Critical Velocity

This is a subject which is being actively researched and developed within the tunnel ventilation industry. The methodology used in this website is taken from NFPA 502 2017. There is some discussion currently ongoing about how to use new scale model research with the observations from full-scale testing. Therefore, ensure that the project that you are using this information for will regard the NFPA 502 2017 method as applicable.

Source: Standard for Road tunnels, bridges and other limited access highways, NFPA 502, 2017 - Annex D

This function will produce a plot showing how the critical velocity vaires with fire size, convective fraction and gradient