Effects of height fire source in CFAST code

[Mubin130]

Dear all,

I would like to share an issue. I used the version 7.7.4 CFAST code.
I noted that the upper and lower temperature are lower when the fire is positioned is higher.
Please find attached an example of scenario.
n°1586.txt

This issue can be seen for all scenario if you do a sensitive assessment on the height of fire.
I hope this issue will able to fix in the next version.

Thanks in advance for your help.
Murat

[Jason Floyd]

You have a 4.5 m tall compartment with 4 air changes per hour of ventilation and a door that is 2.2 m tall. If the fire is at the floor, then it will always see oxygen entering via bi-directional flow through the doorway. If you put the fire high enough up in the compartment, then once the layer grows down to the height of the fire, the fire will no longer see any fresh air entering via the doorway. Check your ouptuts to see if this is what is happening, i.e., are you seeing lower temperatures because the fire has become viatiated and is not releasing as much heat as when it is lower in the compartment.

[Mubin130]

Dear Floyd,
I checked the outputs, you are right, certainly because the oxygen below to the base of fire is not included in the correlations of CFAST and less oxygen is available for the combustion.
So, the results (HRR, temperature...) are lower when the base of the fire is higher.
Regards,
Murat