Reopening Public Facilities After a Biological Attack A Decision Making Framework (2005) / Chapter Skim
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7 Factors Influencing Exposure to Harmful Biological Agents in Indoor Environments
7 Factors Influencing Exposure to Harmful Biological Agents in Indoor Environments
Pages 89-104
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From page 89... ...
Mechanical airhandling systems in many buildings use fans to create pressure gradients that move air through ducts, plenums, and exhaust shafts. The pressure gradients, the buoyancy of heated air, and wind flow around a structure allow for the infiltration or exfiltration of air, which provides conditioned air to the occupied areas or 89
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From page 90... ...
. Several factors determine exposure to biological and chemical agents released indoors, including the dynamic movement of agents throughout indoor enviromments.
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From page 91... ...
efficiency of the wipe method for that contaminant and surface material, Continuing with the example, the area of an adult palm is 150 cm2 and the removal efficiency is estimated at 10%. The removal efficiency varies with the properties of the surface, the contaminant, and the skin and with pressure applied to the surface.
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From page 92... ...
Compliance with the regulatory requirements of the Comprehensive Environmental Reponse, Compensation and Liability Act (the Superfund law) , the Clean Air Act Amendments, and the Federal Insecticide, Fungicide, and Rodenticide Act have led to the development of models that predict the near-field concentrations, surface deposition, and uptake of potentially hazardous matenals.
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From page 93... ...
BUILDING DESIGN AND OPERATIONS When people are exposed to a biological agent indoors, the exposure depends not only on the amount of agent released, which determines the strength of the source, but on how air moves through the building, the rate of exchange between indoor and outdoor air, and the rate at which the agent is removed from indoor air by air filters or surface deposition. The exchange of indoor with outdoor air is referred to as ventilation.
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From page 94... ...
Cleaning or removal might occur because of an active air-cleaning device, because of the naturally occumug deposition of particles onto surfaces, or because of a gradual loss of viability. Although this section of the report describes air-handling systems to illustrate air transport, transport by attachment to clothing for later transfer to other surfaces and possible resuspension is germane to assessing the full extent of biological contamination.
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From page 95... ...
For example, most HVAC systems have air-cleaning filters that typically remove large particles but those are less efficient for particles smaller than I gm. IIEATING, VENTILATING, AND AIR CONDITIONING SYSTEMS In modern public and commercial buildings, which often have sealed windows, some ventilation with outside air is required to provide a safe, fimchonal, and comfortable environment for occupants.
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From page 96... ...
Those relationships, defined as mass balance, imply that concentrations of a biological or chemical agent m a space will increase with the amount released, decrease by the amount of air exchanged in the space (presurnmg the ventilatmg air is cleaner) , and decrease as a result of air cleaning and other removal or deactivation processes.
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From page 97... ...
RESUSPENSION Resuspension and subsequent cleanup of biological and chemical agents deposited on surfaces are of pnmaTy concern for this report. The 2001 anthtax illnesses resulted from direct airborne exposures and from secondary exposure routes.
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From page 98... ...
measured indoor and outdoor particle concentrations in six size ranges for a detailed set of measurements in a single home where a family of four went about normal activities. The researchers used the mass balance method to estimate the amount resuspended indoors, Ferro and colleagues (2004)
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From page 99... ...
PREPARING AND OPERATING BUILDINGS FOR A BIOTERRORISM ATTACK AND SUBSEQUENT OPERATION Although HVAC systems are primarily designed for general ventilation, they can be considered part of the control strategy that might be adopted in the event of an act of bioterrorism. The proper use of HVAC systems for those cases will require a detailed understanding of the infectious or toxicological properties of biological agents, air distribution patterns, air-cleaning or extraction techmques, and the requirements for ongoing operation and maintenance (Ludwig, 2001)
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From page 100... ...
It might not be possible to determine, as it was for the Hart Senate Office Building and NBC, that the agent was distributed indoors. Attacks could involve external releases or introduction of the contaminant into garages, elevator shafts, loading docks, or air intakes.
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From page 101... ...
and are summarized in Box 7-1. 101 FINDINGS AND RECOMMENDATIONS Finding 7-1 Biological agents can spread beyond their point of initial release in air-handling systems, through the reaerosolization of contammants from floors and other sur
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From page 102... ...
I nal runs of emergency shutdown may have unintended consequences creating business disruptions HVAC controls might be restructured to pemmit easy access to quick shutoff switches. · Secure mechanical rooms and outdoor air intakes Relocation of air intakes may be necessary if access can not be restricted or monitored with surveillance cameras and/or alamms.
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From page 103... ...
2004. Source strengths for unmoor human activities that resuspend particulate matter Envimmmental Science and Technology 38(6)
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From page 104... ...
Indoor particulate matter of outdoor origin: importance of size dependent removal mechmisms. Envirommental Science Techmology 36(2)
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