Abstract
Remediation and recovery efforts after a release of Bacillus anthracis (anthrax) spores may be difficult and costly. In addition, response and recovery technologies may be focused on critical resources, leaving the small business or homeowner without remediation options. This study evaluates the efficacy of relatively low levels of hydrogen peroxide vapor (HPV) delivered from off‐the‐shelf equipment for the inactivation of Bacillus spores within an indoor environment. Decontamination evaluations were conducted in a house using both Bacillus atrophaeus var. globigii (Bg; as surrogates for B. anthracis ) inoculated on the carpet and galvanized metal as coupons and Geobacillus stearothermophilus (Gs) as biological indicators on steel. The total decontamination time ranged from 4 to 7 days. Using the longer exposure times, low concentrations of HPV (average levels below 20 parts per million) effectively inactivated Bg and Gs spores on the materials tested. The HPV was generated with commercial humidifiers and household‐strength hydrogen peroxide solutions. The presence of home furnishings did not have a significant impact on HPV efficacy. This simple, inexpensive, and effective decontamination method could have significant utility for remediation following a B. anthracis spore release, such as following a terrorist attack.
1. INTRODUCTION
The impact of a Bacillus anthracis release into the environment, the efficacy of low concentration hydrogen peroxide vapor (HPV) in the laboratory, and the applicability of surrogates for B. anthracis were described previously (Wood et al., 2016). Summarizing, numerous structures were intentionally contaminated with B. anthracis (Ames strain) spores through letters processed by the U.S. Postal Service in the fall of 2001. Several decontamination approaches, including HPV, were used on affected structures (Canter, 2005). Typically, HPV has been tested as a sterilant using high concentrations, 250 parts per million by volume (ppmv), 90 minutes (min) for nonporous hard surfaces (U.S. Environmental Protection Agency [US EPA], 2019), specialized equipment, and liquid HP at concentrations over 30%. High HPV concentrations pose an immediate threat to life and health and after aeration may result in off‐gassing of HPV for extended periods from some materials (Baron, Estill, Beard, Hein, & Larsen, 2007; Meyer et al., 2014). In addition, the high HPV concentrations obtained in the laboratory have been difficult to attain in the field (US EPA, 2013). These results led to the laboratory investigation of the sporicidal effects of long‐duration, low‐concentration HPV. Results showed that laboratory experiments conducted with 4 to 7‐day exposures to low levels of HPV (average levels as low as 5 ppm) effectively inactivated B. anthracis spores on several different materials (Wood et al., 2016). This present study extends those laboratory findings to a field‐level evaluation using commercial off‐the‐shelf (COTS) humidifiers and 3% liquid HP.
2. MATERIALS AND METHODS
2.1. Test organisms and inoculation procedures
Dried spores of B. atrophaeus var. globigii (Bg ) were prepared as described previously (Brown et al., 2007). Using an aerosol deposition method (Lee, Ryan, & Snyder, 2011), spores blended with silicon dioxide particles were inoculated onto 18‐millimeter (mm) diameter material surfaces (coupon) resulting in approximately 1 × 107 spores per coupon.
The commercial biological indicators (BIs) used for this study were purchased from Mesa Laboratories Inc. (Lakewood, CO; P/N HMV‐091). Each BI was made of a 9‐mm diameter by 0.2‐mm‐thick stainless steel (Grade 304) disc inoculated with a nominal 1 × 106 Geobacillus stearothermophilus (Gs ) spores and placed in a Tyvek envelope
2.2. Test material coupons
Discs with an 18‐mm diameter were cut to make coupons from carpet (Multiplicity 54594; Shaw Industries Group, Dalton, GA) and galvanized metal (26‐gauge stock metal; East Coast Metal, Durham, NC), materials which were purposely selected because they were the materials that were the most difficult (excluding concrete) to completely decontaminate using HPV (Wood et al., 2016). All materials were mounted on 18‐mm diameter aluminum stubs (P/N 16119; Ted Pella, Inc., Redding, CA) using double‐sided adhesive tape (P/N 16073‐2; Ted Pella, Inc.). All coupons with their stubs were sterilized before inoculation by exposure to ethylene oxide (Anderson EOGas AN333 Sterilization System, Haw River, NC). Coupon sterilization was performed to eliminate background contamination that could confound analysis and results.
