When I was researching the origin and promulgation of arson mythology in 2004, I reviewed the US Army Field Manual, and was surprised by what I found. The Manual, published in 1985, and reprinted in 1995 was a wonderful resource for mythology fans like myself.

I was reassured to learn that the Manual was being re-written, but that at that time, the new manual was only available to those with a “need to know.” (I am not such a person.)

Well, the new edition is out. Some excerpts are attached. The section on fire behavior is posted here in full.

The new (January 2005) edition contains some information copied from the 2000 NIJ publication Fire and Arson Scene Evidence: A Guide for Public Safety personnel, but mostly it contains stuff from the 1985 version of the Manual.

When the Army fire investigators trained to this Manual come out and join the civilian work force, they will likely provide job security for a whole new generation of fire investigators. Sometimes I just think, “What’s the point?”

Now, for your reading enjoyment, wisdom from your US Army:

Part Three addresses the most common types of crimes investigated by Army law enforcement investigators. Each chapter describes the offense, provides legal considerations and, where appropriate, describes the nationally recognized method of investigation as established by the DOJ, FBI, BATF, and NAFI.

Chapter 7 Arson and Explosives Investigations


Behavior
7-9. Fires behave according to well-defined principles of burning. Fires produce heat, flame, smoke, and gases. These combustion by-products may or may not be readily seen. Flame includes both an open flame and a smoldering glow. Smoke is composed of very fine solid particles and condensed vapors. The composition of fire gases emitted by the burning materials depends on the chemical makeup of the burning material, the amount of oxygen available during burning, and the temperature of the fire. Most fire gases are highly toxic. They are the biggest cause of fire deaths. The biggest single killer is carbon monoxide, not because it is the most toxic, but because it is the most abundant. When large quantities are breathed in, carbon monoxide causes unconsciousness and eventually death. At less than lethal concentrations, it causes disorientation and confusion, subjecting victims to other hazards present in the fire. The second most dangerous gas produced by a fire is carbon dioxide. While not toxic in itself, a 2 percent increase in carbon dioxide in the air causes a 100 percent increase in a human's breathing rate. This doubles a victim's intake of other toxic gases.

7-10. Fire burns up and out. It leaves a V-shaped char pattern on walls and vertical structures. A fire that is hot and fast at the point of origin will leave a sharp V pattern. A slow fire will produce a shallow V pattern. If fire meets an obstruction, such as a ceiling, it will burn across the obstruction looking for a place to go up.

7-11. Fire travels with air currents. It never travels into the wind unless the entire fire load, the combustible material or fuel in an area, is on the windward side of the fire. If this happens, the fire slowly eats into the fire load as its tendency to follow the wind is overcome by its attraction for fuel.

7-12. Fire seeks oxygen. Because fire consumes great amounts of oxygen, it is always drawn toward new sources of oxygen when burning occurs indoors. It is not unusual to see a char pattern going up a wall to the ceiling and across the ceiling toward an open window. It is also common to find deeper charring and evidence of higher heat on window frames and doorways.

7-13. These principles of burning account for most of the fire and char patterns seen during and after a fire. But sometimes there are unusual patterns that are the result of a flashover or backdraft, natural conditions which only occur during fires when conditions are right.

7-14. A flashover occurs when flames instantaneously erupt over the entire surface of a room or confined area. Once a fire starts, it produces gases that rise and form a superheated gas layer at the ceiling. As the volume of this gas layer increases, it begins to move down to the floor, heating all objects in the room regardless of their proximity to the flaming objects. In a typical contained fire, the gas layer at the ceiling can rapidly reach temperatures in excess of its autoignition point. If there is enough existing oxygen, a flashover occurs and everything in the room becomes involved in an open flame all at once. This sudden eruption into flames generates a tremendous amount of heat, smoke, and pressure with enough force to push beyond the room of origin through doors and windows. This combustion process will accelerate more now because it has a greater amount of heat to move to objects.

