For a pool fire, which parameter primarily controls its heat release rate (HRR)?

• A. The evaporation rate from the pool surface
• B. The fuel's melting point
• C. The surrounding air temperature
• D. The fuel's odor threshold

Answer: (A)

In a pool fire, the heat release rate is controlled mainly by how fast the liquid fuel can evaporate from the surface. The flame depends on fuel vapour feeding it; the more liquid that turns into vapour per second, the more fuel is burned and the higher the HRR. That evaporation rate is driven by heat transferred to the liquid surface, the surface area of the pool, and how readily the fuel vaporizes (its volatility). So the rate at which fuel can evaporate from the pool surface sets the pace for how much energy is released.

The other options don’t set the HRR in the same way. The melting point isn’t a limiting factor for a liquid pool fire, since the fuel is already liquid. The surrounding air temperature has some influence on evaporation but is not the primary control, and the fuel’s odor threshold is unrelated to how much energy the fire releases.