Predicting Smoke Concentration in the Ceiling Jet.
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.
Website: http://www.ntis.gov
Order number: PB2001-104052
Keywords:
ceiling jets; smoke
Abstract:
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.
