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Predicting Smoke Concentration in the Ceiling Jet.

pdf icon Predicting Smoke Concentration in the Ceiling Jet. (836 K)
Davis, W. D.; Reneke, P. A.

NISTIR 6480; 13 p. May 2000.

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900.
Order number: PB2001-104052


ceiling jets; smoke


Predicting smoke detector response to a growing fire requires calculating the time dependent evolution of the smoke concentration in the ceiling jet. Typically, the temperature rather than the smoke concentration has been used to predict smoke detector response due to the availability of correlations which give ceiling jet temperature and the assumption that the smoke concentration can be related to ceiling jet temperature. Using temperature to predict smoke detector activation ignores differences in the production of smoke by burning materials that may completely invalidate a temperature/smoke prediction correlation. There have been efforts to use computational fluid dynamic (CFD) methods to calculate the smoke concentration in the ceiling jet and with the increased computer power available today, these methods are becoming practica1. However, there is still a need for an algebraic correlation that would yield smoke concentration in the ceiling jet and not need substantial computer power to obtain the solution. Early work along this line can be found in Alpert's paper on the ceiling jet which resulted in the successful unconfined ceiling jet temperature and velocity correlations in use today. Later, Yamauchi's extended Alpert's work to calculate the smoke concentration and smoke detector activation in the ceiling jet when a hot layer was developing. Yamauchi's method required the solution of a set of differential equations in order to define the ceiling jet properties as well as a zone model to define the depth and temperature of the hot layer. In this paper, an algebraic correlation for smoke concentration in the ceiling jet will be developed. The analysis will be restricted to fires that produce turbulent plumes and can be represented by axisyrnmetric point sources. Once the smoke concentration is predicted, the activation times for smoke detectors can be calculated using a model for smoke detector activation.