I race at IHRA tracks and am an IHRA member, so these rule excerpts are from the IHRA book, but the NHRA ones are pretty much the same. Get the book and check all sections.

BRAKE LINES: Brake lines must be routed outside the frame rail or enclosed in 1/8 inch steel tubing in flywheel area.

BRAKES: All brake lines mounted on the firewall, where they pass flywheel bellhousing on stick cars, must be protected.

BRAKE LINES: Brake lines must be routed outside the frame or enclosed in a 16” length of 1/8 inch (minimum) walled steel tubing, securely mounted, where it passes the flywheel bell housing area