In the 2017-18 financial year, the Lincolnshire Fire and Rescue Service attended 36 deliberately started house fires, 38 per cent more than the previous year. In total, they attended 409 house fires.
Since 2013, four people have been killed in arson attacks.
In total, 20 people lost their lives in incidents attended by fire services over the last five years, four in the last year alone.
There were 146 casualties last year, including 44 people who were taken to hospital as a result of their injuries.
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, 263 people lost their lives in fires in 2017-18, including 20 in deliberately started fires.
The Grenfell Tower fire in Kensington in June 2017, which claimed 72 lives, meant the figure was the highest for any year since 2007-08.
There were more than 30,000 house fires across the country over the year, more than 3,200 of which were started deliberately.