Introducing Decay to FDS

[MahmoudZew]

Hello, I know that I can customize my HRR curve and include a decay phase. My question is whether FDS is validated and capable of handling the decay phase. I recall one of my professors mentioning that “FDS can’t handle the decay phase of the HRR,” but I’m not sure if that statement is actually correct.

I’m not entirely certain, so I wanted to confirm this with you.

Regards,
Mahmoud

[mcgratta]

That is a very broad statement. It depends on the scenario. Suppression? Oxygen-limitations? Sprinklers? All these things matter. What specifically are you interested in?

[MahmoudZew]

My interest is specifically in tenability analysis, not fire suppression or sprinkler interaction.

The intent is to prescribe a realistic HRR curve that includes a decay phase and evaluate tenability conditions (temperature, FED, visibility, etc.) during that period.

So the core question is whether prescribing the decay phase via a custom HRR (from PyroSim) is considered an acceptable and valid approach for this purpose, without relying on FDS submodels (such as sprinklers, oxygen-limited burning, or suppression) to drive the decay automatically.

In other words, I’m not trying to model the physical mechanism that causes the decay, but rather to assess tenability given a specified HRR curve that includes decay. Any guidance on the limitations or validation considerations of this approach would be appreciated.

[drjfloyd]

There are a couple of components here:

1. If you give FDS an HRRPUA and a RAMP_Q, will FDS folow that ramp? The answer here is yes. FDS will give you the prescribed heat release rate you ask for (assuming there is enough oxygen to burn the fuel).
2. This using an HRRPUA and a RAMP_Q appropriate for your specific usage of FDS. That is question you need to decide, potentially in conjunction with any stakeholders or authorities having jurisdiction.