Hollywood Lies to You
Hardly unknown and certainly not surprising when you consider that many scenes shot in Hollywood are done so for dramatic effect. But as forensic science has become part of our everyday lives through television, film and media, all members of the public have preconceived ideas of what is possible and much of what they believe to be true does not hold water in real life. As forensic scientists it is up to us to disabuse those members of the jury who believe they ‘know’ the truth of forensic science from media outlets. Fire Investigation is as susceptible to these myths and misunderstandings as any other form of forensic science. Here we will try to address some of the most commonly encountered ‘facts’ in fire investigation.
Let’s take the film ‘The Usual Suspects’; at the end of the film petrol is poured around a boat and ignited by a lit cigarette flicked from the hand of Keyser Söze. The boat explodes leaving only two survivors. In reality if Keyser Söze (a fictional character but bear with me) had flicked the lit cigarette onto the petrol nothing would have happened as lit cigarettes cannot ignite petrol. This is however a commonly encountered myth that is held to be true by a large percentage of the population! The tip of a lit cigarette reaches a high enough temperature to cause ignition it cannot transfer that heat efficiently to the petrol vapour to cause ignition. An exacerbating factor is that petrol has a narrow flammability range indicating that the oxygen requirement for petrol vapour ignition is not met in the oxygen deprived region of the hot tip of the cigarette.
Another commonly held ‘truth’ is that drinking alcohol will ignite and burn freely off a hard surface. Examples of this can be seen in both Indiana Jones and the Raiders of the Lost Ark and Shaun of the Dead. These contain instances where alcohol from a normal spirit bottle is poured over a bar in a public house and ignited. This mechanism of ignition could be true of a very limited number of spirits; these have high alcohol and sugar contents but lower water content. The spirits usually sold for general consumption are at least 60% water, with beers, wines and ciders containing considerably more water than alcohol. The large water content of these liquids means that they will not ignite when poured onto a surface. However we can cause some spirits liquids to ignite by first heating them; consider a traditional Christmas pudding, the brandy poured on top of it needs to be heated before it will ignite. This causes the alcohol present in the liquid to enter its vapour form and it can then be ignited.
One of the most impressive sights in a movie is an exploding car. Virtually all car chases and crashes end with a car violently exploding, whilst cars can indeed explode or burst into flames under certain conditions this is not an automatic response. There are examples of cars exploding that are not quite right; in No Country for Old Men the actor puts a petrol soaked rag and a disk of card over the fuel filler port and ignites it, a short time later the car explodes in dramatic fashion. The issue with this is that the fuel tank would contain a fuel/air mixture that was too rich to burn in that space. However at the filler port there would be sufficient air to mix with the petrol and burn so there would be a small fire sustained in that area. It is highly unlikely that there would be an explosion under such circumstances. Similarly shooting the fuel tank would result in the release of petrol but the fuel rich composition of the mixture in the fuel tank wouldn’t be within the explosive range.
There are some instances when Hollywood does get it right, but just because it is shown in a movie or on television that doesn’t mean it is a realistic representation of what would actually happen. As forensic scientists Prometheus Forensic Services have come across several cases where these movie myths have been used as a defence explanation. Due to the plethora of movie and television myths it can sometimes be difficult to overcome those ingrained ideas in the minds of a jury with the sometimes complicated scientific explanations required. With so many versions of the same myths in the media it can be very difficult for the lay person to know what is the truth actually is. Hopefully a forensic scientist will be able to sufficiently explain the truth and the court will be able to make their decision on the basis of fact rather than fiction.