Vapor Dispersion Calculator

Estimate downwind hazard distance using Gaussian plume dispersion modeling.

Release Rate (lbs/min)

Wind Speed (mph)

Atmospheric Stability

Molecular Weight (g/mol)

Target Concentration (ppm)

Tab to move between fields

Hazard Distance (ft)

640

Hazard Distance (miles)

0.12

Hazard Distance (meters)195

Hazard Zone Area (acres)14.75

Vapor Density (Air=1)1.24

Heavier Than Air1

Travel Time (min)0.7

How to Use This Calculator

Enter the Release Rate (lbs/min) from the incident report or estimate based on container size and breach type.
Input the Wind Speed (mph) from on-site weather monitoring and select the Atmospheric Stability class (1=Very Unstable to 6=Very Stable).
Enter the Molecular Weight (g/mol) for the released chemical — find this on the SDS or in NIOSH/CAMEO databases.
Set the Target Concentration (ppm) to the ERPG-2 or AEGL-2 value for the chemical to define the protective action zone.
Review Hazard Distance (ft) and Hazard Zone Area (acres) to establish protective action zones for evacuation or shelter-in-place.
Check Vapor Density and Heavier Than Air to determine whether the vapor will accumulate in low-lying areas or dissipate upward.

How the result changes with Release Rate (lbs/min)

Release Rate (lbs/min): Rate of chemical release in pounds per minute.
Wind Speed (mph): Sustained wind speed in miles per hour.
Atmospheric Stability: 1=A(Very Unstable), 2=B, 3=C, 4=D(Neutral), 5=E, 6=F(Very Stable).
Molecular Weight (g/mol): Molecular weight of the chemical (e.g., HCl=36, NH3=17, Cl2=71).
Target Concentration (ppm): ERPG-2 or AEGL-2 concentration threshold.

Identify Input Parameters
4 parameters
Release Rate (lbs/min) = 10, Wind Speed (mph) = 10, Atmospheric Stability = 4, Molecular Weight (g/mol) = 36 = 5 input(s) provided
Calculate Hazard Distance
Hazard Distance
640 = 640
Calculate Hazard Distance
Hazard Distance
0.12 = 0.12
Calculate Hazard Distance
Hazard Distance
195 = 195
Calculate Hazard Zone Area
Hazard Zone Area
14.75 = 14.75