7-15. Backdrafts occur when a structure burns with all doors and windows closed and the fire uses up all of the available oxygen. It then turns into a slow smoldering fire, generating huge amounts of superheated carbon monoxide gas. The hot gases rise to the top of the room and stay there. Because carbon monoxide is a flammable gas and is heated above its ignition point, it only needs more oxygen to burst into flames. Oxygen entering around cracks in doors and windows keeps the fire smoldering. This produces more and more superheated carbon monoxide. Then, when a door is opened or a window melts out, the in-rushing oxygen combines with the superheated carbon monoxide, causing an explosive fire.

7-16. Windows will blow out, and the explosion may be strong enough to damage the structure of the building. Damage caused by a backdraft may look similar to that caused by a low explosive. A backdraft produces an unusual char pattern. Most of the burn damage will be at the extreme top of the room. There will also be a rather sharp line of demarcation at the bottom of the char pattern on the wall. As with a flashover, accelerant residue may not be present.

7-17. When wood burns, it chars a pattern of cracks that looks like the scales on an alligator's back. The scales will be the smallest and the cracks the deepest where the fire has been burning the longest or the hottest. Most wood in structures chars at the rate of 1 inch in depth per 40 to 45 minutes of burning at 1400° to 1600° Fahrenheit, which is the temperature of most house fires. However, no specific time of burning can be determined based solely on the depth of charring since most fires vary with intensity and fuel load. A room fire chars only the upper one half to two thirds of the room. Ceiling damage in a normal structural fire is usually at least five times the floor damage. Sometimes a char pattern has a sharp line of demarcation on one side. This indicates that the fire quit spreading in that direction when a draft entered and blew it back.

7-18. When glass is exposed to fire, it begins to melt at about 1200° Fahrenheit. It becomes runny at about 1600° Fahrenheit. A lot can be learned about a fire from the glass at the scene. Remember, though, to examine all of the glass and not jump to conclusions from the appearance of just one piece. As a general rule, glass that contains many cracks indicates a rapid heat buildup. Glass that is heavily stained indicates a slow, smoky fire.

7-19. Bright metals, like the chromium on toasters, turn colors when heated. These colors may remain after the fire and indicate the temperature of the fire at that location.


7-30. Based on the preliminary scene assessment and analysis of fire patterns and damage at the scene, the investigator should identify a distinct origin (the location where the fire started) and an obvious, fire cause (an ignition source, the first fuel ignited, and circumstances of the event that brought the two together). If neither the origin nor the cause is immediately obvious, or if there is clear evidence of an incendiary cause, the investigator should conduct a scene examination according to recognized national guidelines, such as the NAFI or National Fire Protection Association (NFPA). Investigative guidelines can be found on NAFI, NFPA, and other official government Web sites.

Obtain Equipment and Tools

7-31. Once arson is determined to be the cause of the incident, the investigator will need to obtain specialized equipment to assist with the investigation. These items should be kept on hand and available to the investigator at all times to prevent a delay in the investigation. Specialized equipment includes—
· Barrier tape.
· Clean, unused evidence containers (lined paint cans with friction lift lids, glass jars, or nylon or polyester bags specifically made for fire debris evidence).
· Compass.
· Decontamination equipment (buckets, pans, and detergent).
· Evidence tags, labels, and tape.
· Gloves (disposable gloves and work gloves).
· Hand tools (hammers, screwdrivers, knives, crowbars, and shovels).
· Lights (flashlights and spotlights).
· Marker cones or flags.
· PPE.
· Photographic equipment.
· Rakes, brooms, and spades.
· Tape measure (100 feet).

The full text of this Manual is, as far as I can tell, not available for free downloads, but for $9.00. it can be purchased on CD from the following website:

[www.militarypubs.com]

John Lentini, CFI, D-ABC
Fire Investigation Consultant
Florida Keys
[www.firescientist.com]