Compressed gases can be hazardous due to their chemical properties, high pressure, and that gases are invisible, which have the potential to asphyxiate, burn or harm users but are safe when handled properly. This document explains the hazards associated with compressed gas cylinders and how to eliminate injuries or property damage by providing guidance on hazard identification, safe handling, storage, labeling requirements, engineering controls, and required personal protective equipment (PPE).


These guidelines apply to all Washington University in St. Louis (WUSTL) laboratories, research spaces, and classrooms on the School of Medicine and Danforth Campuses.


Environmental Health and Safety (EH&S)

  • Provide guidance, training resources, and recommendations for departments utilizing compressed gases.
  • Maintain and update compressed gas cylinder guidelines following changes in OSHA regulations, applicable building codes; or as needed following an accident or incident involving a compressed gas cylinder.
  • Conduct inspections to ensure compliance with these procedures.
  • Provide gas system planning guidance related to new construction and renovation.

Principal Investigators (PIs), Directors, Lab Managers, and Supervisors

  • Bear primary responsibility for compressed gas safety in the laboratory.
  • Ensure all staff are aware of compressed gas safety practices and are annually trained in proper storage, handling, and incident response.
  • Enter all compressed gases in Chemical Inventory and update with any changes.
  • Create standard operating procedures (SOPs), thoroughly describing how to safely perform work.
  • Ensure that proper Safety Data Sheets (SDSs) are available.
  • Provide documented training in your lab-specific training (Appendix 4) to compressed gas users.
  • Provide and maintain gas safety equipment in good working order.
  • Establish purchasing specifications (minimize quantity on hand, use just-in-time ordering).
  • Reduce the inventory of hazardous gases.
  • Arrange the return of gas cylinders when gas use is completed.

Users of Compressed Gas Cylinders

  • Receive proper training from PI or designee prior to use of compressed gases.
  • Read, understand, and follow cylinder markings, labels, and SDSs.
  • Wear the appropriate personal protective equipment (PPE) for the task being performed.
  • Inspect hazard control measures and PPE prior to each use.
  • Maintain awareness of hazards associated with the handling and use of compressed gases.


  • Deliver properly labeled compressed gas cylinders with safety caps in place.
  • Provide access to all relevant SDSs.
General Hazards

Compressed gases are used for fuel, refrigerant, instrument calibration, simulating distinctive atmospheres, gas chromatography, and welding. Gases may be flammable, corrosive, toxic, oxidizing, or pyrophoric. Some gases have multiple chemical hazards. These guidelines apply to all Washington University in St. Louis (WUSTL) laboratories, research spaces, and classrooms on the School of Medicine and Danforth Campuses.

Since cylinders are shipping containers, a DOT label is placed on each cylinder indicating its hazardous shipping classification. However, DOT classifications may not define every hazard of a particular product. The SDS is more detailed in hazard identification. Anhydrous ammonia, for example, is classified and labeled as a non-flammable gas in accordance with DOT. According to the SDS, the gas is acutely toxic, corrosive, and flammable. See Table 1 for more examples.

SDSs will also list physical hazards. Inert gases such as argon, helium, and nitrogen pose no chemical-specific hazards but can quickly create an oxygen-deficient atmosphere resulting in unconsciousness or death by asphyxiation. Compressed gases such as oxygen and carbon dioxide are extremely cold when released; exposure to skin will result in frostbite or burns. Every compressed gas cylinder is a potential projectile, even when empty, due to its high internal pressure. When cylinders are exposed to high temperatures or become physically damaged, a sudden release of pressure will result, and the tank may rupture. A ruptured tank releases more than enough energy to propel itself through walls and ceilings. The hazards associated with compressed gas cylinders pose a serious threat to life and property. When possible, use a safer substitute.


Compressed GasDOT LabelHazards described on SDS
Anhydrous Ammonia (NH3)Gas Under Pressure.Gas under pressure, flammable, toxic, corrosive, asphyxiant, marine pollutant
Chlorine (Cl2)Toxic Gas.
Gas under pressure, toxic, oxidizer, corrosive, marine pollutant * Fatal if inhaled
Hydrogen (H2)Flammable Gas.Gas under pressure, flammable
Hydrogen Sulfide (H2S)Toxic Gas.
Flammable Gas.
Gas under pressure, toxic, flammable, marine pollutant * Fatal if inhaled
Oxygen (O2)Gas Under Pressure.
Gas under pressure, oxidizer, cryogenic
Nitrogen (N2)Gas Under Pressure.Gas under pressure, asphyxiant, cryogenic
Silane (SiH4)Flammable Gas.Gas under pressure, pyrophoric, flammable, toxic, cryogenic
Labelings and Markings
  • Ensure labels and markings are seen from any approach to the cylinder.
  • Labels must be visible and legible at all times while in service. Cylinders with damaged or missing labels should be returned to the vendor.
  • Do not rely on the cylinder’s color to identify the contents. Do not repaint cylinders, even if they are dirty or rusty.
  • All gas lines leading from a compressed cylinder must be clearly labeled or identified.
Storage Requirements

