If your grow op is building up enough heat to start a fire, it's probably way too hot for your plants! Conversely, if your plants are doing OK, you are probably safe from a heat build-up fire.
90 degrees f. is on the "hot side" for plants. 451 degrees f. is the point that paper starts to burn. One, well placed, fan can disapate a lot of heat!
What are the actual temperatures that you are dealing with? Both in, and around the growing area.