Evidence From a Fire Scene Investigation

Over the last 25 or more years fire investigation has developed into a unique and valuable profession.  Increasingly accurate determination of cause and effect has led to more reliable statistics, safer convictions, reliable claims resolution, improved consumer products and more robust management systems. It also feeds into fire service equipment and procedure.

Establishment of liability and ‘probable’ cause in the private sector in land and marine cases requires a particularly high level of expertise involving a great deal more than the scope of this article.

Although finding the cause of the fire has become more refined, it is still difficult to link the cause to a culprit at the level required for securing a conviction. This is particularly true of fraudulent arson; but there has been significant progress. Generally, however, criminals and offenders have fortunately not progressed. They still often believe the Hollywood image and assume that fire will cover their tracks. They sometimes still believe that a lit cigarette will ignite petrol and when making up fire setting devices they spend little time testing if they will work efficiently.

Arson is mostly a crime of anger or passion. The perpetrator (usually male) is often in an emotional state and not concerned to make the fire appear to be accidental. Sometimes an apparently innocent act of mere revenge or threat results in unintentional (but nonetheless reckless) damage or loss of life; sometimes their own, sometimes that of a firefighter.

Professional, determined or skilled arsonists are not so easy to discover. This may be worthy of a further article.

Dr. Edmond Locard coined the phrase “Every contact leaves a trace”. But how can that trace survive the fire? Fire is of course extremely destructive but often a fire will fail to develop fully. The fuel may be insufficient or the air circulation so restricted that the fire fails to develop, or it may self-extinguish due to lack of oxygen. Evidence is then easier to recover and may even include delicate items such as a spent match.

But of course, the fire often develops and leads to almost total destruction. This is normally the result of determined fire setting efforts to ensure that the fire develops and spreads fast, usually with the use of some means to accelerate the fire. Multiple seats of fire ignition and the use of naked flames also increase the likely success of the attempt and may even overrun a sprinkler system.

Ironically, rapid spread of fire may not be in the arsonist’s best interest: The faster and greater a fire develops the faster will be the collapse of contents and structure.  Collapsed items cover materials upon which they fall. This smothers the fire at that point and protects those materials from further damage. They are effectively preserved.

The professional investigator approaches any scene like an archaeologist. He or she does not attack the scene with spades and shovels. The weapons of choice are brush, scoop, magnet and sieve. The layers of debris are carefully uncovered to reveal a time-line of events. The story that unfolds begins with the last collapsed elements of structure. This may lead to research into the quality and efficacy of the design or build. It may indicate tampering with fire and security systems.

The next layers may reveal fittings and linings and may show deficiencies in fire precautions. Next may come the contents and appliances. Products that appear to have been defective may warrant further research and possible action under consumer protection legislation.

During all of this work the investigator is reading the scene with a view to finding the point or points of fire origin and evidence that may connect the incident to any person, group or animal (yes, animals cause fires too!).

It is a “forensic” process i.e. relating to the use of science or technology in the investigation and establishment of facts or, evidence in a court of law. Understanding of fundamental science and engineering is important but it is very much an experience-led skill. Every scene attended adds to the ability and value of the practitioner and a fire service background is a distinct advantage. Real fire experience and knowledge of fire behaviour, fire service procedures and equipment are complemented with good quality training, research, study and continuous professional development.

The principals are the same whether for property or structures, all of which (and particularly shipping), have unique features and materials which the investigator must account for.

So what evidence is being sought? What will survive?

Fingerprints – These are more robust in fire than previously thought and techniques have developed to recover better quality prints from a far greater range of surfaces. Prints can be read and digitally recorded on site for immediate comparison to an increasingly wide database. Fingerprints may survive high heat but not direct flame. They will not be easily washed off. Fragments of broken glass can be recovered and reassembled for print recovery.

DNA – Increasingly smaller samples and even just trace elements can be used for accurate DNA sampling. It can be retrieved, for example, from the thumb wheel of a cigarette lighter. Equipment is becoming more efficient and results available faster. DNA also can survive heat and water.

Trace Evidence – Where there is a suspect, the clothing will be confiscated, and hair combings may be taken. When a window is forced most of the fragments will fall in the direction of the force but there is an unseen rebound effect that causes some fragments to travel back toward the force. If glass has been forced before fire development, then minute shards may be found on hair or clothing.

Fibres from a suspect may also be linked to fibres of materials involved in and recovered from the fire scene.