General Storage Requirements

  • Secure the cylinder above its center of gravity (≈2/3 up the cylinder). If the chain or strap is too low or too high, it will not hold the cylinder if it starts to fall.
  • Straps are better for holding a group of cylinders.
  • Do not remove the cylinder’s cap without the tank being secure.
  • Lecture cylinders should be stored upright in a stand or lecture bottle holder.
  • Keep the number of cylinders in storage to a minimum. Use just-in-time ordering.
  • Ensure valves are completely closed and capped while not in use.
  • Keep cylinders away from flammable solvents, combustible material, excessive heat (≥50°C) and ignition sources such as breaker boxes and electrical connections.
  • Empty cylinders will have residual pressure and must be secured and not stored with full cylinders. An empty cylinder is one whose internal pressure equals atmospheric pressure (14.7 psi).
  • Group and store full or empty cylinders by hazard class to avoid incompatible gases from mixing.
  • A fire extinguisher should be kept near compressed gas storage areas.

Outdoor Storage Requirements

  • Store cylinders in a cool, dry, well ventilated, and fire-resistant area.
  • The ground should be graded to avoid the accumulation of water.
  • Outdoor storage areas must be at least 5 feet from any doorway or opening in a building that has two means or egress, and at least 10 feet from the any doorway or opening of any building that has only one egress, and 20 feet from automotive service or fuel dispenser.
  • Protect cylinders from the ground or continuous dampness to prevent rusting.
  • Cylinders stored outside should not be subjected to temperatures above 125 F.
  • Do not subject compressed cylinders to artificially low temperatures.

Indoor Storage Requirements

  • Store compressed cylinders in a well-ventilated area where it will not be knocked over or damaged by passing or falling objects, and at least 20 feet away from highly combustible material.
  • Do not store cylinders in public areas, corridors, stairwells, areas or egress, elevators, or by an unprotected ledge.
  • Cylinders should not be kept in unventilated enclosures like closets.
  • Compressed gas cylinders may not be stored or used in cold rooms.

Safe storage requirements once in the lab

  • Compressed gases must be in your chemical inventory. Update when necessary.
  • Review SDSs.
  • Store cylinders in a dry, well-ventilated place.
  • Do not place cylinders where they might become part of an electrical circuit.
  • All cylinders larger than lecture bottle size must be secured to a wall or other sturdy device using a strap or chain designed for this purpose.
  • Protective caps must be kept on at all times unless connected to equipment.
  • The container valve must be closed at all times (charged or empty) except when the container is in use.
  • When in use, valves on cylinders must be accessible at all times.
  • A flame may never be permitted to come into contact with any part of the compressed gas cylinder.
  • Do not subject cylinders to artificially created low temperatures without approval from the vendor and EH&S. Steel can undergo significantly decreased impact resistance and ductility at low temperatures.
  • Storage Limits – Practice just-in-time ordering. Limit quantities to the foreseeable requirements.
  • Subsurface use of flammable gases should be avoided whenever possible.
Safe Handling & Use Requirements
  • Only trained and authorized employees may handle, use, and store compressed gases.
  • Do not accept corroded, rusty, or damaged cylinders from vendors.
  • Do not accept cylinders from a vendor if the label is missing or defaced.
  • Leave valve protection caps in place until cylinders are secured and connected.
  • Do not use as a ground during electrical welding.
  • Never drop cylinders or strike them against one another.
  • Wear appropriate PPE. All PPE must be inspected for wear, damage or contamination prior to use. Always consider potential interaction with other chemicals/agents in the same experiment during your PPE selection.
  • Discontinue use of the cylinder when it is slightly empty (at most 25psi remaining); close valve to prevent air and moisture from entering.
  • Return unused and empty cylinders to vendor for reuse or refill as soon as possible.
  • Mark or tag empty cylinders “EMPTY” or “MT”.
  • Empty cylinders should be handled as if full.
  • Regularly inspect the entire supply system for leaks and degradation. If leaks are present, see “Responding to Leaks.”
  • Open cylinder valves slowly.
  • Close the cylinder valve when the cylinder is not in use or unattended.
  • Do not grease joints.
  • Pressure relief valves should be installed on all pressure regulators. Not all compressed gas cylinders have safety devices. Some gases are so toxic that their release through a safety device would be hazardous. Cylinders for these gases are built to withstand higher pressures than normal cylinders.
  • Comply with American National Standard Institute (ANSI) Z49.1 when using or storing oxygen-fuel gas containers for welding, cutting, and other similar activities.
  • If possible, purchase cylinders, including lecture cylinders, from suppliers that will accept returned empty cylinders; disposal of gas cylinders is expensive.

Transporting Cylinders

Compressed cylinders should only be moved by trained staff or vendors. Compressed cylinders must be in an upright position during transport.

Hand Transport

  • Cylinders should only be transported using an approved, chained gas cylinder cart. Do not roll or drag the cylinders.
  • Make sure the valve is capped.
  • Do not lift or carry cylinders of any size by the cap.
  • Avoid rough handling and banging.

