Investigation of Fires Controlled with Compressed Air Foam Systems (CAFS)
In today’s fire service world of “do more with less” many agencies are at least investigating, if not outright adopting the use of foam additives and Compressed Air Foam Systems (CAFS). These foaming additives are put to use with the thought of extending water’s capability by increasing the effectiveness of limited supplies, optimizing limited personnel resources, reducing overhaul time and damages, and increasing safety for internal and external customers. All these aspects and more sway the decision tree toward the use of foam, and rightfully so. In many instances these same fire departments realize, only after the fact, that there are other aspects to foam that need attention prior to its implementation. The use of foam in any of its variations can and will influence the fire Cause and Origin investigation. Understanding foam additives, education of staff, and correct handling of the scene and resultant evidence are the keys to a successful and safe scene investigation.
In the past two decades of travels as a fire investigator as well as a CAFS Trainer I have heard many times the overwhelming exclamation of “What have THEY done to MY fire scene?”. In some cases, the mere sight of a foamed scene causes a virtual mind block to the investigator. “How in the world will I investigate what I can’t see and process contaminated evidence?” This scenario can cause an immediate and lasting distaste for foam use in the department. I will explain some of the misconceptions and get the investigator and the department headed toward an understanding of what should, versus what could, occur on the fire that was controlled with Class “A” foam additives and / or CAFS.
The first thing to recognize is that Class A and CAFS are not a passing fad that will just fade away if the investigator waits it out. Many fire services worldwide have known since the early 1900’s that CAFS is the most effective fire control system available. The obstacles to widespread adoption of CAFS was the lack of effective highly concentrated chemicals, reliable state of the art automated hardware and education of the front-line troops. Welcome to the 21st century! The past known and perceived problems with foam and its application systems have been overcome. There are accepted safe practices taught for the use of CAFS in interior and exterior structural applications. One fire truck manufacturer has reported that last year nearly 75% of the apparatus leaving his facilities were in some way foam capable and 25% of those were CAFS capable. CAFS is not going away, in fact I don’t believe we have seen it even approach its peak yet. Now you must understand and deal with its use at home.
You must seek to be educated on the different “Classes” of foaming additives as well as the different “Types” of finished foams. A thorough discussion of all these is beyond the scope of this article, but are essential to investigators and other personnel providing expert testimony in a courtroom. For the purposes of this article, I will address the most common application that may be encountered. That is Class A foam in the form of Compressed Air Foam. This is an aggregation of Class A foam concentrate, water, and compressed air, all of which is enhanced or “Finished” through agitation within the hose line.
Many, but not all, Class A concentrates have some level of one or more hydrocarbon-based components in the formula. Many folks will argue that although this is true, those compounds are diluted to levels so low they will not affect the investigation. This is simply not the case. Along with advances in foams also came advances in hydrocarbon detection and classification. Today’s forensics laboratories employ state of the art gas chromatographs that can ferret out minute traces of hydrocarbons from fire scene evidence. (Photo 1 & 2) The positive aspect of this is that the educated investigator will ensure that the lab is aware of foam usage, prior to the need for their services. Prior to the fire event, have the lab analyze the finished foam the department will use in the same concentrations and foam type that they will employ on normal fire attacks. This will provide a base line for future use as well as show that the department uses foam as a “Normal Operating Procedure” in its day-to-day functions. At the point of submitting actual fire scene evidence (photo 3) and the needed “Comparison Samples”, ensure that both have been exposed to the finished foam so that we have some apples-to-apples comparison. What was considered an evidence contaminate is now accounted for, acknowledged, and generally not a point of contention in testimony.
