Foamed concrete explosion - HSE interim = position 03 December 2009

Foamed concrete explosion - HSE interim position 03 December = 2009

This document has been produced to provide information on an = explosion=20 involving foamed concrete and provide interim advice whilst HSE = continues its=20 investigation.

There was an explosion which injured two people in August 2009. A = contractor=20 had filled a pit with about 6m depth of foamed concrete. Whilst the = concrete was=20 setting, workers started removing steelwork using angle grinders. There = was an=20 explosion underneath the steel walkway on which two contractors were = standing=20 and which blew the steel plates and the workers up into the roof.

HSE is investigating. The foaming agent in this concrete mix was air = produced=20 by the addition of surfactants and agitation. It appears that while the = concrete=20 was setting, the flammable gas hydrogen was produced. The particular = location of=20 the pour within a relatively confined area beneath a walkway appears to = have=20 allowed a flammable/explosive mixture to have developed.

HSE has been investigation the means by which hydrogen was generated. = Aluminium is known to react with cement/concrete mixtures to form = hydrogen. The=20 particular concrete mix included incinerator bottom ash (IBA) which is = suspected=20 of being the source of aluminium. Tests on raw materials and the mixed = concrete=20 revealed the presence of aluminium. Tests to confirm the suspected = mechanism=20 have not yet been completed.

In the meantime the supplier of the IBA has been asked to advise = customers of=20 the following:

foamed concrete mixes containing IBA or other recycled materials = should be=20 poured in the open air;

if such mixes are to be poured within a building or confined area, = adequate ventilation must be provided and the entire surface of the = poured=20 concrete should remain visible until it has set;

sources of ignition such as naked flames or spark-generating tools = (e.g.=20 disc cutters, angle grinders) should be kept away from the concreted = area=20 during the pouring and setting process.

HSE has not taken any action requiring the removal of IBA from = concrete=20 products.

HSE is not investigating any other similar explosions.

HSE estimates that the scientific tests will be completed by the end = of 2009=20 at which time we will consider what further action needs to be taken and = will=20 update this information note.

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