Why is duty cycle one of the factors used to determine safe RF radiation exposure levels?

The term duty cycle refers to the ratio or percentage of time a transmitter is actively producing RF energy during a given time period. Because RF heating in human tissue depends on the total energy absorbed over time, a lower duty cycle means the transmitter is off for a portion of the time, lowering the overall average exposure. Therefore, a high-peak-power transmission with a very low duty cycle (like CW or certain digital modes) might actually result in a lower average RF exposure than a continuous transmission (like FM) at a lower power. Distractors like 'peak exposure' or 'thermal effects of the amplifier' miss the core biological safety factor, which is the time-averaged tissue heating.