2.3. Field‐scale test environment
The structure used in the test was a three‐bedroom, ranch‐style house with a crawl space; a natural gas, a central forced‐air heating system; and an electric air‐conditioning system (HVAC). The structure’s total floor area was 110 m2, and the total living‐space volume was approximately 270 m3. The structure was considered relatively airtight with an average air exchange rate between 0.3 and 0.4 air changes per hour for the ambient conditions experienced during testing.
Whole‐house COTS humidifiers, Figure 1 (Model HCN‐6009; Honeywell, Morris Plains, NJ) were charged with 3% HP solution. This type of humidifier uses a small fan to push air through a sponge that absorbs liquid from the reservoir. Humidifiers had a 12.9 L capacity. The location and number of humidifiers were varied across tests. The HVAC system maintained indoor temperatures at 21°C, and the circulation fan was set to run continuously. A real‐time relative humidity (RH) and temperature meter (Model HMD53; Vaisala, Helsinki, Finland) was used to monitor indoor RH and temperature. The HP (Part No. 512021‐1; Hi‐Valley Chemical, Inc., Centerville, UT) was diluted to a concentration of 3% using deionized water.
Figure 1.
Whole‐house humidifier in the kitchen location. Coupons can be seen in the oven [Color figure can be viewed at wileyonlinelibrary.com]
Three ranges of electrochemical HP sensors were used during fumigation: one HP sensor capable of detecting 0–10 ppm HP (Model B12–34‐1–0010‐1, Analytical Technology Inc. [ATI], Collegeville, PA) for low concentrations and safety monitoring, one HP sensor capable of detecting 0–25 ppm HP (Model B12–34‐5–0025‐1; ATI), and five HP sensors capable of detecting 0–100 ppm HP (Model B120100‐1; ATI). Sensors were connected to a data acquisition system and variable outputs were both stored and monitored in real‐time. The HP sensor capable of detecting 0–25 ppm HP was placed in the center of the house during fumigation, along with one real‐time RH and temperature probe (Model HMD53; Vaisala, Helsinki, Finland). The five 0‐ to 100‐ppm sensors were distributed throughout the house and the 0‐ to 10‐ppm sensor was placed in the garage where monitoring equipment and field personnel resided during testing.
Sets of coupons, BIs, and a temperature and RH monitor were placed in eight locations within the house (Figure 2). Each set of coupons consisted of three inoculated carpet coupons, three inoculated galvanized metal coupons, one uninoculated carpet coupon, one uninoculated galvanized metal coupon, and one BI. The inoculated coupons served as the test coupons for determination of log reduction (LR; as effectiveness) due to exposure to the test conditions. The uninoculated coupons served as controls for indicating any cross‐contamination during coupon handling. Two additional BIs were placed near (in the same room) each coupon set but in more secluded locations, such as in a closet or taped to an exterior wall. In addition, RH and temperature sensors (HOBO® RH/T Onset Data Logger [Model U12]; Onset Computers, Bourne, MA) were placed with each set of coupons. Oscillating fans were also used to help circulate the air. During some of the tests, extra BIs were placed in strategic locations to gauge penetration and decontamination efficacy in those locations (Figure 3). Positive control coupons (inoculated, but unexposed to HPV) and blanks (uninoculated and unexposed to HPV) were covered with a lid and placed in the garage.
Figure 2.
House floor plan with location of equipment, test coupons, and biological indicators for Test 1. BI, biological indicator; HP, hydrogen peroxide; HVAC, heating, ventilation, and air conditioning. [Color figure can be viewed at wileyonlinelibrary.com]
Figure 3.
Biological indicators placed in buttoned pants pocket for testing, Test 4 [Color figure can be viewed at wileyonlinelibrary.com]
The humidifiers were filled with the prescribed amount of HP liquid and turned on (in one case humidifiers were refilled), the house was secured (locked), signage was posted, and parameters were monitored throughout the fumigation process. The HPV concentration at the five different locations as a function of time is shown in Figure 4 for Test 1 as an example. The oscillating peaks observed between 14 and 24 hour (hr) in Figure 4 are the HPV sensor reaction to the heat system cycling on and off in response to the lower ambient temperature. These short‐duration peak values were not included in the maximum HPV concentration determination.
