Effectiveness of Urban Shelter-in-Place. III: Commercial Districts Page: 3 of 32
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28 December 2007; revised 25 March 2008
Time-scale parameters, such as the release duration and the building air-exchange rate, also
significantly influence SIP effectiveness. For chemicals that sorb quickly to indoor surfaces, we
found that timely termination of SIP is not very important for reducing casualties, and timely
initiation of SIP is only moderately important. However, for nonsorbing chemicals with a linear
dose-response relationship, it is essential for the community to implement SIP without time delay
and to exit from shelter when it first becomes safe to do so.
In the present paper, a hypothetical toxic gas release is simulated in the downtown area of
a city. The SIP effectiveness of commercial buildings is evaluated in terms of the casualty
reduction factor (CRF) and the safety factor multiplier (SFM) (Chan et al., 2007a and 2007b).
This assessment differs from our previous work on SIP in houses, because differences in
building scale, in the leakiness of the building envelope (Sherman and Chan, 2006), and in
ventilation system design and operation, can cause the SIP effectiveness of commercial buildings
to differ from that of houses.
2 Air Infiltration and Ventilation in Commercial Buildings
2.1 Air Leakage Measurements
A pressurization test is a common technique for measuring air leakage of buildings
(McWilliams, 2002). An external airflow Q (m3 s-1) is supplied to establish a pressure difference
of AP (Pa) in the building with respect to outdoors. Leaky buildings require a higher airflow than
tight buildings to sustain a given pressure difference. The relationship between the measured
parameters and the air-leakage characteristics of the building is typically represented as follows:
Q = C -A -P" (1)
where the air-leakage coefficient, C (m s Pa-"), and the flow exponent, n (-), are estimated by
means of a curve fit to the pressurization test data. The parameter A (m2) is the surface area of
the building envelope, often defined as the total surface area of the exterior vertical walls and
Submitted to Building Simulation
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Chan, Wanyu R.; Chan, Wanyu R.; Nazaroff, William W.; Price, Phillip N. & Gadgil, Ashok J. Effectiveness of Urban Shelter-in-Place. III: Commercial Districts, article, December 28, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc901807/m1/3/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.