Updated 09 March 2015

Wildfire forensics: how to catch a fire-starter

An investigation into the cause of the Cape Town fires is set to start – but how do you look for clues when the scene is reduced to ash? Enter wildfire forensics.


Now that the devastating fires that raged through the Cape Peninsula have been contained, a specialised breed of sleuth – the wildfire forensic investigator – sets to work.

Cape Town-based wildfire investigator Rob Erasmus and his team from Enviro Wildfire Services, who have been appointed by South African National Parks to investigate the fire, will begin searching for evidence in the sooty veld to discover the cause of the inferno.

Forensics expert Dr David Klatzow will also be investigating the fire for the City of Cape Town.

It is quite possible that the fires were set with malicious intent, says Erasmus. A fire that broke out on Saturday March 8 at Scarborough after the main blaze had been largely contained strengthens this suspicion.

Read: Rampant Cape fires worsen allergies

“There were several ignition points, near to the road, and wind conditions were calm – all indicators that this fire at least was set deliberately,” he says.

Speculation in the media and among the public on social networks that the fire which began on March 1 was started by a carelessly discarded cigarette, is “highly unlikely”, says Erasmus. Still-glowing cigarette butts can start fires, but only if a specific set of physical conditions are met, including the angle the cigarette falls, wind strength, temperature and vegetation type.

Wildfire follows typical patterns

It might seem needle-in-a-haystack ludicrous to sift through a wasteland of scorched earth in the hope of finding evidence the size of a matchstick, but investigators know that, chaotic though wildfires appear, they obey the laws of nature and burn in accordingly recognisable, if complex patterns.

Remarkably, fire doesn't just destroy the landscapes it rampages through; it also leaves behind subtle clues as to where and how it started. To the trained eye, a delicate ash deposit or heat-curled leaf are as significant as a bloodstain to a homicide detective, or a spoor to a tracker.

Tracking the fiery fiend

Like any detective, the fire investigator is ultimately seeking potential human perpetrators, and he employs familiar crime scene methods: interviewing witnesses, taking photographs, rigging up hazard tape against curious members of the public (and sometimes emergency personnel) blundering over frail evidence.

But he is also stalking a non-human entity – the phantom of the wildfire that has recently passed. In his mind’s eye he recreates where this creature was born, gathered its strength, rose up, and ran.

In wildfire forensics, the fire's “origin” refers to a small area only a few metres wide: this forms the heart of the investigation because it contains the exact point at which the fire was ignited, and the best hope of finding any intact evidence. The specific origin, an even smaller area immediately around the genesis of the first spark, is typically not annihilated.

Read: How to help animals caught in the fire

Thus the offending matchbox or flare is seldom, as fire setters might hope, reduced to unidentifiable ash. It is more likely to suffer only partial burns, and, in the case of a cigarette for example, may be sufficiently intact even to warrant collection for DNA testing.

To find the all-important origin, the wildfire investigator reverses the sequence of events, beginning at the most heavily charred, profoundly ruined part of the scene, where the mature hot fire sped full-tilt. Then, carefully, methodically, he picks his way back to the fire’s origin.

A textbook fire burns outward from its genesis in a V-or U-pattern, driven more or less in the direction of the prevailing wind, so locating the origin might seem a simple matter of heading for the point of the “V”.

Typical wildfire burn pattern. This fire broke out beneath Rhodes Memorial on Table Mountain, 2009. Blue arrow: prevailing wind direction. Yellow: fire origin. White “V” and arrow: direction of fire spread. Credit: Rob Erasmus.

But in the real world, fires, especially those deliberately started, may have multiple points of origin, and the picture is further confused by changing wind direction and variations in slope and vegetation. To correctly identify the origin, investigators must look much closer.

Devil in the details

Investigators are guided back to the fire's origin by numerous subtle clues. For example, surfaces facing into the oncoming flames are heavily charred and soot-coated, while the leeward sides of fire-blasted objects often survive relatively undamaged. Leaves "freeze" in place like tiny weather-vanes, curling towards the fire's heat.

Where a fire "backs" – a low, feebler burn against the main direction of advancement, it gnaws away at the base of grass stalks, so that they topple over and lie unburnt on the blackened ground, pointing like pale fingers back towards the origin.

Within the origin, small, mundane objects, which normally wouldn't deserve a second glance, acquire new importance when viewed as potential ignition sources. But human-introduced items are well disguised in the jigsaw puzzle of half-burnt twigs, stones and leaf-litter, and the eye must re-learn to notice what it previously ignored as background clutter.

This process of “re-seeing” is aided by the investigator's second eye – his close-up photos of every section of the specific origin.

The cause of this fire, a matchbook, was only discovered on close examination of photos taken of the origin. Credit: Rob Erasmus.

Close up: Investigators rushed back to the scene, but the matchbook had been removed, almost certainly by the perpetrators. Credit: Rob Erasmus.

Who are the fire starters?

We call wildfires natural disasters, but the only “natural” causes are lightning, and, far more rarely, spontaneous combustion and sparks struck from rockfalls. Wildfires are overwhelmingly the fault of careless or malicious people. An estimated 90% are caused by humans, and about 30% of those on purpose.

In South Africa, accidental human causes are most likely to be homeless people making fires for warmth or cooking, prescribed burns and other agricultural activities like bee farming that get out of control (smoke is used to calm the bees), maintenance work and children playing with fire. Careless smokers are also on the list.

Deliberate fire setters in this country are most likely to be frustrated kids and teenagers in socio-economically deprived settings, followed by those seeking financial benefits such as contract firefighters who might be paid for overtime, and disgruntled ex-employees seeking revenge for being fired.

More unusual motives identified by international research include those by people (often, ironically,  from the ranks of aspirant or volunteer firefighters) who hope to become heroes when they “save the day” by reporting or putting out fires they themselves have started.

True pyromaniacs, who gain psychological relief or excitement from compulsive fire setting, are rare.

Fire forensics: a vital firefighting tool

Erasmus points out that without the foundation provided by “origin and cause” fire investigations, South African Police Service detectives are unable to pursue leads or evidence.

“The result is that reported cases of suspected malicious acts become dead-ends.”

He stresses that investigation is far from an empty exercise performed after the event; it's a vital element of wildfire prevention:

“Investigation provides insight into who (and what) is causing fires in a specific area, and the  information gathered can be used to stop them acting again. The very fact that a fire scene is being formally investigated serves as a deterrent to local fire setters.”

Note: You can help in this wildfire investigation. Please contact Rob Erasmus on 083 411 3378 if you have any information relating to the possible cause of the recent fires.

Erasmus, Rob. Enviro Wildfire Services. March 2015. Pers. Comm.
National Wildfire Coordinating Group Fire Investigation Working Team. 2005. Wildfire Origin and Cause Determination Handbook
Willis, M. 2004. Bushfire Arson: A Review of the Literature

Also read:

Fireproof your home with these expert tips

Smoke inhalation: What you need to know

Safety tips for fire and water

Olivia Rose-Innes is Health24’s EnviroHealth Editor. Read more of her columns and articles or post a question to her expert forum.


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