By Prof. Robert P. Chilcott, Toxicology Research Group, University of Hertfordshire, UK
Introduction
The intentional, large-scale release of a hazardous substance may result in a “mass casualty” situation, potentially affecting several thousand individuals – as was the case following the release of nerve agent on the Tokyo underground transport system in 1995. Many countries have well-established incident response plans that aim to deliver decontamination facilities, antidotes, medical supplies and supportive care to affected individuals. In the case of major public gatherings such as sports events and music festivals, such emergency response assets can be pre-deployed to ensure their immediate availability. This is a proportional safeguard, as many toxic chemicals are rapidly acting and so a delayed response will have an adverse effect on casualty survival. However, it is simply not practical nor economically feasible to maintain such a state of readiness in anticipation of an attack which could potentially occur at any time, in any place and involve any toxic substance. Therefore, an alternative approach is required to address the earliest phase of a chemical incident prior to the arrival of specialist resources. The generic term for this strategy is the Initial Operational Response, or IOR, which can be considered a form of first aid for chemically contaminated casualties.
Several countries have formally established an IOR to chemical incidents including France, the UK and the USA, a common feature of which is to evacuate casualties from the source of exposure followed by immediate removal of clothing (“disrobe”) and instigation of dry decontamination using any readily available absorbent material such as tissue paper or wound dressings. Whilst such an ad hoc approach lacks sophistication, these simple actions may save lives and will substantially reduce exposure to toxic chemicals. Incidentally, dry decontamination is the default option for an IOR as water may enhance the skin absorption (and thus toxicity) of certain chemicals. Dry decontamination is also less likely to result in the inadvertent spreading of a contaminant over the skin surface.
There is ample evidence to support the implementation of an IOR: scientific studies have consistently demonstrated the clinical benefit of rapid skin decontamination. However, this ignores a startlingly obvious feature of the human body – scalp hair.
Getting to the Root of the Hair Problem
The top of the head represents the anatomical location which is likely to accumulate the highest levels of contamination following an overhead exposure to liquids or aerosols. The hair physically acts as a protective layer, reducing exposure of the underlying scalp skin by up to 95%. A further advantage of hair is its affinity to strongly absorb oily (lipophilic) chemicals. In this respect, hair can also act (to a limited extent) as a decontaminant, absorbing chemical contaminants from the surface of the underlying skin. Both characteristics are seemingly advantageous for the more hirsute members of the population. However, there is a yang to every yin. The affinity of the hair for lipophilic chemicals results in the rapid movement of such contaminants from the surface of each hair strand to within, forming an internal reservoir. As the contaminant is no longer on the hair surface, it becomes relatively impervious to both wet and dry forms of decontamination (see graph below).
By unfortunate coincidence, some of the more toxic chemicals of concern (e.g. nerve agents and sulfur mustard) are lipophilic, and so these are likely to form a reservoir within the hair strands and become resistant to decontamination. A second problem relating to the formation of the hair reservoir is off-gassing: the production of toxic vapors from volatile contaminants. It has been demonstrated that chemicals such as sulfur mustard can off-gas from the hair reservoir for several days following decontamination. This represents a secondary hazard through inhalation of the resulting vapor. A final consideration is the bioavailability of the hair reservoir. The roots of each hair strand penetrate deep into the dermis. A chemical diffusing from the reservoir down the hair strand will, in theory, be able to avoid the barrier layer of the skin and directly enter the systemic circulation. The toxicological significance of this route of absorption is poorly understood at present.
Wash and go or stop and chop?
The relative ineffectiveness of standard hair decontamination procedures poses the obvious problem of how to manage such casualties. Aggressive solvents can be used to extract the hair reservoir, but it would neither be practical nor safe to treat a large number of casualties with inflammable liquids. The most recent guidance for dealing with contaminated hair states that “consideration be given to removing hair in circumstances where the following criteria are met: (1) contamination is known to have occurred, (2) the contaminant is known to be toxic and (3) residual contamination has been confirmed following the Triple Protocol [decontamination] using available DIM equipment”. Maintaining the trust and cooperation of casualties during an incident will always be a demanding task for first responders, especially when supervising disrobe and decontamination procedures. Asking casualties for permission to remove their hair is likely to be a far more challenging endeavor.
Summary
Various decontamination strategies have been developed as part of the response to chemical contamination. The most important aspect involves establishing an Initial Operational Response which represents potentially life-saving first aid for chemically-contaminated casualties. However, standard protocols for hair decontamination are relatively ineffective and so contaminated hair may need to be removed.
Acknowledgement
The hair studies referred to in this article were funded in whole or in part by the U.S. Department of Health and Human Services, Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority under Contract HHSO100201500016C.
Recommended Reading
“The United Kingdom’s initial operational response and specialist operational response to CBRN and HazMat incidents: a primer on decontamination protocols for healthcare professionals”, 2019, Emergency Medicine Journal. 36, 2, p. 117-123 (https://emj.bmj.com/content/36/2/117).
Primary Response Incident Scene Management: PRISM Guidance, Volume 1, Second Edition, 2019, Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority, Washington DC (2018). Available from https://www.medicalcountermeasures.gov/barda/cbrn/prism/
“The chemical, biological, radiological and nuclear (CBRN) chain of survival: a new pragmatic and didactic tool used by Paris Fire Brigade”, 2019, Crit Care. 2019;23:66. doi: 10.1186/s13054-019-2364-2. Available from https://www.researchgate.net/publication/331368792_The_chemical_biological_radiological_and_nuclear_CBRN_chain_of_survival_a_new_pragmatic_and_didactic_tool_used_by_Paris_Fire_Brigade