Figure 4.
Test 1 hydrogen peroxide vapor concentration as a function of time at different locations in the house [Color figure can be viewed at wileyonlinelibrary.com]
Following the decontamination process, a sampling team verified that the HPV concentration was below 1 ppm using Dräger HP tubes (Dräger™ Short‐Term Detector Tubes—Hydrogen Peroxide; Cat. No 8101041; Dräger, Inc., Houston, TX), and then entered the house to collect coupon sets and BIs. The one set of positive control and blank coupons that remained outside of the living space (in the garage) were collected at the same time.
Coupons were placed aseptically into sterile 50‐milliliters (ml) conical tubes and transported to the laboratory. To each 50‐ml conical tube, 20‐ml sterile phosphate‐buffered saline with 0.05% Tween® 20 (PBST) was added. The tubes were sonicated for 10 min and subsequently vortexed continuously for 2 min. Aliquots were plated in triplicate using a spiral plater (Autoplate 5000; Advanced Instruments Inc., Norwood, MA). Plates were incubated at 35 ± 2°C for 16–19 hr. The colonies on each plate were enumerated using a QCount® colony counter (Advanced Instruments Inc.). Low count samples were related using a vacuum filtering system (Pall Corporation, Port Washington, NY) to improve the detection limit.
BI discs containing Gs were aseptically transferred to 15‐ml polypropylene culture tubes (P/N 169897; USA Scientific Inc., Ocala, FL) containing 10 ml of tryptic soy broth (TSB). The tubes were statically incubated at 55 ± 2°C. After 7 days, the medium in each tube was visually inspected for turbidity, indicating growth. A 0.1‐ml aliquot was plated to confirm that the colony morphology was consistent with that of the target organism. All sample tubes with no turbidity also were plated (0.1 ml) to confirm that there was no target organism growth.
2.4. Test conditions
The test matrix for the field‐scale experiments is shown in Table 1. To establish a baseline with humidity only, Test 0 was conducted with the seven humidifiers filled with water only. Humidifiers were placed in the living room (two), kitchen (one), den (one), and in each of the three bedrooms (one each). For Test 1 the same locations were used but each humidifier was filled with 7.6 liters (L) of 3% HP. Furniture was added for Test 2 and to increase HP vapor concentrations in the hall bathroom, one of the living room humidifiers was moved to the hallway near the hall bathroom. In addition, several coupons and BIs were added and placed in strategic locations. For Test 3 only two humidifiers were used. Both were placed in the hallway under the house ventilation system return air duct and both were filled to capacity, 12.9 L of 3% HP. One of those humidifiers was set to turn on 24‐hr after the other had been started. Test 4 was a repeat of Test 3 with the addition of refilling the two humidifiers with 3% HP, one with 12.1 L and one with 7.6 L. The humidifier start times were staggered by 24 hr during this run. The volume of liquid 3% HP shown in the matrix is the amount charged into the humidifiers. Humidifiers ran until they automatically shut off when the reservoir was nearly empty. There were 27–37 ml of HP liquid remaining in each humidifier at the end of Tests 1–3 and almost 300 ml in each of the two humidifiers after Test 4. In addition, there were varying amounts 31–542 ml) of HP liquid remaining in the humidifier sponge. Loaded and used HP liquid amounts are shown in Table 1.
Table 1.
Test matrix
| Test # | Number of humidifiers | Amount of HP (L) |
Description | |
|---|---|---|---|---|
| Loaded | Used | |||
| 0 | 7 | 0 | 0 | Water only, 53 L used |
| 1 | 7 | 53 | 51.3 | 7.6 L 3% liquid HP each humidifier |
| 2 | 7 | 53 | 51.8 | Same as Test 1 plus furniture and clothing |
| 3 | 2 | 26 | 25.1 | Same as Test 2 two humidifiers, half the HP |
| 4 | 2 | 46 | 43.8 | Same as Test 3 two humidifiers with refill |
Abbreviation: HP, hydrogen peroxide.
