The rule is 7.4 under General Regulations and states.
7:4 Firewalls
Each car in competition must be equipped with a minimum .032 inch aluminum or .024 inch steel firewall, extending from side to side of the body and from the top of the engine compartments upper seal (hood, cowl, ore deck) to the bottom of the floor and /or bellypan. Firewall must provide a bulkhead between the engine and/or fuel tank and driver compartment. All holes in the firewall must be sealed with aluminum or steel. In certain instances, fiberglass, carbon fiber, or other composites may be used. See Class Requirements or consult NHRA. Use of magnesium prohibited
Getting a rule book helps, if your not sure contact your division tech director.
I hope that helps