The last thing you would expect to find in a shipping container is a living room complete with carpet, sofa and TV – even pictures on the walls and crockery on a dining table.

But this familiar domestic scene is laid out inside one of a number of steel containers at West Yorkshire Fire and Rescue Service headquarters.

Inside another is a bedroom, and a third is home to an office. The ‘rooms’ are crucial training tools for those investigating the causes of fire.

“We set the room alight, let the fire take hold, then extinguish it and let the officers look at how it may have started,” says station manager Chris Clarke, who heads the service’s fire investigation team.

“We may start the fire with a cigarette, which is a fairly common cause,” he adds. “We introduce electrical appliances and wires into the scene too, and red herrings such as a hair dryer, so, under a process of elimination, the possible causes need to be ruled out.”

Being first on the scene, fire officers are trained in what to look for when they arrive at and enter a building. Their observations can be vital evidence as to how the fire started.

Says Chris: “We know from scientific research how different materials react in fire, therefore we can establish beyond reasonable doubt what has happened when something has reacted in a certain way.

“We know that you can’t drop a cigarette on a horizontal timber surface and cause fire, so when people tell us that is what happened, our challenge is to find the real cause.”

Evidence includes smoke stains, the colour of the flames and smoke, soot, damage to furniture and the time scale. Says Chris: “You get people who say, ‘I was having a cigarette five minutes ago and dropped it’. A cigarette will take a certain amount of time to incubate and start a fire.”

In commercial premises – where a high proportion of fires are started deliberately – thick black smoke can pinpoint a substance, such as plastic or rubber, at the seat of the blaze.

Saving life and property are the most crucial responsibilities of firefighters, so the task faced by investigators – who are all former firefighters – can be extremely challenging.

“You could have 3ft of water in a building, which would have to drain out first, and then you go into water-soaked ashes,” says Chris. “Sometimes we have to admit defeat and say we don’t know the cause, but that very rarely happens.”

Most calls come at night, and the team often needs to wait until daylight to proceed with their investigation. They always attend in cases which have seen a fatality.

They check for clues such as whether the property was secure or had been broken into, or possibly been burgled.

Says watch manager in fire investigation Gary Asquith: “Smoke staining can tell us if windows were open, and ventilation within the room will alter the fire dynamics in the room. We look to see whether there is impact damage, and whether a window was broken from the outside before the fire started, or thermal damage.

“If you dig through debris and find clean glass, smashed with a cobweb effect, that would indicate it had been broken before the fire started. Parallel fractures indicate an explosion.”

“It is a bit like being on an archaeological dig,” says watch manager in fire investigation, Glenn Meacham. “Once you have worked out the pattern of the fire and the origin, you set about making a detailed investigation. You are excavating the scene – using brushes, trowels and other tools to go through it with a fine-tooth comb.

“We can also collect information from the fire crews, occupiers and witnesses, and we take photographs.”

The team – who tackle domestic and commercial fires – also detect smells of flammable liquids or other accelerants which may indicate that a blaze was started deliberately.

They work with the police, forensic scientists, the Health & Safety Executive and insurance assessors.

Fingerprints can be recovered using DNA. “Many people believe that fire and water destroys everything,” says Chris. “But thanks to DNA you can still get prints.”

Says Glenn: “You have to think that potentially a crime has been committed, so, until proven otherwise, you treat it as a crime scene. Firefighters are trained to observe and preserve the scene as best as possible.”

Evidence of deliberate acts uncovered by the team include a box of matches taped to a wick in a hospital roofspace, and an aerosol next to an electric heater.

In 2009, of the 137 incidents investigated, seven convictions for arson were secured, including one life sentence, a ten-year jail term, and an undetermined- length hospital order.

“It is very satisfying to be able to walk into a scene of complete devastation and come up with a cause,” says Gary.

Adds Chris: “People think that fire destroys all the evidence, but it creates its own evidence.”