3. RESULTS
For Test 0, water only was used in humidifiers. The RH went from 54% to 85% within an hour of turning on the humidifiers. After 2 days the RH started to decline slowly for the rest of the week‐long experiment, ending at a low of 55%. The temperature was stable at 21°C (±2) throughout the house, over time, and between all tests; thus, temperature data are not reported beyond this result. Growth was observed for all BIs in all Test 0 locations. Recoveries for the test coupons are shown in Figure 5. The use of water only in the humidifiers had no significant effect on spore survivability for galvanized metal coupons (t test, metal: p = .37) as compared to the positive control coupons. And although the effect of humidity on the carpet coupons was statistically significant (t test, carpet: p = .0027), the average 25% reduction was less than one‐LR and was of no practical significance.
Figure 5.
Test 0 spore recoveries on the carpet and galvanized metal coupons by location
Table 2 shows the fumigation conditions throughout the house for Test 1, including maximum HPV concentration, integrated HPV concentration, and average and maximum RH. The integrated HPV concentration multiplied by time (CT) has units of ppm‐hours and is a cumulative measure of fumigation dose. The CT calculations are for the full week (168 hr) of exposure time. With two humidifiers in the living room, the maximum HPV concentration (55 ppm) approaches the immediately dangerous to life and health (IDLH) level for HPV (75 ppm; National Institute for Occupational Safety & Health, 2007). The HPV concentrations and CT in the hall bathroom were very low. Note that these HPV concentrations are values recorded at one location in each of the monitored rooms and do not represent every location within that room, especially where there are closets or other obstructions to vapor penetration.
Table 2.
Test 1—Fumigation and relative humidity conditions by location
| Location | HPV max (ppm) | CT (ppm‐hour) | RH average (%) | RH max (%) |
|---|---|---|---|---|
| Master bedroom | 38 | 1,300 | 72 | 86 |
| Master bathroom | Not measured | 74 | 85 | |
| Hall bathroom | 7.5 | 270 | 72 | 86 |
| Center of den | 33 | 1,300 | 72 | 86 |
| Corner bedroom | Not measured | 69 | 85 | |
| Middle bedroom | Not measured | 72 | 88 | |
| Kitchen | Not measured | 69 | 86 | |
| Living room | 55 | 2,000 | 71 | 88 |
| Air return | 28 | 1,100 | 65 | 82 |
Abbreviations: CT, concentration multiplied by time; HPV, hydrogen peroxide vapor; RH, relative humidity.
Test 1 efficacy results are shown in Figure 6. The LR is calculated by taking the average of the logs of the three positive control coupons and subtracting the average of the logs of the three test coupons for each material. Of the 54 coupons deployed, eight had detectible spores. Both materials averaged over a six‐LR even though some spores remained on some coupons after fumigation. Of the 27 BIs exposed to HPV for 7 days in the living area, four were positive after fumigation: two on the master bathroom floor, one on the bathroom sink, and one in the kitchen.
Figure 6.
Test 1 LR in spore recoveries on the carpet and galvanized metal coupons by location. All samples were nondetect except where numbers in parentheses indicate the mean number of detectable spores in CFUs post decontamination. The average inoculated spore recovered (CFUs) from positive controls were 3.0 × 107 for carpet (SD = 0) and 1.5 × 107 for GM (SD = 1.3 × 107). CFU, colony forming unit; LR, log reduction; GM, galvanized metal; SD, standard deviation
With furniture in the house, Table 3 shows the maximum HPV concentration, the CT and the RH for Test 2. The HPV concentration in the hall bathroom was more than double that of Test 1. This is most likely a result of moving one humidifier from the living room to the hall near the bathroom. One humidifier remained in the living room, yet the maximum HPV concentration (65 ppm) in the living room increased from Test 1 and was nearer to the IDLH for HPV of 75 ppm.
Table 3.
