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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West Midlands Pollen Update: Very high
East Midlands Pollen Update: Very high
Dry and sunny, with very light winds and temperatures quickly rising after a rather cool start in some rural locations.