Fire Investigation Is Not Pattern Matching: Why Context Matters When Interpreting Fire Damage

Vithyaa Thavapalan BSc, MSc, GradDipFI, IAAI-FIT (V), NAFI-CFEI

Forensic Fire Investigator and Founder of Forensic Origin and Cause Investigations

Walk into almost any fire scene and there will be patterns everywhere. There may be V-shaped patterns on walls, areas of deep char, clean burning, melted materials, damaged electrical conductors and sections of the building that have experienced significantly more damage than others. These patterns are important. They can provide valuable information about fire development, fire spread and the potential area of origin. But fire investigation is not an exercise in recognising a familiar pattern and attaching a conclusion to it.

A V-pattern does not automatically tell us where a fire started. The most heavily damaged area is not automatically the area of origin. An electrical arc does not automatically mean that the fire was caused by an electrical fault. Each of these observations is a piece of data that needs to be understood within the context of the entire fire.

For me, one of the most important questions when looking at a fire pattern is not simply, “What does this pattern look like?” It is, “How was this pattern created?” That distinction is important because the damage we see at a fire scene is the result of a process. Fire develops, spreads, changes with ventilation, interacts with different fuel packages and is eventually affected by suppression activities. What remains when the investigator arrives is the final product of all of those events.

Fire patterns are evidence, but they are not conclusions. Kirk’s Fire Investigation discusses the importance of scientifically based fire pattern analysis and the need to understand the physical processes that produce the damage we observe. NFPA 921 similarly places fire pattern interpretation within a broader systematic investigation that considers fire dynamics, available fuels, ventilation, physical evidence and the other information gathered during the investigation.

This becomes particularly important when looking at the area of greatest damage. It can be tempting to assume that the most heavily damaged part of a room must be where the fire started. In some cases, that may ultimately be correct, but the extent of damage can be influenced by many other factors. A large fuel package can produce greater heat release. An open window or doorway can provide additional oxygen. Fire may burn more intensely near an opening once it becomes ventilation controlled. Firefighting activities may also reduce damage in one area while allowing another area to appear comparatively more damaged.

The investigator therefore needs to understand not only where damage exists, but why the damage developed in that way. If one part of a room is substantially more damaged than another, we need to ask what fuel was present, what the ventilation conditions were, whether the fire had progressed to full room involvement, when openings were created and how suppression occurred. The greatest damage may support an origin hypothesis, but it should not create the hypothesis on its own.

V-patterns are another good example. They are probably one of the most recognisable fire patterns, particularly outside the fire investigation profession. There is sometimes an expectation that a V-pattern effectively points directly towards the origin. In reality, the geometry and appearance of a pattern can be influenced by the heat release rate of the fire, the location and geometry of the fuel package, the surfaces involved, ventilation and the development of the fire within the compartment.

Seeing a V-pattern should therefore start the analysis rather than finish it. Was it produced by the initial fire plume? Could another fuel package have produced the pattern later in the fire? Was ventilation influencing flame movement? Did the compartment become fully involved? Could the pattern have been modified by suppression? When we begin asking those questions, we move from simply recognising a pattern to actually analysing it.

We also need to remember that investigators usually arrive at the end of the fire. We do not get to watch the entire sequence unfold. We are trying to reconstruct a dynamic event from the physical evidence that remains. A pattern created early in the fire may later be modified, obscured or completely destroyed. A pattern created much later may appear far more dramatic. The clearest or largest pattern is not necessarily the earliest pattern.

That is why understanding fire dynamics is such an important part of origin and cause investigation. We need to think about the fire through time. How did it begin? What fuel was available? How did the fire grow? What changed in the ventilation? Where could the fire spread? When did windows fail or doors open? When did firefighters arrive and what actions did they take? The final scene needs to be interpreted against that sequence of events.

Ventilation is particularly important because it can substantially alter both fire behaviour and the damage that remains. A door opening, a window failing, mechanical ventilation operating or firefighters creating an opening can change the amount of oxygen available to the fire and alter the direction and intensity of burning. In a ventilation-controlled fire, areas closer to openings may experience significant burning even though the fire originated somewhere else. If we interpret those patterns without understanding when and how the ventilation changed, we risk giving the damage the wrong meaning.

Firefighting activities also become part of that history. Water application, ventilation, overhaul and the movement of contents can all alter the scene. An area that originally experienced intense burning may later appear less damaged because firefighters concentrated their suppression efforts there. Contents may have been moved while searching for occupants or accessing hidden fire. Wall or ceiling linings may have been removed during overhaul. None of this makes the scene unusable, but it means we need to understand what occurred before interpreting what remains.

The same principle applies to electrical evidence. An electrical arc can be significant, but the presence of an arc does not automatically establish an electrical fire cause. Electrical conductors can arc because they were attacked by an advancing fire. The investigator still needs to determine what the electrical evidence means within the sequence of the fire and whether the conditions existed for that electrical event to ignite the available fuel. Arc mapping can provide useful information, but again, it is one component of a much larger investigation.

Ultimately, this is where the scientific method becomes so important. We collect the available data, analyse it, develop hypotheses and then test those hypotheses against the evidence. If I think an appliance caused the fire, my job is not to search the scene for everything that supports an appliance failure. I also need to consider what evidence should be present if that hypothesis is correct, what evidence might contradict it and whether another hypothesis better explains what I am seeing.

The scene should drive the hypothesis. The hypothesis should not drive how we see the scene.

Experience is incredibly valuable in fire investigation. The more scenes we examine, the more familiar we become with different patterns, materials, appliances and fire behaviours. But experience should help us recognise possibilities and ask better questions. It should not become a shortcut around the scientific process. “I have seen this before” may be a perfectly reasonable starting point, but it cannot be the end of the analysis.

Two fire scenes can look remarkably similar and have completely different ignition sequences. Two fires caused by similar mechanisms can also leave very different damage depending on the fuel, ventilation, compartment geometry and suppression activities. Familiarity can help us know where to look, but the evidence still needs to demonstrate what occurred in that particular fire.

Fire patterns remain one of the most valuable sources of information available to investigators. The point is not that we should distrust them. The point is that we need to understand them.

A defensible origin and cause determination should not depend on one dramatic photograph, one burn pattern, one area of heavy damage or one piece of electrical evidence. It should come from bringing together the fire patterns, fire dynamics, physical evidence, available fuel, ventilation, electrical evidence, witness information, suppression activities and timeline, and then testing whether the proposed explanation makes sense against all of that information.

Perhaps the better question when we identify a significant pattern at a fire scene is not, “What does this tell me?”

It is, “What could have created this, and can I demonstrate that from the evidence?”

That is the difference between recognising a pattern and investigating a fire.