Test 2 fumigation conditions with furniture in the house
| Location | HPV max (ppm) | CT (ppm‐hour) | RH average (%) | RH max (%) |
|---|---|---|---|---|
| Master bedroom | 38 | 1,500 | 60 | 86 |
| Master bathroom | Not measured | 61 | 83 | |
| Hallway bathroom | 14 | 660 | 55 | 81 |
| Center of den | 25 | 1,100 | 62 | 85 |
| Corner bedroom | Not measured | 59 | 85 | |
| Middle bedroom | Not measured | 59 | 83 | |
| Kitchen | Not measured | 61 | 89 | |
| Living room | 65 | 2,800 | 58 | 84 |
| Air return | 30 | 1,200 | 50 | 78 |
Abbreviations: CT, concentration multiplied by time; HPV, hydrogen peroxide vapor; RH, relative humidity.
Test 2 efficacy results are shown in Figure 7. Additional coupons and BIs were added to four rooms and designated by placing (b) after the location name. These additional coupons and BIs were removed from the house and processed after 3 days of exposure to the fumigant. The other coupons and BIs remained in the house for the full week. Of the 78 coupons deployed, nine had detectable spores. Of the 27 BIs exposed to HPV for 7 days in the living area, two were positive after fumigation: one on the corner bedroom floor and one on the living room floor. And of the 31 BIs placed in hard‐to‐reach places, just over half were positive for growth as shown in Table 4.
Figure 7.
Test 2 LR in spore recoveries on the carpet and galvanized metal coupons by location, (b) location coupons were collected after 3 days of HPV exposure and all other locations after 7 days. All samples were nondetect except where numbers in parentheses indicate mean number of detectable spores in CFUs. CFUs were 2.8 × 107 for carpet (SD = 4.4 × 106) and 9.2 × 106 for GM (SD = 2.5 × 106). CFU, colony forming unit; LR, log reduction; GM, galvanized metal; SD, standard deviation
Table 4.
Test 2 postdecontamination recoveries on BI discs placed in challenging locations
| Location | Growth | No growth |
|---|---|---|
| Between couch cushions | 7 | 3 |
| Under rug | 10 | |
| Under one piece of paper | 3 | |
| Under five pieces of paper | 3 | |
| In bathroom drawer | 5 | |
With furniture remaining in the house and a reduced amount of liquid HP delivered from only two humidifiers, Table 5 shows the maximum HPV concentration as well as the integrated concentration over the duration of Test 3. The highest maximum concentration was at the return duct, immediately over the humidifiers.
Table 5.
Test 3 fumigation conditions
| Location | HPV max (ppm) | CT (ppm‐hour) | RH average (%) | RH max (%) |
|---|---|---|---|---|
| Master bedroom | 17 | 788 | 41 | 58 |
| Master bathroom | Not measured | 40 | 55 | |
| Hallway bathroom | 12 | 525 | 31 | 46 |
| Center of den | 10 | 432 | 47 | 55 |
| Corner bedroom | Not measured | 38 | 50 | |
| Middle bedroom | Not measured | 47 | 61 | |
| Kitchen | Not measured | 43 | 56 | |
| Living room | 15 | 873 | 45 | 55 |
| Air return | 34 | 1,320 | 44 | 55 |
Abbreviations: CT, concentration multiplied by time; HPV, hydrogen peroxide vapor; RH, relative humidity.
Test 3 efficacy results are shown in Figure 8. The LRs were much lower than previous runs most likely due to the reduced amount of liquid HP used for this test. Of the 72 coupons deployed, 68 had detectable spores. Of the 27 BIs exposed for 7 days in the living area, only four were positive after fumigation: one in the bathroom sink, one in the middle bedroom floor, one in the kitchen floor, and one in the living room floor. The number of no growth BIs was unexpected given the lower LR results for the coupons located in the living area. But the number of growth BIs located in hard‐to‐reach places increased in comparison to Test 2, as shown in Table 6.
Figure 8.
Test 3 LR in spore recoveries on the carpet and galvanized metal coupons by location, (b) location coupons were collected after 3 days of HPV exposure and all other locations after 7 days. CFUs were 3.8 × 107 for carpet (SD = 8.9 × 106) and 1.8 × 107 for GM (SD = 7.8 × 106). CFU, colony forming unit; LR, log reduction; GM, galvanized metal; SD, standard deviation
Table 6.
