Detective Sergeant David Speight says whoever caused the fires may have flash burns on their body.
Michael and Angela Broderick, who are both deaf, had a narrow escape when an arsonist destroyed their home in Burbage in Leicestershire.
Police are appealing for the public to contact them if they have any information.
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Generally dry with sunny spells, although there is a chance of isolated afternoon showers.
Any showers will die away during the evening, leaving a dry night with some clear periods.
Scattered showers around at first this evening will soon move away, as dry and clearer conditions arrive from the northwest.