Interview with an Expert

One of the more specialized areas of crime-scene investigation has to do with searching for evidence of arson. To get some background in this area, we spoke with an individual who has had more than 46 years in fire service, 24 of which have focused specifically on fire/arson investigation.

EVIDENCE TECHNOLOGY: Where would you like to start our discussion?

DECKELMANN: Well, just about any place you would like. Do you want to know about some of the things fire investigators used to believe were true that have been disproved? I can talk about that because I was one of those people who believed those myths. It was what we were taught. It was all we had. But science has finally come along and is disproving a lot of those things.

EVIDENCE TECHNOLOGY: What do you mean about science coming along?

DECKELMANN: Well, they simply didn’t have enough scientists back in those days to study everything. We’ve been begging for science to help us out all along on this stuff. And finally, it is getting to the point where we have some scientists who are stepping forward to bring us the real facts.


DECKELMANN: They are helping us resolve a lot of things. Misunderstood conditions. Myths. There are a lot of us—fire investigators—who have been working for years to improve the scientific value of this stuff. There are people who have been searching for answers by test-burning buildings so we could look at what fire was doing and how it was doing it and why it was doing it.

EVIDENCE TECHNOLOGY: Can you give me an example?

DECKELMANN: Sure. It used to be said that if there was widespread floor burning, there had to be an ignitable liquid involved. For example: I’d look at a burned building where the whole floor was charred, and I’d stop and say to myself, “How can that possibly be? What did they do: pour ignitable liquid from corner to corner in every part of this room?” Well, today, we know that the charred floor is caused by something called flashover. We recognized that phenomenon in the late 1980s.

EVIDENCE TECHNOLOGY: So there have been some fairly recent advances?

DECKELMANN: Quite a few. There is a book called NFPA 921: Guide for Fire and Explosion Investigations. The book is one of many that are published by the National Fire Protection Association (NFPA). This is a book that fire investigators kind of live by right now—and it is a book that has really grown since it first came out. You can pick it up almost anyplace. Or go to their website ( and click on Codes and Standards and then click on Document List. The book just takes fire investigation piece by piece. It takes it to the scientific method. This is a book that was done by peer review.

EVIDENCE TECHNOLOGY: What were fire investigators doing before science starting giving you a hand? Were you just going by instinct or what?

DECKELMANN: A number of years ago, we were basically going by what our predecessors were teaching us. And that stuff was carved in stone. There were things like this: In laboratory tests, they would burn wood. And they would say that the rate of burning is 1 inch in 45 minutes. Well, going by that kind of formula, we’d look at a building and make a quick calculation as to whether it was a slow-burning fire or a fast-spreading fire. Today, we know that the damage has nothing to do with the amount of time that a building burns. It has more to do with the intensity of the fire. And even fighting building fires has changed a lot.


DECKELMANN: There have been a lot of changes in what is used in building the structures today compared to what was used years ago. Years ago, you would most likely find that only natural products were used in construction. Back then, wood was a two-by-four and it was a hard piece of wood. It was very hard and it took a lot of fire to damage it badly. Then came the 1980s when we had an energy crunch that caused contractors to start using a lot of man-made things in structures.


DECKELMANN: Did you know that you can make cyanide by burning certain kinds of compressed woods? During a fire, you can end up with cyanide right in the structure. And the Freon gas in the air conditioners is another example. It’s an old gas and no one is supposed to use it anymore. But in a fire, if we happen to encounter Freon leaking from an old air conditioner or a refrigerator, it can be very dangerous. Why? Because it can make phosgene gas—sometimes called nerve gas or mustard gas—the same thing that was used to kill so many guys during World War I.


DECKELMANN: So a lot of things have changed. And perhaps the biggest change is the fact that everyone has started using polyurethane foam in household and office furniture. And polyurethane foam can drive a room to flashover in a very short period of time. It is unbelievable what it can do and how fast rooms come to flashover. You know what flashover is, right? It is the point where everything in the room—wall to wall, corner to corner, floor to ceiling—jumps to open-flame ignition. In a flashover, everything in the room is burning at the same time, including the contents, the floor coverings, and the wall coverings. It doesn’t take much polyurethane foam to do it.

