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jeseymour
05-16-2010, 04:33 PM
If someone used a Molotov cocktail to start a fire in a house, and that fire burned for an hour or so before the FD got there (rural location, no near neighbors) would any evidence of the glass bottle remain? Would it be better to use a plastic bottle or is that just stupid? We've got a small town in New Hampshire, very rural, dead body in the house. I'm assuming the Fire Marshal and the State Police will help investigate. I'm curious about what they might find for evidence. I don't want the house to burn to the ground, but extensive damage is okay. I want the body to be intact enough for an autopsy. It is a heavy log-frame house with slate floors on the main floor. Full basement. Any help will be appreciated.

MattW
05-16-2010, 05:05 PM
Glass will survive a fire, as will plastic - it would take a very hot fire to destroy all evidence, and even then, chemical residue would be left. Besides, plastic won't break the same way as glass to spread the flames - I'm assuming that is the effect the firebug wants?

There will also be visible and chemical traces of accelerant as the source of the fire.

PeterL
05-16-2010, 05:21 PM
If you use an accelerant, then there will be chemical traces, unless the fire is extremely hot. So the thing to do would be to use an accelerant that is already there. If the one to be killed had just refilled his gas can, and it was still on the porch, instead of being stowed in the shed, then the vapor could catch from a spark.

jeseymour
05-16-2010, 05:47 PM
Okay, so glass it is. Yes, I did expect that there would be the smell of gasoline in the ruins. But the guy stored his gas cans in the basement, so that's almost a red herring. The pieces of glass in the living room will be a clue that somebody started it with the Molotov cocktail.

Thanks!

shaldna
05-17-2010, 12:56 PM
Yes. the glass would still be there because a house fire doesn't generally burn hot enough to melt glass.

jclarkdawe
05-17-2010, 04:36 PM
As always with this type of question, what the plot needs is important. I can make this work in different ways by simply changing the facts. First question, and this is a biggie, is what's the weather like? Are the windows open or closed? What is the floor plan like? Lots of open spaces or small rooms?


If someone used a Molotov cocktail to start a fire in a house, and that fire burned for an hour or so before the FD got there (rural location, no near neighbors) would any evidence of the glass bottle remain? I doubt someone would use a Molotov cocktail in this situation. Just pour the gas out and drop a match. Glass would remain, although it is questionable whether it would be found. The gas would be detectable either through chemical tests or a trained dog. Question as to whether there would be enough of the structure left after an hour plus of burning. Good probability that everything would be in the basement.

Let's assume the windows are closed when the fire starts. Fire starts with from one to five gallons of gas. You get a very rapid burn as the gas burns up, using large amounts of oxygen. Quickly the air becomes thin of oxygen (fires use up a lot) and the fire dies down and starts smoldering. Smoke is produced as well as heat. Relatively slowly, the house will fill with a thick, dark smoke, and towards the ceiling, temperatures will start rising to the plus 1500 degree range.

Problem is there's not enough oxygen to support a fire. Suddenly, explosively, a window will blow out from the heat and the pressure difference. The entire house will then start burning, including the actual air within the house (the air will be filled with incompletely burning carbon). This is called a flashover. See http://en.wikipedia.org/wiki/Flashover. One type of a flashover is a backdraft and watching the movie of the same name will give you some idea of how it works.

Up until the window blows out, there won't be much external smoke. In other words, the neighbors won't see a thing. In a rural location, with this type of fire, you're not going to have much, other than maybe the walls, left. And this is what your arsonist would want.

A more even burn would result by opening the windows. The better vented a fire is (oxygen in and smoke lifting), the better it burns.

Would it be better to use a plastic bottle or is that just stupid? Just stupid. Glass works because as it is thrown, upon impact it hopefully breaks, setting off the reaction.

We've got a small town in New Hampshire, very rural, dead body in the house. I'm assuming the Fire Marshal and the State Police will help investigate. Fire marshal initially would be the investigating unit, and the State Police would only enter the situation after the coroner had made a determination of murder. All bodies in this type of situation have an autopsy.

I'm curious about what they might find for evidence. Depends upon how good the arsonist is.

I don't want the house to burn to the ground, but extensive damage is okay. After an hour, there's not going to be much left.

I want the body to be intact enough for an autopsy. There's going to be plenty of body left for an autopsy. First sign of murder/death prior to the fire would be lack of smoke in the lungs. Body may or may not have contracted tendons from the heat, regardless of time of death. If a lot of debris falls onto the body quickly, then body could be very intact visually with little burning.

