Most industrial gases occur naturally and are extracted from the atmosphere. Transporting gases at their ordinary temperatures and pressures is not a practical or economically viable option for the chemical industry due to the size of containers that would be required. Viable storage and transport options rely either on cooling, applying pressure or dissolving gases.
The favoured option is to use pressure to liquefy a gas, but for every gas there is a critical temperature. Gases below their critical temperatures are often called vapours and can be liquefied by applying pressure so they can be transported or stored as liquids at ambient temperature. Above this critical temperature, gases cannot be liquefied by applying pressure alone. When a pressurised liquid is warmed above the critical temperature it will exert a critical pressure on its container.
Gases with a critical temperature below ambient temperature can be stored or transported as compressed gases in small quantities at ambient temperatures. When bulk quantities are required they are usually cooled to below critical temperature and transported as refrigerated or cryogenic liquids (See Hazard – Cryogenic material release).
Emergency responders may come across gases under pressure at many different locations. It is vital that they recognise them quickly when firefighting. The Carriage of Dangerous Goods Regulations set out the safe conditions for transporting gases by road.
For further information see A foundation for hazardous materials.
Initial cordon/hazard areas
Responders inside the initial cordon should use shielding and don appropriate personal protective equipment (PPE). For example, responders likely to be affected by a fireball or blast should wear breathing apparatus (BA) and full structural firefighting kit
The following key questions will assist incident commanders in assessing the immediate risk:
- Are there cylinders at the incident?
- Are the cylinders involved in fire? (i.e. is there direct flame contact, fire damage or radiated heat damage from the fire)
- Are any cylinders leaking, venting, bulging or steaming?
- What gases are involved?
- How many cylinders are there and what size are they?
- What is the temperature of the cylinder(s)?
- Is any shielding provided by any buildings or structures?
- What type of adjacent structures are there and what is their extent?
- What is the local topography (e.g. protection provided by slopes and gradients of ground levels etc?)
- What would be the effect of:
- A potential blast pressure wave
- A fireball (can travel up to 25 metres)
- Projectiles (a cylinder may be thrown up to 150 metres* and cylinder fragments and other projectiles such as the valve assembly may be thrown up to 200 metres*)
- Flying glass and other structural material?
- What structural damage could be caused to buildings in the vicinity?
- Is there a need for an exclusion zone within the hazard area?
- Are other hazards inside or close to the initial cordon?
- What is the proximity and importance of adjacent occupancies and key infrastructure, such as major roads and railways
*Possible maximum travel distances for a cylinder in the open (i.e. not within a structure or building that would provide substantial shielding and therefore reduce the distances projectiles could travel)
If cylinders, including acetylene, have not been heated then they do not represent a hazard and should be handed over to the site operator. In a developing fire situation, consider carefully moving them if there is a risk that the fire will spread and involve them.
Where members of the public are within the identified hazard area, the incident commander may wish to consider evacuation. Where this is not possible or appropriate, attempts should be made to warn of the risks and give advice to stay away from windows and doors and stay in rooms furthest away from the risk.
For further information regarding evacuation see National Operational Guidance: Operations.