Alpert's Ceiling Jet Correlations

Alpert's ceiling jet correlations predict the temperature and velocity of a ceiling jet if the fire size, ceiling height, and radial distance from the fire are known. These correlations are useful for sprinkler and heat detector response applications and apply to steady-state fires without a hot layer (where the effect of walls does not affect the ceiling jet).

Theory

The Alpert correlations are based on experimental data collected for fuels such as wood and plastic pallets, cardboard boxes, plastic products in cardboard boxes, and liquids with heat release rates ranging from 668 kW to 98 MW and ceiling heights ranging from 4.6 to 15.5m. The maximum temperature and velocity of a ceiling jet is given by the following expressions;
Metric: English:
H:
r:
Q':
Tamb:
T:
U:

Instructions

  1. Select Metric or English units.
  2. Enter values for ceiling height, radial distance from the fire, and heat release rate.
  3. Click on the "GO" button.
where:
T - Tamb = 16.9Q'2/3/H5/3 for r/H < 0.18
  • T - ceiling jet gas temperature (oC or F)
    		•
    T - Tamb = 5.38(Q'/r)2/3/H for r/H > 0.18
  • Tamb - ambient temperature (oC or F)
    		•
    U = 0.96(Q'/H)1/3 for r/H < 0.15
  • Q' - heat release rate of fire (kW)
    		•
    U = 0.195Q'1/3H1/2/r5/6 for r/H > 0.15
  • H - ceiling height (m or ft)
    		•
  • r - radial distance from fire (m or ft)
    		•
  • U - ceiling jet gas velocity (m/s or ft/s)
    		•
    Equations used are from The SFPE Handbook of Fire Protection Engineering, 2nd edition, page 2-33.
    Send e-mail to: ierardi@wpi.edu

    Last Modified: Thur 19 Jun 2:35:45 EST

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