Hi, I am trying to convert CFAST's optical density output to visibility.

Visibility, S
Optical Density, D
Light Extinction Coefficient, K
A non-dimensional constant characteristic of the type of object being viewed through the smoke, C

In a previous thread on the FDS Google Group, Jason clarified that FDS uses K rather than D. See below:
https://groups.google.com/g/fds-smv/c/feHHTKYyJOY

This would imply that S = C/K (Eq. 22.22 from the FDS User Guide) could simply be replaced with S = C/D.

However, the FDS Guide states, "The gas phase output quantity ’EXTINCTION COEFFICIENT’ is K. A similar quantity is the ’OPTICAL DENSITY’, D = K/2.3, the result of using log10 in the definition", i.e. K = 2.3D.

This would imply that S = C/K should be replaced with S = C/2.3D.

Has anyone noticed this, looked into the topic before, or have thoughts on which is correct?

Thanks in advance