Firefighters have warned farmers over the possibility of hay bales spontaneously combusting thanks to the combination of warm and wet weather.
Devon and Somerset Fire and Rescue Service issued the warning after a rise in barn fires in the south west of England.
They included one in Cewkerne, Somerset, which saw 50 tonnes of hay and 50 tonnes of straw set alight in a single-storey barn on 7 July.
The spate of fires has prompted the service to warn farmers about storing wet hay, which can spontaneously combust when temperatures get high enough.
A spokesman said: "We're asking farmers to be aware of the fire risk when making and storing hay - particularly at the moment due to recent damp weather.
"When hay is stored with a high moisture content, the temperature can build.
"If it rises above 55c, a chemical reaction begins to produce a flammable gas that can ignite if the temperature gets high enough."
The service urged farmers to remove hay and straw from fields as soon as possible after harvesting, and to ensure it is properly dry before it is stored.
It also encouraged farmers to monitor the temperature of haystacks and be wary of any "caramel or musty smell" which can indicate that the hay is heating.
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