Complex sentence: Regardless of what state it is in, vapor, liquid or solid, it ignites easily and burns very rapidly, necessitating special provisions to accomplish a fire-resistance rating based on an internal grease fire as well as an external fire.
Split into simpler sentences: Regardless of what state it is in, vapor, liquid or solid, it ignites easily and burns very rapidly. A fire-resistance rating is intended to certify resistance to an internal grease fire as well as an external fire.