the rate at which heat is generated by fire. The HRR can be viewed as the engine driving the fire. This tends to occur in a positive-feedback way: heat makes more heat. HRR is measured in Joules per second (also called Watts). Since a fire puts out much more than 1 Watt, HRR is usually quantified in kilowatts (1000 W) or megawatts (a million watts).