Compressed Gas Cylinders
Using compressed gases in the laboratory can be dangerous if they are not handled properly. Many gases can be explosive, flammable, corrosive, and toxic. Because the gases are under high pressure in tanks and cylinders, any release of gas can spread quickly and endanger lab personnel—including the possibility of
death from explosion or asphyxiation. Less-deadly safety risks include physical injuries from mishandling tanks, especially to the hands, feet, and lower back.
A safety plan for transporting, using, and handling
Because of these risks, standards have been established for transporting, using, and handling compressed gas tanks and cylinders. These regulations include:
Department of Transportation 49 CFR
- 49 CFR 171—general information
- 49 CFR 172—hazardous materials tables
- 49 CFR 178 – shipping container requirements
- OSHA 29 CRF 1910
- Comprehensive rules that discuss gas types, how to ensure the safety of tanks, handling and storage as per the Compressed Gas Association (CGA), pressure relief devices, and other safety recommendations
- NFPA 55 Compressed Gases and Cryogenic Fluids Code
- Handling and proper storage of tanks, safety data sheets, personnel training, operating procedures and best practices, employee training, other safety recommendations
Handling and transportation
The safety process starts when a full compressed gas cylinder is delivered to a facility. All tanks and cylinders must be carefully inspected before being accepted. Safety caps should be in place. Regulators should not be attached. Do not accept tanks that look damaged or poorly maintained (for example, oxidation or pitting). Prior to installation, inspect all piping, regulators, and stems. Be sure that tanks are marked with clear, easy-to-read labels that identity the type of gas, with the certification date from the vendor. Do not rely on cylinder color to identify the gas (color codes vary from supplier to supplier). Status (full, empty, in service) should also be identified and visible even after installation. Ask for the material safety data sheets (MSDS) for each gas type being received. Refuse to accept any tanks or cylinders that don’t meet these requirements (and don’t try to fix them yourself).
Once received, compressed gas cylinders must be secured in a vertical position. This includes during transport, storage, and use. Tanks should only be moved using wheeled carts—available from gas vendors and other laboratory supply companies—that are designed for this purpose. Check that the safety caps are screwed on securely. To minimize physically moving the cylinder, move the cart close to the cylinder and then carefully “walk” the cylinder on to the cart and fasten it securely with straps or chains so that it cannot slide, tilt, or fall over. Carts should always be used to move cylinders, even for short distances.
Even though they seem sturdy and safe, cylinders should always be handled carefully, without hurry. Cylinders that are dropped, or strike other tanks or hard surfaces, could explode, causing serious damage or even death. Never drag cylinders or roll them horizontally. Never lift a cylinder by the cylinder cap or by using magnets. If a cylinder must be moved manually, tilt it slightly sideways and roll it carefully along its bottom edge, maintaining good grip. Be sure the path of travel is clear of obstacles; use a spotter if needed for negotiating ramps or lift gates.
Caps, valves, and regulators
Cap all cylinders when not in use; this protects the valve stem and prevents any accidental release of the compressed gas, even if the cylinder falls. Do not try to force or fix any cylinder connection that is not working properly. If a connection is malfunctioning, it is likely broken or not the proper connection/valve for that cylinder. Never try to repair, pry, hammer, or “unstick” any valves, regulators, or pressure-relief devices. If it does not open easily by hand, call the gas distributor, even if this means a work delay.
To prevent leaks, be sure main valves are closed when the cylinder is not in use, even if it is empty. Air that enters an empty cylinder can also bring in moisture and other contaminants that can lead to corrosion, or possibly even an explosive chemical reaction. Any pressure in the regulators should also be released when the cylinder is not in use. Every time a cylinder is brought into service, a leak test should be performed to confirm there are no leaks when the cylinder is connected.
Regulators control the delivery pressure of gas from the cylinder so that it can be delivered at the optimum pressure for the work performed. Requirements for regulators vary according to gas type and cylinder size. It’s good practice to double-check that the correct regulator is being used for the gas and cylinder. It should also have the appropriate pressure range for the work being performed. Ideally the regulator should be twice as high as the required pressure. Use pressure regulators equipped with pressure relief devices and vent them if appropriate given the type of gas being used.