EVIDENCE TECHNOLOGY: What causes this flashover event?

DECKELMANN: Flashover is caused by heat radiating down from the top of a room. If you take just one polyurethane cushion from a sofa, you can drive a small room to flashover in nothing flat. It gives off enough heat to raise the ceiling temperature beyond 1100°F— and that’s enough to ignite all of the cellulosic materials within that room. Polyurethane is causing a tremendous hazard, both to the homeowners and to the firefighters who are fighting these things. It is especially dangerous to the homeowners. We are losing civilians like you wouldn’t believe.

EVIDENCE TECHNOLOGY: Does this flashover phenomenon have any effect on your fire investigations?
DECKELMANN: Flashover does not destroy the burn patterns that were in the structure, but it does disguise them. And if it goes on for a long time, then it will destroy the burn patterns. So it has just made it much harder to do a fire investigation. You really have to be on your toes.


DECKELMANN: You have to know what you are doing and what to look for. Training is essential. There are a lot of organizations out there that are working very diligently to make sure the training is there and that fire investigators are recertified on a regular basis. Part of that recertification is schooling so they will be current with the scientific method. The State of Illinois has its own Certified Fire Investigator (CFI) requirements through the office of the State Fire Marshal. Every four years, you have to recertify. A portion of that recertification has to be done working fire scenes. And the rest of it is done with education. Much the same thing applies to the International Association of Arson Investigators (IAAI). They also have a recertification program. We are moving forward to get everyone educated. A lot of old wives’ tales are disappearing, even though some of them keep hanging around. As a result, some people just don’t get a valid update on the state-of-the-art knowledge.

EVIDENCE TECHNOLOGY: What kind of “old wives’ tales” are you referring to?

DECKELMANN: Well, take the story about spalling of concrete, for example. Spalling of concrete means flaking or chipping on the surface of concrete. The old wives’ tale says that some type of accelerant had been poured onto the concrete and that is what caused the spalling. But today, we know better. We know that spalling can be caused by several things. It can be caused by thermal expansion. Or any kind of high heat can cause concrete to flake off at the top. Or you can even get some kind of concrete spalling by putting salt on your concrete driveway in the wintertime. Some scientists say the reason this happens is because the moisture in the concrete starts to expand—and as it expands, it flakes the particles off. And other scientists think that it is caused by thermal expansion. Actually, it’s probably a combination of both. There are a lot of reasons for the spalling. But it is not caused by a liquid accelerant or a flammable liquid.

EVIDENCE TECHNOLOGY: What does cause spalling, then?

DECKELMANN: What happens is this: The concrete cannot get any hotter than the liquid that is on top of it. If we get that liquid hot enough, it will vaporize and then it will be gone and there will be nothing left to burn. Consequently, it will never get to the level of heat that is needed to cause spalling. On the other hand, if I turn around and put a pile of wood on the concrete with some air space under it, I will get spalling. It will spall off big chunks. But that has nothing to do with an accelerant of any kind. That was the old way of thinking. Today, we know better: It’s not accelerants. It’s the high sustained heat from the available fuel load within a structure.

EVIDENCE TECHNOLOGY: Where is the scientific information coming from to discount these old wives’ tales?

DECKELMANN: This proof is coming from everywhere you can imagine. There are all kinds of scientists who are working in this area. One of the very finest sources for fact, in my opinion, is Kirk’s Fire Investigation written by Dr. John D. DeHaan. That is where I get a lot of information that I use in my teaching. This book keeps changing because DeHaan is always willing to change. When he finds something new, he puts it in his book. The sixth edition is available right now and the seventh edition is in the works. Writing like this is one way we’re able to stay on the cutting edge in this field.

EVIDENCE TECHNOLOGY: Has there been improved communication between fire investigators in recent years?

