Use of Flammable, Explosive and Toxic Gases


  • Leakage or escape of flammable gases can produce a serious explosive hazard in a laboratory.
  • Acetylene, hydrogen, ammonia, hydrogen sulphide, propane and carbon monoxide are especially dangerous.
  • Hydrogen flames from leaks can be almost invisible and thus difficult to detect.
  • Apart from explosive hazard, gases can be reactive e.g. oxygen and highly toxic e.g. carbon monoxide. 
    "Inert" gases such as nitrogen, carbon dioxide and argon can cause asphyxiation if released in quantity.


Escape of any gas that is flammable, explosive or toxic is very serious and poses extreme danger to all the occupants of a laboratory as well as those beyond.



  • Use may be made of these gases only in a fume-hood or in a well-ventilated laboratory.
  • Naked flames or other sources of ignition must be rigorously excluded from the vicinity.
  • Gas cylinders, control valves and pressure regulators and gauges should all be used carefully and according to the manufacturers' recommendations. Broken or damaged equipment should not be used but must be replaced. Only equipment that is appropriate i.e. specially designed for use with toxic, explosive or corrosive gases may be used.
  • The smallest cylinder size that is practicable should be used e.g. a lecture bottle that can be sited in a fume hood.
  • There should be a regular check for leaks especially in joints. However, leak-detecting fluids on oxygen lines must not be used unless they are compatible. A FLAME MUST NEVER BE USED WHEN TESTING FOR LEAKS. Consideration should be given to using a gas sensor to detect leakage.
  • Consideration should be given to using automatic gas cylinder shut-offs for use in an emergency.
  • Receiving containers must be capable of accepting the gas at the required operating pressure.
  • Prior to introducing a flammable gas into a reaction vessel, the equipment must be purged of oxygen by evacuation or by flushing with inert gas at least three times.
  • Exhaust lines must be properly vented e.g. to a fume hood.
  • Cylinders of "fuel" gases must not be sited on the same rank as oxygen.
  • As far as possible, cylinders of flammable gases e.g. hydrogen must not be sited on emergency escape routes 

Training Requirements

Training by an experienced person is essential


Risk Remaining

The handling of flammable and toxic gases will always have some degree of risk and constant vigilance is required in their use.


Emergency Procedures

  • Leak

    • If the leak is small, attempt to close off the cylinder valve but do not endanger yourself. Eliminate all sources of ignition, ventilate and evacuate the laboratory. BEWARE of approaching a possible hydrogen leak since the gas burns with an almost invisible flame - carry a rolled up newspaper in front of you to check for a flame.
    • If the leak is large, evacuate the laboratory and sound the fire alarm.
    • Following large scale leakage of an asphyxiating gas e.g. nitrogen, argon never re-enter a laboratory without permission. Lack of oxygen may not be apparent but the effect will still be deadly. Be aware that asphyxiating gases may be heavier than air and accumulate at floor or lower levels.
  • Fire

    • Evacuate and sound the alarms.

Back to Completed Risk Assessment Forms

Adapted with permission from School of Chemistry, University of Bristol