Arson and Explosions

ARSON AND EXPLOSIONS
"The first outbreak of war is always an explosion" (Thucydides)

Part investigative science and part forensic science, the field of forensic arson/explosion investigation encompasses a variety of people in various positions -- police officers who work on arson and bomb squads; firefighters and fire marshals; safety professionals, insurance and private investigators; forensic chemists and other criminalists; civil, electrical, and mechanical engineers; and a number of private industry representatives. The United States invests as much, if not more, resources in the "war on fire" as it does in the "war on crime", so it's not surprising that many experts in this field are government employees, yet the private sector also plays a large part. Arson investigators sometimes think of themselves as counterparts to homicide investigators (arson as murder by fire), and explosives experts (who often think of themselves as counter-terror specialists) usually fall into one of two types: field operatives or laboratory personnel. The traditional typical classifications (despite some variation in terminology) of fires are as follows: a) natural; b) accidental; c) unknown origin; d) suspicious; e) incendiary.

It's difficult to say who's the forensic scientist in this field, that is, the one who testifies as an expert on the stand who may just be an expert witness testifying from hypotheticals. Police bomb squad duties usually consist of mostly retrieval and disposal, responsibilities more in common with HAZMAT than forensic arson/explosion investigation. Likewise, many firefighters don't have the specialized talents of arson investigators. Add to this the problems of jurisdiction and overlap between police and fire departments, and you begin to see the confusion. A lot depends upon job title and work-related responsibilities. In this forensic area, job function determines expertise.

Fires and explosions, by their very nature, require extensive on-site investigation, so it's a safe bet to say that the one who testifies as the forensic expert will be the one who is most able to make sense of chemical tests conducted by criminalists AND has practical on-site crime scene skills. In most cases, this will be someone called the arson investigator, although explosion experts can be found separately. In rare cases, forensic chemists, pathologists, and other experts also testify. In the homeland security field, and especially in the private sector vendor industry, some distinct distinctions are made between blast containment, blast resistance, and blast mitigation. Blast mitigation involves some material or product which actually mixes with or interferes with the explosion. Cutting-edge products are always coming out.

Any expert witness in this area should have an understanding of the chemistry of fire and the principles of combustion. They should not only keep up-to-date with the research literature, but they should have actual experience in the handling of explosives. Few fire safety education programs exist, so forensic law doesn't require any college degrees (although it's a plus). Both basic and advanced training courses exist at various institutes, and these are commonly sought-after credentials. Laboratory personnel must usually be qualified at recognizing chromatographic patterns. Experts are also generally expected to be familiar with manufacturer and association tests and standards, not that there are any proficiency tests, but that belonging to a professional association goes a long way in qualifying as an expert and in keeping one's skills sharp. The National Fire Protection Association (NFPA) is the leading professional organization in this regard and has developed numerous guides, such as NFPA 921 (Guide to Fire and Explosion Investigations 2004) which have added immensely to overcoming confusion over procedures in the field.

All forms of fire and explosion are subtypes of the larger term, combustion. Fire is a fundamental chemical reaction based on oxidation. Explosion is a two-tiered chemical reaction based on the volatility of mixing at least two substances. The following list of definitions might be helpful:

Heat is one of the most basic terms. It is produced from the breaking and formation of chemical bonds. In a chemical reaction, atoms are not lost but merely redistributed. Molecules absorb energy when their chemical bonds are broken apart, and release energy when their bonds are reformed. All oxidation reactions give off more energy than they absorb, which is released in the form of heat, light, shock, noise or some combination thereof, depending upon the single- or double-bonding that takes place when the molecules reform. Most reactions are exothermic, which means they need very little energy to get started (a lower ignition or kindling temperature), and some reactions are endothermic, which means they need more energy to get started (a booster).

Reactions also take place at various rates of speed. Fire, for example, is a fairly slow reaction because molecular change usually only takes place on the surface of substances (this is called glow as opposed to pyrolysis which is flame and indicates irreversible molecular change). Pyrolysis only takes place when fire has a continuous source of oxygen. Fuel-air mix determines what is called the flammable range, and below this is the ignition range, and even further below is the flash point (vapor) range. Conditions are right to support combustion (give an outside source) at the flash point range, reactions will sustain themselves at the ignition range, and fuel-air mix is perfect at the flammable range. How quickly reactions move through these three ranges is the speed of the reaction. Speed can be increased by temperature, however, as any 18 degree Fahrenheit increase in temperature usually doubles or triples the reaction rate. Fires, for example, burn faster once they can raise the environment's temperature.

