More than one in six house fires in South Yorkshire last year were started deliberately, figures from the Home Office show.
South Yorkshire Fire and Rescue Service tackled 132 incidents of arson last year - 19 per cent of all the house fires in the county.
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The figures also reveal that since 2013, 11 people have been killed in arson attacks in the county and, in total, 41 people lost their lives in incidents attended by the fire service over the same period.
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In the 12 months to September 2017 alone, the most recent data available shows that seven people died in fires in South Yorkshire.
There were also 156 casualties, including 94 people who were taken to hospital as a result of their injuries.
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Dave Green, national officer at the Fire Brigades Union, said: "Starting fires deliberately in the home is a heinous crime.
"Rightfully, it is a serious criminal offence punishable by law.
"Arsonists do not just put the immediate victims at risk; they put whole communities and firefighters themselves in jeopardy.
"The fire and rescue service is already stretched to the limit in the fire cover they can provide.
"If firefighters are dealing with an arson at the same time as another fire call comes in, then those other victims are looking at a long wait before we can get to them."
Across England, 346 people lost their lives in fires between October 2016 and September 2017, including 47 in deliberately started fires.
The Grenfell Tower fire in Kensington in June 2017, which claimed 71 lives, meant the figure was the highest for any 12-month period since the data was first recorded in 2009.
There were more than 30,000 house fires across the country over the year, over 3,000 of which were started deliberately.
Area Manager Steve Helps, of South Yorkshire Fire and Rescue, said: "Arson is a serious crime carrying a maximum sentence of life in prison.
"We investigate the cause of all fires and, in cases of arson, work closely with our police partners to ensure those responsible are brought to justice.
"We would urge anyone with information about people starting fires in their area to contact the police."
Call South Yorkshire Police on 101 or Crimestoppers on 0800 555 111.