Decontamination Methods

A crime or accident scene often contains fluids, including blood. These fluids could also contain noxious biological or inorganic compounds. It is necessary to carefully handle fluids when collecting evidence to avoid contamination. Additionally, after the survey of the crime or accident scene is complete, steps must be taken to decontaminate the site in order to remove any potential danger to others.

Human decontamination can involve removal of a contaminant from the skin. Usually such decontamination must be done quickly, since the contaminant may be absorbed through the skin where it can cause internal damage. Washing with regular hand soap or the antiseptic soap used in hospitals allows for the rapid removal of personal spills. Portable emergency response personal decontamination kits can also be carried to the scene.

Decontamination of an investigation scene often utilizes a variety of physical and chemical decontamination methods and strategies. The method selected depends on the nature of the contaminant. For example, vacuuming up a spill of a powdery chemical can be a prudent step, while the same technique might be inappropriate for a liquid spill.

Liquids such as blood are removed from inert surfaces or living surfaces (i.e., skin) by the use of sorbents. The sorbent can be a natural material, such as soil, diatomaceous earth, or activated charcoal, or can be synthetic (i.e., Amberlite XAD-2 and XAD-7 resins). Absorption involves the concentration of a substance from the liquid phase onto the surface of the adsorbent material due to the chemistry of the surface molecules.

The most recognizable solid absorbent is a clay material known as Fuller's Earth. This material is commonly found in cat litter. When solid absorbent materials like Fuller's Earth, soil, or diatomaceous earth are used, the contaminant is usually not altered. For example, petroleum products are readily absorbed, but are not changed in their character. Thus, the sorbent material becomes toxic and so must be collected and disposed of afterwards. Caution needs to be taken during the collection process, as fine dust or particles can be inhaled or stuck to exposed skin.

A different type of physical decontamination involves washing the contaminant away using another fluid like water, an alcohol, or freon. The aim here is to dilute the contaminant in the wash fluid, which should itself be collected for proper disposal. Washing is not a complete decontamination. Residual contaminant can remain behind in cracks or other hiding places. However, the use of high-pressure sprays can be an effective and rapid means of decontaminating surfaces like walls and floors.

Chemical decontamination goes further than merely removing a contaminant from the environment. Rather, in chemical decontamination the adsorbing chemical neutralizes a contaminant. One example of chemical neutralization is the adsorption of a contaminant by material that is impregnated with an alkaline chemical. Another general example is the use of chemically reactive compounds that interact with the contaminant and change its structure into a form that is non-toxic.

A popular chemical decontamination strategy relies on the use of oxidizing agents. Bleach is a well-known example of an oxidizing agent. The use of oxidizing compounds such as calcium hypochlorite or sodium hypochlorite inactivates a variety of chemical compounds as well as dangerous microorganisms such as bacteria and viruses.

Oxidizing agents can be wiped onto a spill and collected in an absorbent material. As well, some oxidizing agents can be incorporated into topical lotions, which are smeared onto the skin to help inactivate a chemical or biological spill.

A recent innovative example of an oxidizing agent is L-Gel. Developed at Lawrence Livermore National Laboratory, L-Gel uses potassium peroxymonosulfate to deactivate a variety of biological agents, including anthrax spores and Yersinia pestis (the bacterium that causes plague). The thick gel is able to cling to surfaces better than water, especially to steeply sloping surfaces like walls, which keeps the decontaminant in contact with the target longer than using a straight water-based decontaminant.

Strong bases, such as hydroxide forms of calcium, sodium hydroxide, and potassium, are other useful chemical decontaminants. These agents disrupt chemical bonds in the contaminant and so destroy the offending compounds' noxiousness.

Water is an ideal fluid for decontamination because a variety of chemically different detergents and soaps readily dissolve in water. These compounds can loosen or bind contaminants and so remove them from a surface. The friction of scrubbing also aids in decontamination of the skin during hand washing.

The different tendencies of chemicals to dissolve in water (a property known as solubility) affect the efficiency of a decontaminant. For example, a longer period of decontamination is needed when using a compound that is not readily soluble in water. This problem can be somewhat overcome by the use of micro-emulsions, which are essentially very small droplets of the decontaminant. The droplet coat is a material that is less water-soluble. The effect is best seen when oil is added to water. Then, a sheen of oil appears on the water, rather than a homogeneous oil-water mixture. If a contaminant is not water soluble, it will quickly partition into the hydrophobic ("water-hating") decontaminant portion of a micro-emulsion. This can speed up the action of a decontaminant. Micro-emulsions can be applied to a contaminated surface as a spray, which can be washed off later.