Vehicle Transport

  • Transport via vehicle is not permitted
Personal Protective Equipment (PPE) Requirements

  • Skin protection
    • When using gases that are harmful by skin contact, wear protective gloves, lab coats, aprons, long pants or other clothing depending on the risk of skin contact. Select PPE made of materials that resist penetration or damage by the chemical. The SDS should recommend appropriate, compatible PPE. If it does not, contact the gas supplier or EH&S for specific information.
  • Eye and face protection
    • Always wear eye protection when working with compressed gases. Avoid ordinary safety glasses. Wear safety goggles which form a seal around the eyes to prevent vapors from entering the eyes. For splash protection, a face shield should be worn over safety goggles to protect the face.
  • Foot protection
    • Closed-toe shoes are required.
  • Respiratory protection
    • If proper engineering controls are used, respiratory protection should not be required.
    • If a fume hood or proper ventilation is not available or applicable and a respirator is required, contact the contact the Respiratory Protection Program Administrator in EH&S to complete a mandatory medical questionnaire, fit test, and training (314-362-6816).
Tubing and Piping Connections, Regulators and Valves

Hazardous gases must be dispensed using systems that are properly designed and compatible with the gas in use. Tubing and piping must be burst resistant with a burst pressure twice the maximum pressure on the second stage regulator. Researchers should contact the gas supplier to determine the correct piping and/or tubing for the gas being used. The following should be followed in regards to tubing and piping for compressed gas use.

  • Hard piping is the preferred method of piping for compressed gas use. Piping should be copper or stainless steel. Cast iron is not acceptable for use with compressed gases. Flexible tubing can be used in approved applications. Always contact your vendor to verify that piping is compatible with your gas.
    • When flexible tubing must be used, select tubing compatible with the gas in use. Flexible tubing is not for use with highly toxic gases. Flexible tubing can only be used within “line of sight”. Do not run flexible tubing through walls, ceiling spaces, doorways or other non-visible pathways.
    • Flexible tubing must be kept as short as possible. Do not exceed 5 feet.
    • 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 tubing. The system’s weakest component determines the overall pressure limit.
    • Flexible tubing deteriorates with age or exposure to chemicals or UV light. Inspect tubing regularly and replace when wearing is noticed.
  • Do not use Teflon tape on pipe threads where the seal is made at the threads. Compressed gas connections have metal to metal seals or gasket seals.
  • Leak-check tubing or piping connections when using hazardous gas.
  • Build a purge step into all experimental procedures to ensure that no gas is left in the tubing. This is especially important when disconnecting the tubing and removing it from a fume hood.
  • Secure and support tubing or piping to keep it in place and to prevent injuries if the connection fails under pressure.
  • Clearly label distribution lines and their outlets with the type of gas contained.


Pressure regulators are used to control the pressure of the gas within the cylinder so that it can be safely used in an operating system. The regulator reduces the pressure of the gas coming from the cylinder but it does not measure or control the flow of the gas, unless the regulator is equipped with a flow meter designed for that purpose.

When connecting a regulator to a cylinder, check that both the regulator and cylinder valve are completely free of dirt, dust, oil, and grease. If your compressed cylinder contains a non-hazardous gas, open the valve slightly and reclose slowly to blow out dust and debris. The most common regulator failure is caused by an internal leak.

  • Do not over-tighten or use excessive force to connect equipment.
  • Do not connect incompatible regulators; this could lead to valve and regulator thread damage, and an uncontrolled release of gas.
  • If your regulator does not fit your cylinder contact your vendor for a replacement cylinder.
  • Do not use Teflon tape to connect the regulator. Typically, connections are intended to be metal-metal, and tape may interfere with the connection.
  • After the regulator is attached, the cylinder valve should be opened enough to just indicate pressure on the regulator gauge, no more than one full turn. Check connections for leaks with SNOOP Liquid Leak Detector.
  • When you are ready to use the compressed gas cylinder, fully open the cylinder valve until you feel it stop. Then, close it one-quarter turn.
  • Never use the regulator as the shut off to a cylinder no longer in use. Close the valve. Then bleed the regulator.

Regulator Care and Safety

Regulators can explode frontward and/or backward. If a flow meter is not attached to your regulator, then angle the face of the regulator upward. Always stand to the side of a regulator with the valve between you and the regulator. Avoid reaching in front of the regulator face to open the valve.

  • When not in use, store the regulator in a clean, dry, and safe place.
  • Regulators for combustible gas should be cleaned carefully after each use to prevent residue from acting as a combustible fuel.
  • Inspect and test at least every 6 months after first use.
  • Regulators should be removed from service at least every five years and returned to the manufacturer for inspection and/or refurbished.
  • Only qualified repairmen service, test, and clean the regulator.
  • Regulators should be labeled with the last inspection date.
  • Use thread sealants that are compatible with the gas being used.
  • Regulators do not have an infinite life span.
  • DO NOT remove valve guards or valve protection rings.
  • Valve protection caps must remain on cylinders when not secured or not in use.
  • Return cylinders to vendor with the valve in the closed position and the protection cap on.
  • Never lubricate, modify, force, or tamper with cylinder valves.
  • Do not force valves open or closed.
  • When in use, cylinder valves in the fully open position can become stuck. To prevent this, ensure the valve is turned back half a turn.

