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Update of NFPA 502 Critical Velocity Calculator for 2020

Reading Time: 1 minute

Created with software version: 2020.1

The NFPA 502 Standard for Road Tunnels, Bridges, and Other Limited Access Highways has been updated for 2020 and includes a new Annex D Critical Velocity Calculation. We have updated the Tunnel Critical Velocity Calculator to make this calculation.

A comparison of the 2020 calculation with the 2017 version is shown in Figure 1 below for a tunnel with a height of 5 m, width of 12 m, grade of -4%, ambient temperature 20 C, ambient density 1.1454 kg/m^3, and ambient heat capacity of 1.005 kJ/kg K. The comparison shows the critical velocity including the grade effect for a range of heat release rates from 5000 kW to 30000 kW.

pyro graph critical velocity calculator — Figure 1. Comparison of 2017 and 2020 NFPA 502 tunnel critical velocity calculations.

Check out our other calculators for both PyroSim and Pathfinder.

To download the most recent version of PyroSim, please visit the the PyroSim Support page and click the link for the current release. If you have any questions, please contact support@thunderheadeng.com.

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