What is one way fire is spread through the transfer of heat across airspace?

The correct answer is radiation, which involves the transfer of heat through electromagnetic waves. In the context of fire, radiation allows heat to travel through the air without needing a medium, which means it can transfer energy across distances in a straight line. This is how heat from a fire can warm up nearby objects not in direct contact with the flames, as they absorb the radiated heat energy.

In contrast, conduction requires direct contact between materials for heat transfer, making it less applicable for spreading fire through air. Convection is related to the movement of heat through fluids, including air, but primarily involves the physical movement of air and heated gases rather than direct heat transfer over distances. Evaporation relates to the transition of liquid to gas and does not pertain to heat transfer regarding fire spread. Therefore, radiation is the most suitable method of heat transfer through airspace in the scenario of fire spread.