The earth's atmosphere consists of 21% oxygen, and most fires will extinguish themselves at less than 16% oxygen. However, it's not a simple matter as the external supply of oxygen. Chemical reactions have their own way of extracting the oxygen they need. With a fire involving hydrocarbons (wood), the reaction extracts oxygen from carbon dioxide, carbon monoxide, sulfur oxide, and nitrogen oxide. With a fire involving plastic, the reaction relies on poisonous gases released: hydrogen cyanide, hydrogen chloride, and phosgene. Explosions rely upon oxygen released from nitrates or potassium substances, usually potassium nitrate, potassium phosphate, or nitrogen itself. Much of what chemical reactions need to supply their own oxygen is abundantly available in the air (carbon dioxide) or nature (nitrogen and potassium). These readily-available substances are called oxidizers.

Steps to the most scientific and pragmatic approach are to be found in DeHaan (2002), and to a more technical extent, in NFPA 921 (Guide to Arson and Explosion Investigation). In both places, the step-by-step procedures involve analyzing and probing material with technical instruments. There is a process of hypothesis formulation and testing similar to the scientific method which leads to the acceptance or rejection of alternative hypotheses. Care is taken not to spoil any evidence at the crime scene. Patterns of any particular fire are compared to patterns from other fires to generate further leads and hypotheses.

In the common law tradition, arson law requires that a fire reach a structure and a burn result. Explosions are treated as burnings for the purposes of arson law. It doesn't matter how much burning takes place. The common law rule is that however slight the burning, the arson is complete. A few states distinguish between "sooting" (smoke damage), "scorching" (blistering), "charring" (external surfaces destroyed), and so forth, but the main point is that a structure does not have to burn to the ground. The kind of structure and amount of damage are circumstances to be considered. An arson can occur inside a house if the item damaged qualifies as a permanent fixture. Sinks, lighting, and appliances qualify; personal property such as furniture, clothing, or documents usually do not. At law, there's a difference between "setting a fire" and "burning" in that it is possible to set fire to something, but it gets extinguished before any burning occurs. For this reason, it's important that one read the precise wording of a state statute. If the statutory language contains the word "OR" sandwiched in between "setting a fire" and "burns," then that particular state considers the act of setting a fire an arson even if no burning occurs. Arson is a crime of general, rather than specific intent. At common law, the mens rea of arson is "willfully and maliciously," but as a crime of general intent, malice can be inferred from the act itself. All that's necessary is proof that the person (at any MPC level of intent, even recklessly, although that's called RECKLESS BURNING in some states) started the fire. Criminal intent with arson, however, is sometimes a separate thing. The fire department, not the police, get to determine this, which is sometimes called a fire of INCENDIARY ORIGIN (as opposed to one of unknown origin). A fire inspector must then testify in court that he/she also suspected arson, and then an expert witness must be called to corroborate the fire inspector's opinion.

Arson is typically graded into 1st degree (homes, schools, churches), 2nd degree (unoccupied structures, vehicles), and 3rd degree (personal property). Arson is a crime against possession, not ownership, so it's possible for a person to be charged with burning their own house, or committing an arson against themselves. State statutes usually do not grade arsons in terms of motive, although they ought to. There are clear differences between arson-for-profit, revenge arson, and pyromania. Some states reserve their harshest punishments for ARSON WITH INTENT TO DEFRAUD (arson for profit or arson for hire). Some states have the offense of AGGRAVATED ARSON which is kind of like felony murder, but carries additional penalties if a firefighter gets injured while trying to put out the fire. A person who's party to the crime is typically charged with arson rather than being an accomplice to the crime. Actions preliminary to arson, like pouring accelerant on the floor of a building or possessing firebombs, may be offenses related to arson under some state statutues. Making a false bomb threat or false fire alarm is also a separate, but related offense in most states. Arson involving damage to federal property is almost always prosecuted in federal court, as is anything (warehouses, truck facilities) involving interstate or foreign transport.

