Update of NFPA 502 Critical Velocity Calculator for 2020
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
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