Is Dry Powder a catch all for ADR Vehicles?
June 8, 2012barriehol
Recently a Sainsbury’s tanker caught fire in Whitby, North Yorkshire, not far from the superstore while fully-laden with almost 40,000 litres of fuel.
The quick thinking driver had the presence of mind to drive his tanker away from the main built up area before tackling the blaze with the on board dry powder fire extinguishers. Mercifully the fire appears to have started in the cab away from the fuel tank but despite using all three fire extinguishers he failed to extinguish the fire. An oxygen leak was feeding the fire causing re-ignition.
The drivers experience raises an interesting issue regarding the ADR regulations covering vehicles carrying dangerous loads. Since 2007 ADR vehicles over 7.5 tonnes GW have to carry a minimum of 12kg dry powder extinguishers 4kg of which must be in the cab. ABC dry powder is preferred as it is rated for solid combustibles, liquid fuels and flammable gases. However as anyone who has used a dry powder extinguisher can vouch it is quite difficult to discharge in a confined space like a cab as the air instantly fills with choking powder. In addition if the fire is around or under obstacles to then target the extinguisher at the fire source is doubly difficult.
The added oxygen clearly would not have helped. For a fire to sustain itself it needs the three elements of the fire triangle i.e. a source of fuel, oxygen and heat. Remove any one of these and the fire will go out. In this case the driver could do nothing to remove the flammable materials in the cab or the oxygen from the leak leaving removing the heat as his only option. For all their versatility dry powder extinguishers do not extinguish by cooling the fire but by choking off the oxygen with a barrier of powder. The powder also has an oxygen displacement element but constant oxygen replenishment would encourage reignition. Water extinguishers and Water additive fire extinguishers and to a lesser extent Foam fire extinguishers are the only types of extinguisher that work by cooling the fire.
Fortunately two businesses close to the scene saw the driver’s plight and came to his assistance with their own fire extinguishers. Apparently it took a further 10 canisters before the fire was brought under control. It would be interesting to know what type of extinguishers used eventually killed the fire but as one company was a bakery I suspect water or foam was involved.
Vehicle cab fires must be quite common and are filled with solid combustibles so possibly having a backup water based extinguisher might be a useful extra safeguard for ADR vehicles – particularly those carrying highly flammable and explosive loads. If you have a view please share your opinion by adding a comment.