Holy smoke! A cigarette end simply can't set petrol alight

Arson investigators found they could hardly create a flicker of a flame let alone the kind of fireball beloved of film and TV directors and seen in movies such as The Usual Suspects and Alfred Hitchcock's The Birds.

Researchers at America's Bureau of Alcohol, Tobacco and Firearms, did a variety of tests at their Maryland laboratories.

They came after a series of suspected arsonists tried to claim that fires were started accidentally by cigarettes rather than deliberately with naked flames in a bid to avoid prosecution.

The bureau conducted 2,000 attempts to start a fire from exposed petrol using a cigarette, including spraying a mist of petrol directly on to a lit butt.

They tried concentrated pockets of fuel and even spreading the petrol out in a baking tray to cover a wider area.

They dropped a variety of cigarettes of different brands into the petrol to see if it made any difference and used a vacuum device to ensure that the tobacco burnt at the highest possible temperature.

But the petrol did not ignite, leaving chief investigator Dr Richard "Rick" Tontarski to assume Hollywood was stretching the truth a little.

He said the film industry probably realised this, adding: "Actually they are pretty well aware of it. They don't care."

The bureau explained: "Despite what you see in action movies, dropping a lit cigarette on to a trail of gasoline won't ignite it, assuming normal oxygen levels and no unusual circumstances.

"That's because the gasoline has limited contact with the hottest, glowing part of the ash, and X-ray thermography has shown that this is very localised."

In dozens of films and TV programmes major explosions and blazes are started, either accidentally or deliberately, by a cigarette dropped into petrol.

The most famous example is perhaps the Sixties classic The Birds, in which a giant flock of seagulls attack motorists at a filling station.

One victim drops the petrol pump to the ground and the fuel trails down the street, where a smoker throws his cigarette into the stream, which ignites all the way back to the station.

In The Usual Suspects, a fire on a boat which ends up killing 27 people is started by an unseen stranger dropping his butt into a trail of fuel. And in Kevin Costner's 3,000 Miles to Graceland, the star flicks a cigarette out of the window of his car and blows a petrol station to bits.

The US tests were backed up by the physics-based website Intuitor, which has a section called "Insultingly Stupid Movie Physics" that knocks the pseudo-science in many Hollywood productions.

The website conducted tests using 223 cigarettes of 11 different types on trays of petrol and even paper tissue soaked in fuel. In one experiment, 40 glowing cigarettes were thrown into a pan of petrol and they all smouldered out without causing a fire.

The site said: "We used long tongs for reaching far away objects to hold glowing cigarettes over the pan at various heights. More than once we placed several glowing cigarettes in the pan.

"Our record was 40 glowing cigarettes at one time. In most cases, we allowed the glowing cigarettes to smoulder until they went out.

"Various experiments were conducted at different times of the day with different air temperatures and humidity.

"Yet, at the end of each experimental session, the gasoline was successfully lit using a single match attached to a long pole."

Hollywood directors take note. To start a fire from a trail of petrol you need a lit match - but not a cigarette.