Highways Agency

• Traffic Incident Management Bulletin

February 2008

During January 2008 a vehicle carrying acetylene gas bottles was involved in an incident on the M6. This article will give a brief overview of the incident and also highlights the work the Highways Agency is currently doing to minimise the impact of an acetylene related incidents on or adjacent to the network.

The Incident

On Thursday 24th January, a van reported to be carrying three acetylene cylinders, two propane cylinders and an oxygen cylinder was involved in a road traffic collision at M6 junction 19 in Cheshire at 16:20. Cheshire Fire and Rescue Service attended the scene.  A 200m hazard zone was established, resulting in the total closure of both carriageways. The bottle was cooled with water for a period and the Fire Service then confirmed the cylinder had cooled appropriately with a thermal image camera.

In this instance the Fire and Rescue Service were concerned that the cylinder may have become unstable. The motorway was re-opened at 20:00 and the junction 19 slip road was re-opened at 20:50 once the recovery operation had been completed with the aid of the gas industry’s Competent Person (CP) at the scene.

An Important Learning Point

In this incident the cylinder had not been involved in a fire yet it still required to be treated with extreme caution. The paragraph below explains why.

Current knowledge of Acetylene is that it is safe if used, stored and transported correctly. Direct exposure to fire can initiate a heat generating decomposition reaction within the gas leading to the potential for explosion if it is not controlled. This uncertainty in itself leads to a careful approach.

Since 2004 the UK Fire service has employed a very safe protocol for dealing with Acetylene incidents, though the UK method is at odds with what happens in other countries and there are questions as to whether the UK way may be beyond what is needed.The uncertainty surrounding how fire-fighters approach such incidents has resulted in further research work being commissioned by the National Acetylene Stakeholder Group, of which HA is a member, to look into the properties of the gas. With further evidence-based research, it is hoped that this will support the earlier collapse of restrictions placed by Fire and Rescue Services, resulting in revised policy and guidance, enabling the road to return to normality much sooner. Gas industry members currently operate a Competent Persons Scheme designed to help Fire and Rescue at the scene by informing the Fire Officer in Charge that the cylinder is safe.  In the case of the M6, J19 incident, the CP was delayed in getting to the scene by queuing traffic on the approach to the incident. Upon on arrival of the CP at the scene it was cleared after 20 minutes. Network Services and Network Operations are working with ACPO to agree blue light escort for the CP now at Acetylene and other incidents requiring specialist input. 

Acetylene gas has been used widely in industry for metal cutting and welding for over 100 years. The Fire Service are aware that all gas cylinders will ultimately explode if exposed to fire, as the rising gas pressure overcomes the falling tensile strength of the cylinder casing. In general terms, once the fire is out and the cylinder shell has been cooled its strength recovers and the risk of explosion diminishes with time. With acetylene, the explosion risk can continue for some hours after the fire is out due to the potential for internal re-heating caused by decomposition. It is this background that defines acetylene cylinders being quite different to others. As opposed to being simple hollow shells, acetylene cylinders contain a fine porous mass throughout which the gas is dispersed. The mass is designed and type tested to control decomposition but it also acts as a thermal insulant, meaning that any ongoing heat generation deap inside the cylinder cannot always be easilly detected at the surface by normal methods available to the Fire Service, such as thermal imaging.

Research Work Ongoing

The Highways Agency’s Safety Standards and Research (SSR) Directorate is carrying out a study into methods of managing acetylene related incidents. The project is split into two aspects.

Firstly, research to allow better prediction of acetylene’s behaviour such that those on scene can manage the risks with the best available information. This work is being carried out via the National Acetylene Stakeholder Group (detailed above) which includes bodies such as the HSE, Network Rail and the Association of Chief Fire Officers. This research is still in its early stages but the TIM Bulletin will keep you informed.

Secondly, work to investigate robotics that enables close inspection, identification and potential handling of cylinders within the standard 200 metres hazard zone is underway. SSR is currently negotiating with the Army’s Explosives Ordnance Division, private company, Qinetiq and Fire and Rescue Services about robot trials to deal with acetylene cylinders involved in fires at incidents on the strategic road network. The trials are planned to start in April 2008.

The idea behind the trial is that remotely operated vehicles (ROVs) can enter the 200m hazard zone without risk to human life. In addition to identifying the cylinder type and condition, the robots will be expected to put the fire out at close range, carry out the gas industry’s ‘wetting test’ and lift/manipulate the cylinder into an adjacent container on the verge, which will be capable of withstanding any potential blast. This will enable the road to be reopened much sooner

The ability for existing robots to carry out inspection and identification is being trialled in London by Network Rail and London Fire and Rescue, but the Agency’s trials are designed to test the abilities of existing ROVs beyond this. The results of the trials should confirm the adequacy of current ROVs and point toward areas of improvement or the design for a new bespoke piece of equipment.

If you have any comments on the above article please email TIMbulletin@highways.gsi.gov.uk. If you have not done so already why not subscribe to receive an email each month when the new bulletin is published.