Investigators were concerned about how the use of the foam would impact the use of accelerant detection canines, conceal scene hazards or create slippery conditions and how much time was required for the foam to dissipate in order to conduct an origin and cause examination.
The suppression of fires using compressed air foam - does it affect your origin and cause determination?
This was the question asked by investigators at the Montgomery County Fire and Explosive Investigations Unit in Montgomery County, MD when they learned that the department was in the process of purchasing 26 new engines that would be equipped with Compressed Air Foam Systems (CAFS). Specifically, investigators were concerned about how the use of the foam would impact the use of accelerant detection canines, conceal scene hazards or create slippery conditions and how much time was required for the foam to dissipate in order to conduct an origin and cause examination.
With these questions and others in the minds of investigators, the Fire and Explosives Unit in Montgomery County embarked on a research project to examine the overall impact on fire investigations where CAFS was used as the primary extinguishing agent.
Investigators within the unit, including the accelerant detection canine handler and the Fire Marshal, started to make contacts and search for any information related to the use of CAFS. Field tests of the CAFS were performed by the Boston Fire Department during most of 1992 into early part of 1993. The report "Compressed Air Foam for Structural Fire Fighting: A Field Test Boston, Massachusetts" (1), however, focused on the effects of CAFS as a suppression agent and not the post fire suppression impact on fire investigators.
Two other articles that were more closely related to the concerns of the Montgomery County investigators were both on Class A Foam. Investigators Ryan and Boone examined Class A foams in four phases and used accelerant detection canines and forensic personnel to assist with these tests (2). The authors concluded that more education and training must be conducted with the fire investigation community to determine how Class A foams can hinder or enhance an origin and cause investigation.
The second article was written as a certified fire investigator research paper required by the Bureau of Alcohol, Tobacco and Firearms and Explosives (ATF) examined what impact Class A foam had on a canine's ability to locate ignitable liquids (3). Special Agent Marshall concluded that further real-life testing should be performed to evaluate canine performance in burned structures that were suppressed with foam. His study also found that the use of Class-A foam did not hinder the abilities of the canines to locate ignitable liquids. He did caution that investigators should consider providing the Material Safety Data Sheet (MSDS) to their local lab so that the forensic chemists are familiar with the constituents of the foam.
In addition to the literature search, contact was made with 21 individuals, representing 17 fire departments, across the country. The departments ranged from large cities to rural departments. All the departments were asked "Do you believe that CAFS has an affect on your origin and cause examination and/or your accelerant detection canine?" Most of the responses received were from fire investigators within these departments. Upon review of the responses, it was determined that only one-third of the respondents believed that CAFS had an affect on origin and cause examinations. Of this group, the most common response was that when excess foam was applied, it took a period of time for the foam to dissipate. In some cases, 24 hours were required for the foam to dissipate in order for the investigators to clearly see the scene. One investigator mentioned that some times a garden hose or blower was used to remove the foam from the scene. Another investigator stated that there was some hesitation on the part of the accelerant detection canine to examine the scene due to the amount of foam present. No reports were received where a forensic laboratory was having any issues with the examination of the materials because the foam masked or broke down any ignitable liquids submitted for examination.