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eTools Home :Anthrax Credits

How should I decontaminate during response actions?

Anthrax CollageThis page provides information on decontaminating buildings or specific areas, systems, or items within buildings after an actual release of anthrax. Anthrax decontamination is a repetitive process that may involve the use of multiple decontamination processes and technologies. Selection of appropriate technologies varies depending on factors specific to the release and to the technologies themselves, but the primary considerations are always the effectiveness and safety of the products and processes.

Planning for Decontamination
Cleaning an area or item contaminated by anthrax involves numerous and variable issues that are specific to individual locations. No single technology, process, or strategy will be effective in every case. Responders must develop a decontamination plan that takes into account the following:
  • The nature of the contamination: including the type of anthrax involved, how it entered the facility, and the physical characteristics that affect the spread of contamination.

  • The extent of contamination: including the amount of contamination and possible pathways by which it could have or will spread.

  • The objectives of decontamination: including the intended re-use of the facility and building systems and whether items will be decontaminated for re-use or treated for disposal.
The extent of contamination and how the contamination spread are critical considerations in isolating affected areas and selecting appropriate decontamination technologies. For example, if spores are widely dispersed and have traveled through the air, decontamination may involve extensive isolation and fumigation. In contrast, if the contamination is limited to a small area and spores are not likely to become airborne, then minimal isolation and surface decontamination methods alone may suffice.

All stakeholders--local authorities, building owners and residents, federal, state, and local environmental and health agencies, the affected public, and others--should be consulted before decontamination begins. A site health and safety plan (HASP) is needed to protect workers inside and outside the contaminated area, as well as the surrounding population. The facility manager should notify employees and others (such as union representatives) of the nature and scope of the work and its expected duration.

More detailed information about HASPs can be found on the HASP page of this eTool.

Preparing for Decontamination
The results of the sampling for extent of contamination should make it possible to distinguish between contaminated and uncontaminated areas and to determine the types of surfaces involved. To prevent the spread of contamination by movement of workers or equipment, it may be advisable to isolate the contaminated area, depending on the impacted area and the extent of contamination.

Decontamination should address the following:
Hidden sources of contamination: Desktop computers and other objects with internal fans that draw air into the case may have filters or electrostatic devices to control dust intake.
Hidden sources of contamination: Desktop computers and other objects with internal fans that draw air into the case may have filters or electrostatic devices to control dust intake.
  • Hidden sources of contamination: Desktop computers and other objects with internal fans that draw air into the case may have filters or electrostatic devices to control dust intake. These filters or the equipment chassis may be a reservoir of contamination. If selected technologies may damage the item or may not penetrate to hidden locations, then these items may be dealt with in an alternative manner. The manufacturer of the device should be consulted if it is to be saved for re-use.

  • Pre-cleaning: Excessive amounts of dirt or other organic material on the surface to be cleaned may decrease the effectiveness of the selected decontamination method. Using certain techniques, such as HEPA vacuuming, to remove some of the dirt and debris could reduce the need to perform more aggressive chemical decontamination.

  • Removal of items: To reduce potential spread of contamination, items should be decontaminated in place. If the selected technology will destroy an item that must be salvaged, then the item may be removed and decontaminated elsewhere with an alternative technology. This requires a means of safe transport and a separate isolation chamber, which adds complexity to the decontamination process.
Additional, more detailed information about sampling for Bacillus anthracis, can be found on the Sampling page of this eTool.

Decontamination Technologies
Decontamination technologies can be divided into three categories:
  1. Surface decontamination products, which are used to treat spores on hard, non-porous surfaces such as desks, walls, and hard flooring. There are two methods to treat surfaces:
    • HEPA filters can be attached to high-volume vacuums such as this.
      HEPA filters can be attached to
      high-volume vacuums such as this.
      Liquid Antimicrobial Products - Not for Porous Surfaces
      Liquid Antimicrobial Products - Not for Porous Surfaces
      High Efficiency Particulate Air (HEPA) Vacuuming: accomplishes two purposes: (1) it helps remove dirt and other debris that may reduce the effectiveness of subsequent decontamination, and (2) it also removes some of the spores, reducing the number that must be killed by subsequent decontamination. An advantage of this technology is that there is little potential for damage to furnishings. A limitation of this technology is that it can only remove surface contamination. The operator must also avoid allowing the exhaust to stir the air in the affected room and must safely dispose of contaminated filters.

