Not All Chlorine Dioxide is Created Equal

A number of different methods can be used to generate ClO₂. Because of their pH dependency, however, many of these alternative methods produce ClO₂ solutions that are heavily contaminated with chlorine and other undesirable chlorine species. These impurities are undesirable because they can cause the formation of trihalomethanes and other potentially carcinogenic compounds during their use. The low pH exhibited by these impure ClO₂ solutions also makes them unacceptably corrosive for many industrial applications.

Sabre has solved this impurity problem by employing a special process that produces high purity ClO₂ in a pH neutral solution through the controlled reaction of sodium hypochlorite (i.e. bleach), hydrochloric acid, and sodium chlorite according to the following reaction:

ClO₂ Generation

In the Sabre process, the three precursor chemicals are reacted in a "column" under a strong vacuum created by water flowing through an eductor. The ClO₂ formed in the column is subsequently educted into the flowing water stream, where it becomes a dissolved gas in the water at a very safe concentration level of approximately 0.3 percent (i.e. 3,000 ppm). Once formed, the high purity ClO₂ can be applied as either a liquid solution or a gas.

When applied as a liquid, freshly generated ClO₂ solution is diluted to an effective concentration level of approximately 500 ppm and applied directly to areas of known microbial contamination.

When utilized as a fumigant gas, liquid ClO₂ solution is pumped from the generation area to locations inside the building where treatment is needed. The ClO₂ gas is then "stripped" back out of the water solution by means of an "emitter" at the point of use. Depleted solution flows back to the generator in a flow loop where it is "recharged" to a level of 0.3 percent and used again. ClO₂ gas is added to the building until the average concentration in air throughout the treatment zone is in the range of approximately 750 ppmv. After an average ClO₂ concentration of 750 ppmv has been reached everywhere in the treatment zone, this level is maintained for a period of at least 12 hours through continual monitoring and addition of supplemental ClO₂ as deemed necessary. The target "dose" of ClO₂ shown to be efficacious against even the heartiest of spore-forming bacteria, such as Bacillus anthracis (i.e. anthrax) is around 9,000 ppmv-hours.

At the conclusion of either a liquid or gas treatment, the ClO₂ decays naturally to harmless concentrations of various sodium salts including chlorite, chlorate and chloride. Given an adequate amount of time (i.e. 24 hours or less), a gaseous ClO₂ concentration in the range of 750 ppmv will normally "disappear" completely on its own without any action being taken. In the event that quicker removal of ClO₂ gas is desired, this may be readily accomplished by converting emitters in the treatment zone into active scrubbers.

Long before a contaminated building is ready for re-occupancy, there should be no evidence that ClO₂ was ever used. ClO₂ does not persist in the environment and its by-products are essentially innocuous.