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Back to Archives | Back to February 2004 Contents 

Contamination of Evidence Seized at Chemical Agent Crime Scenes

By Elizabeth Aton, Principal Investigator, and Bradley Evanoff, M.D., M.P.H., Washington University School of Medicine, Saint Louis, Missouri, and Sergeant Vincent R. Stehlin, Emergency Planning Specialist, Saint Louis Metropolitan Police Department

The potential exists for a chemical agent to be used as a weapon against the civilian population of the United States. An element of the response to such an event involves protection of life by decontamination of victims in the field prior to emergency medical care. While it is generally accepted that decontamination reduces the dose of contaminant received by victims, there is little available documentation of the effectiveness of decontamination under field conditions. Important too in the resolution of such an event is the handling of evidence seized at the scene. Knowing whether a contaminant remains on victims' clothing and personal effects is important for the safety of those persons and agencies handling such evidence at the scene and in the laboratory.

To assess the contamination potential of evidence from seized clothing, the Saint Louis Metropolitan Police Department, the Saint Louis Fire Department, and the Saint Louis City Local Emergency Response Commission undertook a study using a chemical surrogate to mimic contamination of victims undergoing decontamination in a field setting. A surrogate contaminant was applied to victim volunteers and their clothing, and assessment was made after the exercise as to whether contaminant remained on their persons or effects. The major finding was that although most contamination was removed from victims' skin and hair, the clothing worn by victims remained contaminated. Persons who handle such evidence must be aware that the potential remains for hazard associated with secondary and tertiary exposure to such materials. This sends the new message that law enforcement agencies must establish procedures appropriate for protecting those who handle evidence from these cases.

Although this article reports the study on decontamination, the study was performed as a part of a large-scale field training exercise that simulates deployment of a chemical agent against a civilian population in which many other valuable lessons were learned.

Materials and Methods
Setting: This study took place during the conduct of a field training exercise for response to deployment of a chemical weapon against a civilian population, in Saint Louis, Missouri, in May 2002. The weather was warm, with temperatures in the range of 80 degrees Fahrenheit.

Contamination Methods: Sodium fluorescein was selected as a chemical surrogate for this investigation. Fluorescein has a number of properties that make it a desirable test agent for this assessment. It is soluble in water, so it mimics many of the caustic or corrosive agents that may be used in an actual event. It is only poorly visible in natural or room lighting, so victims are not aware of specific locations on their person where contamination may remain, but it fluoresces readily in the presence of black ultraviolet light. The chemical surrogate remaining after decontamination was assessed with ultraviolet light.

Ten victim volunteers from the Saint Louis Metropolitan Police (SLMPD) Academy class were issued used SLMPD uniform shirts and pants for this exercise. A water solution of the sodium fluorescein was applied to victims and their clothing with a spray bottle before they took their places at the scene of the purported release. Emergency response personnel gathered at the scene of the field training exercise and were organized under a unified command structure.

Fire department hazardous materials specialists set up an outdoor chemical decontamination corridor, according to generally recognized methodologies (SBCCOMM 1998). This was a two-step process, with a first step of gross decontamination in a high-volume water spray. Although in a real event the victims would remain in gross decontamination until secondary decontamination is set up to receive them or as long as they can be instructed to do so, in this study we were able to instruct victims to remain in gross decontamination for at least 10 minutes. Victims were then sent through secondary decontamination. In secondary decontamination, victims remove clothing and personal effects and then walk or are carried through a shower and scrubbing process. As clothing and other personal effects were removed, they were seized and bagged as evidence by the evidence technicians.

The evidence collection process (SLMPD Code 1200/Terrorism Annex) involves several steps. As victims enter secondary decontamination areas they are instructed to stand on a plastic trash bag. They remove clothing and other personal effects and drop it all into the bag. Evidence technicians then close the bag and place it inside two more bags. Tracking labels are placed on the external bag.

Data Collection: After decontamination, victims and their effects were examined with ultraviolet light. Any visible contamination remaining was noted.

Scanning of clothing collected as evidence showed that residual contamination remained on the pants from each of the 10 victims. No contamination was identified on the skin of victims at the scene, following the gross decontamination procedure. Water leakage was noted from the evidence bags collected at the scene. Outer bags in which evidence was collected were free of contamination in all cases.

Preserving Evidence and Protecting Life
The purpose of field decontamination is to protect life and health in a victim population, and the process is set up to maximize that protection. While it is inevitable that some contaminant may be removed from the clothing of a victim who completes the gross decontamination process, particularly if the contaminant is water-soluble, this is not the primary objective of decontamination.

Many factors may contribute to the retention of contaminant in clothing and personal effects, including the clothing weave, how long the victim remains in decontamination, how vigorously the individual is able to scrub at their person while in decontamination, and the physical and chemical properties of the contaminating agent. It is important to note that in this study the surrogate contaminant was water-soluble and therefore more likely to have been removed by water shower in the gross decontamination process. Contaminant was not observed on the shirts surveyed, which we believe reflects the nature of gross decontamination with its large volumes of overhead water deluge. Removing contaminant from other clothing is much more difficult in that setting.

The process of triple bagging appears to reduce the potential for external contamination on the collection bags, since no contamination was noted on examination of the outer bags. Because victim clothing remained contaminated in this study, handling it poses significant potential for hazard to persons conducting forensic investigation of such items after an event.

It is prudent for each jurisdiction to assess their procedures for victim decontamination and evidence collection, and consider evidence seized from victims in a chemical event to be contaminated until definitively proven otherwise. Given that leakage was observed from the bags in this study it is possible that water-soluble chemical agents could be carried off in this water, although it was beyond the scope of this study to confirm this. Jurisdictions should plan for secondary containment of evidence bags, and to work with response staff from the FBI for managing the collection and storage of these items in an event.

Compile Provisions to Safely Handle Chemical Evidence
The goal of field decontamination in an event involving deployment of a chemical agent in a civilian population is to reduce the dose of the agent received by the victims. While some contamination may be removed from clothing and personal effects as victims undergo gross decontamination with large volumes of water, the primary objective of the process is to begin to remove the agent from the individuals. This study confirms that clothing collected from victims after gross decontamination remains contaminated. Individuals who prepare response plans for law enforcement agencies must compile these plans to address this reality, and include provisions appropriate to protect the life and health of those individuals who may handle such evidence.

1 Saint Louis Metropolitan Police Department Code 1200/Terrorism Annex.
2 U.S. Army Soldier and Biological Chemical Command (SBCCOM), "Guidelines for Mass Casualty Decontamination During a Terrorist Chemical Agent Incident," January 2000.

Authors' note: This work was undertaken with the endorsement of the Saint Louis Metropolitan Police Department, the Saint Louis Fire Department, and the Saint Louis City Local Emergency Response Commission.


From The Police Chief, vol. 71, no. 2, February 2004. Copyright held by the International Association of Chiefs of Police, 515 North Washington Street, Alexandria, VA 22314 USA.

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