Decontamination of Bioaerosols within Engineering Tolerances of Aircraft Materials

Abstract

DECONTAMINATION OF BIOAEROSOLS WITHIN ENGINEERING TOLERANCES OF AIRCRAFT MATERIALSBacillus 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 iii on the data and showed that 2 of the 4 tests displayed a lognormal distribution, while the other 2 tests were inconclusive. All data was therefore treated as a lognormal distribution. Contour plots were then constructed to determine if a discernible pattern was present. While these contour plots showed a somewhat even dispersion, there were no discernible patterns.Additionally, the plots showed a wide range of spore deposition throughout the four tests.Finally, the equations derived for spore deposition were validated. The data showed that 8.67%up to 31.0% (average of 20.25%) of the spores modeled could actually deposit and be recovered through culture methods. These losses could have occurred during the nebulization through inactivation or clumping after the spores were aerosolized. Regardless, this showed that the equations could be used after accounting for these losses. 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 (10 6 spores per c...