Wind tunnel measurements of the resuspension of ideal particles

This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10 10 to 10 11 viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10 ؊3 and 10 ؊5 per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.The threat from a bioweapon agent such as anthrax remains problematic. Because of the biological, technical, and pathological characteristics of Bacillus anthracis, it is attractive as a bioweapon (2, 10). When used as a weapon of mass destruction, the agent is dispersed in particles less than 5 m in diameter, a size that allows penetration into the pulmonary alveoli (18). Minimal data on human infective doses for inhalational Bacillus anthracis are available (14,24,25). The problem is further compounded by variations in individual susceptibility, B. anthracis strain virulence and spore preparation technique, and physical characteristics of the bioparticle. Thus, studying the fate and transport of fluidized spore concentrations is necessary in order to better predict the area of contamination and to more accurately model potential health risk.Ventilation systems provide a conduit to contaminate a building and the surrounding area. Such systems can become entry points or distribution systems for hazardous contaminants, including biological weapon agents (BWA) (15). Air circulation in ordinary buildings can assist the spread of airborne disease and can disperse contaminants (11,22). Reaerosolization of these hazardous bioparticles deposited onto surfaces can be a continuing source of contamination. For example, a study of reaerosolization of B. anthracis after dispersal in a postal facility found that a mail sorter remained contaminated many days after processing B. anthracis-contaminated letters ...

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“…on May 10, 2018 by guest http://aem.asm.org/ they are closer to agreement with previous work involving smoother surfaces (6,26).…”

Section: Discussionsupporting

confidence: 92%

Reaerosolization of Fluidized Spores in Ventilation Systems

Krauter

Biermann

2007

Appl Environ Microbiol

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“…Shao et al (1993) demonstrated that impacts by saltating particles, as opposed to direct aerodynamic resuspension, are the primary mechanism of resuspension for smaller particles from outdoor sand and dust. Additionally, Fairchild and Tillery (1982) found the resuspension flux of <10 μm aluminum spheres to increase by factors of 1.33 and 2.3 when 100 and 200 μm saltating particles, respectively, were injected in the upstream airflow. Lastly, resuspension may occur due to the fragmenting of saltating particle aggregates, that is, the breaking apart of the aggregate into smaller fragments as the aggregate impacts the surface (Kok et al 2012).…”

Section: Saltationmentioning

confidence: 99%

Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment

Boor

Siegel

Novoselac

2013

Aerosol Science and Technology

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Particle deposits on indoor surfaces can be as complex and diverse as the indoor environments in which they exist. Dust loading can range over several orders of magnitude, suggesting the existence of different types of particle deposits. These deposits can be broadly classified as either a monolayer, in which particles are sparsely deposited on a surface, or a multilayer, in which particles are deposited on top of one another and there is particle-toparticle adhesion and interaction. Particles within these diverse structures of settled indoor dust can become airborne through a process known as resuspension, which can occur due to airflow in ventilation ducts or human activity indoors. The dust loading and deposit structure on an indoor surface may have important implications for resuspension in the indoor environment. This literature review provides a summary of dust loads found on indoor surfaces in field studies and classifies each dust load as either a monolayer or multilayer particle deposit. The article highlights the unique attributes associated with resuspension from both types of particle deposits by summarizing key findings of the experimental resuspension literature. The fundamental differences in the resuspension process between monolayer and multilayer deposits suggest that resuspension may vary considerably among the broad spectrum of dust loads found on indoor surfaces.

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“…Since sandy particles defi nitely fall in a size range which is much larger than PM 10 , emission of fi ne particles was believed to come from disaggregation of soil containing silt and/or clay caused by the impact of large sandy grains having high kinetic energy (Shao et al, 1996). This is in agreement with some evidences (Gillette, 1977;Gillette and Walker, 1977;Shao et al, 1993;Alfaro and Rajot, 2002) indicating that sandblasting is two to seven times more effi cient in generating fi ne suspended particles than purely aerodynamic forces (Fairchild and Tillery, 1982).…”

Section: Introductionmentioning

confidence: 58%

Evaluation of a wind erosion model in a desert area of northern Asia by eddy covariance

Fratini

Santini

Ciccioli

et al. 2009

Earth Surf Processes Landf

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For the fi rst time, vertical fl uxes of mineral dust measured by Eddy Covariance in two desert sites of Northern Asia have been used to test the performances of a wind erosion model in the fi eld. Soil parameters required by the model were obtained through fi eld and laboratory determinations. Model predictions and direct measurements have been compared. The main fi nding was that the direction of the horizontal wind relative to the orientation of nebkhas played a crucial role in determining the emission of particles in one of the investigated sites. Being unable to simulate such interaction, the model generally overestimated the actual emission. It provided, instead, reliable predictions (r 2 = 0·87) when the wind direction was suitable in detaching loose erodible elements placed on nebkhas thanks to their normal orientation.

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Wind tunnel measurements of the resuspension of ideal particles

Cited by 47 publications

References 9 publications

Reaerosolization of Fluidized Spores in Ventilation Systems

Reaerosolization of Fluidized Spores in Ventilation Systems

Monolayer and Multilayer Particle Deposits on Hard Surfaces: Literature Review and Implications for Particle Resuspension in the Indoor Environment

Evaluation of a wind erosion model in a desert area of northern Asia by eddy covariance

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