(1) A person is guilty of arson in the first degree when, with intent to destroy or damage a building, he starts a fire or causes an explosion, and;
(a) The building is inhabited or occupied or the person has reason to believe the building may be inhabited or occupied; or (b) Any other person sustains serious physical injury as a result of the fire or explosion or the firefighting as a result thereof.
(2) Arson in the first degree is a Class A felony.