Decontamination of Bioaerosols Within Engineering Tolerances of Aircraft Materials

Details

• Personal Author:
  Frazey JS
• Description:
  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 degrees 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 (106 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. 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 (106 spores per coupon), low direction inoculation (104 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. Five different test conditions of temperature and humidity (ranging from an upper limit combination of 180 degrees F and 90% relative humidity [RH] to a lower limit of 160 degrees F and 70% RH) were evaluated over 24 hour increments with an upper time limit of 120 hours. Decontamination tests showed that the high concentrations of spores were all inactivated within 24 hours at 180 degrees F with 90% RH and partially inactivated at 170 degrees F with 80% RH. Tests using low direct inoculations showed complete kills at 48 hours when treatment was 180 degrees F with 90% RH and at 96 hours when treatment was 170 degrees F with 80% RH. All spores deposited by aerosols were inactivated within the 120 hour time period. A stepwise regression was performed to determine which variables are significant to predict the inactivation rates (aplha = 0.05 was used to keep or discard terms). For this regression, there were three variables required to be in each model.time, temperature, and humidity. The data for the stepwise regression retained more variables for high direct inoculation (10 predictors) than low (8 predictors) or aerosol deposition (5). The only variable retained by all three models, besides the mandatory variables, was Temp2*Time2. For both of the direct inoculation methods, several of the same variables were retained, which included Temp*Humidity, Temp*Time, Humidity2, and Temp2*Time2. These variables were then used to complete a final regression model to determine inactivation rates. The final regression models had R2 values for high and low inoculation methods of 76.4% and 71.5%, respectively. The R2 for the aerosol deposition model was not as strong, being only 38.5%. The ideal humidity and temperature range is clearly the highest levels that can be delivered, reasonably maintained, and within proper engineering specifications. If 90% humidity cannot be easily generated or maintained throughout the body of an aircraft, the results show that 80% at the proper temperature (170 degrees F or higher) can be effective as well. 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 degrees 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 degrees F with 90% RH and 170 degrees F with 80% RH. Additionally, all spores were inactivated at 120 hours 160 degrees F with 90% RH. Aerosol deposited spores were inactivated within 48 hours for all five test conditions, except for treatment with 160 degrees 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 (alpha = 0.05 was used to keep or discard terms). For this regression, there were three variables required to be in each model-time, temperature, and humidity. The stepwise regression resulted in approximately the same number of terms being retained in the models with high, low, and aerosol deposition have 7, 6, and 8 terms, respectively. Besides the mandatory variables (time, temperature, and humidity), there were no variables retained in all three models. The statistical analysis does indicate humidity is a critical factor, as nearly all variables retained in these models contain humidity-each model only has one variable that does not contain humidity. The R2 values are reasonable for these models, with the values being 76.6%, 68.8%, and 77.8%, for high and low direct inoculation and aerosol deposition, respectively. Thus most of the variability for the spore inactivation is explained by the models. Data from Chapters 3 and 4 were compared to determine if there were significant differences in the inactivation rates between aluminum and plastic. The slopes for inactivation plots were compared for plastic and aluminum coupons for each test condition. For high direction inoculation, there was a significant difference for test condition 5 (170 degrees F with 80% RH) and test condition 7 (160 degrees F with 90% RH). For low direct inoculation there was only one test condition that was significantly different-test condition 7 (160 degrees F with 90% RH). A tobit analysis showed the plastic coupon inactivation rates were significantly different, indication a faster inactivation for plastic coupons at test condition 3 (180 degrees F with 70% RH), 5 (170 degrees F with 80% RH), and 7 (160 degrees F with 90% RH). This shows that only 6 of the 15 test conditions were significantly different for plastic versus aluminum coupons. All of the 6 tests that were significantly different showed the plastic coupons were inactivated with less time, thus demonstrating that if the spores are inactivated on aluminum coupons, they will likely be inactivated on plastic coupons as well Taken together, these three studies demonstrate that high heat and humidity can safely and effectively decontaminate aircraft materials at the proper time intervals. Furthermore, it appears that plastic coupons can be decontaminated at a faster rate for some of the temperature and humidity ranges. Finally, the spores that were deposited by aerosol were decontaminated more effectively than the spores inoculated directly. [Description provided by NIOSH]
• Subjects:
  Aerosols Hot Temperature Humidity Occupational Health Safety Temperature
• Keywords:
  Aerosol Dispensers Aircraft Parts And Auxiliary Equipment Anthrax Bacteria Bioaerosols Biological Agents Decontamination Heat Temperature Effects Tolerance Threshold
• Publisher:
  Colorado State University
• Document Type:
  Text
• Funding:
  Cooperative Agreement
• Genre:
  Dissertation
• Place as Subject:
  Colorado ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-324
• NIOSHTIC Number:
  nn:20052275
• Citation:
  Fort Collins, CO: Colorado State University, 2012 Fall; :1-324
• Federal Fiscal Year:
  2012
• NORA Priority Area:
  Agriculture, Forestry and Fishing
• Performing Organization:
  Colorado State University - Ft. Collins
• Peer Reviewed:
  False
• Start Date:
  20030915
• Source Full Name:
  Decontamination of bioaerosols within engineering tolerances of aircraft materials
• End Date:
  20270914
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:94c073d38d14b436963cd9c366fdbe85c533b86acbc6df9007018f3a57ea4fab34996874c67c264b5012abaa43acf7a4e7de539d8940fcc6cd1eb3ddabab6d05
• Download URL:
  https://stacks.cdc.gov/view/cdc/211829/cdc_211829_DS1.pdf
• File Type:
  [PDF - 4.20 MB ]