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Chlorine Dioxide and Bleach Play a Major Role in Anthrax Remediation of the Hart Senate Office Building

When the news first broke in October 2001 about anthrax-contaminated letters intentionally sent through the U.S. mail, the full effects of simply receiving and opening contaminated letters were not immediately known. But over the days and weeks that followed, this simple yet effective method of dispersing a deadly biological agent had a chilling impact on everyone. Those handling the mail and opening the envelopes became part of a large-scale medical emergency, the likes of which our society has not seen in recent memory.

Letters containing anthrax (Bacillus anthracis) were sent to several targets. A media company in Florida, newsrooms in New York and U.S. Senate offices in Washington, DC were among the first affected. These attacks set in motion an exhaustive and unprecedented effort to destroy anthrax contamination in several areas of the Hart Senate Office Building. Despite decades of experience remediating hazardous waste sites, cleanup operators and personnel had never encountered this type or scale of biological contamination. The decontamination effort provided important lessons that could be applied to other buildings and will help public health officials across the country prepare to respond to future biological terrorist threats.

Determining the Nature and Extent of Contamination

As with any remedial action, determining the nature and extent of contamination was the critical first step. The Hart Senate Office Building contains approximately 10,000,000 cubic feet of office space that houses 50 Senators and their staffs as well as committee and hearing rooms. A letter containing anthrax spores was opened on October 11, 2001 on the sixth floor of the building. Once anthrax was identified as the biological contaminant, it became imperative to examine the extent of contamination. To do so, the U.S. Capitol Police, in conjunction with the U.S. Environmental Protection Agency and several other government agencies, conducted extensive testing of hard, soft, porous and non-porous surfaces throughout the building. Samples taken in the following days confirmed contamination on the first, fifth and ninth floors. The elevator in one corner of the building and the heating, ventilation and air conditioning system also tested positive for anthrax spores. It was evident at a very early stage that anthrax spores were widespread and they had found their way into several offices, as well as the ventilation system.

Evaluation of Remedial Alternatives

The most obvious solution for restoring use of the building was to use a chemical agent, one that was highly mobile, yet had sufficient strength to destroy anthrax spores. After consideration of a wide range of remedial alternatives, chlorine dioxide was selected as the primary agent because of its effectiveness for anthrax treatment. In addition, the ability to use chlorine dioxide (ClO2) in both liquid and gaseous forms, were characteristics considered very important by the remediation team. While other antimicrobial agents, including bleach (sodium hypochlorite), were employed in remediation of the Hart Senate Office Building, chlorine dioxide was the primary weapon used against the anthrax spores in the building space.

Several factors required consideration in decontaminating the building. Because of the different types of contaminated surfaces, the remediation team considered ease of application, obtaining desired contact time, and ability to decontaminate. These factors were important considerations in the selection process.

Meeting the Challenge of Decontaminating a Building

Fumigation using gaseous chlorine dioxide was identified by the remediation team as the best balance between efficacy and ease of application. Delivery of any gas into a building presents an enormous logistical challenge. While there was little doubt that chlorine dioxide could be an effective remediation tool, getting the gas into confined spaces became paramount. Anthrax spores are very small (1012 spores in one gram of Bacillus anthracis) and, once airborne, can easily infect humans.

Establishing the conditions required for efficacious destruction of anthrax in a building without damaging the building itself became the key issue. Prior to this event, such a task was thought to be impossible. While chlorine dioxide was known to be effective in the laboratory, field conditions became an important consideration. Remediation contractors established a test site at the Brentwood Post Office in Brentwood, Maryland to test chlorine dioxide under field conditions. A simulated office was treated with the gas to establish basic treatment parameters. These tests provided the basis for full-scale remediation of the Hart Senate Office Building.

Beginning Fumigation

The field tests identified several critical conditions required for effective remediation. First, the humidity in the building would need to be held at 75% throughout the application. Second, the temperature needed to be kept above 70o F during the entire fumigation period. Third, circulation of the gas throughout the contaminated areas was important to help ensure exposure of the gas to the anthrax spores, even in confined spaces. All these conditions must be met in order to effectively destroy anthrax spores.

In preparation for the fumigation, three thousand test strips of surrogate spores were placed in Senator Tom Daschle's office. The Senator's suite was isolated and windows were blacked out to minimize degradation of the chlorine dioxide gas that occurs when it is exposed to ultraviolet light. The surrounding block was cordoned off and air sampling monitors were put in place.

Once the humidity was raised to the identified level by pumping in steam, chlorine dioxide gas was circulated in the isolated area for over 20 hours. The gas was removed and treated with sodium bisulfite before it was discharged to the atmosphere. Wipe test samples analyzed after the initial fumigation indicated that chlorine dioxide was extremely successful in killing anthrax spores. After a second application of chlorine dioxide gas, along with liquid chlorine dioxide and bleach on hard surfaces, other areas were decontaminated. Some items were removed from the building and treated separately to complete the remediation, and the building was considered ready to be occupied.

Achieving Success

This type of remediation had never been done before. Now, it is the blueprint for additional sites including the Brentwood Post Office and dozens of other sites contaminated with anthrax. While no single chemical, or family of chemicals, will be the only alternative, the effectiveness of chlorine dioxide and bleach has demonstrated that chlorinated disinfectants and antimicrobials provide a critical defense against biological attacks of this type.

For more information visit the following web sites:

EPA's Role In Responding to Anthrax Remediation:

Additional Information on Chlorine Dioxide:

Additional Information on Bleach:

The author is the Director of the American Chemistry Council's Sodium Chlorite-Chlorine Dioxide Panel

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