Acetylene is an extremely flammable gas and can form an explosive atmosphere in the presence of air or oxygen.
The Dangerous Substances and Explosive Atmospheres Regulations 2002 (‘DSEAR’)
A risk assessment must be undertaken by employers under DSEAR when acetylene is or is liable to be present in the workplace and suitable controls put in place where an explosive atmosphere may occur in the workplace (see eg DSEAR regulations 5, 7 and 11).
The Acetylene Safety (England and Wales and Scotland) Regulations 2014 (‘ASR 2014’)
Acetylene gas poses an additional hazard to other flammable gases as it is also reactive. Under certain conditions, even in the absence of any air or oxygen, it can decompose explosively into its constituent elements, carbon and hydrogen. This hazard is not fully addressed by DSEAR and so additional legal requirements for the safe use of acetylene gas at equal to or greater than 0.62 barg (“compressed acetylene gas”) and the equipment used with this are provided by the ASR 2014 which came into force on 1 October 2014 to consolidate and modernise existing legislation . The ASR includes, in certain circumstances, the requirement for a flame arrestor to stop the progression of a flame resulting from the decomposition or uncontrolled combustion of acetylene gas, which could lead to an explosion.
Simple acetylene welding, cutting and related processes
It is recommended that acetylene gas is only used by those trained to use it using suitably designed handling equipment.
HSE guidance which provides information for basic users of acetylene is available:
- Working safely with acetylene INDG327
In addition users may also find the following guidance useful:
- British Compressed Gases Association (BCGA) – GN13- DSEAR Risk Assessment
- European Industrial Gases association (EIGA) SL04/10 – The safe transport, use and storage of acetylene cylinders
Guidance does not replace the need for compliance with the regulations, with which you will also need to be familiar.
Complex/specialist uses of acetylene gas
Acetylene users with more complex or specialist needs should check the information provided by their acetylene gas supplier and the manufacturer of the equipment being used before it is first put into use. It is recommended that modifications to equipment used/to be used with acetylene gas should only be made by those trained to do this; even changes that appear minor may pose significant risks.
Cylinders used with acetylene gas following an exposure to a flame
All pressurised cylinders regardless of their contents are at greatest risk of failure whilst being subject to direct-flame contact.
If a cylinder filled with compressed acetylene gas is exposed to a flashback, starts to warm up or vibrate, or if such a cylinder was involved in a fire, its contents may have begun to decompose. This process can become self-sustaining causing the cylinder to explode, in some cases hours after the initiating event.. Such cylinders pose a risk to anyone in their vicinity and it is strongly advised that they should not be approached until they are made safe. It is recommended that an area of 200 meters around the heated cylinder is evacuated immediately and the Fire and Rescue Service (FRS) is called straight away. The Fire and Rescue Services have specific procedures for dealing with cylinders containing acetylene. It is strongly advised you do not attempt to move such a cylinder nor make any attempt to release its pressure by venting it as this could accelerate decomposition.
Further information and industry guidance can be found at:
- Cylinders in fire – British Compressed Gases Association
- The BCGA have also reproduced the relevant section for such cylinders from ‘Fire and rescue service operational guidance: incidents involving hazardous materials ’
Colour coding of cylinders containing Acetylene Gas
Misidentification of cylinders in an emergency situation can increase risks or may result in unnecessary disruption. For this reason, cylinders filled with compressed acetylene gas must be coloured ‘Maroon’ (RAL 3007) on both the shoulder and body of the cylinder If the colour of the cylinder is different or has become obscured for some reason (eg paint overspray, abrasion, corrosion) it will be unlawful for you to use it with compressed acetylene gas. It is advised that you contact your supplier for advice.
Article source: http://www.hse.gov.uk/fireandexplosion/acetylene.htm