FIREFIGHTERS are warning farmers to check their barns in a bid to combat the spontaneous combustion of crops.

This unusual and complex chemical reaction is thought to be behind three recent barn fires attended by Dorset Fire and Rescue Service (DFRS) in two days.

Among them was a barn containing 4,000 tons of straw, which was destroyed in a blaze at a farm at Chilbridge, near Wimborne, on Monday.

This emergency was attended by retained crews, as DFRS members of the Fire Brigades Union (FBU) are currently backing eight days of consecutive strike action, amid a continued pension row with Whitehall.

Fire safety experts say spontaneous combustion can occur if crops are not dry enough when stored in bulk and put away too soon. Heat slowly builds, cannot dissipate, and a fire is sparked.

Andy Fox, head of fire safety at Dorset Fire & Rescue Service, said: “We are issuing a warning to farmers, asking them to check their barns regularly, looking for heating of hay, and a distinctive chocolate/caramel or musty smell, which indicates the stack is heating up.

“If you do suspect there may be a deep-seated fire, call us immediately on 999 and then move any livestock, then machinery and hazardous items from the area, as any investigative movement of the bales can cause the fire to rapidly spread.”

DFRS says the problem can be prevented by stacking bales further apart or in smaller stacks. Using bigger bales means the crop is packed tighter together, which can increase the risk of the devastating chain reaction starting.

Mr Fox said: “If farmers can think about leaving about 50 centimetres gap between the bales, that would help the air to circulate and cool them down.”