The Emerging Forensic Science of Arsonist Profiling

Numerous motives compel arson: financial reward, politics, concealment of another crime, attention seeking, revenge, and anger. A fundamental tenet of behavioral profiling is that if you know the what and why, the who will follow. Therefore, sometimes behavioral profilers are called in to testify during an arson trial. They usually present research findings which suggest a profile of the typical arsonist as someone who may be seriously mentally ill and/or intoxicated at the time of the offense, which can be argued as mitigating responsibility. A full-blown pyromania defense usually doesn't work, as in the forensic setting, pyromania is actually quite rare. Below is a summary of some well-known personality characteristics for arsonists:

AGE: 10-14 (26%), majority under 18 (51%) if adult, late 20s, never over 35 if adult, revenge or profit motive
SEX: 9 out of 10 times (90%) a male; if female, revenge type
RACE: 3 out of 4 times (75%) a white; black (20%) of time if first-timer; Native Americans 3rd largest group
CLASS: majority from lower to working class; middle class if vandalism or excitement
IQ: vast majority subnormal (70-90) with 22% in retarded range (below 70), rare genius
FAMILY: absent or abusive father, history of emotional problems with family/mother
SCHOOL: learning problems and usually held back a grade in school, normally in 10th grade; younger (grades 6-8) if vandalism
PEERS: social misfit, interpersonal problems with opposite sex, appears physically and emotionally weak compared to peers
WORK: usually chooses subservient position and then resents it (both ambivalent and resentful toward authority-repressed); unemployed if vandal, excite, or profit
CRIMINAL HISTORY: numerous status offenses as juvenile, property crimes, almost all have arrest records
DRUG/ALCOHOL: no problem
MENTAL: lack of remorse may appear as psychopathy, but more typically result of obsessive-compulsive disassociative trance-like state during firesetting
ARREST: majority remain at crime scene except revenge, conceal, profit types; some attempt suicide in lockup; most easily confess thru cooperation

TYPES other than concealers or for profit (who constitute 22% of total):

ARSON FOR REVENGE (41%) - precipitating factor is a real or imagined affront that occured months or years ago; attack is focused on individual rivals, a business chain, schools, or some facilities connected with offender
ARSON FOR EXCITEMENT (30%) - precipitating factor is boredom, (sexual) thrill cycle, or need for attention; attack is focused on large or outdoor targets, like parks, construction sites, arenas, as well as residential areas
ARSON FOR VANDALISM (7%) - precipitating factor is family disturbance or peer pressure; attack if usually focused on educational facility as well as residences and outdoors
ARSON FOR PROFIT (5%) & ARSON FOR CRIME CONCEALMENT (17%)

Bombs can be made very simple or very sophisticated, depending upon how much chemistry the suspect knows. If your suspect is fairly unsophisticated and just wants to make a quick bomb, then they will make a "pipe bomb" where they simply cracked open some shotgun shells, put the black powder in a pipe, closed the ends, and added a fuse. What happens with a pipe bomb is that the explosion, being confined to a sealed container, produces a large volume of gas that actually causes the walls of the pipe to balloon and stretch until broken pieces of shrapnel fly out. Gas compression bombs of this nature have a strong shock wave effect, to the order of 7000 mph. More serious damage is done by the blast effect than the fragmentation effect. It's like having a hurricane in a box.

Bombs can be classified as "low explosives" or "high explosives" depending upon the speed of detonation (which is just the chemical reaction time). With a low explosive (like black powder), the shock wave is only about 2300 meters per second, no primer is really needed, and the bomb is sensitive to heat, friction, and temperature (so don't drop it). With a high explosive (like TNT), the shock wave is as high as 6900 meters per second, some kind of primer or blasting cap is needed, and the bomb is relatively insensitive to heat, friction, and temperature (although don't play football with it). Low explosive materials are only lethal when they are confined in a container. If you sealed natural gas, a gasoline/air mixture, charcoal, sulfur, starch, phosphorous, magnesium, or just about any other household commodity in a container, you would have a low explosives bomb. Mixtures in the "lean" range (20% oxygen or more) generally explode more than create a fire. Mixtures in the "rich" range (10% oxygen or less) generally explode, then suck surrounding air in (with a "whoosh" sound), creating more destructive fire than explosion.

