By Jonathan Duffy BBC News Online

Fighting fires is now as much about tactics and strategies as hoses and ladders. Things have changed since soldiers last stepped in for striking firefighters. You don't have to be "big and burly" to be a firefighter, according to the Fire Service's recruitment leaflet, but these days you do need something up top.

Firefighting used to be about donning a hard hat and pointing a jet of water at the flames. And that's pretty much where public perceptions of the job remain.

	Fire-fighting strategies Ventilation: Can be vertical (through holes in roof) or horizontal (open doors or windows) & helps clear smoke to enable search & rescue Fan ventilation: Known as positive power ventilation, uses a powerful fan to force in fresh air Water-fog: Spraying water droplets to cool & create atmosphere of wet steam Smooth-bore attack: Opposite of water-fogging & effective when directed into fire's source

But in recent years, the role of the average firefighter has changed almost beyond recognition. Today firefighters consider themselves "skilled professional workers".

It seems these days there is an art, not to mention a science, to firefighting.

When a fire crew is called to a "shout" - an incident - saving lives is always top of the priority list. Where they can, they will also hope to limit the damage to property.

The problem is that no two fires are the same, says Paul Grimwood, a former London fireman and author on firefighting techniques.

"Take each building as a box. Now place into that box a large number of compartments (rooms) of different sizes; variable-sized openings (doors and windows); some are open, some closed; a variable number of people depending on occupancy type," he says.

"Now add in different construction methods, wall and ceiling linings, furniture and fuel load. There are unknown parameters because of the black smoke but the firefighter must 'risk assess' each situation to try and anticipate how the fire is likely to behave and develop."

Breathing apparatus allows access to the source of a fire

If chemicals are involved, then a firefighter must know how they will react. Some can be extinguished with water while others would explode if treated in the same way.

It means all new firefighters must study chemistry as part of the initial three-month training. Other elements of the induction course include building construction - to know how a building collapses - team building, handling equipment and physical fitness.

In terms of putting out a fire, the aim is to get inside the building for "offensive" firefighting, rather than remain outside, which is called "defensive".

Ever-present dangers

Flashover - burst of sustained fire in a room Backdraft - explosion caused by sudden inlet of oxygen in a burning room

"The image of a fireman standing on the street with a hose pointed at a burning building is just for the cameras," says ex-fireman Bob Parkin, who is now a fire safety consultant.

Breathing apparatus allows firefighters to get inside, but the danger in a burning house is that fuel vapours will get heat up to the point of exploding.

Taming the flames

The trick is to tame the fire, before extinguishing it, and there are a number of tactics for doing so. They include ventilating the house to drive out the lethal smoke, and spraying a room with bursts of water droplets. This works by cooling down inert dangerous gases that rise up in a fire.

Four years of training

New recruits get three months initial training Followed by 18 months assessment Followed by 36 months to fully qualify Recruits also expected to get HGV driving licence

But sometimes these strategies can do more harm than good. This means firefighters must make crucial decisions quickly.

"Over the past 10 years, the job of a firefighter has become more reliant on thought processes than individual strength," says Mr Grimwood.

"Modern-day firefighters must process 'risk assessments' with great speed, under tremendous stress, based upon a widening knowledge of fire behaviour."

The army's Green Goddess crews are unlikely to be able to match firefighters' expertise in this area, although some of them do have specialist breathing apparatus and cutting equipment. They could have their first tests if strikes scheduled for 29 October take place.