If petrol or other volatile liquids have been used, then traces may be found but also the initial heat from the ignition flash may cause minute heat damage to the fibres of synthetic clothing recovered from the suspect.

Materials – Many different materials can be used to accelerate the growth of a fire. They can be dry (paper or cloth) wet (flammable liquids) or chemical (oxidising compounds or oils). The investigator will look for evidence of any item introduced or adapted for the purpose fire setting.

Dogs are now commonly used and trained to detect up to ten different flammable vapours. They are fast and accurate and can cover a large area. Any indications or ‘hits’ made by a dog must be backed up by laboratory analysis. Dogs can make mistakes too!

Protection marks left by the material itself may yield a good sample for laboratory analysis. It is not uncommon for the initiating item to be used to lead to a larger fire load. This may draw the fire away from that point and the initiating item and material is thus preserved. The material may also have been partially protected by collapsed items as stated earlier in this article.

Microscopic analysis can determine the nature of the material and match it to places or items associated with a perpetrator. To be successful, accelerants often need to be used in quite copious amounts. This increases the chances of traces being found even in the most severely damaged areas. They also have distinctive qualities that leave distinctive burn patterns to the trained eye.

Blood – Unless blood has been spilled outside of the fire area it will not look like blood. The investigator will look for unusual stains or spatter patterns. On-site testing kits can determine if the stain is blood and samples can be taken for laboratory analysis. Analysis of the spatter pattern itself is a particular skill and can lead to accurate reading of how the blood came to be as found. This analysis can be linked to traces found on confiscated clothing.

Blood will not survive the main burning area unless it has migrated by capillary action to ‘Pinch spots’ such as carpet under table legs. However, it may not be found at all unless the investigator knows or suspects it may be there.

Laboratory Analysis - The investigator will take key samples from the scene for detailed analysis. Sampling is far from random. Experience and application of scientific knowledge will guide the investigator to the optimum sampling areas.

Samples are carefully and appropriately bagged and tagged to ensure there is no cross contamination and that continuity of evidence is maintained. Exemplar or ‘Control’ samples must always be taken in order to provide a measure of ‘normality’ of the scene, to further validate the sampling and to provide fairness for any defence.

Laboratory examination and testing and skilled, scientific analysis is often pivotal, but it is important to understand that laboratory results must be applied logically to the incident as a whole and not held alone in an attempt to establish cause or guilt.

Tool and Foot Marks – In the same way that guns leave a distinctive and repeatable pattern on a bullet, pry bars and other breaking-in tools leave their mark on window and door frames. The point of break in is often preserved by the air-flow of a developing fire. Footwear tread analysis and comparison is now well advanced and established with a national database in the UK.

Software – Intelligent fire and intruder alarm systems can be built with fire resistant chips that can be recovered and interrogated to reveal crucial information. Some systems may have automatic, movement-triggered CCTV and sound recording that is monitored and recorded elsewhere and thus not vulnerable to the fire. Mobile phone and computer memory chips may also survive to be interrogated.

Trend Analysis – Local knowledge of fire setting, research and offender profiling may lead to beneficial narrowing down of potential suspects. Effective reading of the fire or explosion scene may indicate a known offender methodology.

Accidental fires often follow trends and ultimately, by skilled investigation, result in product recall or system changes.

The foregoing list is necessarily brief. Each topic can be expanded into volumes, such is the nature of progress in these fields.

Fire investigation combines experience, knowledge, training, research and sheer determination into an exceptional ability to ‘read’ a fire scene. It is a fact-gathering exercise conducted often in the absence of any reliable and independent witnesses. Hypotheses are often found to be uncannily accurate when confirmed after the event by talking to the owners, occupiers and sometimes, perpetrators.

Retrieving evidence from fire is certainly not an easy matter when compared to any other crime scene but the evidence is there. A skilled and experienced practitioner will often find it.

Skilled scientific sampling, analysis, testing and evaluation will provide reliable and irrefutable support to the burn pattern analysis. This is the core forensic process applicable to all fire whether accidental or deliberate. In fact, all fire should be treated as a potential crime scene until crime can be positively eliminated.

Andrew Moore and Associates provide the essential fire and science skills required for effective and thorough investigation of land and marine fires globally.

In marine cases this is backed by substantial engineering, surveying and naval architecture skills.

David Townsend has been in the fire industry for over 40 years. This includes fire fighting, fire command, enforcement, risk assessment, training and investigation. Investigation has been his specialism now for over 20 years with over 2000 primary investigations in many countries involving land, marine and transport property.