It is a heavy log-frame house with slate floors on the main floor. This means the house may not drop into the basement. Slate reflects heat, rather than absorbing it. Full basement. The lower the location of the fire starting, the more thorough the burn. Fire doesn't tend to burn down very well. Any help will be appreciated.

No matter what you do with a house fire, short of a lot of chemicals in the situation, you're going to have plenty of body left for an autopsy. Bodies from fires can be surprising intact, and even when there are substantial destruction to the body, it is only the skin that suffers significant damage.

Best of luck,

Jim Clark-Dawe

jclarkdawe
05-17-2010, 05:30 PM
On thinking about it, let me give you some more tidbits. One is watch BACKDRAFT. It has some good stuff about arson investigation, as well as showing how a backdraft works.

In rural areas, the classic sign there is a body in the house is a registered, inspected (New Hampshire does auto inspections annually) vehicle. Upon arrival of the fire department, a car and no screaming owner is viewed as a sign that there may be a victim. Police are notified, and they immediately start searching every place but the fire for the person, such as his/her place of employment, other houses, family, et cetera. Fire marshal and coroner would also be advised of the situation. Remember that in New Hampshire a vehicle might be registered to avoid zoning problems, but not inspected.

After the fire is out and the structure has cooled down, the fire department would begin a search for any bodies. If there is a sign that there may be a body, this is going to be a very detailed search. Fire fighters would begin a slow, methodical search, with safety being a major concern. As soon as the body is found, the search stops. Nearly all of the fire fighters back out of the structure and the coroner comes in. Pictures are taken and the remaining debris is removed. Coroner may examine the body carefully, but probably would not at this point. Internal temperature of the body has never been taken in my presence, but maybe if there was a reason to suspect murder it would be.

Body is then removed, maybe in a body bag, but possibly using a tarp. Rigor would not be broken unless there's absolutely no way to get the body out otherwise. The door will be made bigger if it has to.

I don't know what the signs of smoke in the lungs are, but apparently it is very distinct. If you're not breathing (i.e., dead), there will be no smoke in the lungs. And all bodies from structure fires are autopsied. The presumption when the coroner finds the person died prior to the fire is that the fire is arson and murder, until determined to the contrary

Although glass on the floor might be an indicated, it might not be seen quickly. Bottle glass is distinct from window glass both because the windows will blow out, rather than in, and bottles are round, rather than flat.

The smell of gas would be very minimal. It would mostly have burned off long before the fire department got there. Depending upon the size of the person and the size of the fire, the body may provide a notable odor to the fire.

Beyond chemical traces of the gas, gas fires produce a distinct burn pattern. Wood can be heavily scorched on one side, with little very depth to the scorching. In other words, the gas burned, very hot, but the wood barely burned. Even in a total burn, you're going to get some pieces like this, especially baseboards. (Decorative molding helps in identifying this.)

Once the coroner determines that the person was dead prior to the fire, a very detailed search is undertaken. The fire marshal will start looking at individual pieces of wood.

Best of luck,

Jim Clark-Dawe

L.C. Blackwell
06-06-2010, 10:12 AM
I haven't yet found a reason to burn a character's house down, but that was so interesting, I'm noting the information anyway. Thanks, Jim!

Sarpedon
06-06-2010, 05:31 PM
Many of the materials used in modern construction, like drywall, plaster, tile and concrete, don't burn. While they may break up as the building collapses around them, they will remain, and by studying them, the investigators can get a very good idea of where the fire started and how it spread. If a molotov cocktail were used for example, the splashes from the burning material would be evident on whatever concrete or drywall surfaces that remain.

Only in a lightly framed, all wood structure, with no plaster, concrete, or masonry to speak of, would all evidence be effaced, though of course the glass would remain. Such construction would be virtually alien in the United States.

Drachen Jager
06-07-2010, 02:35 AM
Given an hour to burn any house fire would totally destroy a normal house.

One method I heard of which leaves no forensic trace was to take a cigarette, start it going, fold the middle of the cigarette over into a pack of matches (so as it burns down it will touch off the matches. Then, leave the matchbook and cigarette down between the cushions on a sofa. The sofa goes up like a candle and it's enough to set pretty much anything ablaze and the small matchbook and cigarette are overlooked. Even if traces are found it's assumed that someone was smoking and started the fire accidentally.

There was a firebug in California who used this method for years. The only reason they caught him was that he was also a fire investigator and he just happened to be on hand at a coincidentally high number of fires that were out of his jurisdiction to lend a hand. They only busted him in the end by tailing him around and catching him in the act.

Smiling Ted
06-07-2010, 07:54 AM
The question isn't so much "Will there be any evidence?" as it is "Will the investigators find it?"

