Fire Investigations: The battle between science and myths

This blog post will be discussing the main myths and biases in the fire investigation. It will also give a brief historical timeline to the main publications and changes that happened to the fire investigation community. There will be a focus on the American fire investigation society.


The first goal of the fire investigation is usually to prove whether the fire was deliberate or not. Based on that, it is logic to start with defining the arson fire and what are its motivations. An arson fire is the willful or malicious burning or attempt to burn, with or without the intent to defraud. It requires intent to cause harm and the person setting the fire does it with criminal intent.There are different motivations behind setting these fires and it is better to be categorized and analysed so the size of the problem of arson fires will be well understood.

Pyromaniac: It is usually random with no conscious motivation, usually because of a psychological problem and not for material gain.
Revenge: Usually because of problems in controlling their anger, the reaction will be in an aggressive manner by setting fires. The targets usually have a personal connection to the fire setter, sometimes due to the influence of alcohol or drugs. It is often set in the bed room or closet to destroy personal possessions of extreme sentimental value. It is one of the most destructive fires and usually needs professional fire investigators to come up with evidence and analysis.
Arson for profit: least emotionally- or psychologically-motivated, very high level of fire damage but not personal. As there is no emotional component to these fires, the scenes will tend to be highly organized and rational.
Hero or vanity: Usually because of a psychological problem as the person seeks some attention and wants to play the hero role will set a fire. Sometimes the fire setter causes harm to others and sometimes he/she will try to put out the fire after igniting it.
Crime concealment: Usually there no previous interest of fire, the setter will use it to destroy physical evidence or divert attention from another crime. Fires usually are opportunistic and started with materials found at the scene.
Terrorist or social protest: Usually the work is done in groups, the methods and materials are more sophisticated, the fires are usually striking symbolic, political or economic targets.

Based on that, fire investigation is considered one of the most complicated and critical fields. To prove that a fire is arson or not, needs in-depth knowledge about the science of fires and research not just experience in fire investigation. Beside the knowledge and experience, the investigator also needs flexibility to change the commonly held beliefs and not just follow the old un-scientific and inaccurate generalizations.
By reading the history of fire investigation, it is clear that there were too many myths that were used for decades without any revision. It is understandable, why the fire investigators were opposing any change in their field`s (knowledge base or expertise) constraint as it means that their previous judgments were incorrect.
Unfortunately, the fire investigation leaders are the same people that write the text books and teach the new investigators in school. So, there is a continuous promulgation of these myths, only those who take updated courses or read more about fire science can break the cycle and be re-educated.

The myths are usually developed and exist without any scientific reason or evidence, it is more a result of inaccurate generalizations. As an example, if an investigator detects the presence of small fragments of crazing glass when an accelerator was used in a fire, the next time he/she observes small fragments of crazing glass he/she might conclude the presence of an accelerator, which may have nothing to do with accelerators. This example can show how critical is it not to base the analysis on generalized rules of thumb. Some of the highly respected fire researchers in NIST wrote about it in the (Fire Investigation Handbook) in 1980 and proposed that the size of glass crazing is highly useful to predict the origin of the fire. David R. Redsicker in his book (Practical Fire and Arson Investigation) proposed that when glass crazed into small segments or pieces, that it was subjected to rapid heating up and that the larger the pieces of the glass means the more distance it was from the fire source.

In 1977, the first step to be taken against these myths was done by the Aerospace Corporation with the Law Enforcement Assistance Administration (LEAA) with the publication (Arson and Arson Investigation: Survey and Assessment). The authors of this publication started to point out the fact that most of the currently used fire accelerator indicators are not based on scientific testing. They also urge that an urgent scientific research plan should be set to scientifically prove these indicators, the LEAA text was based also on surveying the fire investigators about the most commonly held myths and the following list consists of the most contentious myths:

1. Alligatoring effect: It means that charring wood will look like alligator skin, the large blisters indicates rapid intense heat while the small flat blisters indicate long low heat.
2. Crazing of glass: It means the presence of irregular cracks in glass because of the rapid heating which usually was an indication of accelerators.

3. Depth of char: It means how deep the burning char from the surface of the wood was, it was used to indicate the burning time including the location where the fire originated.
4. Line of demarcation: it is a boundary line between the charred and uncharred material, the presence of puddle shapes usually indicates an accelerator and a distinct line indicates rapid burning.

5. Sagged furniture springs: usually high temperatures are needed to collapse the springs and also due to the insulation effect of upholstery, the sagged furniture springs usually indicate that the fire started inside the cushions or the use of accelerators.
6. Spalling: spalling means chipping or pitting of concrete or masonry surfaces, it requires intense heat so usually it is matched with the presence of accelerants especially in those cases were brown strains are also observed.
7. Fire Load: it was believed that the expected damage from (Normal) fire can be estimated from the energy content of the fuels presented in the building.
8. Low burning and holes in the floor: they believed that because usually the heating goes up, the presences of any holes on the floor or under furniture is a proof of the origin of the fire.
9. V-pattern angle: the presence of a narrow v-shape indicates a fast and hot burring fire.

10. Time and Temperature: It was believed that by calculating the expected time and temperature using the building dimensions and the fuel load, the investigator can expect whether or not there was a use of accelerants.

For the sake of completeness, I will give some details about one of these myths:

  • Alligatoring:

NIST [5] stated in its handbook in 1980 that, the char alligatoring can be used to indicate the acceleration of the fire. If the fire was slow, the alligatoring shape will be flat and if it is a rapid burning the alligatoring shape will be more like a hump.
In 1982, IFSTA (The International Fire Service Training Association) declared the same, it stated that large alligatoring is evidence of the presence of flammable and combustible liquids.


NFPA had a totally different opinion here, they criticized the way it was explained and how the investigators over-estimate the importance of the charing shape. The NFPA provided pictures of different shapes of alligatoring from the same fire and stated that there is no scientific proof that an accelerant was present during the fire if the hump alligatoring shape appeared in the scene of the fire. Also, there was no scientific evidence that the shininess or the colour of the char had anything to do with the presence of accelerants or the fire growth rate.

The impact of the NFPA report appeared to be positive in the publication of Practical fire and arson Investigation by O’Connor who published the first edition in 1986 and stated that the same explanation about the alligatoring and proposed the presence of accelerants when there are large rolling blisters, however, in 1997 it seems he was influenced by the NFPA report and mentioned in his second edition that there isn’t scientific evidence to prove what he mentioned about alligatoring in the first edition and advised that it should be used with extreme caution.

However, the myths did not disappear totally, Randall Noon in 1995 in his publication (Engineering Analysis of Fires and Explosion) not only included the myth about alligatoring in his publication, but also, he proposed a totally wrong explanation. Randall wrote that the (Scientific) explanation is that when the wood is exposed to heat, the water will be evaporated. If the water was rapidly evaporated there will be a rapid loss in the volume which will cause high tension in the wood surface and end up with bigger and deeper charring shapes.

This explanation is totally not based on any scientific experiments and should not be used as a reference by fire investigators . It is just a repetition of the myths with some non-scientific inclusions from the author.This can show how hard it is to change the perception of these myths and how some authors keep publishing these un-scientific rules and show it as if they could be taken for granted, not shouldering any responsibility or even advising that there is a need to be cautious in your interpretation of what you observe.

To summarize, the myths are diminishing and disappearing with time, however, disproving the myths is too slow compared to the work done disproving myths in other fields of science and also when you consider the effect these myths have on many innocent people.

Some references were used to write this blog:




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