Dangers of acetylene

Acetylene - what is it?

Oxy-acetylene welding, commonly referred to as gas welding, is a process that relies on combustion of oxygen and acetylene. Acetylene has been used in steel welding and other heat treatment processes for more than a century. The mixture of oxygen and acetylene is used as it has been the only gas combination with enough heat (up to 3100^oC) to weld steel. Despite the fact that in most industrial applications oxy-acetylene welding has given place to other methods such as:

• Oxy Propane
• Electric Arc Welding
• Tungsten Insert Gas Welding (TIG)
• Metal Inert Gas Welding (MIG)
• Mechanical Cutting

acetylene is still preferred by users in the field of maintenance, reparation and some other applications. It is also very hazardous and energy costly. It is an extremely flammable gas and differs from other fuel gases due to its very unstable nature. It is also notorious for its pollution.

Under certain conditions acetylene may decompose explosively into carbon and hydrogen, this decomposition is usually triggered by heat if the cylinder is involved in a fire, scorched by the flame of a torch or involved in a flash back.

Acetylene fires

Fire and rescue services nationally attend many hundreds of fires and incidents each year involving acetylene cylinders, either directly or indirectly.

A fire involving acetylene cylinders causes major disruption and the risk of explosion remains for up to 24 hours, unlike all other gases which are safe once the initial fire has been extinguished. Because of the explosion risk an exclusion zone of up to 200 metres radius will be set up around the incident every time these cylinders are in danger of exploding at a fire.

Where a cylinder explodes during or following a fire, the resulting dangers can include a travelling fire ball, projectile hazards, flying glass and structural damage to nearby buildings.

Any fire situation involving or in the vicinity of acetylene cylinders is likely to cause severe disruption to your business and any other businesses and residents in the surrounding area for a considerable period. On arrival at such an incident the fire and rescue service will place an immediate exclusion zone around the incident of up to a 200 metres radius.

The exclusion zone has been agreed following consultation between the gas industry and the emergency services and results from the distance that cylinder fragments have been found following the explosion of acetylene cylinders at incidents. The zone may be in place for more than 24 hours in order for the affected cylinders to be cooled and to ensure no decomposition of contents is taking place.

Examples of incidents attended involving acetylene cylinders:

• Fire involving acetylene cylinder - 31 August 2008, Waltham Chase
• Fire involving acetylene cylinder - 19 October 2007, Sankey Road, Fleet
• Fire involving acetylene cylinder - 17 May 2007, A3090, Ampfield

What can I do to avoid an acetylene incident?

Ask yourself the following questions:

• Have I carried out a fire risk assessment? (Read our guidelines on carrying out a risk risk assessment).
• Do I really need to keep acetylene?
• Have I got more than I actually need?
• Is there a safer alternative?
• Is my storage area safe and secure?
• Am I and/or my staff suitably trained and competent to use the equipment?
• Is my equipment safe and regularly tested?
• Have I provided any warning signs?
• If cylinders are stored inside are they on a trolley close to an exit?
• Are staff trained in what to do in the event of a fire? The cylinders can be treated as a person and if safe to do so be evacuated in the event of a fire.
• Do I have plans of the location of the cylinders?

What to do in the event of a fire

• If safe, remove acetylene cylinders whilst evacuating.
• Evacuate the building to assembly point.
• Dial 999 to call the Fire and Rescue Service; tell them cylinders are on the premises.  
• Take plans of the building with you.

If you a have a fire involving acetylene

• Dial 999 to call the Fire and Rescue Service; tell them cylinders are on the premises.  
• Tell everybody to leave the premises and go to a safe place well away from the installation.
• If you have a fire alarm, activate it.
• Never try to put out a fire involving cylinders; leave it to the Fire and Rescue Service.
• It is safer to evacuate everyone from the area. An overheated cylinder can explode.

Acetylene - how can I dispose of unwanted cylinders?

Unwanted cylinders should be disposed of safely by contacting the gas supply company, the details can usually be found on the printed label on the shoulders of the cylinder.

Advice concerning safe disposal can also be obtained by contacting BOC Industrial and following the advice provided. They have a 24-hour helpline and can be reached by telephone on 0800 111 333.

Fire safety legislation

New legislation was introduced in 2006, The Regulatory Reform (Fire Safety) Order 2005 applies to any place (with certain exceptions) including outdoor locations. The Fire Safety Order places the responsibility for fire safety firmly with employers and requires employers to carry out a fire risk assessment to identify and manage and fire risks on their premises. Existing fire certificates are no longer valid and may not be relied upon. More information on fire safety in the workplace...

The Dangerous Substance and Explosive Atmospheres Regulations 2002 requires businesses to assess the risk of work activities with dangerous substances and to eliminate, substitute or reduce the risks as far as reasonably practical.

Acetylene - where can I get further information?

More detailed advice on the safe use of gas welding equipment can be found in the following publications:

• Your guide to safer acetylene  411Kb, published by Hampshire Fire and Rescue Service
• The safe use of compressed gases in welding, flame cutting and allied processes - HSE Books 1997
• British Compressed Gases Association Code of Practice CP7
• British Standard BS EN 730

HSE

HSE books and publications both priced and free are available by mail order from:

HSE Books
PO Box 1999
Sudbury
Suffolk
CO10 2WA

Tel: 01787 881165

Website: www.hsebooks.co.uk

British Compressed Gases Association

British Compressed Gases Association is the British trade association representing companies in the industrial gases industry that manufacture and distribute gases, manufacture receptacles to contain them or equipment to use them.

Tel: 01332 225120

Website: www.bcga.co.uk

Hampshire Fire and Rescue Service

For advice relating to the use of acetylene and any general fire safety advice, please telephone Hampshire Fire and Rescue Service on 023 8062 6890 or email: business.education@hantsfire.gov.uk.