(a) A person commits the crime of arson in the second degree if the person knowingly damages a building by starting a fire or causing an explosion.
(b) In a prosecution under this section, it is an affirmative defense (1) that no person other than the defendant had a possessory, proprietary, or security interest in the building or that all persons having such an interest consented to the defendant's conduct; and
(2) that the sole intent of the defendant was to damage or destroy the building for a lawful purpose.
(c) Arson in the second degree is a class B felony.