Explosion in a trays cleaning unit

A wash machine was being used to clean aluminium trays with burnt on product. The auto wash in normal situations cleaned steel trays, and not aluminium. The cleaning fluid contained sodium hydroxide (NaOH). When it entered in contact with the cleaning fluid a "froth" formed in the wash tub, accompanied with hydrogen gas.

A cleaning worker was requested to clean up the froth, and used a wet vacuum cleaner. This cleaner seemingly also removed the hydrogen element with the froth, which in turn ignited due to sparking from the vacuum cleaner motor.

The INITIATING CAUSE was the accidental formation of hydrogen when washing aluminium tray with sodium hydroxide.

There was a lack of understanding of the cleaning product used and its applications, as COSHH sheets on this product, available on site, explicitly stated that this product was not to be used on aluminium.

The ROOT CAUSE is failure to understand and apply procedures.

Industrial vacuum cleaner

The cleaner was uninjured but took time off due to shock, which resulted in the incident being reported.

This incident is an example of a low-technology industrial process where things went wrong when something was changed to the process. The process had been designed for washing used for steel parts. When washing aluminium parts, the cleaning fluid behaved differently. In absence of an extensive knowledge of the ongoing chemical process, operators try usually to remediate to the unexpected results with what is available onsite.

However, to avoid the incident would hace been enough to read the safety sheets held by the company, which specifically stated not to use on Aluminium. There waas a lack of understanding and availability of this information on behalf of manager.
Nevertheless, the investigation conclusions were that