Vapour cloud explosion blasts - TNT method

Yield factor:
Mass of fuel involved:		kg
Distance from the explosion center:	m

Equivalent mass of TNT:	kg
Scaled distance:	m/kg1/3
Peak side-on overpressure:	kPa

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For typical hydrocarbons, such as methane, propane, butane etc., the heat of combustion is 10 times higher than the heat of reaction of TNT. The relation between the mass of hydrocarbons W_HC and the equivalent TNT charge W_TNT is then

W_TNT ≈ 10 ⋅ η ⋅ W_HC

where η is a yield factor (η = 3%-5%), based on experience, see Gugan, 1978.

In order to take the geometrical effects into account in the TNT equivalence method, Harris and Wickens (1989) proposed to use a yield factor of 20% (η=0.2) and the mass of hydrocarbon, W_HC, contained in Stoichiometric proportions in any severely congested region of the plant.

The data can be scaled through a normalised length scale (Hopkinson scaling) R*

R* = R/W^1/3

where R [m] is the distance from the centre of the explosive source and W [kg] is the mass of the explosive source.

Reference: Bjerketvedt, D., Bakke, J.R. and Wingerden, K. van (1993)"Gas explosion handbook" Version1.2