How is thermal dose expressed in fire safety terms?

Thermal dose in fire safety is expressed as an energy per unit area, which is essential for assessing the impact of heat exposure on materials and the human body during a fire incident. The units kW-hr/m² and J/m² both represent energy absorbed per unit area.

Specifically, kW-hr/m² indicates the total energy transferred in kilowatt-hours over a square meter, while J/m² expresses the energy in joules per square meter. The joule is a standard unit of energy, and the relationship between kilowatts and joules is defined (1 kW = 1000 J/s). Since fire safety assessment often requires analyzing the amount of energy that reaches surfaces or individuals, these units are particularly relevant.

In contrast, the other options represent different forms of energy measurement or rates of heat transfer but do not specifically capture the concept of thermal dose in the same way. For instance, kW/m² and BTU/h denote heat flux, describing how much heat energy is transferred per unit area in a given time rather than total energy absorbed. Therefore, the first option is the most appropriate for expressing thermal dose in fire safety.