to cause asphyxiation. And no one who has seen the results of a cylinder which has fallen and taken off with the force of a bomb or rocket, could ever doubt the physical hazard presented by the innocuous appearing gas cylinder.

Despite these hazards, the gas cylinder is rarely considered by lab personnel as a threat to their safety. It remains the "sleeping giant".

FLAMMABILITY AND HEALTH CHARACTERISTICS OF COMMON COMPRESSED AND LIQUEFIED GASES

"W" indicates water reactivity, "oxy" indicates oxidizing hazard.

"*" indicates the material is present as a liquefied gas.

Please note those gases which have a health hazard rating of 3 or 4. These gases should always be stored in a continuously ventilating hood.

Warnings for Commonly Used Gases

Safe Handling and Use Guidelines

1. Plan carefully when setting up an experiment which involves gaseous materials and gas cylinders.

• Ask questions of the suppliers when purchasing gaseous materials - especially with regards to waste disposal and their cylinder return policy. Only purchase cylinders from companies that will accept the cylinder back for disposal. The cost of disposal for gas cylinders is dependent upon the material, but even non-hazardous cylinders can be costly to dispose.
• Don't purchase a larger cylinder size than necessary, excess reactant can be a problem for disposal, increases the risk to a larger area if accidentally released, is more difficult to store in a ventilated area if required, and takes up more room in the hood or on the floor.
• NFPA sets limitations on the number of cylinders that should not be exceeded in a laboratory. Do not acquire more than:
  • three 10" x 50" flammable gas or oxygen cylinders and
  • three 4" x 15" cylinders of toxic gases (such as arsine, chlorine, fluorine, hydrogen cyanide, nitric oxide)
  • NFPA allows for the use of liquefied petroleum gas cylinders within the lab, however, Texas laws state that no liquefied petroleum gases (i.e., C₃ or C₄ such as butanes, propanes, etc.) may be kept within an occupied building (Texas Railroad Commission rules).
• Make sure you have adequate ventilation to bring in and work with toxic gases. These materials will require constant local ventilation to ensure the safety of the personnel. Adding ventilation is not usually a straight forward task - it usually takes considerable money and time to have installed, so plan accordingly.

2. Be familiar with the guidelines on safe transport of high pressure cylinders:

• when the cylinder is not in use the valve protection cap must be in place to protect the valve;
• never drag, slide or roll the cylinder - get a cylinder cart or truck and use it;
• always have the protective cap covering the valve - never transport with the regulator in place; and
• make sure the cylinder is secured to the cart during transport.

3. Special precautions are also required when storing cylinders:

• cylinders must be secured at all times to a fixed location - a wall, the labbench, etc.;
• they must be secured at a point approximately 2/3 of its height, using appropriate material - chain, plastic coated wire cable, commercially available cylinder straps, etc.;
• as with any hazardous material, you may not store gas cylinders in public hallways or other unprotected areas;
• cylinders must be secured individually, i.e., one restraint per cylinder; and
• cylinders should be segregated in hazard classes while in storage, at the minimum, oxidizers (such as oxygen) must be separated from flammable gases, and empty cylinders should be isolated from filled cylinders.

4. Before the cylinder is first used the following precautions should be taken:

• make sure the cylinder is equipped with the correct regulator. Always use the regulator designed for the material in use, and be especially careful that under no circumstances is grease or oil used on regulator or cylinder valves because these substances may cause an adverse, dangerous reaction within the cylinder.
• the cylinder should be placed so that the valve handle at the top is easily accessible at all times.
• open the valve slowly and only with the proper regulator in place - the valve should be opened all the way. Never leave a valve part way open - either open it all the way or close it all the way.
• the valve should never be left open when equipment is not in use, even when empty; air and moisture may diffuse through an open valve, causing contamination and corrosion within the cylinder.
• if using a toxic or irritating gas, the valve should be opened only while the cylinder is in a working fume hood and even so, it would also be prudent to direct the valve and potential gas flow away from lab personnel.

5. When cylinders are in use consider the following:

• never heat the cylinder to raise the pressure of the gas - this may defeat the safety mechanisms built in by the supplier.
• keep the cylinder clear of all sparks, flames and electrical circuits.
• never rely on the color coding to identify the gas! Different manufacturers may use different coding systems.
• never refill a cylinder - mixing of residual gases in a confined area may result in a serious and devastating reaction.
• don't use oxygen in place of compressed air.
• don't use copper fittings or tubing on acetylene tanks - explosion may result.
• wear safety equipment appropriate for the hazard potential of the material you are working with.

6. Leaking cylinders constitute a threat that may be so serious that entire facilities may be called on to evacuate and outside help may be required to assist. Leak detection procedures should be implemented prior to use of any system using compressed gas. This can be accomplished in the following manner:

• for a flammable gas, a flammable gas detector, a soapy water solution or a 50% glycerin-water solution may be used;
• at temperatures at or below freezing, the 50% glycerin-water solution should be used;
• for systems where toxic or corrosive gases will be used, first test the system with an inert gas before introduction of the hazardous material.

7. If a leak is detected, consider the following options:

• if the cylinder contains a flammable, inert or oxidizing gas, remove it to an isolated area, away from incompatible materials. Allow it to remain isolated until the gas has discharged, making certain that appropriate warnings have been posted.
• if the gas is corrosive, remove the cylinder to an isolate, well-ventilated area, away from incompatibles. The stream of leaking gas should be directed into an appropriate neutralizing material. Be careful of any reaction product that may be formed as the leaking gas and neutralizing material react! Be especially cautious that the reactant is not allowed to be sucked back into the cylinder where further dangerous chemical reaction could occur.
• if the material is toxic, the cylinder should be removed to an isolated, well-ventilated area, but only if this is possible while maintaining personal safety. It may be necessary to call for a general evacuation of the facility and the cylinder approached only by trained emergency response personnel wearing protective apparel and self-contained breathing apparatus (SCBAs).
• if the leak is at the junction of the cylinder valve and cylinder - DO NOT try to repair! Instead, contact the supplier and ask for response instructions.

8. After the cylinder is no longer needed, the following steps should be taken:

• never completely empty the cylinder; always leave a residual gas pressure of 30psi.
• if the research experiment is over and the cylinder still contains hazardous material, the cylinder should be submitted for disposal or arrangements made for its transfer to a colleague that will use the material.
• do not keep hazardous materials in the lab beyond the time they are needed. Cylinders have a finite life expectancy. This is especially true for cylinders containing corrosive materials. If you are not using it - get rid of it!
• if the cylinder is empty, replace the cap and remove it to the storage area for empty cylinders. Mark it "MT" or label in some other fashion that will allow everyone to know its status.

Copyright © 1996 by College of Science, Texas A&M University