Scientific method used in US in fire investigations

Those guilty of arson must go to jail, and those who are innocent must be cleared of any suspicion in the event of a fire. This simple idea prompted America’s National Fire Protection Association (NFPA) to implement the scientific method in all fire investigations. And now the same method is on its way to Denmark.

In 1992, the National Fire Protection Association (NFPA) started something new. That year, the non-profit organisation, which develops consensus guidelines for fire safety in the US, introduced NFPA 921: Guide for Fire and Explosion Investigations.

But it was not just the guide that was new. For the first time, the scientific method was to be applied in fire investigations, and this was precisely the theme of Richard J. Roby’s keynote lecture at the Technical University of Denmark (DTU), held in June 2014. Roby is the technical director of Combustion Science and Engineering, Inc. and holds a Ph.D. in mechanical engineering.

– Traditionally, fire investigations were conducted by people who had experience in putting out fires, and they followed certain rules of thumb. Today, though, these rules are considered by many to be poor science, Roby says.

Rules of thumb didn’t hold water
Just because one is good at extinguishing a fire doesn’t mean that one is good at developing tests for determining how a fire is started and spreads. The proof was not always valid.

– If there was a fire in a house that was for sale, for example, it was often viewed as an indication of arson as experts believed the seller needed the money. However, can’t a person who happens to be selling his house also be the victim of an accident? Roby asks.

Experts also used to believe that certain types of fires showed evidence of flammable fluids, and that was thus a strong indication of arson. It has since become clear, though, that fires can occur both as a result of flammable liquids and of regular accidents.

In worst-case scenarios, people were found guilty based on the fire investigator’s incorrect conclusions, or in light of evidence that later proved doubtful or outright false. The problems associated with conducting fire investigations based on rules of thumb prompted the NFPA to issue its 1992 guide, which is, however, only a voluntary set of guidelines.

– When people became aware of the problem, they began researching which methods were available to determine who was guilty and who wasn’t. And the answer was the scientific method, asserts Roby.

Testing one’s way to a single hypothesis
Today, a ‘for sale’ sign no longer plays a role when American fire investigators are on the job. By applying the scientific method, they focus solely on the facts that can be observed at the site and – with certain reservations – to witness testimony. The investigators thus develop one or more tests to determine what caused a given fire, and why it spread. These tests much furthermore be scientifically verifiable, e.g. through the use of computer simulations or by focusing on expert knowledge in the areas of radiant heat, flash fires and the spread of flames, which today are all described mathematically.

– Modern science allows us to recreate situations and provides fantastic possibilities for confirming or dismissing – with a very high degree of certainty – our hypotheses about what’s happened. And we test our hypotheses until there’s only one left, Roby explains.

The spread of the method has had clear consequences in the US. Most notably, the convictions of scores individuals are being overturned after years in prison. These are people who were convicted based on evidence that simply did not hold water.

The method makes its way to Denmark
Even though the method is scientific, one need not be a scientist to utilise it in fire investigations conducted in the US.

– The most important thing is to know which tools are available through today’s technology and how to apply them, Roby notes.

This approach is also being given a closer look in Denmark today, and it need not result in the build-up of highly specialised scientific competence by the police. That is because, as in America, the most important thing in Denmark is to know what possibilities exist.

– The right level of expertise is already found in Denmark. However, the police need to know who they can ring up to gain access to the right skills, says Claus Schmidt, chief specialist of COWI and one of the participants in the subsequent panel debate at DTU’s Fire Safety Day.

In the US, the new method was initially met by criticism when it began to become more widespread. According to Roby, such criticism is almost inevitable.

– Some people said it would serve as a shield for the guilty, while others said innocent people would end up in prison. But it’s a transition phase. In the end, the method helps to convict the guilty and clear the innocent of suspicion – and that’s something everyone is interested in, he concludes.