What atmospheric humidity is assumed for thermal radiation calculations?
The thermal radiation emitted by a fire is attenuated by water vapour in the atmosphere, therefore the flux at a target is inversely proportional to the humidity. In the UK, humidity varies considerably, but an average value of 60% is often assumed for hazard calculations. This figure is probably overly optimistic for F2 weather conditions, but an Operator should justify the use of significantly higher values that could result in optimistic predictions.