Test 3 postdecontamination recoveries on BI discs placed in challenging locations
| Location | Growth | No growth |
|---|---|---|
| Inside closed book | 3 | |
| Pants pocket | 2 | 1 |
| Coat pocket | 3 | |
| Behind light switch plate | 6 | |
| Window sill | 1 | 2 |
| Door jams | 6 | |
With furniture in the house, using only two humidifiers and refilling those two humidifiers after 3 days, Table 7 shows the maximum HPV concentration, CT, and RH for Test 4. Note that the maximum concentrations were not much different from Test 3, however, the integrated CT was significantly higher due to the refilling of the humidifiers after 3 days.
Table 7.
Test 4 fumigation conditions
| Location | HPV max (ppm) | CT (ppm‐hour) | RH average (%) | RH max (%) |
|---|---|---|---|---|
| Master bedroom | 14 | 1,217 | 49 | 57 |
| Master bathroom | Not measured | 51 | 60 | |
| Hallway bathroom | 8 | 767 | 52 | 61 |
| Center of den | 21 | 1,239 | 52 | 63 |
| Corner bedroom | Not measured | 49 | 57 | |
| Middle bedroom | Not measured | 45 | 60 | |
| Kitchen | Not measured | 52 | 63 | |
| Living room | 33 | 2,274 | 50 | 61 |
| Air return | 27 | 2,053 | 51 | 64 |
Abbreviations: CT, concentration multiplied by time; HPV, hydrogen peroxide vapor; RH, relative humidity.
Test 4 efficacy results are shown in Figure 9. Of the 78 coupons deployed, 28 had detectable spores. Of the 27 BIs exposed for 7 days in the living area, one placed on the living room
Figure 9.
Test 4 LR in spore recoveries on the carpet and galvanized metal coupons by location, (b) location coupons were collected after 3 days of HPV exposure and all other locations after 7 days. Numbers in parentheses indicate the mean number of detectable spores in CFUs. CFUs were 3.4 × 107 for carpet (SD = 5.5 × 106) and 1.2 × 107 for GM (SD = 4.0 × 106). CFU, colony forming unit; LR, log reduction; GM, galvanized metal; SD, standard deviation
Floor was positive after fumigation. Of those placed in challenging locations, about half of the 63 BIs resulted in growth, as shown in Table 8.
Table 8.
Test 4 post decontamination recoveries on biological indicator discs in challenging locations
| Location | Growth | No growth |
|---|---|---|
| Between couch cushions | 3 | |
| Under carpet or floor mat | 6 | |
| Under one piece of paper | 3 | |
| Under five pieces of paper | 3 | |
| Under ten pieces of paper | 3 | |
| Door jams | 6 | |
| Pants pocket | 3 | |
| Coat pocket | 3 | |
| Inside book | 3 | |
| Inside light switch plates | 6 | |
| Inside pillowcase | 3 | |
| Between bed sheets | 3 | |
| Under bed comforter | 3 | |
| Inside light fixture | 3 | |
| Inside closed hall closet | 3 | |
| Inside closed drawer | 3 | |
| In open drawer | 3 | |
| Window sill | 3 | |
| Totals | 33 | 30 |
Table 9 shows a summary of results, which includes the amount of 3% HP liquid used, CT (dose) calculated, number of coupons (carpet and galvanized metal) with >6‐LR, number of coupons with no detection of spores, and number of negative BIs used in the house (not inside furniture, under rugs, etc.). The CT data are correlated with the number of coupons sets >6‐LR (0.95) and a number of coupons without detectable spores (0.96), but to a lesser degree with a number of negative BIs (0.38). The coupons correlate better with CT and may give a better indication of decontamination efficacy than the BIs.
Table 9.
Test results matrix
| Test no. | Amount of HP (L) | CT (ppm‐hrs) | No. coupon sets >6‐LR | No. coupon w/out CFUs | No. negative BIs | |||
|---|---|---|---|---|---|---|---|---|
| 1 | 51.3 | 1,220 | 18/18 | 100% | 46/54 | 85% | 20/27 | 74% |
| 2 | 51.8 | 1,520 | 18/18 | 100% | 48/54 | 89% | 25/27 | 93% |
| 3 | 25.1 | 655 | 2/18 | 11% | 7/54 | 13% | 23/27 | 85% |
| 4 | 43.8 | 1,370 | 17/18 | 94% | 43/54 | 80% | 26/27 | 96% |
Abbreviations: BI, biological indicator; CFU, colony forming unit; CT, concentration multiplied by time; LR, log reduction.
