The unit used to express radiant heat flux that signals the onset of flashover is which of the following?

The unit used to express radiant heat flux that signals the onset of flashover is which of the following?

• A. W/cm2
• B. W/m2
• C. BTU/hr-ft2
• D. J/s

Answer: (A)

Radiant heat flux is the amount of radiant energy striking or leaving a surface per unit area each second. The threshold for flashover is described in terms of how much energy per area is delivered in a given time, and in many fire investigation and fire-testing references that critical value is expressed in watts per square centimeter. This unit makes the magnitude of the heat load easy to compare to the rapid heating seen at flashover, since a few watts per square centimeter correspond to tens of kilowatts per square meter. So the best choice is the unit that conveys energy per area, at the scale typically used to signal flashover. While watts per square meter is a valid SI unit for radiant flux density, the context here commonly reports the flashover threshold in W/cm^2, which is why it’s the preferred answer. The other options either aren’t per-area units (J/s, which is power) or use different customary scales (BTU/hr-ft^2) that aren’t the standard reference for this criterion.

Radiant heat flux is the amount of radiant energy striking or leaving a surface per unit area each second. The threshold for flashover is described in terms of how much energy per area is delivered in a given time, and in many fire investigation and fire-testing references that critical value is expressed in watts per square centimeter. This unit makes the magnitude of the heat load easy to compare to the rapid heating seen at flashover, since a few watts per square centimeter correspond to tens of kilowatts per square meter.

So the best choice is the unit that conveys energy per area, at the scale typically used to signal flashover. While watts per square meter is a valid SI unit for radiant flux density, the context here commonly reports the flashover threshold in W/cm^2, which is why it’s the preferred answer. The other options either aren’t per-area units (J/s, which is power) or use different customary scales (BTU/hr-ft^2) that aren’t the standard reference for this criterion.