Research Highlights

Fumigant Technologies Used to Inactivate Biological Agents on Indoor Materials

In 2001, the anthrax mailings not only caused loss of life, but also interrupted the daily functioning of the United States government when affected buildings had to be taken out of service until decontamination and restoration efforts were complete. Because of these events and their consequences, EPA has evaluated the performance of several decontamination technologies designed specifically to inactivate biological agents. Table 1 lists four fumigant technologies used for this purpose.

EPA tested each fumigant technology’s ability to decontaminate indoor materials spiked with biological agent spores. Qualitative factors, such as ease of use and surface damage from physical degradation of the materials, were also evaluated.

Test Design

The four technologies were applied to seven types of porous and non-porous indoor surfaces:

• Industrial-grade carpet (porous)
• Painted concrete (porous)
• Bare wood – pine (porous)
• Glass (non-porous)
• Decorative laminate (non-porous)
• Painted wallboard paper (non-porous)
• Galvanized metal (non-porous)

Figure 1. Surface Coupons

Test surface coupons (shown in Figure 1) were contaminated with the following biological agents at challenge levels of approximately 1 x 10⁸ viable biological spores per coupon:

• Bacillus anthracis Ames strain (B. anthracis)
• Bacillus subtilis (ATCC 19659) surrogate (B. subtilis)
• Geobacillus stearothermophilus (ATCC 12980)
  surrogate (G. stearothermophilus)

B. subtilis and G. stearothermophilus are surrogates for B. anthracis.

The quantitative effectiveness of each decontamination technology was evaluated by comparing the number of viable spores after decontamination to the number of viable spores from a control surface that had not been subjected to the decontamination technology.

Performance and Results

Because of the large difference in the number of spores on the control surfaces compared to the number on the decontaminated coupons, the efficacy was reported as the log of the ratio of these two numbers. For example, a 1,000‑fold reduction in spores after treatment was reported as a log reduction of 3 (the log of 1,000). Table 2 summarizes the decontamination efficacy for each technology, surface, and biological agent/surrogate combinations. 

BQ, Clarus C Generator

• The results from the test coupons contaminated with B. anthracis showed varied decontamination efficacy according to the type of test material. After decontamination, viable spores were recovered from test coupons of industrial-grade carpet, bare wood, and painted concrete.
• The unit’s calculated decontamination efficacy for B. anthracis ranged from 3.01 to 7.92 across the seven test materials. Based on industrial-grade carpet and bare wood results, decontamination of B. anthracis from porous materials may be less effective than decontamination of non-porous materials.
• Different material types influenced the unit’s decontamination efficacy for all three organisms. Industrial-grade carpet and bare wood had the lowest decontamination efficacy levels for B. anthracis Ames and B. subtilis; however, industrial-grade carpet and galvanized metal ductwork had the lowest decontamination efficacy for G. stearothermophilus.

CDG, Bench-Scale Chlorine Dioxide Gas: Solid Generator

• The results from the test coupons contaminated with B. anthracis showed varied decontamination efficacy according to the type of test material. After decontamination, viable spores were recovered from test coupons of industrial-grade carpet, bare wood, glass, decorative laminate, and painted concrete.
• The unit’s range of decontamination efficacy for all seven test materials was:
• B. anthracis - 4.33 to 7.79
• B. subtilis - 4.44 to 5.57
• G. stearothermophilus - 3.22 to 5.79
• Different material types influenced the unit’s decontamination efficacy for all three organisms. The observed differences in the results for B. anthracis, B. subtilis, and G. stearothermophilus spores suggested that the test material composition and/or porosity affected decontamination efficacy and spore recovery. Significant differences in decontamination efficacy were observed between B. anthracis and B. subtilis on painted concrete, painted wallboard paper, and galvanized metal ductwork (B. anthracis had higher decontamination efficacy results).

CT, 1414 Formaldehyde Generator/Neutralizer

• The results from the test coupons contaminated with B. anthracis showed varied decontamination efficacy according to the type of test material. After decontamination, viable spores were recovered from test coupons of decorative laminate and painted concrete.
• The unit’s calculated decontamination efficacy for B. anthracis ranged from 5.17 to 7.86 across all seven test materials. Although no viable spores were detected on painted wallboard paper, the associated decontamination efficacy was 5.17 due to lower control recoveries.
• For all seven test materials, the range of decontamination efficacy for B. subtilis was 6.02 to 8.04 and the range for G. stearothermophilus was 5.68 to 7.64.
• Different material types influenced the unit’s decontamination efficacy for all three organisms. For porous materials, a significant difference was observed between the industrial-grade carpet decontamination efficacy for B. anthracis and G. stearothermophilus (B. anthracis had higher decontamination efficacy results). For non-porous materials, a significant difference was observed between the painted wallboard paper decontamination efficacy for B. anthracis and both surrogates (B. anthracis had lower decontamination efficacy results), and a significant difference was also observed between the galvanized metal ductwork decontamination efficacy for B. anthracis and B. subtilis (B. anthracis had higher decontamination efficacy results).

ST, Bench-Scale Chlorine Dioxide Gas Generator

• No viable spores were detected on any material test coupons contaminated with
  B. anthracis, B. subtilis, and G. stearothermophilus spores after decontamination.
• The unit’s decontamination efficacy was 7.14, 6.73, and 6.25 for
  B. anthracis, B. subtilis, and G. stearothermophilus spores, respectively.
• Because of the lack of any detectable viable organisms after decontamination, it was not possible to draw conclusions about the differential efficacy between agent/surrogates and material groups.

For each technology tested, the decontamination efficacy for each of the surrogates (B. subtilis and G. steorothermophilus) differed from decontamination efficacy for B. anthracis.

Subsequent to decontamination, test coupons were examined for visible surface damage. With the exception of the industrial-grade carpet being bleached by the two chlorine dioxide technologies (CDG, Bench-Scale Chlorine Dioxide Gas: Solid Generator and ST, Bench-Scale Chlorine Dioxide Gas Generator), there was no observed damage to any other test surface.

The operational assessment indicated that each technology could be set up and programmed for use within minutes. The only maintenance required was adding new decontamination reagents at the beginning of each run. Unused reagents and waste water needed to be disposed of properly at the end of each use. In most cases, the automation of these technologies left little room for operator error. 

For more information about biological agent decontamination using fumigation, view the Fumigant Decontamination Technologies page.

Contact: Shawn Ryan