FLD and FIC units

[Matthew Bilson]

Hi 

It appears there is a unit conversion issue when I run irritant species with SPEC input lines like the following:

 

&SPEC ID = 'HYDROGEN CHLORIDE', LUMPED_COMPONENT_ONLY = .TRUE., FLD_LETHAL_DOSE = 114000.0,FIC_CONCENTRATION = 900.0 /

&SPEC ID = 'SULFUR DIOXIDE', LUMPED_COMPONENT_ONLY = .TRUE., FLD_LETHAL_DOSE = 12000.0, FIC_CONCENTRATION = 120.0 /

&SPEC ID = 'ACROLEIN', LUMPED_COMPONENT_ONLY = .TRUE., FLD_LETHAL_DOSE = 4500.0, FIC_CONCENTRATION = 20.0 /

&SPEC ID = 'FORMALDEHYDE', LUMPED_COMPONENT_ONLY = .TRUE., FLD_LETHAL_DOSE = 22500.0, FIC_CONCENTRATION = 30.0 /

 

The inclusion of the FLD and FIC values should be in ppm according to the User Guide (17.10.11), but when looking at SLCF or DEVC file results, the FIC expected is out by 10^6 (too low).  The same thing is likely happening with the FLD.

 

When running with the FLD and FIC removed, there is no problem:

 

&SPEC ID = 'HYDROGEN CHLORIDE', LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'SULFUR DIOXIDE', LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'ACROLEIN', LUMPED_COMPONENT_ONLY = .TRUE. /

&SPEC ID = 'FORMALDEHYDE', LUMPED_COMPONENT_ONLY = .TRUE. /

 

We tested this on one of the verification models - file attached, with concentrations specified to verify the result.

 

It is an easy enough fix – just don’t specify these quantities and let FDS use the defaults, but the User Guide does not say this.  I was surprised that specifying these caused such an effect (i.e. it looks like FDS works in volume fraction and when an FLD or FIC is specified in ppm - for a pre-defined species per Section 17.10.11 in the User Guide - the result is that the FLC or FIC is 10^6 too small).

Regards

Matt

[Randy McDermott]

Matt,

Thanks for reporting.  We'll take a look.  Please follow Issue here:

https://github.com/firemodels/fds/issues/6416

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[Randy McDermott]

Thanks for the report.  Should be fixed with next release.

[Matthew Bilson]

Great, thank you

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