Valve outlet threaded

  • The valve outlet on toxic, poisonous, or flammable gases are screwed left-hand (anti-clockwise) to tighten and will have a cut mark through the nut. Non-flammable gases are screwed right-hand (clockwise)to tighten
  • Lecture bottles all have identical valve threads, irrespective of the gas contained within.
  • Valve outlet threads on air and nitrogen are sized differently from oxygen to prevent the connection of oxygen to applications where only air (21% oxygen) is required or applications requiring inert gas.

Pressure Relief Valve

Most cylinders are fitted with a pressure relief device (PRD) to prevent the rupture of a cylinder. Compressed cylinders can rupture if exposed to fire, high temperatures or when excess pressure has built up inside of the tank. The PRD is designed to discharge some or all of the contents of the cylinder. When this happens, you will hear a high-pitched noise and a jet of gas at high speed.  PRDs are either a burst disc, fusible plug, pressure relief valve, or combination burst/rupture disc/fusible plug device. Never plug, restrict, or remove any relief device. Never attempt to cap or seal a venting relief device in any way.

A Burst Disc (Rupture Disc) is designed to burst open at a predetermined pressure leaving an open passage for gas to escape in the event of over-pressurization. The pressure rating of the disk is stamped onto the face of the device. Compressed air, argon, helium, nitrogen, oxygen, and carbon dioxide typically have a burst disc PRD.

Fusible Plugs are made of fusible metal alloy that will melt at a lower temperature than the surrounding plug body. If the plug is exposed to elevated temperatures the fusible alloy will melt and completely release the cylinder contents.  An example gas that uses this type of device is acetylene.

When a cylinder is equipped with a Combination Rupture Disc/Fusible Plug Device, which is a non-reclosing device, you have a pressure and temperature requirement before the disc will rupture. This device will not protect a cylinder from over-pressurization if the fusible alloy is not heated to its yield temperature. The fusible metal prevents premature rupture disc failure from momentary over-pressurization and protects the disc from external corrosion. Medical grade gas cylinders typically have this type of pressure relief device.

Pressure Relief Valve has a spring-loaded valve that is designed to discharge the cylinder’s contents if the tank exceeds the pressure setting. Once the excess pressure is relieved the valve will reseat without leakage. Low pressure liquid nitrogen cylinders are equipped with a pressure relief valve as primary protections and a rupture disc as secondary protection. The burst disc is a backup in the event the pressure relief device is not working.

Hazard-Specific Requirements

Flammable Gases flammable

Examples: Acetylene, ammonia, hydrogen, methane, propane and propylene

Lab-Scale Open Flames


  • Store flammable gases in well-ventilated areas, away from open flames, sparks, and other sources of heat or ignition.
  • Separate flammable gas cylinders at least 20 ft from flammable liquids, highly combustible materials, and oxidizers (oxygen tanks) and where electrical sparks could occur.
  • If separation is not possible, isolate the flammable gas cylinders by a non-combustible barrier that has a fire resistance rating of at least ½ hour extending at least 18 inches above the tallest container.
  • Storage and use of flammable gases outside of buildings must be separated from building openings by 25 ft (7.6 m). Fire barriers will be permitted to be used as a means to separate storage areas from openings or a means of egress used to access the public way. (NFPA 55
  • Storage and use of flammable compressed gases cannot be located within 50 ft (15.2 m) of air intakes. (NFPA 55
  • Separate LPG and acetylene by at least 20 ft. NOTE: No separation is required if the storage quantity of LPG is less than 1000 pounds.
  • Store acetylene containers with the valve end up. If an acetylene cylinder has been accidentally left on its side, set it upright for at least an hour before use. Otherwise, it will emit a burst of solvent instead of gas when the valve is opened.
  • To determine quantity on site, full and partially full cylinders are counted as full cylinders.


  • Signs are required and must be posted in areas with flammable gases. Signage must state that smoking or the use of open flame is prohibited within 25 ft (7.6 m) of the storage or use area perimeter (NFPA 55
  • Hazard labels and markings must be visible.

Engineering Controls

  • Flammable gas detection may be needed. Please contact EH&S for an evaluation
  • Sprinkler protection for gas cabinets and other protective features may be required.
  • Maintain portable fire extinguishers (carbon dioxide or dry chemical types) or other fire protection or suppression systems at storage locations.
  • EH&S requires labs to use a flash arrestor when working with flammable gases. A flash arrestor will prevent flashback, reversing the flame so it will not travel back through the line back into the pressure regulator or cylinder.
  • Ensure that all lines and equipment associated with flammable gas systems are grounded and bonded. Use intrinsically safe electrical devices.
  • Use non-sparking tools.
  • Portable blast shields may be used to supplement other controls to increase the user’s protection against explosions or sudden pressure releases.
  • Do not interchange flammable and oxidizing gases on the same equipment.
  • Do not use copper tubing in contact with acetylene gas. Acetylene may react with copper to form potentially explosive copper acetylide.