4. DISCUSSION AND CONCLUSIONS
This study shows that the efficacy of low‐concentration HP, as seen in the laboratory (Wood et al., 2016), is transferable to the field scale. Results from the 165 carpet coupons, 165 galvanized metal coupons, and 250 BIs used in these test runs to support the conclusion that, at the conditions tested, 20 L of 3% HP liquid evenly dispersed within every 100 m3 of indoor volume would be efficacious for inactivating Bacillus spores on most non‐occluded surfaces. The noted exception may be for concrete surfaces. Previously, HPV was not efficacious against Bacillus spores on concrete (Rastogi, Wallace, Smith, Ryan, & Martin, 2009), but that condition was not specifically assessed in the current field‐scale study.
A direct impact of adding furniture cannot be made using Test 1 and Test 2 data because one living room humidifier was moved to the hall before running Test 2. However, there was not a significant change in HP concentration or efficacy between those two tests. In fact, for the locations where measurements were taken, the CT was higher for Test 2 than Test 1. A reduction in efficacy did accompany the reduction of the total amount of HP delivered, comparing Test 2 and 3. Conducting the HPV fumigation with only two COTS humidifiers was effective when the two humidifiers were refilled at day three, Test 4. Staggering the two humidifiers to run sequentially rather than concurrently kept the maximum air concentration of hydrogen peroxide below 33 ppm but still achieved 1,370 ppm‐hours CT. The carpet and galvanized metal coupons responded to fumigation with a better correlation with CT than the BIs. Material coupons may be a better predictor of decontamination efficacy than the BIs.
An intriguing and critical aspect of this study was seen by the placement of BIs into difficult‐to‐reach locations, into and beneath objects. These results illustrate the penetrating potential of HPV. This method of fumigating with HPV was efficacious when BIs were placed under one or five pieces of paper, in pants pocket that was hanging in an open closet, under bedsheets, and under a comforter, in a light fixture, in a closed closet, in an open drawer, and on a window sill. However, this method of fumigating with HPV was not efficacious for BIs placed between couch cushions, under carpets or floor mats, under 10 pieces of paper, inside a winter coat pocket hanging in an open closet, inside a book, inside a light‐switch box with the plate attached, in a closed drawer, and near leaky door weather stripping. Considering all these BI results gives a good indication of the HPV penetration potential. With respect to penetration into and through materials, it would be interesting to compare this low‐concentration approach to the typical HPV fumigation parameters as well as comparing the difference in off‐gassing of HP from materials after fumigation. Neither was performed in this current test.
The use of the method shown in this study has the potential to significantly reduce spore concentration along with the potential exposures and the health risks associated with those exposures. The current cleanup criteria with respect to a B. anthracis release is, “no detection of viable spores” as measured by current sampling methods (Center for Disease Control and US EPA, 2012). The scarcity of response and recovery resources including sampling will play a major role in a response strategy. The appropriate strategy for applying this method, along with many other remediation and sampling methods, to a wide‐area release was not in the scope of this study; however, this method may increase our capacity to respond and positively impact future response strategies.
The threshold limit value (American Conference of Governmental Industrial Hygienists) and the permissible exposure limit (Occupational Safety and Health Administration) for HPV are both designated as 1 ppm, indicating that healthy workers may be exposed up to that level during typical work hours without expecting adverse health outcomes. When the humidifiers were dispensing HPV the resulting concentrations were lower than typical fumigations; however, the concentrations throughout the house were above this 1 ppm level. Thus, entering the house during that time would require appropriate respiratory protection. When entering the house after this fumigation cycle was complete the concentration of HPV was always below 1 ppm without the need for additional aeration at the end of the fumigation cycle. A closer look at the kinetics of desorption of HP from household materials and the concentration of HPV near those materials after fumigation may be warranted before the widespread application of this method.
The utility of using this method of decontaminating structures after a wide‐area incident may be profound in that it would greatly increase the current response capacity. Allowing individuals to decontaminate their own properties without specialized equipment or workforce could have a significant impact on recovery times and costs. Effectively relaying this information, how to carry out the low‐concentration fumigation with an understanding of potential health risks, to the general public for their personal use would have to be carried out in a thoughtful manner.
