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CAFS And Its Impact In Fire Scene Investigations

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.

Some of the respondents stated that the foam was less destructive to the scene than water and that the foam protected the areas where an ignitable liquid was present. Those that had accelerant detection canines reported that the canine gave positive alerts and did not have any issues when the foam was present.

Additional Assistance

Montgomery County investigators contacted a subject matter expert in CAFS field, Dominic J. Colletti, Global Foam Systems Product Manager for Hale Products, Inc. Mr. Colletti provided information and demonstrations on the use of CAFS and agreed to assist in potential test burns at a future date. He also educated fire investigators on the differences between standard nozzle aspirated class A foam, and compressed air Class A foam applications. When using CAFS, less foam concentrate will typically be exhibited within the structure or room of origin as compared to what would be seen when using standard nozzle aspirated Class A foam for fire suppression or overhaul. The reason: CAFS application results are in one way different (as compared with the application of standard nozzle aspirated Class A foam) in that typically from two-thirds to about half of the total water supply (total gallons of foam solution) is required to extinguish a given size fire.

It was then determined that the next course of action was to enlist the assistance of the ATF Fire Research Laboratory located in Ammendale, MD. The Montgomery County Fire Department has had a long standing relationship with ATF as their laboratory was previously located within Montgomery County. ATF Special Agent/CFI Gregg Hine and Section Chief Kenneth Steckler were contacted to discuss a potential research project to further examine the impact that CAFS would have on fire investigations. Special Agent Hine, who has worked with Montgomery County, concurred with the concerns expressed by fire investigators and canine handlers. The use of foam was also a concern for the new ATF Fire Research Laboratory because of the potential that foam would be used in the future to suppress fires in the laboratory. At the Fire Research Laboratory, all run-off from fire suppression is treated on-site by a water treatment center. Section Chief Steckler was particularly interested in how the foam would be handled by the water treatment system and to determine any problems that may arrive from inserting foam into the treatment system.

Testing Methodology

To evaluate the impact of CAFS on fire investigations in a real-life scenario, two burn cells were constructed at the ATF Fire Research Laboratory (FRL). Both burn cells were identical in size and geometry. No instrumentation was placed within the burn cells during the tests, however, both tests were photographed using a digital SLR camera and a digital video recorder.

The burn cells were constructed of standard wood framing materials and the interior was finished with gypsum sheetrock panels screwed to the walls. The cells measured eight feet deep by 22 feet wide. A large six-foot opening that was eight feet deep, similar in geometry to a hallway, provided access and ventilation to each cell. This opening allowed clear visibility into the burn cell during the tests and allowed ample ventilation. The ceiling was the standard eight feet and the floors of the burns cells were a combination of both carpet and vinyl sheet goods applied directly to a sheetrock sub-floor. The interior of each burn cell was furnished with various residential items to replicate a typical residence.


Two fire tests were conducted at the ATF FRL. An ignitable liquid was utilized in each burn cell as an accelerant, thus providing a substance to examine canine performance. Ignition of the liquid was conducted using a standard ATF FRL technique involving a propane torch affixed to a 10-foot wand. The fire was allowed to spread throughout the interior of each burn cell and then progress to a flashover. Each burn cell was then allowed to continue to free burn for approximately one minute post-flashover to replicate a normal room and contents fire as seen in Montgomery County, MD. Fire suppression of both burn cells was conducted by a representative of Hale Products utilizing Hale Products equipment. Additional fire suppression support was provided by the ATF FRL Fire Brigade utilizing standard firefighting hose lines connected to standpipes within the facility. In addition, positive pressure ventilation (PPV) was utilized after the fires were knocked-down with the CAFS to removed trapped smoke and identify any hot spots within the burn cells.

An ATF-certified accelerant detection canine, Iris, and handler Doug Wilson from the Anne Arundel County, MD, Fire Investigators' Office, were utilized to examine the fire scene. The following issues were of specific concern to the fire investigators and the accelerant detection canine team:

  • Would the use of foam prevent the handler from performing a scene safety check to protect the canine?
  • Would foam hinder the search capabilities of the canine?
  • Would the foam prevent the accurate marking of the canine alert site?
  • Would foam contaminate the accelerant sample or be washed away or diluted to the point that it would not show up during a canine search or lab analysis?

Test #1

Test # 1 was a room and contents fire with approximately three to four cups of commercially available Kingsford brand charcoal lighter fluid poured across the floor covering and over to a double bed. The liquid was spread in a standard "trailer" fashion recognized by fire investigators. The liquid was ignited and allowed to burn to post flashover.

In Test # 1, the limited amount of charcoal lighter fluid utilized resulted in a slow growing fire. As a result, there was not rapid fire growth and it took nearly 15 minutes for the contents to become involved and reach flashover conditions. Fire suppression was conducted approximately one minute later with the application of Compressed Air Foam from a single handline at a setting of five-percent (0.5%). The nozzle man was an experienced CAFS user and applied the foam judiciously. Little or no visible foam was observed within the compartment after fire suppression.

Ofter approximately 30 minutes, ATF personnel monitored the atmosphere until it was safe to enter. Once it was safe to enter, Investigator Wilson calibrated his canine partner Iris on a drop of 50-percent evaporated gasoline placed on a piece of carpet outside of the scene. This calibration is per ATF canine training and serves several purposes. First it lets the handler know that his canine partner's nose is working and second it lets the canine know they are going to work. Fire Investigator Wilson conducted a search of the fire scene with Iris, who gave numerous primary alerts. Four samples were collected and placed in clean metal evidence cans. The collected samples were placed in a discrimination line for the canine. This discrimination line examination provided confirmation of the canine alerts made in the scene.

