Effectiveness of Urban Shelter-in-Place. II: ResidentialDistricts Page: 3 of 31
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Submitted to Atmospheric Environment
1 Introduction
In the event of a sudden, large-scale release of a toxic chemical into the atmosphere,
nearby populations may be advised to take shelter indoors. Shelter-in-place (SIP) requires simply
being indoors, closing doors and windows, and turning off fans. Broadly, SIP offers protection
through two modes. First, lower peak indoor concentrations compared to outdoor concentrations
are encountered after a short-term release because building envelopes limit indoor-outdoor air
exchange. Second, sheltering may reduce cumulative exposures through one or more
mechanisms, including transformations of toxic chemicals on building surfaces and time-
dependent manipulation of ventilation rates.
The effectiveness of SIP for protecting public health can depend upon many factors.
Attributes of the release, such as the quantity emitted, toxicity of the chemical, release duration,
and atmospheric transport and dispersion, influence the effectiveness of protection. Building
characteristics, including leakiness of the building envelope and the interactions between the
toxic chemicals and building surfaces, also play an important role. Finally, human factors such as
delays in notification and response, and the timing of shelter termination, can impact the
effectiveness of the strategy.
Most prior studies of SIP effectiveness focused on characterizing single residences
(Engelmann, 1992; Siren, 1993). Existing software that assesses indoor concentrations during an
atmospheric release event, such as ALOHA (Areal Locations of Hazardous Atmospheres),
assumes a typical air leakage value for all low-rise buildings (US EPA, 2006). However, studies
of air leakage reveal substantial variability among residential buildings (Chan et al., 2005). This
variability can lead to considerable differences in their ability to protect building occupants
against outdoor releases. Vogt et al. (1999) speculate that residences constructed before 1970
may be more leaky then newer residences, owing to changes in building codes and construction
practices. As a result, older dwellings may be less fit to function as emergency shelters. This
dependency is supported by the detailed analysis presented in Chan et al. (2005).3/31
November 21, 2006
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Chan, Wanyu R.; Nazaroff, William W.; Price, Phillip N. & Gadgil, Ashok J. Effectiveness of Urban Shelter-in-Place. II: ResidentialDistricts, article, December 1, 2006; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc898848/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.