BCGA -

Background

All gas cylinders present risk if exposed to fire. Fire and Rescue Services (FRS) are aware of this and have safe methods for dealing with cylinders involved in fires.

Dissolved Acetylene (DA) has a distinct property which requires special precautions. The heat of a fire may, in extreme circumstances, initiate decomposition of Acetylene. This is an exothermic (heat creating) reaction which can cause a DA cylinder to reheat after the fire is extinguished. The FRS protocol for dealing with DA involves cooling the cylinders for 24 hours.

An initial hazard zone of 200 metres is supposed to be reduced once the facts have been established, but often the 200m zone is maintained for the whole 24 hours. Whilst very safe, this can lead to major road and other infrastructure disruption, which may in turn prejudice safety away from the incident.

The UK protocol is at odds with what previously operated safely in the UK prior to 2003 and still operates safely in other countries.

DA is the most flexible fuel gas across multiple applications

There are other metal cutting and welding technologies, but none can match the high flame temperature which oxy-acetylene provides, nor its flexibility across its spectrum of applications. It welds metals other options cannot and it cuts metals more quickly.

When handled, stored and transported correctly, Acetylene is perfectly safe and has been invaluable to industry for over one hundred and fifty years. It remains irreplaceable.

What is being done to minimise disruption?

In 2006 the BCGA joined senior representatives from the Fire Service, Health and Safety Executive (HSE), Department for Transport (DfT), Department for Communities and Local Government (DCLG), Highways Agency, Police, Network Rail, Transport for London (TFL) and others, to form a National Stakeholder Group (NSG) to work together on the issue. A profile of the group can be seen – Click here.

What are Acetylene suppliers doing?

BCGA members are co-operating closely and have offered various initiatives to help:-

A new advice leaflet has been prepared for DA users – BCGA Leaflet L6. This is free to download. Click the document to the right to download.

New reflective marking is being applied to cylinders, to help the FRS identify DA more easily. Some suppliers are applying this directly to the cylinder, others are choosing to mount it on a plastic collar around the valve assembly.

The UK’s DSEAR (Dangerous Substances Explosive Atmospheres) Regulations require users to undertake a comprehensive risk assessment that mandates the use of flashback arrestors (it is not clear that all users are fully aware of DSEAR). BCGA fully endorses the mandatory use of flashback arrestors.

BCGA has developed a simple risk assessment model for oxy-acetylene users – available free to download at TIS15 –Click the document on the right to download.

A full DSEAR risk assessment model is summarized in a new BCGA Guidance Note GN13. Members : click the document on the right to download. Non-members: click here to purchase.

BCGA has made agreement with EBAY to ban the sale of DA cylinders through their site as a way of restricting access to the product by untrained and unskilled individuals.

BCGA are helping the Fire Service through training and provision of training material to hazmat officers within the Fire Service. In addition, BCGA members offer the emergency services expert help at incidents through our Competent Person Scheme.

BCGA has also offered clarification on the potential effects of mechanical impact to DA cylinders, which will help police and Highways agency staff when dealing with road traffic incidents.

In summary this takes account of global empirical evidence as well as many specific trials and concludes that cold impact alone to an acetylene cylinder CANNOT initiate decomposition. For the full statement - click here (PDF).

Research

Four of the Stakeholder parties, namely BCGA, DfT, HSE and TFL co funded two phases of research. Conducted in the second half of 2008 by BAM, the German Federal Institute for Materials Research and Testing. BAM is world renowned in Acetylene science and research.

Their task was to find out, with certainty and taking account of all variables – after how many hours of realistic cooling can we be sure that no decomposition can be ongoing and therefore that it is safe to close out an incident completely?

The results from the BAM phase I/II work were reported to the NSG in December 08 and may be summarised as follows:-

Mechanical impact alone CANNOT initiate acetylene decomposition
A robust combination of heat transfer experimentation and modelling has produced a model which can be questioned for various ‘’what if?’’ scenarios, eg cooling rates etc.
Porous mass type variations make no difference, their effect being swamped by the effect of heat capacity of the solvent.
Decomposition of acetylene cannot be initiated until at least 350c, meaning that only a cylinder which has been exposed to direct flame impingement can be at any risk.
Polymerization reactions of acetylene can occur at temperatures below 300c, but these are pressure-reducing reactions and therefore not of concern, as gaseous acetylene turns to liquid and then solid species.

Indications from the BAM work also support global empirical evidence that the 24 hour precautionary cooling period may be significantly excessive.

A further phase of research work, Phase III, will entail full scale filled DA cylinders, experimenting with a variety of heating and cooling rates. The purpose if this Phase would be to further validate the model above and hopefully give the FRS confidence to alter existing procedures.

The scope and validity of the Phase III work was discussed extensively with the Fire Service and with DCLG’s expert consultants. Negotiations took some time, but in October 2009 BAM were given the go-ahead to start Phase III work – the results of which should be available around April 2010.

Whilst the BAM Phase I/II work was going on, London Fire Brigade were also doing their own research, going back over 6 years worth of cylinder incidents to see what could be learned. LFB were also supporting trials with robotics, which can help with some incidents. LFB summarised their work in both areas in a report dated March 09. To view the LFB report – click here.

Doug Thornton –January 2010.