as of 2007 rules, any NHRA sanctioned track (which have to follow NHRA tech inspection rules) require the use of an approved fire suit (jacket only) for any car running an aftermarket power adder. nitrous qualifies as one. as does a turbo upgrade, supercharger upgrade, or even an aftermarket intercooler.
I believe a full suit is required for any car running 11.99 or quicker, but I'd have to look that up. When summitt heard of the new rules, they brought a few thousand jackets into stock and you can get them at a reasonable price.