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Hi, I am new to CFAST so apologies if I am missing something obvious here. |
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The HRR does not instantly go to zero as the oxygen mole fraction drops below 15 %. There is a gradual decrease, according to this description in the CFAST Technical Reference Guide 
In your case, I increased the run time to 1800 s and deleted the HRR ramp lines that decreased the HRR to zero. That is, the fire ramps up to 26 MW and remains constant, at least assuming it has enough oxygen. In the simulation, the HRR drops to about 20 MW and the oxygen drops to about 13.6 %. This state remains indefinitely as there is enough air entrained through the doors to sustain the fire, albeit at a slightly lower HRR. Check if the description in the Tech Guide is consistent with your observations. |
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That makes sense and reflects what I've seen for other simulations - much appreciated thank you Kevin |
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The HRR does not instantly go to zero as the oxygen mole fraction drops below 15 %. There is a gradual decrease, according to this description in the CFAST Technical Reference Guide
In your case, I increased the run time to 1800 s and deleted the HRR ramp lines that decreased the HRR to zero. That is, the fire ramps up to 26 MW and remains constant, at least assuming it has enough oxygen. In the simulation, the HRR drops to about 20 MW and the oxygen drops to about 13.6 %. This state remains indefinitely as there is enough air entrained through the doors to sustain the fire, albeit at a slightly lower HRR. Check if the description in the Tech Guide is consistent with your observations.