Background

During the Anthrax attacks following September 11, 2001 the U.S. Government hired a major U.S. Government contractor to fumigate the 9 story, 100,000 square foot Hart Senate Office building in order to eliminate any anthrax spores inside the building. This fumigation was done with chloride dioxide, (CLO₂ ). CLO₂ was applied as a sterilizing agent.

Problem

Prior to the fumigation baseline nitrogen dioxide (NO₂ ) levels were determined in the areas surrounding the building.The NO₂background was important because NO₂ is a major interferant to the CLO₂ detection system that was to be deployed during fumigation events. The major sources of man-made NO₂ emissions are high-temperature combustion processes, such as those occurring in automobiles and power plants. Home heaters and gas stoves also produce substantial amounts of NO₂ in indoor settings. Because NO₂ is a interferant of CLO₂ and it's presence would indicate an elevated levels of CLO₂ if not removed from the readings at time of fumigation.

Solution

Air samples from a number of different locations and at different times were necessary. It was decided a portable system, easily carried would the best solution. By walking the neighborhoods for three hours at different times of the day the baseline information could be gathered. A Logic Beach ModuLogger MINI was mounted in as a "backpack" on the CLO₂ sensor. An individual walking the targeted areas could then easily carry the whole setup. Air samples were taken every 10 seconds and recorded in the MINIs on-board memory. Using the power of the data loggers on board programming the voltage input from the gas sensor was immediately converted to parts per billion as well as the minimum and maximum values. The ModuLogger MINI performed flawlessly and within minutes of ending the sweep the contractor "had all the information they needed for that slice of time." 18 recording sessions were undertaken which revealed the average levels of NO₂ and a maximum of 60ppb. Once the fumigation began the presence of CLO₂ above these levels was then considered a risk. The sample program NET was used to record the NO₂ data and produce baseline levels for use when sterilizing took place.