(a) A person commits the crime of arson in the second degree when he knowingly damages a building or inhabitable structure by starting a fire or causing an explosion.

(b) A person does not commit a crime under this section if:

(1) no person other than himself has a possessory, proprietary, or security interest in the damaged building, or if other persons have those interests, all of them consented to his conduct; and

(2) his sole purpose was to destroy or damage the building for a lawful and proper purpose.

(c) The defendant has the burden of injecting the issue under subsection (b).

(d) Arson in the second degree is a class C felony.