Biographies
Ronald Leroy Mickelsen, M.S., P.E., has worked for 12 years for the Chemical, Biological, Radiological, and Nuclear Consequence Management Advisory Division within the US EPA preparing and responding to chemical, biological, and radiological hazards. His position there allows him to work with laboratory researchers as well as in the field with responders. Areas of interest include recovery from a biological agent release, ventilation for controlling hazards, and general health and safety topics.
Joseph Wood, M.S., P.E., is a senior research engineer with US EPA’s National Homeland Security Research Center (NHSRC). He has been with the US EPA since 1991 (previously doing air pollution engineering work), and with NHSRC’s Decontamination and Consequence Management Division since 2004. Currently, his research focuses primarily on the development, testing, and evaluation of technologies for the decontamination and disposal of materials contaminated with biological agents and biotoxins. He is the primary author or coauthor for many peer‐reviewed journal articles and US EPA published reports. He holds a master’s degree in environmental engineering from the University of Illinois (Urbana‐Champaign), and is a licensed professional engineer.
Michael Worth Calfee, Ph.D., is a research microbiologist within US EPA’s NHSRC. He has over 20 years of microbiological research experience with 10 years at the US EPA in decontamination and consequence management of chemical, biological, radiological, and nuclear (CBRN) agents. His research foci include sampling, decontamination, and management of wastes from CBRN contamination incidents. Dr. Calfee received his Ph.D. in 2007 from East Carolina University, where he studied coastal and estuarine microbial communities. He also earned a B.S. in molecular biology from East Carolina University in 1999.
Shannon Serre, Ph.D., has worked for the US EPA for 21 years, six of those with the CBRN Consequence Management Advisory Division preparing and responding to chemical, biological, and radiological hazards.
Shawn Ryan , Ph.D., is a chemical engineer within US EPA’s NHSRC. He has over 18 years of research experience at the US EPA in decontamination and consequence management of CBRN agents. His research outputs include publications on the decontamination of chemical and biological agents on surfaces and assessing the impact of decontamination processes on equipment and materials. Dr. Ryan received his Ph.D. in 2001 from Rensselaer Polytechnic Institute in Troy, New York. He also earned a B.S. in environmental engineering from Rensselaer Polytechnic Institute in 1995.
Abderrahmane Touati , Ph.D., is a Senior Research Engineer with Jacobs Technology Inc. Since 2015 he has been the Jacobs Homeland Security Research Department Manager where he leads a research program supporting the US EPA’s NHSRC Decontamination and Consequence Management Division. He provides expertise in the selection and implementation of decontamination methods and leads projects designed to provide the scientific basis for significant reductions in decontamination time and cost.
Francis Robbins Delafield, has a B.A. in natural sciences and has been performing and supporting laboratory research at the US EPA for 27 years on a variety of projects.
Lola Denise Aslett, Ph.D., is a Senior Microbiologist at Jacobs Technology Inc. and has worked for 3 years supporting laboratory research for the US EPA. Areas of Bacillus research interest include remediation, cell metabolism, sporulation, spore architecture, germination, and detection of spores in complex matrices such as soil and water.
Contributor Information
Ronald Leroy Mickelse, U.S. Environmental Protection Agency, Office of Land and Emergency Management, Durham, North Carolina.
Joseph Wood, U.S. Environmental Protection Agency, Office of Research and Development, Durham, North Carolina.
Michael Worth Calfee, U.S. Environmental Protection Agency, Office of Research and Development, Durham, North Carolina.
Shannon Serre, U.S. Environmental Protection Agency, Office of Land and Emergency Management, Durham, North Carolina.
Shawn Ryan, U.S. Environmental Protection Agency, Office of Research and Development, Durham, North Carolina.
Abderrahmane Touati, Homeland Security Department, Jacobs Technology Inc., Durham, North Carolina.
Francis Robbins Delafield, Homeland Security Department, Jacobs Technology Inc., Durham, North Carolina.
Lola Denise Aslett, Homeland Security Department, Jacobs Technology Inc., Durham, North Carolina.
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