Two types of regulators are available for pressurized tanks: single-stage or two-stage. Single-stage pressure regulators are used when inlet pressure is steady throughout the application. With a two-stage pressure regulator, the first stage decreases the inlet pressure to a pre-set level; the second stage then further reduces this pressure to the desired pressure needed for the work being performed.
It is essential to keep regulators (especially for oxidant gases) free of surface oil and grease. These surface contaminants will combust in the presence of pure oxygen (this also reaffirms the importance of leak tests). Regular maintenance of cylinders, valves, regulators, and other devices is best performed by the original manufacturer or provider.
Storage of compressed gas cylinders
Cylinders must be stored according to hazard classification in a well-ventilated, above-grade, weather-proof storage area that is a safe distance from combustible materials, ignition sources, or intense heat. Store the oldest cylinders at the front, so they can be used first. Gas types should be separated from incompatibles. For example, flammable gases should be separated from oxidizing gases. Separation of incompatible gas cylinders can be achieved by open space (20 or more feet is recommended), fireproof partitions, or approved storage units.
Because they conduct electricity, metal cylinders must be kept away from electrical circuits, open flame, sparks, etc. Never place a cylinder close to an electrical conductor, such as metal pipes, that could accidentally carry current.
Storing cylinders in areas that exceed 130°F (54°C) violates Department of Transportation regulations. Gas expands when heated and increases pressure in the cylinder, increasing the risk of explosion. Tanks should not be stored in direct sunlight. Personnel sometimes overlook the fact that direct sunlight can increase temperatures in storage areas to well above 100°F—a potentially dangerous situation if compressed gas cylinders are stored there.
As during transportation, compressed gas cylinders must be stored in an upright position. Don’t store tanks on gas carts and do not strap cylinders together. Secure each tank with a chain, strap, or bracket to a stationary surface, such as a bench or wall. Two straps, one at about one-third of the cylinder height and the other at two-thirds of the cylinder height, are recommended to keep the tank from tipping or sliding.
When cylinders are empty, mark them as “empty” and arrange for the supplier to pick them up. Cylinders that contain “safe to breathe” gases like oxygen, nitrogen, and argon may be vented to allow residual gas to escape. If you choose to vent the residual gas, please consult your safety officer or gas provider regarding the best procedure. Venting oxidants (for example, oxygen) in a hazardous environment is not recommended. Cylinders that contain flammable or toxic gases cannot be vented and may need to be disposed of as hazardous waste.
Education = Safety
The most important step in the safe handling of compressed gas cylinders is to create an overall safety plan based on sound knowledge of the Department of Transportation (DOT), OSHA, and NFPA regulations for the handling, storage, transportation, and use of compressed gas cylinders. These standards are the basis of any comprehensive safety plan.
Employees who handle compressed gas cylinders should be familiar with the regulations. Gases are classified according to their physical and chemical properties—therefore staff must also have a deep understanding of these properties and the risks that they present in a laboratory or storage setting.
Much of this knowledge comes from the MSDS that vendors provide for each gas, including their safety hazards. These sheets, as well as other reference materials, should be placed in several areas in the workspace to provide easy access to this information. In the event of an emergency, this material must be available for first responders and safety personnel.
Lab directors or safety directors must follow the DOT, OSHA, and NFPA regulations and MSDS information (as well as other laboratory safety guidelines and resources) to develop a comprehensive safety plan (including an emergency response plan) that can be taught to employees, posted in the laboratory, practiced periodically, and updated when needed.
Train all employees and provide each worker with a copy of the safety plan. This will include a safety and response plan for each gas. Requirements should also be established for use of personal protective equipment, safe handling of compressed gas cylinders, the ergonomics of safe lifting and handling, and keeping aisles and pathways clear of obstacles or clutter.
Hopefully the comprehensive safety plan will prevent any serious accidents. However, in the event of an emergency, laboratory personnel must be able to react quickly (for example, know where to find emergency equipment, such as fire extinguishers, eyewash, etc.). Enforce the safety plan at all times and practice it regularly to ensure the safest workspace possible (and quick and correct responses, should an emergency occur).
In-house gas generation
In-house generators are available for each gas and multiple-gas generators are also available. The cost of operating an in-house gas generator is extremely low, since the only raw materials are air and electricity. Running and maintaining a gas generator system typically costs only a few hundred dollars a year. Return on investment takes about 12 months, depending on the specific usage and required purity. This is a significant ongoing savings compared to the recurring costs of cylinders.