Heating and Ventilating


Disused back boilers pose blast threat

Following five back boiler blasts, heating professionals are being urged to follow HSE guidelines concerning disused solid fuel boilers left behind fireplaces.
Disused back boilers pose blast threat
The HSE is aware of five cases in the last five years involving exploding back boilers, where a fire is lit in front of a solid fuel boiler and has issued a safetyalert

In November 2007, a woman died after a back boiler blast in Twyning, Gloucestershire. In several cases, an explosion occurred when a fire was lit for the first time following a heating system conversion.
The back boiler unit typically consists of a fire grate, which carries the combustible material (e.g. coal, and a water chamber 'surrounding' it).

As the units are difficult to drain completely residual water left in the boiler will turn to steam when heated.

In tests carried out in 2002, the top and sides of a solid fuel back boiler, without circulating water, reached temperatures in excess of 7000C. Previous advice recommended that a disused back boiler left in situ must be left in a condition that prevents an unsafe level of pressure building up in unit.

The HSE recommends that at the decommissioning stage, the system should have been drained and redundant pipework removed along with, the back boiler itself. If not removed the boiler should be left in a 'vented' or 'open' condition.

The HSE said 'In some cases the decommissioning may have been carried out by an individual, or heating or building organisations that were unaware of the potential problem or had not seen the advice'.

Other dangers can arise with continued use of a fireplace and redundant back boiler even if it is vented, for instance if connected pipework is left in situ, corrosion of the water jacket sidewalls may allow flue gases to enter the pipework and spread through the property.

HETAS the independent DEFRA-recognised association responsible for testing and approving domestic solid fuel burning appliances, said in a statement 'The only positively safe and reliable way to proceed, when a solid fuel back boiler is no longer needed and the customer wants to continue using the fireplace, is to totally remove the back boiler installation by breaking up the chamber that used to carry the hot water system and removing any pipe work.

'When an open fire is left in use (or could be brought back into use) a replacement Milner fire back needs to be installed to ensure that the fire can be safely used'.

12 May 2008


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