CFAST for inert environment

[Vera-MVD]

Hi!

I am new to CFAST community, have been going through all the manuals and examples to figure out if it could be useful for what I am trying to model. The task is to model a compartment filled with an inert gas (ambient condition on the outside). At some point there is a breach in the wall of the compartment. Due to buoyancy and pressure oxygen starts to ingress through the breach. When the oxygen level in the compartment reaches a certain point, a fire inside the compartment starts. I do have characteristics of the environment inside and outside the compartment, and for the fire as well, but I am puzzled on how to set the initial inert environment and for the fire starting on the oxygen level inside the compartment. I feel like CFAST is capable of modeling this, but maybe I am wrong. Is this something that CFAST can handle or am I asking too much from it?

Any advise would be highly appreciated while I continue going through the old discussions in here to see if this have maybe already been discussed at some point, nothing so far.

Almost forgot, the version I am using is CFAST v 7.7.5 that comes with SMV6 GUI.

Thanks,
Vera

[drjfloyd]

This does not sound like a problem where CFAST is the appropriate tool.

[Vera-MVD]

Thank you for your response. TBH, I was both expected and dreaded that would be the case. You know the feeling when it is all there in front of you and looks like with a few modifications it all going to work, but you are struggling to make the right changes to get there? That's how I am feeling. But yes, I understand CFAST was not designed for this. Thank you again!

[mcgratta]

I don't know if CFAST would allow a breach. The geometry is fixed from the start.

[Vera-MVD]

Oh, I can work with a breach present at time zero as long as the inert environment is set inside the compartment at that time. I just need to see how fast the oxygen level rises depending on the size of the breach and the inside/outside condition and the fire progression after it starts. Thank you!

[mcgratta]

Others might know better, but I am not sure one can set an initial environment inside that is different than outside. This would start the simulation off with a non-sensical discontinuity at the boundary between zones. I think the CFAST solver would choke on that.

[Vera-MVD]

Well, I cannot even get to that point to see if CFAST would choke on that.

I got a false hope from chatGPT (guilty of going that route, to my defense I only went there after going through the user manuals, examples, and youtube videos of CFAST). AI's answer was "Sure, it is possible", but needless to say none of it's solutions actually worked.

Thank you!

[mcgratta]

Think of us as ChatBots that don't pander or patronize. We give it to you straight.

[Vera-MVD]

I'd much rather hear that than false hope statements. I appreciate all the responses I've gotten here today!

[mcgratta]

You're welcome, and you're still Amazing!!

[Vera-MVD]

Thank you!

[Vera-MVD]

Before I completely give up the idea of using CFAST for my task, I want to ask: can the Nitrogen and Oxygen mass fraction of the initial environment be changed by a user from their look-like-preset values of 77% and 23% respectively (from CFAST Technical Reference Guide (p.10)) ? I understand that I cannot do it from within the GUI itself, but is it possible to make the changes manually in the code? Would all the code's calculations and results be valid still after that or they are all based on that 77/23 ratio?

Thank you in advance for any input on this,
Vera

[drjfloyd]

You would have to edit the source code and compile your own version of CFAST.

[Vera-MVD]

Thank you for your response. Oh, so it is possible? Is cfast.f90 in the Code tab, updated 2 yrs ago the right source code file?

[drjfloyd]

You will need to carefully review the source code so you understand which variable(s) or type structure(s) need to be modified.

[Vera-MVD]

I understand. For this particular task I would have to step down and let someone else to do the changes to the source code. To work with the GUI is one thing, but messing with the source code manually is a completely different level, which unfortunately I am not at. Thank you, I appreciate your responses!

[gforney]

try cfast posted here.
https://github.com/firemodels/test_bundles/releases/tag/CFAST_TEST
To define initial O2 concentration for all interior rooms use INTERIOR_O2_CONC on the &INIT line - default is 0.23 kg/kg. Likewise, to define O2 concentration for the outside use EXTERIOR_O2_CONC on the &INIT line. Nitrogen concentration is set to 1 - O2 concentration. Concentrations must be between 0.0 and 1.0.

The following defined interior O2 concentrations to 0.1 kg/kg and exterior O2 concentration to 0.2 kg/kg
&INIT INTERIOR_O2_CONC=0.1, EXTERIOR_O2_CON=0.2 /

[Vera-MVD]

Thank you so much for your response! I will be testing it today. If I may ask, what software do I have to have on my computer to be able to recompile the code if I make any further changes to it? I'm contacting my IT group today, so I could ask them to install it for me.

[mcgratta]

A Fortran compiler. We use the Intel oneAPI Fortran compiler. It is free, but requires some IT know-how to install and use. These instructions are a bit out of date, but will get you started.

[Vera-MVD]

Thank you!