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Advice issued by regulator following foamed concrete ‘explosion’
HSE has issued interim advice following after an explosion that occurred during use of foamed concrete. The incident is still under investigation.
The explosion in August 2009 injured two workmen after a pit had been filled with foamed concrete. Whilst the concrete was setting work started with angle grinders on steel and the explosion occurred.
It appears that hydrogen gas was generated producing a flammable/explosive mixture to develop in the confined space. HSE is investigating the means by which hydrogen was generated.
Aluminium is known to react with cement/concrete mixtures to form hydrogen. The particular concrete mix included incinerator bottom ash (IBA) which is suspected of being the source of aluminium. Tests on raw materials and the mixed concrete revealed the presence of aluminium. Tests to confirm the suspected mechanism have not yet been completed.
The supplier of the IBA has been asked to advise customers of the following:
- foamed concrete mixes containing IBA or other recycled materials should be 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 concrete should remain visible until it has set;
- sources of ignition such as naked flames or spark-generating tools (e.g. disc cutters, angle grinders) should be kept away from the concreted area during the pouring and setting process.