THEY can be as little as two feet tall. They can sit for months in the corner of a workshop or factory without causing anyone any problems.

But if they get too hot, or if they are dropped, they get angry. So angry that they could explode. Literally.

Acetylene cylinders have been used for years in welding factories in Jersey and across the world. But recently the safety of this volatile gas has been called into question after it was involved in three major Island fires.

The cylinders were first thrust into the limelight on the evening of 14 July, when a dozen or more of them exploded in the Broadlands lodging house inferno in St Peter.

A day later a cylinder being used by a welder at the Bellozanne incinerator overheated, forcing scores of workers to flee the area as firefighters tried desperately to keep it cool. And earlier this week haulage firm A A Langlois in St Lawrence was shut for a day after one of its acetylene cylinders briefly caught fire.

So how dangerous are acetylene cylinders? Here is a video of an acetylene cylinder fire at a factory in the United States.

And how do firefighters prevent them from blowing their top?

Martyn Maguire, director of safer communities for the Fire and Rescue Service, said: ‘If someone phones the control room and says that an acetylene cylinder is involved in a fire, then alarm bells really do start to ring. A fire involving one of these cylinders is one of the most dangerous incidents we have to deal with. We have to treat it as a bomb which could explode at any time.

‘We would normally only get one of these incidents a year, but we have had three in the last couple of weeks. This is just an unfortunate series of events, however, and there is no link between the three.

But we have had to treat each fire with extreme caution and carry out a dynamic risk assessment of the scene.’ A dynamic risk assessment involves analysing the site and any potential risks and ensuring that a cordon – usually 200 metres -– is placed around the site. The cylinder must then be kept cool with a constant jet of water for at least 24 hours.

Mr Maguire said: ‘After 24 hours we will check the heat of the cylinder using a thermal imaging camera. If it is still too hot, we will continue to keep it cool with water for another 24 hours.’

Once the cylinders have cooled sufficiently, firefighters will remove the cordon and hand the premises back to the owners. The Fire and Rescue Service will then notify the Health and Safety Executive as well as the suppliers of the cylinders.

As well as being difficult to calm down, acetylene cylinders are notoriously expensive to deal with. The fire at the A A Langlois site only lasted a matter of minutes and had extinguished itself even before the firefighters arrived, but because of the risk of an explosion, two fire appliances were dispatched and firefighters had to remain at the scene for 24 hours to ensure that the cylinder remained cool.

The average cost of sending out a fire engine and crew is £245 an hour. In the Langlois fire, two appliances were sent and a retained crew had to be called in to provide cover. The Fire and Rescue Service estimates that the cost of dealing with the incident, which started with a fire that lasted only a couple of minutes, was about £23,000.

An acetylene cylinder fire can cause severe disruption to the affected business, as well as nearby premises which may also have to be evacuated. Motorists can also be affected, as roads may have to be closed. It is essential that people are kept as far away as possible from the potential bomb.

Mr Maguire said: ‘Putting up a cordon can inconvenience a lot of people, and I’m sure that many don’t really understand why we do it. But the damage that can occur if these cylinders explode is tremendous. They can go through concrete walls, and firefighters in the UK have been killed trying to deal with them.’

So what can Islanders do to minimise the risk of angering the temperamental cylinders? The answer is simple: treat them with care.

They should only be used by people who have been fully trained. The hoses should be checked regularly and flame arresters should always be used to ensure that the heat does not get within the canister. They should be stored in an upright position and should not be dropped or rolled across the floor.

Mr Maguire said: ‘The cylinders must be handled with extreme care. If they get hot they can become unstable and explode. But even if they are dropped, a chemical reaction can occur inside and this can spark a fire.’

An unstable cylinder on fire in the open is bad enough, but one hiding away inside a van or car is even worse. A number of UK firefighters have been seriously injured or even killed in explosions while tackling what they thought was a routine vehicle fire.

Mr Maguire urged Islanders to clearly mark vehicles containing acetylene cylinders and always inform the Fire and Rescue Service of the presence of such a canister when reporting a fire.
• Acetylene was discovered in 1836 by British scientist Edmund Davy.
• It was ‘rediscovered’ in 1860 by French chemist Marcellin Berthelot, who coined the name ‘acetylene’.
• The Nobel Lauréate Gustaf Dalén was blinded in an acetylene explosion.
• A welder once caused £1 million worth of damage to his factory when a cylinder he was using exploded. He escaped unharmed.
• Last year in London more than 2,000 homes were evacuated because of fires involving acetylene cylinders.