    • Liquid Antimicrobial Products - Not for Porous Surfaces: may be used to inactivate spores on hard surfaces only. These products--which can be applied by pouring, mopping, or spraying--include oxidizing, bleaching, or other agents such as aqueous chlorine dioxide, sodium hypochlorite, hydrogen peroxide, and peroxyacetic acid combined. Several factors should be considered when deciding which liquid antimicrobial products to use and how to apply them. Each product affects surfaces differently in terms of corrosivity, staining, and residue. These products will be effective only if the directions for use of the product are followed precisely (such as mixing directions, application method and dosage rate, pre-cleaning of surfaces, and contact time).
  1. Fumigation, which involves use of an antimicrobial gas or vapor to destroy aerosolized spores and spores adhered to non-porous and porous surfaces. In addition to decontaminating a variety of surfaces, fumigants are able to decontaminate airborne spores that a surface cleaner would miss.
  1. Other decontamination products, which are primarily used in chambers or other specialized equipment. Technologies that can be used to decontaminate specific items outside the affected area or environment include the following:
  • Chemical Sterilization: chemicals such as ethylene oxide, chlorine dioxide, or paraformaldehyde are used to kill spores on discrete items placed in a sterilization chamber. Sufficient aeration of the items following treatment is necessary to remove residual amounts of the sterilant and any toxic by-products that may have formed.  For effective decontamination, each chemical sterilant has specified ranges of temperature, relative humidity, concentration, and duration of application.
  • Irradiation: irradiation techniques, including cobalt-60 and electron beam technologies, can effectively destroy anthrax. These techniques are generally available only for off-site decontamination. They may destroy magnetic media such as film or videotape, and they tend to be expensive.
Selection of the appropriate technology will require an evaluation of the specific site conditions and nature of contamination. Other considerations include the conditions required for effective application (for example, humidity for fumigations or pH for certain surface treatments), how the technology will affect the area or item being treated, and the risks associated with use (such as physical, chemical, and toxicologic parameters of the product).

The Environmental Protection Agency's (EPA) Technology Innovation Office (TIO) has developed an information clearinghouse as a centralized location to collect and disseminate information about decontamination technologies and also for technology vendors to provide information.

Judging the Effectiveness of Decontamination
There are separate criteria, described below, for judging the effectiveness of decontamination of objects in an off-site sterilization chamber, and for decontamination of sites such as offices or buildings.
  • For objects decontaminated in an off-site sterilization chamber, biological indicators such as surrogate spore test strips, may be placed in the chamber along with the objects. Although the optimal results of decontamination would be if the biological indicators showed no evidence of bacterial growth, OSHA believes that there may be safe alternatives to the "no growth" decontamination.

  • To determine whether decontamination of a site has been effective, a rigorous round of environmental sampling should be performed following the decontamination process, and the samples should be cultured for Bacillus anthracis in a nationally accredited lab. Rigorous environmental sampling should be done in all decontaminated sites, regardless of type of technology used or the extent of the decontamination. In areas that have been fumigated, biological indicators (such as surrogate spore strips) may be used to determine whether the fumigant has effectively permeated the area under specific conditions (such as concentration, time, temperature, and relative humidity) sufficient to kill Bacillus anthracis spores. The results of the culture of both the environmental samples and the biological indicators should be evaluated to determine the effectiveness of the fumigation. Again, the optimal results of decontamination would be if the biological indicators showed no evidence of bacterial growth. However, OSHA believes that there may be safe alternatives to the "no growth" decontamination.
A different technology may be used for further decontaminating an area in which sampling showed the presence of viable anthrax spores. For example, if evidence of bacterial growth is found only on a desk in an office that was fumigated, an approved liquid sporicidal product may be applied to complete decontamination of the desk. 

Once an area has been determined to be effectively decontaminated, there is no guarantee that all viable spores have been eliminated, even when post-decontamination samples show no growth. Moreover, statistical calculations of the effectiveness of sampling and analytical methods indicate that some spores may remain in a decontaminated area even though environmental sampling shows "no growth." Nevertheless, the potential risk of a person contracting the disease in such an area is considered to be extremely low. 

Although the "no growth" decontamination goal may be the best possible way to ensure safety in re-occupying a decontaminated area, OSHA believes that there may be safe alternatives, especially in workplace situations where the use of PPE, special work practices, or other engineering controls might also minimize the risk of disease.

This approach is consistent with the NCP, which allows case-by-case decisions based on the future use of the site and other controls that might be used to ensure safety. Decisions on alternative options such as these would have to be site-specific, and supported by experts in epidemiology, public health, industrial hygiene, and environmental protection. The basis for these types of decisions should also be thoroughly documented.

Additional information about decontamination techniques and process, and post-decontamination sampling strategies can be found on the Sampling page of this eTool.
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