Other Handling Considerations

  • Do not use acetylene in its free state at pressures exceeding 15 psig.
  • To reduce the risk of explosion, do not open acetylene or other flammable gas cylinder valves more than ½ turn of the spindle.
  • Do not take cylinders containing oxygen, acetylene, or other fuel gas into confined spaces.
  • Do not leave gases to flow unattended.
  • Do not use combustible tubing or piping with flammable gases.
  • Practice just-in-time ordering. Only purchase for near-term work.
  • Tanks that have not been used for 3 or more months must be returned to the vendor.

Corrosive GasesCorrosive

Examples: Ammonia, chlorine, hydrogen chloride and methylamine.


  • Corrosive gases should be stored for the shortest possible periods before use, preferably less than three months. Practice just-in-time ordering/near-term work.
  • Tanks should not be kept on hand more than 6 months, up to one year maximum. Submit tanks to vendor once your research is completed.


Engineering Controls

  • Ensure emergency showers and eyewash fountains are available in areas where corrosive gases are used. Emergency showers and eyewash stations must be located on the same level as the hazard and accessible within 10 seconds (roughly 55 feet), and the path of travel shall be free from obstructions.
  • Activities that pose an inhalation hazard should be performed in a chemical fume hood to control exposure.
  • Manufacturer’s label with hazard information must be visible on all compressed cylinders.

Other Handling Considerations

  • Do not store tanks in areas where you have equipment that is sensitive to corrosion.
  • Frequently check cylinders to ensure the valve has not corroded. If corroded, contact the vendor.
  • Warning properties such as odor or eye, nose or respiratory tract irritation may be inadequate with some substances and should not be relied upon as a warning of overexposure.
  • Ensure that regulators and valves are closed when the cylinder(s) are not in use and properly purged, and cleaned with dry air or an inert gas such as nitrogen.
  • Ensure that when corrosive gases are discharged into a liquid, a trap, check valve or vacuum break device is employed to prevent dangerous reverse flow.
  • Wear appropriate PPE to protect all exposed skin and eyes from contact with corrosive or irritating gases and vapors.
  • Open in a fume hood or appropriate cylinder cabinet.
  • You must contact EH&S if a fume hood is not available or practical.

Toxic and Highly Toxic Gases:Toxic Gas.

Examples: Carbon monoxide, chlorine, hydrogen sulfide, and sulfur dioxide

Always consult with EH&S prior to the start of a project involving the use of highly toxic gases!


  • The outdoor storage or use of toxic or highly toxic compressed gases shall not be within 75ft (23m) of lot lines, streets, alleys, public ways or means of egress, or buildings not associated with such storage or use. (NFPA 55
  • Storage and use of toxic or highly toxic compressed gases cannot be located within 75ft (23 m) of air intakes) (NFPA 55
  • Do not storage hazardous gases in corridors or public areas of the building.


  • All areas in the lab where toxic gases are used must be labeled with a Particularly Hazardous Substances (PHS) label or symbol, including fume hoods and bench tops.
  • Manufacturer’s label with hazard information must be visible on all compressed cylinders.

Engineering Controls

  • Continuously mechanically vented gas cabinets are required for highly toxic gas cylinders.
  • Contact EH&S for recommendation on the appropriate sensors and alarms. Continuously-monitoring gas alarms are required when working with some hazardous gases.
  • Only open in a fume hood or appropriate cylinder cabinet.
  • Toxic gases should be purchased with a flow-limiting orifice.
  • Safety shields should be used when researchers are working with hazardous gases that pose a risk of explosion, splash, or exothermic reaction.

Other Handling Considerations

  • Tanks must be labeled if they are full or empty.
  • Flexible tubing is not for use with highly toxic gases
  • Purchase the smallest volume of gas needed for near-term work.

Experiments that require low concentrations of hazardous gases mixed with inert gases must be purchased pre-mixed.

Oxidizing Gases:Oxidizer

Examples: Chlorine, fluorine, nitrous oxide, and oxygen

  • Ensure equipment is free from grease, oils and other contaminants.
  • Do not handle cylinders with oily hands or gloves.
  • Use an oxygen-compatible material to clean all equipment that has been used with oxidizing gases.
  • Store oxidizers separately from flammable or combustible materials. Maintain a minimum distance of 20 feet, or establish a non-combustible barrier at least 5 feet high, having a fire rating of at least ½ hour.

Do not store near fuel-gas cylinders.

Pyrophoric Gases:Pyrophoric

Examples: Arsine, diborane, phosphine, and silane

Always consult with EH&S prior to the start of a project involving the use of pyrophoric gases!