Levels of expertise and resources vary depending where you are. Not every police department is CSI savvy.

A Molotov cocktail would be pretty obvious arson. But if the firebug had instead tried to start an explosion near a gas line or a water heater, an overworked cop without a lot of arson/forensic training might miss the signs...

jeseymour
06-07-2010, 04:18 PM
Thank you for all the info! I haven't worked out all the details yet, but this gives me a lot of good ideas.

:)

jclarkdawe
06-07-2010, 07:20 PM
Many of the materials used in modern construction, like drywall, plaster, tile and concrete, don't burn. While they may break up as the building collapses around them, they will remain, and by studying them, the investigators can get a very good idea of where the fire started and how it spread. If a molotov cocktail were used for example, the splashes from the burning material would be evident on whatever concrete or drywall surfaces that remain.

Only in a lightly framed, all wood structure, with no plaster, concrete, or masonry to speak of, would all evidence be effaced, though of course the glass would remain. Such construction would be virtually alien in the United States.

Nonflammable material such as tile or concrete has to be scorched enough by the gas burning for the scorch pattern to remain despite massive amounts of water. Drywall sucks up water like crazy, making it hard to use. But if a structure fire is left to burn without human interference, it still won't destroy completely even things like wood. Especially because of collapse, areas will not burn completely. Sometimes a piece of paper will survive a structure fire, because it didn't reach sufficient temperature to ignite before being buried in an oxygen poor environment, such as underneath a wall. Complete structure fires are interesting because of how the fire travels. Sometimes entire walls are left untouched. Wild fires exhibit this issue even better.

The flash marks of a Molotov cocktail would be very evident if the fire is suppressed quickly. This is the case with any accelerent. But as the fire burns longer and longer, it does more destruction, and the suppression efforts are stronger, such as water and tearing down walls, increasing the destruction. After a significant length of time of burning, it becomes very difficult to determine the cause of a fire.


Given an hour to burn any house fire would totally destroy a normal house.

One method I heard of which leaves no forensic trace was to take a cigarette, start it going, fold the middle of the cigarette over into a pack of matches (so as it burns down it will touch off the matches. Then, leave the matchbook and cigarette down between the cushions on a sofa. The sofa goes up like a candle and it's enough to set pretty much anything ablaze and the small matchbook and cigarette are overlooked. Even if traces are found it's assumed that someone was smoking and started the fire accidentally.

There was a firebug in California who used this method for years. The only reason they caught him was that he was also a fire investigator and he just happened to be on hand at a coincidentally high number of fires that were out of his jurisdiction to lend a hand. They only busted him in the end by tailing him around and catching him in the act.

The cigarette in the matchbook is now old, but it never left no forensic evidence. It frequently leaves the bottom of the matchbook where it is all stapled together and the striker strip is located. Problem is when the technique was new, investigators didn't know what to look for. Further, although finding such a strip is indicative that the fire is arson, it doesn't help you one bit at finding out who started the fire.

Remember that evidence can indicate a crime happened, it can indicate a certain individual committed the crime, or it can indicate both. For example, video of van der Sloot with the victim indicates that he was with the victim, and nothing more. By itself, it is meaningless. The dead girl in a room indicates a crime happened by the manner of her death. But the dead body does not indicate who committed the crime. You have to add all the evidence together.

In the case of the cigarette/matchbook trick, it indicates a crime happened, but is highly unlikely to indicate who committed it.

If you live in the US or the UK and have a newish sofa, it won't burst easily into flames. All material such as mattresses, sofas, and chairs are required in those countries to be treated with flame retardant. There's at least one video showing the difference between being treated and not being treated.


The question isn't so much "Will there be any evidence?" as it is "Will the investigators find it?"

Levels of expertise and resources vary depending where you are. Not every police department is CSI savvy.

A Molotov cocktail would be pretty obvious arson. But if the firebug had instead tried to start an explosion near a gas line or a water heater, an overworked cop without a lot of arson/forensic training might miss the signs...

Most arson investigation is done initially by the fire department. Until you've been in a significant number of fires, you don't understand the nature of the beast. Fire is a living, breathing creature that operates in ways that are both predictable and unpredictable. Until you understand fire, you can't understand how to investigate it.

With arson investigation, one issue is when people develop new ways to start fires. It takes a while before the investigators catch up, although this is a problem in many types of crimes.

Arson investigation tends to be a volume business. Small police and fire departments don't have one. In New Hampshire, all arson investigation is done by two or three people. They do it for our larger cities as well as towns with populations in the three digits. It takes a very big city to warrant an arson investigator, even then, the total number is small.

Best of luck,

Jim Clark-Dawe