What is relative humidity?

Relative humidity is defined as the ratio of the current amount of moisture in the air to the maximum amount of moisture that the air can hold at a given temperature. This measurement is typically expressed as a percentage. When the air is completely saturated with moisture, the relative humidity reaches 100%, indicating that the air cannot hold any more water vapor. As a result, higher relative humidity levels suggest a greater potential for condensation and precipitation, which are crucial factors in fire investigations, as they can influence the behavior and spread of fire.

The other choices do not accurately depict this concept. For instance, the moisture content in dry air does not relate to relative humidity, which specifically involves the saturation point dependent on temperature. Similarly, while air temperature can affect humidity levels, it is not a measure of humidity itself. Finally, the percentage of dryness in the atmosphere is an indirect way to reference humidity but does not capture the essential relationship between moisture content and capacity that defines relative humidity.