DECKELMANN: Absolutely! That is the truth. Just recently, I spent a week in Denver, Colorado at the International Association of Arson Investigators annual conference. There were more than 500 people registered at that conference. Everyone spent most of their time in classes and lectures and workshops—learning and networking. Networking between the different investigators is the important part of educational meetings. Because of these meetings, you always end up getting informative e-mails and links from across the country.

EVIDENCE TECHNOLOGY: What about the future of fire/arson investigation?

DECKELMANN: Where do things go from here and into the future? Well, with regard to fire/arson investigation, I guess we will go where science takes us. But fire fighting is another issue.

EVIDENCE TECHNOLOGY: What do you mean by that?

DECKELMANN: I would hope that some of the companies that supply building materials and home furnishings would begin to put fire safety into the home and stop these places from burning so profusely and killing our citizens. If we could just do something simple—like taking the foam rubber out of homes - it would be a big step forward. But builders are using more insulation in these structures and they are actually tightening them up so much that fire fighters aren’t getting the chance to go in and rescue anybody anymore.

EVIDENCE TECHNOLOGY: How about some more myths and old wives’ tales?

DECKELMANN: I can give you a whole bunch of them. For example: It used to be said that the size and appearance of a charred surface indicated the use of a liquid accelerant. In other words, the large, shiny blisters—or alligatoring as we refer to it—were evidence that a liquid accelerant was involved in the fire. In reality, charring—large or small, dull or shiny—has no relationship to the presence of a liquid accelerant. If you look it up in Kirk’s Fire Investigation, you will find that it has to do with the rings in the wood and the way it is cut. If you cut it a certain way, there will be larger alligatoring than if you cut it another way. It has nothing to do with a liquid accelerant.

EVIDENCE TECHNOLOGY: Does the way the wood is finished have anything to do with it?

DECKELMANN: The finish does have something to do with the way it’s going to burn. If it has been shellacked or varnished, it will burn quite a bit faster and quite a bit deeper. We have done experiments where we poured a mixture of gasoline and fuel oil on several different types of flooring, including hardwood floors, carpeting, and linoleum. We let them burn right out to see what kind of patterns the burning would leave. And believe me, it did not leave anything like what you would expect. It was more of a scorching and wasn’t deeply charred. It wasn’t bad at all, even on linoleum. The carpeting, of course, was different. There would be a well-defined path in carpeting.


DECKELMANN: That’s another thing: You will usually be able to find an accelerant in carpeting. Some people —when they can’t find an accelerant that they think was there—will tell you “It all burned up.” That is not really true. When accelerants are poured, the only way they will burn up completely is if the building is totally consumed and is just a black hole. Even then, you have a chance of finding some of the accelerant. For example: You can use an accelerant-sniffing dog and it can probably find accelerants in the debris. Accelerants can survive a lot of heat. When you pour that stuff, it doesn’t just pile up: it has to run someplace—in the carpeting or into some cracks in the flooring. And if it gets down below where it’s protected from the fire, it won’t totally burn up.


DECKELMANN: Consider this: For any-thing that burns, it is actually the vapors that are burning. Look closely at a match or a candle: There’s a separation between the end of the match or the wick of the candle and where the fire is actually located. It is the vapors that are coming off of the match or candle that are burning. Look at a log burning in your fireplace and you’ll see a separation. It’s the vapors that are being cooked out of the wood by radiant or convective heat. The gasses come off the wood—and they are what burns.

EVIDENCE TECHNOLOGY: So it is not the material—it’s really the gasses?

DECKELMANN: Right. Back to a topic we talked about earlier: flashover. This is what causes flashover. There just needs to be enough heat to cause the gasses to start coming up from the carpeting and furniture and other things. And then those gasses auto-ignite. The whole thing lights right up and comes across the room like a freight train.

