Analysis of Aggressive Air Sampling for Bacillus anthracis Indoors
Citation:
Archer, J., S. Lee, D. Hook, AND L. Brixey. Analysis of Aggressive Air Sampling for Bacillus anthracis Indoors. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-20/281, 2020.
Impact/Purpose:
Aggressive air sampling (AAS) has been used as a sampling technique for multiple chemical and biological contaminants, including asbestos, beryllium, and bacterial spores (Bacillus anthracis or surrogates). AAS should be considered a complementary sampling option to traditional surface sampling techniques, but as shown in this study, AAS has several distinct advantages over surface sampling when comparing area of coverage and cost. The advantages and limitations of AAS must be evaluated to determine its effective use following an indoor biological contamination incident. This research will provide data to support adaptation of a sampling method that has been previously used for other contaminants and shed light on its applicability for sampling biological spores in an indoor environment. Responders and decision makers can directly use results from this study for characterization and clearance decisions.
Description:
The primary objectives of this project research effort were to analyze the potential for application of an aggressive air sampling (AAS) technique for measurement of spores resulting from a dissemination of a biological agent, Bacillus anthracis (Ba), in an indoor environment and provide approaches for application. This goal was accomplished first by a review of lessons learned from published studies on the application of aggressive air sampling for asbestos clearance sampling, sampling for biological spores or other particulates, and in the post-remediation sampling of facilities contaminated with Ba. Secondly, a first principles model was developed for aggressive air sampling indoors to reveal the critical parameters that determine the efficacy of its application. This model was then used to examine the recovery efficiencies and costs of aggressive air sampling compared to a standard reference method of microvacuum surface sampling. Finally, optimal conditions for aggressive air sampling indoors were outlined, and gaps in research inhibiting the implementation of the sampling technique for Ba were identified. Lessons learned from asbestos, beryllium, and spore sampling publications included information regarding site preparation, personal protective equipment, supplies required, implementation, and sample analysis. The derived model for aggressive air sampling showed that settling can have a significant impact on sampling efficiency, so design of sampling rate versus enclosed volume is paramount, and sampling should be long enough for three times the enclosed volume of air to be pulled through the sampler (three air exchanges). With careful attention to sampling design, sample collection efficiencies of >90% of particles in the air can be achieved. The main factor impacting sample recovery is the ability of the aggressive air technique to resuspend particles from the surfaces. From a cost perspective, as the area of interest increases to the size of a room or office floor, aggressive air sampling cost becomes comparable and even less than the cost of microvacuum surface sampling, even if the surface sampling incorporates only 1% of the available surface area. Considering the sample recovery and limit of detection, if the room size is greater than 200 square feet (ft2) and the resuspension fraction is greater than 0.1%, aggressive air sampling has an equivalent or better total sample recovery and limit of detection compared to microvacuuming sampling, assuming a uniform dispersal of material in the air. With lessons learned from previous experiments and information gathered from the model and cost analysis, optimal conditions for indoor aggressive air sampling were determined. These conditions include: 1) areas that can be isolated so that particles are not transported out of the area of interest; 2) areas with minimal dust and dirt; 3) areas of sufficient space for a decontamination line; 4) large enough surface area of interest so that contamination would result in detectable material from AAS; and 5) sufficient access to power outlets for all necessary AAS equipment.