Background

Like all closed metal containers, gas cylinders present explosion risks if exposed to fire. Fire and Rescue Services (FRS) are aware of this and have safe methods for dealing with cylinders involved in fires.

Clearly if the contained gas is flammable, or is oxygen, this can considerably increase fire loads. But dissolved Acetylene (DA) has distinct properties which require special precautions. The direct heat of a fire may 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 has, only since 2003 and initially only in the UK, has involved 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 disruption, which may in turn prejudice safety away from the incident. The UK protocol has been 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 oxy-fuel gas and is used across multiple welding and metal cutting applications.

Put simply, there is no replacement for it and when handled, stored and transported correctly, Acetylene is perfectly safe and has been invaluable to industry for over one hundred and fifty years.

What could be done about the 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.

What are Acetylene suppliers doing?

BCGA members offered various initiatives to help:-

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

Special retro-reflective marking tape is being applied to DA cylinders, to help the FRS identify DA more easily.

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 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 advised 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 cold impact alone to an acetylene cylinder CANNOT initiate decomposition. For the full statement - click here (PDF).

Research

Five Stakeholder parties, namely BCGA, DfT, HSE ,TFL and, latterly, CFOA co-funded major research conducted over a period from 2008 to 2010, 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 - 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 computer 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 might be significantly excessive.

Further research work, Phase III, entailed full scale filled DA cylinders bonfire tests, 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 panel of consultant Professors - the results of which were presented in September 2010. In summary, the BAM science indicated that the UK protocol could be changed to something which would be safe but far less disruptive. A recommendation was accepted that just 1 hour cooling followed by a futher 1 hour monitoring precaution would be prudent. It is no coincidence that the findings of the BAM research agreed exactly with the empirical evidence found at real incidents and best monitored by London FRS.

The Executive Summary report on BAM's work may be viewed by clicking here.

And BAM's Opinion on the proposed 1+1 hour protocol may be viewed by clicking here.

As at April 2011, the Fire Service is incorporating this new way into a broader revision to HazMat guidance which Brigades should receive later in May/June as new best practice guidance.

Whilst the BAM 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.

The findings of the BAM Research is of Global significance to both Fire and Rescue Services and others alike and we trust that the new UK protocol may be adopted in other countries too and thereby mitigate needless disruption.

Doug Thornton –April 2011.