What Is a Flame Spread Rating?

The flame propagation limit refers to the range of the proportion of fuel and air that the flame can propagate in the premixed combustible gas mixture. It consists of the lower flame propagation limit and the upper flame propagation limit. Regardless of whether the combustible mixture is too lean or too rich (that is, the volume percentage of the fuel in the mixture is too small or too large), the heat released from combustion will be significantly reduced, and the temperature level in the combustion zone will therefore be lower. ^[1]