# Calculating vulnerability zone distances for EHSs in solutions

When calculating vulnerability zone distances, how would the quantity released (QR) be handled for an extremely hazardous substance (EHS) in solution?

If the EHS is in solution, a facility can make a rough estimate of the QR using equation (1) on page G-2 of the "Technical Guidance for Hazards Analysis." If the facility has information on the physical properties of the EHS in solution, this data can be input into equation (1) to get the QR of the EHS.

(60 sec/min x MW x K x A x VP x 929cm2/ft2)

Equation (1) QR = ----------------------------------------------------------------------

R x (T1+273)x (760 mm Hg/atm) x 454 g/lb

Where:

QR = Rate of release to air (lbs/min);

MW = Molecular weight (g/g mole);

K = Gas phase mass transfer coefficient (cm/sec);

A = Surface area of spilled material (ft2);

VP = Vapor pressure of material at temperature T1 mm HG);

R = 82.05 atm cm3/g mole K; and

T1 = Temperature at which the chemical is stored ( C).

If physical properties of the EHS in solution are not available, the QR can be estimated using the physical properties of the EHS. This would reflect the QR of the EHS in its pure form. Since the EHS is in solution, the QR would need to be multiplied by the mole fraction of the EHS in solution to accurately reflect the QR of the EHS. If the facility only has the weight fraction of the EHS solution, the weight fraction can be used instead of the mole fraction to estimate the QR of the EHS.

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- Topic #: 23002-14405
- Date Created: 7/17/2009
- Last Modified Since: 4/10/2014
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