Safety Services


Compressed Gases

Compressed gas sign

This guidance is intended to increase awareness of the risks and the precautions to be taken when using compressed gas and handling compressed gas cylinders.


In order to assess the risk of working with compressed gas, its important to consider the ways that gases can accumulate or be released into air within the workplace. They include leaks or releases as a result of:

  • damaged or poorly maintained hoses, pipes and valves;
  • poor connections;
  • accidentally opening valves;
  • not closing valves properly after use;
  • poorly ventilated work areas.

The consequences of leaks or releases will depend on the hazardous nature of the gas but in general they are:

  • explosion e.g. release of flammable gas can create an explosive atmosphere
  • enrichment e.g. increase of carbon dioxide can result in asphyxiation
  • depletion e.g. increase of nitrogen leading to a decrease in oxygen leading to asphyxiation

NB Some gases have more than one hazardous property; for example carbon monoxide is toxic and flammable.

Other risks can result from:

  • poor manual handling technique causing injury to the operator or damage to the cylinder resulting in the release of high pressure gas;
  • over pressurisation of some experimental chambers where an inert gas is used as a purge. In these circumstances a pressure relief valve must be incorporated into the experimental set-up.

The destructive potential from the uncontrolled release of gas should not be underestimated.


Safety data sheets provide information that helps users to make a risk assessment and these should be available at the point of use or storage. They describe the hazards and give information on handling and emergency measures in case of an accident. In addition, the safety data sheet provides information about storage, particularly segregation e.g. gases that are incompatible and shouldn't be stored together like oxygen and acetylene. See: Risk Assessment


Managers must:

  • supervise those with least experience until competence has been gained;
  • intervene and stop work if there is any variance to agreed procedures.

Managers who supervise work or processes which involve the use of compressed gases must be competent (through training and experience) to do so.
Anyone who uses compressed gases should be given information about the risks and instructed in gas cylinder safety. Instruction should include:

  • moving cylinders safely;
  • connecting regulators and hoses;
  • pre-use checks of cylinder and attachments.

Records should be kept of the information, instruction and training that individuals have received.
Instructions and procedures must be documented in the form of safe operating procedures, arrangements for safe working or codes of practice.


Managers must ensure that areas where compressed gases are used and stored are inspected periodically to ensure the effectiveness of risk control measures. Guidance on inspection can be found at the following link:

Safety Monitoring

When compressed gas cylinders are introduced into a work area or building for the first time e-mail fire@ucl.ac.uk with details of the type of gas, number of cylinders and the location where they will be used and stored. This information will be used by the Fire Safety Team to update the fire and rescue information packs available in the Premises Information Box.


Gas cylinders

Whenever possible, select the smallest size of gas cylinder available. When siting gas cylinders in the workplace, make sure that:

  • they are supported with chains or straps in an upright position;
  • they are protected from mechanical damage and sources of heat;
  • the gas supply is turned off at the cylinder when not in use;
  • the area where the cylinder is used is well ventilated;
  • oil, grease or jointing compound is NOT used on cylinder fittings.

If possible, arrange to have gas cylinders delivered to the point of use. If this is not possible, make sure that:

  • anyone moving cylinders is trained to do it safely;
  • a trolley is always available to move cylinders from the storage area to the work area;
  • personal protective equipment is worn to protect feet and hands. 
  • gas cylinders are never moved with the valve open.

Restricted access sign

Cylinders should ideally be stored outside the building. If this is not possible, the number of stored cylinders should be kept to a minimum.

Access to cylinder storage areas should be restricted to authorised people only. The storage area should be well ventilated and cylinders should be stored in the following way:

  • support the cylinders with chains or straps in an upright position;
  • empty cylinders should be labeled 'empty' and stored separately from full ones;
  • segregate gases according to type and compatibility (refer to the safety data sheet if in doubt).

Doors to areas where compressed gas cylinders are used and stored should display hazard warning signs indicating the presence of compressed gas cylinders and any additional hazard associated with the type of gas e.g. flammability. This information is essential to fire and rescue personnel when carrying out operations. Guidance on signage can be found at the following link:
Hazard Signage System for Laboratories pdf (TN095)


Gas Regulator

Gas regulators are designed to reduce the pressure of the gas from the cylinder to the lower pressure required for the operation of the equipment or process.
Regulators typically have the following features:

  • inlet pressure gauge which indicates the pressure in the cylinder;
  • delivery pressure gauge which indicates the reduced pressure being delivered to the equipment or process;
  • a pressure adjusting valve which controls the volume of gas entering the gas delivery gauge.