EVIDENCE TECHNOLOGY: You’re on a roll here…

DECKELMANN: Here’s another myth: It used to be thought that the condition of springs in furniture would be a big tip to fire investigators looking for cause. They called it the annealing of springs. When you had annealing of springs, it was supposed to be the sign of a slow, smoldering fire—such as a cigarette that had been dropped between cushions or onto a mattress. But it is just a simple technical term that means to heat-treat, strengthen, or toughen. I wish I had a dime for every report that said the cause appeared to be smoking materials because of the localized annealing of spring in a sofa. But that was another myth. We went to a leading mattress company and they told us that even their own engineers couldn’t tell us when a spring was going to anneal or lose its tension. As a result, annealing of springs can still be used as a directional-type thing, but it can’t be used as a causation-type thing.

EVIDENCE TECHNOLOGY: There is a lot of logic involved here, isn’t there?

DECKELMANN: I don’t know how many times I’ve told my students that if they use common sense, they are going to go a long way in this business. That’s what you have to do: You have to use common sense. I have a friend who does research in this area. He experiments by blowing up houses. He has come up with a lot of good information. For example: It used to be said that when the vapors from gasoline or propane—vapors that are heavier than air—are confined inside a structure and that structure blows up, the walls should be pushed out at the bottom. Why? Because the gasses are heavier than air and would be at the bottom of the structure. Likewise, if we have a fire that involves natural gas—which is lighter than air—in the structure, an explosion should cause the walls to be pushed out at the top. But my friend showed that it does not make a bit of difference whether you are dealing with gasoline, propane, or natural gas. What happens is the explosion lifts up the roof of the building and the weakest point of the wall is forced outward. It’s that simple. It’s going to happen that way all the time.

EVIDENCE TECHNOLOGY: That is some complicated research....

DECKELMANN: There have been some simple discoveries, too. A lot of people think that if you get an electrical spark in a wall, you’re going to have a fire. But generally, what happens is a spark will cause a fuse to blow. That spark is so short-lived that it’s here and then it’s gone. It won’t cause wood to burn. It won’t ignite insulation. But if we get a high-resistance fault, that can heat up and cause a fire very quickly.

EVIDENCE TECHNOLOGY: Things have obviously changed a lot. What about the future of fire/arson investigation?

DECKELMANN: Where are we going in the future? We are going to continue trying to find out exactly what causes every one of these fires. We are getting a lot of support from engineers and scientists. There are many things that have been out there that have been changed through science, but nobody wants to keep the old myths alive. Fire investigators are always looking for answers. We are truth seekers—and we are always pushing forward to find a better way. What we’re looking for is what actually causes the fires. And for that reason, we would prefer to go into each and every investigation with no preconceived notions.

EVIDENCE TECHNOLOGY: Thank you for speaking with us today.

A brief look at the background and experience of Michael C. Deckelmann

Michael C. Deckelmann is a second-generation firefighter who has spent 46 years in the fire service. He began his career in 1962 as a volunteer with the Columbus Manor Fire Department in Oak Lawn, Illinois. In 1964, he took the exam for the Chicago Fire Department—and then waited three years for the job. During those three years, he worked as a patrolman and juvenile officer with the Evergreen Park Police Department. He joined the Chicago Fire Department in April 1967. In 1984 he transferred into the Office of Fire Investigation with the Chicago Fire Department. With the rank of Captain and the title of Senior Supervising Fire Marshal, Deckelmann was third in command of Chicago’s Office of Fire Investigation. He is a State of Illinois Certified Fire and Arson Investigator. As an Illinois State Certified Fire Service Instructor, he is on the field staff of the University of Illinois Fire Service Institute. Deckelmann is a member of the International Association of Arson Investigators (IAAI). He was elected to the presidency of the Illinois Chapter of the IAAI in 2002 after being on the board of directors and co-chair of the Training and Education Committee for a number of years. He also served on the board of directors of the Illinois Advisory Committee on Arson Prevention. He has participated in more than 100 live-burn demonstrations, many of which were thermocoupled to measure compartment temperatures prior to, during, and after flashover.

His e-mail address: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

  May-June 2008 (Volume 6, Number 3)
Evidence Technology Magazine
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