Scaled Overpressure:
$$p_s = p/p_a $$

$p$	Overpressure (Pa)
$p_a$	Atmospheric Pressure (Pa)

Sachs Scaled Distance:
$$\bar{R} = R /(h_{combustion} \cdot V/p_a)^{1/3} $$

$R$	Radius ($m$)
$h_{combustion}$	Heat of combustion of stoichiometric hydrocarbon-air mixture ($J/m^3$)
$V$	volume of congested area (or in the case of DDT entire flammable cloud volume) ($m^3$)

Tool for calculating TNO overpressure

This tool does the above calculation to determine overpressure based on radius and chosen TNO curve

Volume of Congested Area ($m^3$):
Distance from Explosion center ($m$):

Sachs Scaled Radius ($\bar{R}$): 10

Find the R value on the x axis and find the corresponding $p_s$ value on your chosen TNO curve, and input here.

Scaled Overpressure ($p_s$):

Overpressure at distance: 10psi

References

TNO Yellow Book … etc.