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Asphyxiating Atmospheres from Cryogenics and Compressed Gas Cylinders

The Hazard

Most asphyxiants have no smell or odour and can go undetected. They are commonly used in laboratories, workshops and other areas of the campus. If they are not managed effectively, leaks and spillages can lead to oxygen displacement in the work area, which without suitable early warning systems such as oxygen monitors, the resulting asphyxiating atmosphere can lead to unconsciousness and death.

Common Asphyixiants

Some of the most common asphyxiants used at the Univeristy include:

• Liquid nitrogen
• Argon
• Nitrogen
• Carbon Dioxide
• Helium

If in doubt, always check the Safety Data Sheet for the substance or check the GESTIS database.

Risk Assessment

If you use asphyxiants in your work area, you need to carry out a Preliminary Risk Assessment to calculate the O2 Levels within the work area in a worst case scenario of a full release of the substance. If O2 levels will fall below 19.5%, then a full risk assessment will need to be carried out. You can use our Generic Gas Storage Risk Assessment to help you with this. You will need to adapt the risk assessment to cover the hazards associated with your work area.

Control Measures

Control measures that you should look to implement when working with asphyxiants include:

• Only use asphyxiants outside in the open air, or arrange for an external manifold to be installed so that substances can be piped into your work area.
• If this is not practical, asphyxiants used and stored inside should be reduced in number and size and stored in a compressed gas 90 minute cabinets.
• The area must be well ventilated, with fresh air circulating at a minimum of 5-10 air changes per hour under normal operating conditions.
• Warning signs should be displayed at the entrance to the work area informing others of the hazard.
• The work area should be secured to prevent unauthorised access.
• Suitable detectors for the asphyxiants you are using should be fitted at suitable heights and locations in the work area, which are set at a higher percentage than the minimum required to provide early warning of O2 levels dropping.
• A display showing the O2 levels in the work area should be placed outside the entrance and the alarm should sound both inside, and outside the work area.
• Training, information and instruction must be provided to those working in the area or who may need to follow emergency procedures.

Effects of Reduced Oxygen Concentration

Emergency Procedures

You must have emergency procedures in place for responding to a leak or spill that has resulted in O2 levels dropping to dangerous levels. These procedures must be communicated to those who need to be aware and the procedures must be tested periodically to ensure everyone remains aware of their role and what to do. In most situations, a full evacuation of the immediate building will be required, unless there is a means of increasing ventilation in the work area without entering.

In any emergency situation invovling asphyxiants, do not rush in to help, as you may end up being the next victim. Only those trained to respond should attempt to rescue anyone inside the work area and they must be trained and be provided with suitable personal protective equipment, such as:

• Self-contained breathing equipment
• Safety belts / harnesses and winches
• Personal monitors suitable for the asphyxiant
• Resuscitation equipment

If equipment such as the above is not available and/or individuals have not been trained in the emergency procedures, a rescue must not be undertaken. The Fire & Rescue Service should be called immediately, by contacting Security on x3333.

Useful Documents and Links

Preliminary Risk Assessment for Asphyxiants.

Generic Compressed Gas Storage Risk Assessment Template

British Compressed Gas Association website

HS G031 Compressed Gas Cylinder Guidance

HS F054 Safe Storage of Compressed Gas Cylinders Risk Assessment Template

HS G064 Compressed Gas Cylinders note