Hi. The table was referenced from the user guide for cfast.

What is the Table number? I cannot find it in the latest CFAST User's Guide.

Hi. I believe it's in page 24 of version 6 user guide (see photo 1 below).

Reason for referring to V6 and not V7 is that because this table is not found in V7. However a similar query was brought up in Apr, and it appears that these values are still applicable for V7 (see photo 2 below).

Screenshot_20250815_230530_Chrome

Screenshot_20250815_230700_Chrome

I thought W/H < 0.2 meant a shaft like geometry where the issue is the plume fills the plan area and can no longer be considered an unbounded, axisymmetric plume.

Hi. Thanks for your clarification that length and width are the same, with length being the longer side. However, I would still like to understand, is it a necessity to adhere to all 3 ratios when modelling the corridor. Because it doesn't seem like it's possible.
Also, when I was referring to the validation model for ATF corridor, it doesn't seem like the aspect ratio were followed either.
Hence I am a little confused on what these ratios are meant for.

Once again, thank you in advance for your help.

I thought W/H < 0.2 meant a shaft like geometry where the issue is the plume fills the plan area and can no longer be considered an unbounded, axisymmetric plume.

Hi Dr Flyod, does this mean that there is no issue for not complying with the aspect ratio. Since the corridor is 3.6m high, with a width of 2.2m, the W/H being 0.61 (> 0.2) does not fall into the corridor/shaft algorithim. However there shouldn't be any concern as I'm simulating for a corridor flow, and not a shaft flow.

And if you don't mind, what about the L/H ratio as well. As the calculated ratio is 4.17 (< 6.0).

Thank you.

I cannot make the decision on the appropriateness of CFAST as a tool for your specific intended use. That is a decision you need to make as the modeler based on your understanding of how CFAST operates given the specific details of your use. L/H of 4 would, per the table you show, put you in the special consideration category ( 3 < L/H < 5).

CFAST is a zone model. It assumes that a room can be represented by two uniform layers that are coupled by an axisymmetric, unbounded plume.

If a room is very tall compared to its plan area (a shaft), then the plume can expand and fill the cross sectional area at which point you no longer have an unbounded plume.

If the aspect ratio of a room's plan area is very large (a corridor) then you will have the case where the time for the ceiling jet to reach the walls across the short distance is very different from the long distance. This impacts the assumption of a uniform upper layer and impacts calculations of ceiling jet times for things like detection and sprinkler operation.