Use of a Time Constant for Designing a Smoke Control System in Car Parks

摘要

The fire environment in thirty-six car parks of volumes varying from 2,000 m~3 to 50,000 m~3, ceiling heights of 3 m, 4 m and 5 m are simulated using the fire zone model, CFAST version 2.0 developed at the Building and Fire Research Laboratory, NIST in U.S.A. The concept of using the space volume as a criterion to determine the requirement of smoke extraction system is reviewed. The concept of time constant in an atrium hall is proposed to be used in car parks and underground spaces. The empirical expression fitted by experimental data appearing in NFPA-92B is applied to calculate the time constant. This is then correlated with the smoke filling time for those thirty-six car parks with and without natural horizontal ceiling vents. Design of the smoke extraction system for underground spaces is also studied.