High explosives (like TNT, RDX, and PETN) are available only commercially or militarily. Dynamite, however, has been around since Alfred Nobel discovered it in 1890, but his nitroglycerin-based methods have been replaced in recent years by ammonium-based or emulsion-based methods. Nobel's dynamite was a rather solid mixture of 78% sodium nitrate and 12% nitroglycerin; modern dynamite is a gel that mixes oxygen-rich ammonium nitrate with guar gum or uses water/oil droplets in a hydrocarbon base with micron-sized glass, resin, or ceramic microspheres. That's why one of the modern terms for dynamite is "gelignite" and although it still causes headaches when absorbed through the skin, it is less water soluble. Ammonium nitrate is a common fertilizer. When mixed with fuel oil, it's called ANFO, and this was the kind of explosive used on New York's World Trade Center in 1993.

TNT is also unaffected by moisture (because it's sealed in wax), and is the stuff inside of WW II-era bombs, shells, and grenades. Nitroglycerin is derived from Toluene (a petroleum by-product), hence it's name Trinitrotoluene. TNT is trinitrotoluene while nitroglycerine is glyceroltrinitrate, derived from glycerin. Nitroglycerine is extremely shock-sensitive and unpredictable. TNT is nitrated toluene, and is much more stable. It is more closely related to the nitrated phenols.

RDX, a British invention during WW II (standing for Research Dept. Explosive) is what the military uses today. Sometimes, they mix RDX and TNT in what is called Cyclotol or C-6, but RDX alone is more commonly used and called C-4 (for military designation Composition 4). It has a very plastic, dough-like consistency and charges can be shaped for special detonation effects. Breathing the dust off of it can cause epilepsy and amnesia.

PETN (Pentaerythritol Tetranitrate) is a nitrate ester. "Esters" are a special kind of substance created in chemistry labs in a distillation process not unlike making alcohol. They belong to a class of chemicals called carboxylic acid derivatives, and in the scheme of things, they are classified between amides and anhydrides (amide < ester < anhydride < halide). The distinguishing feature of PETN is the ring size at the molecular level (Oxy -1, Oxy-2, Oxy-3, or Oxy-4). It is used in "primacord" which can also shape charges.

Bombs in packages, suitcases, boxes, etc. are usually triggered by a battery-powered switching mechanism (clock, mercury switch) which is activated when the package is opened. A few bombers prefer a more steady, reliable external source. Car bombs, for example, are usually powered by the vehicle's ignition switch. Most of whatever ingenuity is invested in the bombing by the bomber goes into the switching mechanism.

Color spot tests exist for most common volatile materials. X-ray examination and infrared spectrophotometry will reveal most organic explosives. Chromatography is necessary for detecting traces of plastic or military-grade explosives.

PRINTED RESOURCES
Crippin, J. (2005). Explosives and Chemical Weapons Identification. Boca Raton, FL: CRC Press.
DeHaan, J. (2002). Kirk's Fire Investigation, 5e. Englewood Cliffs: Prentice-Hall.
Inciardi, J. (1970). The Adult Firesetter: A Typology. Criminology 8: 145-55.
Kocsis, R. & Cooksey, R. (2002). "Criminal Psychological Profiling of Serial Arson Crimes." International Journal of Offender Therapy and Comparative Criminology 46:631-656.
Lentini, J. (2005). Scientific Protocols for Fire Investigation. Boca Raton, FL: CRC Press.
Midkiff, C. (1982). "Arson and Explosion Investigation" in R. Saferstein (ed.) Forensic Science Handbook, Englewood Cliffs: Prentice-Hall.
Moenssens, Starrs, Henderson & F. Inbau. (1995). Scientific Evidence in Civil and Criminal Cases. Westbury, NY: Foundation Press.
Pickett, M. (1998). Explosives Identification Guide for First Responders. NY: Delmar.
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Saferstein, R. (1998). Criminalistics: An Introduction to Forensic Science. NJ: Prentice-Hall.
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Last updated: Jan 17, 2012
Not an official webpage of APSU, copyright restrictions apply, see Megalinks in Criminal Justice
O'Connor, T. (2012). "Arson and Explosions," MegaLinks in Criminal Justice. Retrieved from http://www.drtomoconnor.com/3210/3210lect05.htm.