Test #2

The second room and contents fire was set by using approximately one to one-and-one-half quarts of gasoline, which was poured across the floor covering, over chairs and up onto a table and chairs. This fire grew extremely rapidly and progressed to flashover in approximately two minutes. After an additional minute, fire suppression was initiated using CAFS from a single handline at a setting of three-percent. However in this test, the experienced nozzle man was instructed to apply additional amounts of foam to replicate an inexperienced or novice user. It was believed that this may more accurately represent a real fire scene where more foam is utilized.

After fire suppression, foam was visible in pools on the floors and other horizontal surfaces. It appeared that the foam pooled in lower areas, much as water would pool. The remaining foam, however, was not excessive enough to cause a delay in the fire scene investigation. Some of the remaining foam could obscure small items at floor level. Yet, it was not perceived that the lingering foam created a safety hazard by obscuring openings or large objects. After approximately 20 minutes, pockets of foam were still visible on the floor and under a desk. This slowly dissipated over the next hour until it was nearly invisible.

As in the first test burn, the atmosphere was monitored and once it was safe to enter, the accelerant detection canine team conducted a search using the same protocol as for the first room. The canine gave numerous primary alerts, and four samples were again collected and placed in clean metal evidence cans. The collected samples were placed in a straight line and a discrimination line examination was again conducted by canine Iris.


At the conclusion of both tests at the ATF Fire Research Laboratory, the following observations were made by the members of the project team.

  • Both rooms had gone to flashover and produced considerable damage
  • There was considerable charring to all furnishings
  • The flooring was charred
  • The fire was extinguished with a controlled application of Compressed Air Foam
  • The Compressed Air Foam seemed to dissipate fairly quickly
  • There was not a large amount of foam, but pockets remained for over one hour in Test # 2
  • Do to the minimal amount of foam - no slip hazard was detected

Fire Investigator Wilson and his partner Iris were closely monitored throughout the entire process and the following observations were made:

  • There was no apparent difficulty in conducting a K-9 scene safety check
  • The Compressed Air Foam used for extinguishment did not give K-9 Iris any problems conducting her search for the ignitable liquids
  • The Compressed Air Foam had dissipated sufficiently for canine Iris and Investigator Wilson to conduct their search of the entire scene and mark Iris' primary alerts
  • Investigator Wilson was able to accurately mark K-9 Iris' alerts and collection of these alerts was done without problem.

Laboratory Analysis

The samples collected from both of the test burns and a sample of the foam was submitted to the ATFE National Lab for analysis. The chemical make-up of the foam was consistent with what would be expected for such a product. However, there were some components in the foam that may interfere with ignitable liquid analysis. These components could be classified as a heavy normal-alkane product by ASTM E 1618. These components, if observed in debris or in combination with a heavy petroleum distillate such as kerosene or diesel, may pose some problems with chromatographic analysis.

Three of the four samples collected from Test 1 were positive for the presence of a medium petroleum distillate (MPD), which is consistent with the use of the Kingsford brand charcoal lighter fluid. Only one of the four samples collected from Test 2 was positive for the presence of gasoline. For these positive samples, the chemical components of the foam did not interfere with the analysis of the data.

One of the three negative samples from Test 2 had indications of gasoline, but the level was too low to make a positive identification. The remaining two negative samples from Test 2 and the negative sample from Test 1 showed no indications of their respective ignitable liquids (gasoline and MPD). In fact, the chemical components from the foam predominated the observed chromatographic data for all of the negative samples. The reasons for the negative laboratory results for some of the samples may be due to various reasons. One possibility may be the amount of time from when the samples were collected to when they were analyzed. The collected samples were analyzed approximately 30 days after the tests. This possible effect of the foam on the collected samples needs to be examined further under controlled conditions.


Based upon the review of existing research and the fire tests conducted, it is believed that the Compressed Air Foam did not interfere with the ability of the ATF-certified accelerant detection canine's or the handler's ability to conduct an effective scene search, marking or collection of potential evidence. In addition, no significant impact was noted to the fire scene investigation in the tests. However in Test #2, the foam did remain in pockets on the floor for over one hour after application. The foam was minimal and it is not believed that this would have created a significant problem for fire investigators. Should more foam have been used, it may have caused a delay in the scene investigation, obscured hazards or presented a slip hazard. Even though some of the samples tested positive for the presence of the respective ignitable liquids, the overall effect of the foam on laboratory analysis needs to be evaluated further.


  • Firefighters receive adequate training in the proper application of Compressed Air Foam to avoid excessive amount of foam build-up
  • Fire investigators take a proactive approach to familiarize themselves with the product and the foam application procedures if their department is using or is planning to utilize Compressed Air Foam
  • Fire investigators and canine handlers conduct a more comprehensive scene safety search when Compressed Air Form has been applied to ensure that no hazards could be obscured by the foam
  • Fire investigators must ensure that a control sample of the Compressed Air Foam that was used to suppress the fire is submitted to the lab with other evidence that has been collected
  • Additional laboratory testing and evaluation is still needed to determine the effects of Compressed Air Foam on ignitable liquids
  • Canine handlers and fire investigators should obtain a Material Safety Data Sheet on the foam that is being used within their departments prior to any exposures

The authors hope that the information provided will be helpful to the fire investigation community conduct origin and cause examinations where the use of Compressed Air Foam has been used as the primary extinguishing agent. Readers with questions should contact them directly.


(1) "Compressed Air Foam for Structural Fire Fighting: A Field Test Boston, Massachusetts"; United States Fire Administration, National Fire Data Center.
(2) "Class A Foam: A Field Study"; J.P. Ryan, J.C. Winchell; Size Up; Winter 2002.
(3) "Class A Fire Fighting Foam and its Affect on the Abilities of the ATF Accelerant Detection K-9"; W. F. Marshal; ATF Certified Fire Investigator Research Paper, 2000