The gas regulator must be selected for use with the gas it was designed for - they are not interchangeable! Using the wrong regulator can damage it or result in a serious accident.

NB Gas regulators are precision instruments and can be easily damaged - treat them with care!


Gas regulators should be:

  • regularly inspected to confirm they are free from damage or contamination;
  • tested and inspected annually by a competent person to ensure they are functioning correctly. BOC carry out the annual test and inspection on behalf of departments;
  • replaced at least every 5 years whether they have been used or not because they contain parts that deteriorate with time.

Managers responsible for the work with compressed gases must ensure that regulators are inspected, tested and replaced at the intervals specified.

Never attempt to alter or repair gas regulators or valves.


The condition of the hoses used to connect the cylinder to the equipment is vitally important to safety.
Hoses should:

  • be protected from mechanical damage, heat, sparks, oil and grease;
  • not be longer than needed and they should not be kinked or twisted;
  • be replaced if they show any signs of damage and therefore must be visually inspected frequently;
  • be compatible with the gas with which they are to be used;
  • be used at the pressure for which they are designed.

Always use:

  • pressure hoses to connect gas cylinders to equipment;
  • retaining clips or ferrules to secure hoses to gas cylinders and/or equipment.

Examples: Acetylene, Hydrogen, Methane

UCL Mandatory requirements when working with flammable gases
  1. Heads of Department must appoint a person to be responsible for the management of flammable gases
  2. The person appointed must be recorded in the departments Responsible Persons Register as Appointed Person (Flammable Gases)
  3. The Appointed Person (Flammable Gases) must maintain an inventory of flammable gases used or stored in their area of responsibility and issue a 'Flammable Gas Safe to Connect' certificate for each delivery of flammable gas

The Flammable Gas Safe to Connect Certificate will be issued to confirm that:

Safe to connect certificate image
  • a risk assessment has been conducted and is available at the point of use;
  • the people working with the flammable gas are competent to use flammable gas and there is a record of the information, instruction and training they have received;
  • the location where the gas is to be used is suitable;
  • cylinders of flammable gas are located separately from sources of ignition. If this is not possible then a suitable enclosure must be used.


Use the following link to download a copy of the certificate:


NB BOC will not deliver flammable gases unless a current (i.e. dated within 5 days of the delivery) 'Safe to Connect Flammable Gas' certificate is displayed.


Flashback arrestors must be fitted to cylinders delivering flammable gases. Flashback arrestors should be:

  • regularly inspected to confirm they are free from damage and contamination;
  • tested and inspected annually by a competent person to ensure they are functioning correctly. BOC carry out the annual test and inspection on behalf of departments;
  • replaced every 5 years.

Managers responsible for the work with flammable gases should ensure that flashback arrestors are inspected, tested and replaced at the intervals specified.


What are gas monitors?
Gas monitors measure levels of gases that are normally present and are installed to warn of raised levels of gases for example carbon dioxide or reduced levels of oxygen.
What are gas detectors?
Gas detectors are installed to warn of the presence of a gas that is not normally present in air in significant quantities, such as hydrogen.
Where should the monitor or detector be installed?
In general, if the gas is lighter than air, then the monitor or detector should be mounted well above the breathing zone, and if it's heavier than air, it should be mounted well below the breathing zone. (The breathing zone is defined as within a 10-inch radius of the worker's nose and mouth.)

Monitor repeater

Repeater Unit
A repeater unit can be mounted outside the room to mimic the alarm and warn against entry. If the monitor or detector alarm sounds frequently during routine operations DO NOT SWITCH IT OFF. Review the system of work and the location of the monitor or detector. On all occasions when the alarm sounds, the reason for the alarm and the actions that were taken to rectify the situation should be recorded. RiskNET UCL's incident reporting system should be used for this purpose.

The risk assessment and the resultant arrangements for using compressed gases must take account of the possibility of the alarm sounding out-of-hours and the consequences of for example security staff entering areas of low oxygen when investigating the reason for the alarm. Other vulnerable groups would be cleaning and maintenance staff.

Do not enter sign

A sign must be displayed on the door describing the action to take if the monitor or detector alarm is sounding. i.e. 'do not enter if alarm is sounding'. Include the contact details of who should be told if the alarm is sounding.


Monitors and detectors should be calibrated, maintained and serviced at intervals specified by the manufacturer and resources (funding) should be allocated for this purpose.
And finally always remember! Gas monitors and detectors are not an alternative to the provision of a safe system of work but are an additional measure, which give an early warning that something has gone wrong.