Fire investigators that have been on the line for many years but haven’t followed the technology of Class A foam firefighting are many times appalled at the thought of investigating an event controlled with CAFS. They imagine a structure filled to the brink with foam bubbles obscuring the vital evidence for days on end. This image is a misconception, visions from years gone by of over application of Medium or High Expansion naturally aspirated foam. The CAFS agent used today is proportioned at 0.3% of Class A concentrate and is of the Low Expansion variety. The normally encountered depth of finished foam is less than a half inch. Indeed, this could obscure the scene and related evidence. This could also be construed as a safety hazard to the investigator. All this is true if your investigator is arriving immediately after fire suppression. Tests have shown that much of the visible finished foam in the structure drains out and breaks down thus disappearing from the scene in less than an hour after proper application. If investigative duties require the removal of the finished foam quicker, then the process can be accelerated by the application of a very low GPM spray of plain water fog into the air over the foam. The physical impact of the falling water droplets immediately pops the bubble structures. This can be accomplished with a booster reel or even a hand-held spray bottle if delicate evidence is in question.
As always, keeping safety at the forefront of the investigator’s thoughts, remember these basic ideas. You can’t avoid what you can’t see. Avoid rushing into foam covered scenes; there are many other functions that need to be addressed that will allow the needed break down time of the foam. Also, consider that the basic detergent components of Class A foam have virtually little to no effect on some of the residual fire gases in the building. Currently there is testing underway that shows very promising results in the absorption of some carcinogenic byproducts when using CAFS. Additional testing and time will give us verifiable data on this front. Wear all protective gear, especially respiratory & eye protection. The dermal effects of Class “A” foam can be compared to severe dish water hands. The detergent qualities of the foam super clean the oils from your skin quite rapidly so wear appropriate gloves.
Other differences encountered during the investigation of fires controlled with CAFS are descriptions of fire behavior, visible smoke changes, and possible unusual patterns seen in the smoke demarcations. Personnel that are new to CAFS firefighting may make statements concerning fire behavior that could lead an investigator to minimize the thoughts of accelerant use. Since CAFS can drop and hold down interior temperatures at the rate of 20.5 degrees F. per second, one might be misled that a fire so easily controlled couldn’t have been accelerated. Not so! Small quantities of flammable or combustible liquids are easily extinguished with CAFS and have fewer tendencies to flare back up. Be sure to account for or exclude the use of accelerants via other accepted means beyond firefighter reports of quick temperature drops and lack of flare ups.
Descriptions of changes to the smoke issuing from structures by fire personnel and layman will sound dramatically different and somewhat unbelievable until you’ve experienced it yourself. One of the most misunderstood qualities of class A foam is its affinity for carbon. When class A CAFS is correctly generated and applied it sticks to virtually all surfaces in the structure, because they are carbon based. The dramatic and near instant change to visible smoke is due to this same quality. The foam within the structure acts as a chemical magnet to virtually all the unburned carbon particulates in the smoke. (Photo 4 & 5) The resultant discharge of smoke from the building immediately turns white. It’s not all steam, it’s still smoke with all the accompanying poisonous gases, it’s just absent the carbon particulates. Most firefighters can find all kinds of positives for this effect such as visibility and the reduction of fuels that cause fire roll over. The fire investigator that’s new to CAFS may find these descriptions befuddling.
An accompanying phenomenon to this smoke change is the possibility of unusual marks found within the smoke demarcation areas of the fire scene. Once again, the affinity for carbon comes into play. This is enhanced by the type of stream used in correct CAFS applications. CAFS is applied most effectively via a smooth bore tipped nozzle. This high velocity stream carrying a carbon loving agent will cause stripes of smoke stain to be erased from the smoke demarcation areas. This is commonly referred to as racing stripes. In some instances, the investigator can count the number of times the nozzle man swept the area by counting racing stripes on the walls of the fire area. These may well show up in your photographs. With this knowledge in hand, it’s now simple to explain and account for these unusual marks.
The job of many fire investigators goes well beyond Cause and Origin determination. One must be adequately educated in the department’s newest state-of-the-art suppression systems, chemicals, and tactics. Another layer to the knowledge base and experience must be added to the fire investigators toolbox to stay current with the advancements in fire suppression. Your fire scene may very well look different to all involved in the judicial system and you can find yourself educating the prosecutor and most importantly the jurors as to what they are seeing and what has occurred at the scene of a fire controlled with Class “A” foam and CAFS.
Mark Tracy
Flagstaff Fire Department (Ret.), Flagstaff AZ.
Foam & CAFS Instructor Coordinator for the Waterous Co.
