Decontamination of bioaerosols within engineering tolerances of aircraft materials

Bacillus anthracis spores are generally considered the most difficult biological agents to decontaminate or inactivate. Inactivation of these spores is further complicated on aircraft because engineering specifications do not allow for chemical disinfectants to be used. Aircraft, however, must meet strict engineering specifications, requiring extended storage at temperatures greater than 185° F at 100% relative humidity (RH). Heat and humidity near these levels have been tested to determine if they can inactivate spores; however, these studies have only evaluated spores in high concentrations (10 6 spores) on aluminum coupons. This dissertation research was designed to evaluate the effectiveness of high heat and humidity on Bacillus atrophaeus subsp globigii (BG) spores, a simulant commonly used for Bacillus anthracis, when delivered via three different methods onto two different materials.;In Chapter 2, an innovative bioaerosol deposition chamber design and testing is described. The test chamber was designed to deposit Bacillus atrophaeus subsp globigii (BG) spores onto coupons modeling real aircraft components. Deposition equations were derived to model the spore deposition. Initial deposition tests with fluorescent particles were inconclusive because the limit of quantification could not be reached; therefore, the BG spores were used to test deposition. Initial tests demonstrated the parameters that could be manipulated throughout the experiments to control the spore deposition. After these were evaluated, four final tests were completed to perform more in-depth statistical analysis. The coefficients of variation for these tests were within acceptable ranges (all were 25.5% or less). Ryan-Joiner tests were performed on the data and showed that 2 of the 4 tests displayed a lognormal distribution, while the other 2 tests were inconclusive. The study demonstrated that the test chamber can be used for spore depositions with the caveat that future studies include an appropriate control coupon next to each sample.;In Chapter 3, decontamination of aluminum coupons was evaluated using the BG spores inoculated in three different methods—high direct inoculation (106 spores per coupon), low direction inoculation (10 4 spores per coupon), and an aerosol deposition using the test chamber from Chapter 2 (deposition goal of 104 spores per coupon). Initial tests found the optimal method to remove the spores from coupons was sonication followed by vortexing, which was nearly five times more effective at removing the spores than shaking. Equations, derived to model spore depositions in the aerosol test chamber, were tested and showed that 10% of the spores could be effectively recovered.;The study in Chapter 4 evaluated decontamination rates on plastic coupons, using the same inoculation methods as Chapter 3. Decontamination tests showed that the high concentrations of spores were inactivated within 48 hours at 180°F and 90% RH. No other treatment temperatures or humidity ranges inactivated all spores within the time allotted of 120 hours. Tests using low direct inoculations showed complete kills at 48 hours with a treatment of 180°F with 90% RH and 170°F with 80% RH. Additionally, all spores were inactivated at 120 hours 160 °F with 90% RH. Aerosol deposited spores were inactivated within 48 hours for all five test conditions, except for treatment with 160°F with 70% RH, which still had active spores at the 120 hour point. A stepwise regression was performed to determine which variables are significant to predict the inactivation rates (α = 0.05 was used to keep or discard terms). (Abstract shortened by UMI.).