The reference to "exponential growth" is mathematical representation of how the fire grows in size (HRR) with time. Q = (alpha)*(time)^2 This assumes that the fire grows exponentially when time > 0.

The point of this section in 921 is two-fold. The first point is that there can be an incipient stage of HRR that may not be exponential in nature due to the characteristics of the materials or environment. This incipient stage is characterized as producing a relatively low HRR over some significant time. The duration of this "stage" does not have a bearing on the the magnitude of the peak HRR, but will have a bearing on when the peak HRR will occur.

The second point is that when the exponential growth rate is initiated, these four fire grow rates have a similar exponential term of 2 and a similar growth rate constant (alpha).

I am not sure if I have fully answered your inquiry.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
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