  • Continuously mechanically vented gas cabinets are typically required for pyrophoric gas cylinders larger than lecture size and in use.
  • Pyrophoric gas cabinets must be sprinkled. (NFPA 55 6.17.3 Fire Protection)
  • Appropriate sensors and alarms should be used.
  • The workspace must be equipped with a continuous gas detection system.
  • The gas detection system must initiate a local alarm that is both visible and audible.
  • Activation of the gas detection system must automatically shut off the flow of gas related to the system being monitored.
  • The gas detection system must detect the presence of gas at or below the Lower Explosive Limit (LEL). Since all pyrophoric gases are also highly toxic, the system must detect the presence of gas at or below the OSHA permissible exposure level or ceiling limit of the gas. Review SDS for this information
  • Emergency power must be provided for the exhaust ventilation, gas detection system, and alarm systems when required.
  • All pyrophoric gas cylinders must be equipped with a Restricted Flow Orifice (RFO). RFOs are designed to allow the gas to flow during normal operation but limits the potential danger of an uncontrolled flow of gas during a failure by restricting the flow rate by a factor of 100..
  • Use appropriate PPE for handling pyrophoric gases, including a flame-resistant lab coat and safety glasses or goggles with a face shield.

See the Pyrophoric and Water-Reactive Materials Guidance and Policy for more information on pyrophoric gases and requirements for their use.

Inert Gases:Inert Gases

Examples: Argon, helium, krypton, neon, nitrogen, and xenon

  • Do not store asphyxiant gases in areas without proper ventilation, like cold rooms, closets, or a confined space. NOTE: Any gas that has the potential to displace oxygen in sufficient quantities can cause asphyxiation.
  • Inert gases that periodically vent may be safely stored  in well-ventilated areas, such as loading docks and large storage rooms.

Contact EH&S for an evaluation of inert gas storage areas and where cryogens are stored.

Examples: Liquid helium, liquid nitrogen and liquid oxygen

Cryogenic Liquids:

Low pressure liquid nitrogen storage tanks are in high use on campus. Cryogenic liquids build high pressure easily due to the large expansion ratio (700:1) from liquid to gas. As the liquid evaporates high pressure can occur, which can cause an explosion if the chemical is stored in a sealed or insufficiently vented container or compressed cylinder. Pressure will build up inside of liquid nitrogen tanks that are not frequently used. Since these cylinders are equipped with a pressure relief valve, loud bursts of air will be released from the pressure relief valve to decrease the internal pressure of the cylinder. The valve will then reseat after the release without leakage. This type of venting is normal and indicates the container is being protected from over-pressurization. Continuous venting through this valve may indicate the valve is frozen open. If the pressure relief malfunctions, a secondary valve, burst disc, will open to release pressure. Isolate any cylinders that are continuously venting through any of the relief devices and contact the vendor for removal.


  • Contact EH&S for an evaluation of your storage area and to determine monitoring requirements.
  • Do not store or use cryogenic liquids in cold rooms, regardless of volume. Simple asphyxiants such as
    liquid nitrogen do not have good warning properties. You might not feel “light-headed,” or you may simply
    pass out without any warning. Due to the large liquid to gas expansion that takes place upon evaporation,
    liquid nitrogen is capable of displacing sufficient oxygen to create an oxygen deficient environment in a
    small or insufficiently ventilated space, leading to the risk of asphyxiation

Engineering Controls

  • Use only equipment, valves, and containers designed for the intended product, service pressure, and temperature.
  • Inspect containers for loss of insulating vacuum. If the outside jacket on a container is cold or has frost spots, some vacuum may have been lost.
  • Contact supplier and/or EH&S. Repairs should be made by the manufacturer or an authorized company.
  • Ice or other foreign matter should not be allowed to accumulate beneath the vaporizer or the tank. Excessive ice buildup could result in the discharge of excessively cold gas or structural damage to the cryogenic container or surroundings.
  • All cryogenic systems, including piping, must be equipped with pressure relief devices to prevent excessive pressure build-up. Pressure reliefs must be directed to a safe location. Do not tamper with pressure relief valves or the settings for the valves.

Oxygen monitors should be in place in locations where large amounts of inert cryogenics are transferred or where a single failure mode can lead to oxygen levels below 15%. Liquid nitrogen is heavier than air, so it is recommended that the monitors are mounted closer to the ground as opposed to higher up in the air.

Required PPE

  • Lab coat
  • Goggles
  • Face shield
  • Closed-toe shoes
  • Long pants
  • Cryogenic gloves – these are not designed for full immersion and provide protection for short-term exposure

Transporting large low-pressure liquid nitrogen cylinders

  • Check that wheels are attached and in good condition.
  • Move cylinders by pushing them, never pull cylinders.
  • Use caution around uneven floors as the cylinder could tip.
  • Rotate the cylinder in a circular motion over lips and uneven surfaces, one wheel at a time.
  • If traveling between floors the cylinder should be transported on a freight elevator, if available.
  • Passengers are not allowed on the elevator when transporting low pressure liquid nitrogen cylinders. The liquid nitrogen cylinder must be loaded into the elevator by the user, with a sign warning others not to ride in the elevator. Before sending the elevator to the desired floor, ensure that another lab member is at the other end to immediately receive the cylinder.

