Compressed gases, though widely used in USC research laboratories, USC shop locations (instructional, fabrication), and USC facilities, present physical, chemical, and health hazards. It is critically important then to consult key references (including manufacturer’s safety guidelines) before planning and executing work with compressed gases. See the sections below to get started.



Compressed gases have inherent hazards that include:

  • Uncontrolled release of energy (pressure) e.g., 2,000 – 3,000 psi of compressed nitrogen is equivalent to a stick of high explosive.
  • Asphyxiation. Inert and non-flammable gases may displace oxygen and cause rapid suffocation or death.
  • Toxicity
  • Flammability, including possible explosion from ignition (e.g., spark of static electricity) of a gas-air mixture
  • Corrosion of skin, eyes, respiratory tract
  • Corrosion of incompatible tubing, valves, and fittings
  • Fire or explosion hazards from oxidizing gases
    • High-pressure oxygen may cause spontaneous ignition or explosion if equipment is contaminated by traces of oils or grease, or if loose particles are present which may ignite due to impingement in a rapid gas flow! NOTE: Compressed oxygen service requires pipework and fittings to be “oxygen-cleaned” via recognized NASA (NASA MSFC-SPEC-164) or CGA (CGA G-4.1) standards.
    • Other strongly oxidizing gases (e.g., fluorine, oxygen difluoride) exhibit similar or higher hazards of ignition due to contamination.

Effective safety management to eliminate or greatly reduce the risks these hazards present utilizes the Hierarchy of Safety Controls.

NOTE: Ensure that the lab has adequate safety/engineering controls (e.g., cross-purge assemblies, gas cabinets, gas alarm systems, and automatic shutoff in case of exhaust failure) in place prior to gas purchases.

Cylinder Valve Safety

Follow these safety measures to extend the life of gas cylinder valves.

  • Avoid opening valves when gas cylinders are empty as this may result in unnecessary diffusion of air and moisture inside the cylinders. This can lead to corrosion and contamination.
  • Disconnect regulators from gas cylinders that are removed from service.
  • Valves must be protected by cylinder caps when not in use to prevent potential damage (applicable to all cylinders equipped to accept caps).
  • Never over-tighten valves as this can cause serious safety problems. An over-tightened valve can be very difficult to re-open and may lead to valve breakage, damage to the sealing surface, and possible leaks.
  • Never: (a) lubricate cylinder valves, (b) use cylinder valves in lieu of a proper regulator to try and control flow or pressure, or (c) use a cylinder valve as a handle to move a cylinder.
  • Wrenches or other tools shall never be used to open or close a cylinder valve equipped with a hand-wheel, as this can cause over-torquing and damage. If the cylinder valve is designed to be opened with a tool, ONLY use a compatible cylinder key specifically designed for that purpose.
  • For most applications, opening the cylinder valve a couple of turns is more than sufficient to give an unimpeded flow of gas.
    • Fully opened valves are prone to jamming and take significantly longer to close in emergency situations.
    • For high-flow situations (uncommon in labs) requiring a fully open valve, do not leave the valve opened against the backstop, but instead, turn it at least half a turn in the closing direction. Leaving the valve open against the backstop may cause it to seize open.

Hierarchy of Safety Controls

  • Elimination – remove gas cylinder usage. Remove flammable, toxic, or corrosive gases from your procedures.
  • Substitution – replace highly hazardous gases with less hazardous ones. Use a low pressure system/process over a high pressure one.
  • Engineering Controls – physical controls to isolate workers from the hazard.
    • Employ gas detection systems to monitor for leaks and automatically shut off gas supplies if dangerous levels are detected.
    • Use gas cabinets or storage areas with proper ventilation and containment features to store hazardous gases (e.g., toxic, corrosive, pyrophoric) safely.
    • Work in fume hoods and other local exhaust ventilation for protection against health-hazardous gases or to prevent build-up of flammable gases.
  • Administrative Controls – policies, SOPs, training, and other forms of communication that mitigate the threat of a hazard (or hazards) to individuals.
    • Conduct risk assessments to identify: (a) potential hazards associated with new projects/equipment and gases, (b) potential system weaknesses, stress points, or failures, and (c) new SOP content (see SOPs), PPE selection, and system re-design, if needed.
    • Participate in safety training. This includes GLS training, SOP review and sign-off, review of SDS for a specific gas and sign-off, and site-specific safety training.
    • Maintain full recordkeeping of all trainings, gas cylinder inventory in EHSA or RSS , and service and maintenance of all gas equipment.
  • Personal Protective Equipment (PPE)
    • Always wear appropriate PPE when handling compressed gases – see PPE standards. Nomex or FR lab coats for flammable gases; Nomex is mandatory for pyrophoric gases.
    • Wear safety glasses or splash goggles. Safety glasses for working with gases e.g., changing regulators. Compressed gases are considered projectile hazards, at a minimum. If liquid splash hazards are also present, safety goggles will be required.
    • If handling many gas cylinders, consider wearing industrial gloves for added protection and grip – see glove example.
    • Steel-toed shoes are recommended when moving gas cylinders.
    • Respirators are generally NOT needed when working with gases. They are only used as a last resort in preventing harmful exposures and NOT a substitute for other control measures. In rare instances where respiratory protection is needed (e.g., certain maintenance procedures on toxic gas systems), individuals must first enroll in the Respiratory Protection Program. Respirator usage is NOT permitted outside of the USC Respiratory Protection Program.

Additional Considerations and Maintenance

  • Never use oil, grease, or PTFE (Teflon™) tape on regulators or cylinder fittings for any cylinders, especially oxygen services.
    • If oil or grease is found at the cylinder valve, discontinue use immediately and contact the supplier.
    • The threads on a cylinder fitting are NOT a sealing surface and PTFE tape has no function being there. Instead, tape tends to break up into pieces which can get inside the regulator and foul the internal mechanism.
  • If a regulator will not seal to a cylinder when tightened to a reasonable level, then:
    • Do NOT overtighten as this may cause damage
    • If the cylinder fitting uses a “bullnose” metal-metal seal, check the cylinder and regulator for scratches or damage to the sealing surfaces. If damage is found, the regulator and/or cylinder will need to be professionally repaired.
    • If the cylinder fitting uses a gasket, replace the gasket with a correct compatible new gasket.
    • Consult the Tubing and Fittings section for more information.
  • Never force connections that do not fit.
  • Always follow the equipment manufacturer’s operating guidelines.
  • Never tamper with the pressure relief device on a compressed gas cylinder or regulator.
  • Inspection and Maintenance
    • Conduct routine visual inspections of cylinders for signs of damage, corrosion, or leaks. Inspect valves, fittings, and pressure relief devices for integrity and proper functioning.
    • Ensure regulators and other cylinder equipment are properly maintained according to the manufacturer’s recommendations.
  • Equipment Maintenance
    • Ensure that all equipment used for handling compressed gases, such as regulators, cylinders, and storage containers, are properly maintained and inspected on a regular basis.
    • Maintain equipment per manufacturer’s recommendations.
    • Log maintenance/service to equipment as well as routine use of hazardous equipment.
  • Monitoring and Reporting
    • Inspect compressed gas cylinders and affiliated equipment for signs of damage or leaks regularly.
    • Promptly address and report any safety concerns or incidents to the PI or appropriate personnel with delegated safety responsibilities (e.g., lab manager, lab safety officer).