Case Studies - Mass Decontamination Following Exposure to Toxic Materials

Speedy and efficient decontamination of casualties exposed to toxic or corrosive materials released during a chemical explosion or other incident is essential to minimise the harmful effects at the scene before hospitalising casualties for further treatment. This can be achieved with portable decontamination units, which comprise hot showers in which able-bodied casualties wash themselves while specialist teams scrub injured people. The decontamination units are designed to deal with up to a hundred persons an hour.

At the request of HM Fire Service Inspectorate (HMFSI), HSL assessed the decontamination efficiency of six Mass Decontamination Units as part of a comprehensive HMFSI field trial that also examined speed of assembly, robustness and throughput of ‘contaminated’ individuals.

A team of volunteers was exposed to a fog of simulated chemical agent containing fluorescent dye, which settled invisibly onto their exposed skin and inside their clothing. Their initial level of skin contamination was recorded by photographing the volunteers in swimwear under ultraviolet light to indicate the body areas contaminated with the fluorescent dye. The volunteers showered for a defined period of time in the decontamination unit and were photographed again to record the residual fluorescence. The photographic equipment, designed at HSL, was then used to calculate the amount of dye on the skin before and after showering, and this provided an indication of the washing efficiency of the decontamination unit.

The evaluation showed that the volunteers transferred material onto their hands from the most contaminated areas such as their hair, and from their hands onto areas previously covered by clothing. There was a lot of vigorous arm and armpit rubbing, although, unknown to the volunteers, these were not the most contaminated areas. The real hotspots such as underneath the nose and the backs of the hands were not always cleaned effectively because the contamination was invisible to the volunteer. Differences in the washing efficiency of the units were identified and recommendations made on where best to concentrate washing efforts for maximum decontamination.

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