Transporting Dewars

  • Dewars should be loosely capped or have a vented lid and transported on a cart.
  • Dewars holding less than 500mL can be hand carried for short distances down a hall or between labs if:
    • The dewar has a vented lid.
    • The dewar is the only thing you are carrying.
    • You are wearing proper PPE.
    • You carry the vessel with both hands as far from your face as comfortably possible.
  • Do not transport dewars of liquid nitrogen via the stairs.
  • Dewars of liquid nitrogen should be transported on cart via the freight elevated, if available in your building, without passengers. Post a sign on your dewar warning others not to ride in the elevator. Before sending the elevator to the desired floor, ensure that someone from your lab is at the other end to immediately receive the dewar.

Other Handling Considerations

  • Remove metal jewelry from hands and wrists before you begin working with cryogens.
  • When retrieving samples from dewars use forceps. Never place your fingers or hand directly into liquid nitrogen. Forceps need to be long enough to retrieve your samples so the cryogen does not enter your protective gloves.
  • In the event of skin contact with a cryogenic liquid, do not rub skin; place the affected part of the body under warm water (not to exceed 40°C [105°F]). Report all skin contact with cryogenic liquid to Protective Services/WUPD, your supervisor, and seek medical attention.
  • Transferring liquid nitrogen from open cryogenic containers, such as dewars, must be conducted slowly to minimize boiling and splashing of the cryogenic fluid.
  • Do not use a funnel when transferring liquid nitrogen from one container to another container.
  • Hot air, steam or hot water should be used to thaw frozen equipment. Exception: Do not use water to thaw liquid helium equipment.
  • Glass dewars should be taped solidly around the outside even if it is supplied with a mesh cover.
  • Liquid nitrogen may enter sample tubes that are not closed properly. These tubes will become projectiles as the liquid boils and pressure builds up. Always wear safety glasses when working with samples that were in liquid nitrogen.
  • Work with liquid nitrogen in a well-ventilated area and keep the liquid nitrogen vapor away from your face.
  • Do not sit liquid nitrogen dewars on bench tops when working, leave them on a cart or on the floor next to where you are working and out of the way of foot traffic.
  • Never pour cryogens down lab sinks.
  • For vehicle transportation, cryogenic liquid containers must only be transported by certified vendors and not within a personal vehicle.


Do not attempt to clean up a spill of liquid nitrogen. Evacuated from the lab and contact WUSM Protective Services or WUPD

Lecture Bottle Cylinders

Although small and easily transported, lecture bottles are still pressurized cylinders and present the same hazards
as larger cylinders. Lecture bottles are typically used for holding calibration gases or in applications where large
quantities of gases are not used. Unlike other gas cylinders, lecture bottles are not refillable and are purchased
outright by the laboratory. Most gas manufacturers do not take back lecture bottles and disposal costs are
expensive. Consult the gas supplier to find out if a refillable cylinder is available, and if possible, only order from
manufacturers who will accept lecture bottles for return.

  • Inspect the lecture bottle and regulator prior to use. Never use lecture bottles or regulators that are
    damaged or corroded. Dispose of lecture cylinders through EH&S.
  • Only use regulators and tubing that are appropriate for the gas. For example, stainless steel regulators
    and tubing must be used for corrosive gases. Using the wrong regulator can compromise the gas purity,
    cause equipment failure and cause injury to laboratory personnel.
  • Lecture bottles must be properly secured during use and lecture bottles containing hazardous gases must
    be used in a fume hood or gas cabinet.
  • Lecture bottles must be stored in an upright position in a lecture bottle stand or carrier.
  • Segregate incompatible gases, such as flammable and oxidizing gases.
  • Store toxic gases in a fume hood or a ventilated gas cabinet.
  • Regulators must be removed during storage. Label the regulator with the gas it is used for to prevent
    accidental misuse in the future.
  • Lecture bottles must be properly labeled. Re-label the lecture bottle if the label becomes illegible or falls
  • Do not store lecture bottles of hydrogen fluoride, hydrogen chloride, hydrogen bromide, or hydrogen
    iodide for long periods of time. These gases can react with the bottle over a period of years to produce
    dangerously high pressures of hydrogen gas in the lecture bottle

Cylinder Storage

Examples of proper storage-

Cylinder must be securely strapped or chained.

Use lecture cylinder stands.

Examples of poor storage-

Cylinder is not in use
and should be capped.

Cylinders are not protected by the chain.
Lecture bottles stored on their side are more susceptible to damage, corrosion and leaks.
Lecture bottles stored on their side are more susceptible to damage, corrosion and leaks.
Never store cylinders near a heat source.
Gases expand while heated.
Never store cylinders near a heat source. Gases expand while heated.
Maximum Allowances

The maximum allowed usage and storage of flammable or toxic compressed gases within a laboratory work area are mandated by the St. Louis City and County Fire Departments per the International Building Code (IBC). Limits vary depending on the type of gas and floor of the building the gas is being stored and used. Please contact EH&S for maximum volume limits for your area

Responding to Leaks

Proper quality control of materials and inspections, as required by DOT, minimize the probability of cylinder leaks. Compressed gas suppliers, such as Airgas and Praxair, are required to inspect cylinders for visual damage each time the cylinders are filled. In addition, gas producers must ensure the cylinder closure is completely leak-tight, and that cylinders are internally inspected and hydrostatically tested at the prescribed time intervals. Call the gas supplier to inform them of any problems.

When leaks occur inside a room, toxic gases create poisonous atmospheres, oxidizing gases create an atmosphere which promotes or accelerates combustion, and flammable or pyrophoric gases can result in fire and exploding cylinders.

Minor leaks pose a low risk of injury or exposure. If a controllable, slow release is present follow these steps:

  1. Notify personnel in the area. Notify Lab Supervisor, PI, and EH&S.
  2. Wear appropriate PPE such as safety goggles, face shield, gloves, aprons, etc.
  3. If the leak is in the gas supply system, close cylinder valve and tighten leaking connections.
  4. If the leak is at the cylinder valve stem, attempt to tighten the packing nut. Be careful not to over tighten. If the leak cannot be stopped, move the cylinder into a fume hood, under a local exhaust, or to an isolated, well-ventilated area to vent cylinder contents.
  5. If the leak is at the valve seal, valve threads, or other areas on the cylinder, move the cylinder into a fume hood, under a local exhaust, or to an isolated, well-ventilated area to vent cylinder contents.
  6. Keep flammable or oxidizing gases away from combustible materials.
  7. Evacuate the immediate area and post warning signs to prevent access by others.
  8. Remain outside the immediate area until cylinder contents have been exhausted.
  9. Contact supplier for removal and repairs.

Major leaks pose an immediate and serious hazard to personnel, property and the environment. This includes any leak from a toxic, pyrophoric, or corrosive gas. Follow these steps:

  1. Immediately notify affected personnel to evacuate the area.
  2. Activate building and fire alarms.
  3. Avoid breathing vapors of the leaked material. Seek medical attention for exposures.
  4. Call the appropriate emergency contact for your location to report the incident.
    • Danforth Campus: 314-935-5555
    • School of Medicine: 314-362-4357
    • North/West/South Campus & Tyson Research: 911 then 314-935-5555
  5. Provide emergency response officials with details of the incident upon their arrival.

Compressed Gas: According to the OSHA Hazard Communication Standard:

  • a gas or mixture of gases in a container having an absolute pressure exceeding 40 pounds per square inch (psi) at 70°F (21.1°C)
  • a gas or mixture of gases having an absolute pressure exceeding 104 psi at 130°F (54.4°C) regardless of the pressure at 70°F (21.1°C)
  • a liquid having a vapor pressure exceeding 40 psi at 100°F (37.8°C) as determined by ASTM D-323-72

Corrosive Gas: A gas that causes visible destruction of or irreversible alterations in living tissue by chemical action at the site of contact. (NFPA 55)

Cryogenic Liquid: A liquefied gas used to produce very low temperatures [below -153°C (-243°F). (OSHA)

DOT (Department of Transportation): Agency responsible for promulgating regulations controlling the transport of compressed gas cylinders.

Engineering Controls: A physical method of eliminating or controlling a hazard.

Flammable Gas: A gas having a flammable range with air at 20°C (68°F) and a standard pressure of 101.3 kPa (14.7 psi). (OSHA)

Highly Toxic Gas: A gas that has a median lethal concentration (LC50) in air of 200 ppm by volume or less of gas or vapor, or 2mg/L or less of mist, fume, or dust, when administered by continuous inhalation for 1 hour. A highly toxic gas is classified by the globally harmonized system (GHS) as category 1 for acute toxicity. (OSHA)

Leak Test: Testing pressurized apparatus by a reliable method. This may include coating all non-welded joints with a soap solution which is capable of forming bubbles at leak points, a pneumatic leak-down test using accurate gauges, or other effective measures. Gas systems must be leak tested at the following intervals: upon receipt, at installation, periodically during operation and at disconnect/shipping.

Lecture Bottle: A small compressed gas cylinder, typically 12-18 inches long and 2-3 inches in diameter.

LEL (Lower Explosive Limit): The minimum concentration of a particular combustible gas or vapor necessary to support its combustion in air.

NFPA (National Fire Protection Association): Organization which sets standards for the fire service and produces guidelines and best practices for industry.

OSHA (Occupation Safety and Health Administration): Agency under Department of Labor which ensures safe and healthful working conditions for working men and women by setting and enforcing standards and by providing training, outreach, education and assistance.

Oxidizing Gas: A gas that can support and accelerate combustion of other materials more than air does. (NFPA55)

PEL (Permissible Exposure Limit): The maximum concentration of an airborne contaminant to which a worker may be exposed for an 8-hour shift.

Personal Protective Equipment (PPE): Clothing and equipment worn by employees, students, contractors or visitors to protect or shield their bodies from workplace hazards.

Pyrophoric Gas: A gas with an autoignition temperature in air at or below 130°F (54.4°C). (NFPA 55)

Toxic Gas: A gas that has a median lethal concentration (LC50) in air of more than 200 parts per million but not more than 2,000 parts per million by volume of gas or vapor, or more than two mg/L but not more than 20 mg/L of mist, fume, or dust, when administered by continuous inhalation for one hour. (OSHA)