Cleaning for Facility Decontamination

When is it Time to Clean for Facility Decontamination?

Simulated organic load with six common food products and dust covering the biological indicators.

In association with sterilizing and disinfecting agents for food processing, the term bioburden is exactly that—a burden. Materials which provide a safe-haven for unwanted microbes by covering and protecting them from decontaminating agents are considered bioburdens. Whether that bioburden is dirt, food remnants, or any other organic load, facilities have always been encumbered by the essential, timely, and overall costly task of its removal. Failure to physically rid focused areas of all bioburden prior to the administration of the decontaminating agent will in all likelihood result in inadequate kill. Due to this constraint, a study was performed to gain a better understanding as to “how clean is clean.” The goal was to determine how clean a facility needs to be for a gaseous chlorine dioxide (CD) fumigation to be successful.

Gaseous CD is an ideal sterilizer. CD is a true gas under ambient pressure and temperature and, when paired with its small molecular size, can be easily distributed into an area to reach inside nooks and crannies smaller than a micron. Its unique molecular composition can be advantageous over those of bleach (hypochlorous acid), ozone, and hydrogen peroxide by removing 5 electrons opposed to only 2 when reacting with organic loads. Through this process, gaseous CD’s reacting power is sustained for longer periods of time, which in turn, makes it more penetrable.

To understand “how clean is clean,” varieties of bioburdens and an indicator to denote the penetrability of gaseous CD needed to be established. In regard to the former, powdered milk, powdered baby formula, protein powder, flour, sugar, grains, and general dust/dirt were selected to simulate various bioburdens. This selection was based upon food material commonly found in food processing facilities that require physical removal prior to any form of decontamination. Whereas the latter, a Tyvek-wrapped biological indicator (BI), was selected to validate CD’s penetrability through the aforementioned organic loads while still demonstrating a 6-log sporicidal reduction.


Unlike antiseptics, germicides, sanitizers, or disinfectants, a sterilizer is the only antimicrobial pesticide that is considered by the U.S.-EPA to eliminate all forms of microbial life, including spores. Spore forming bacteria is amongst the most difficult bacteria to kill; therefore this is the reason why it is used to validate sterilization. In almost all cases of facility decontamination, validity is gauged by the results of BIs or through the practice of swabbing. The advantage of BIs is that they contain a known amount of organisms and those organisms are in the spore form, which is the most difficult to kill. Generally, a BI used to validate the success of a gaseous decontamination consists of a spore forming bacterium inoculated onto a stainless steel disc or paper strip. Otherwise known as a carrier, the disc or strip is enveloped in either Tyvek or glassine. The population, or amount of individual spores that are inoculated onto the carrier, is critical in determining the logarithmic reduction capabilities of that decontaminating agent.

The logarithmic reduction of microorganisms by a decontaminating agent directly reflects its efficacy. Because BIs have a fixed population of microbes, they are an ideal tool to gauge this effectiveness. In regard to gaseous CD, it is easily capable of yielding a 6-log reduction of all forms of microbial life. To better understand this, a 1-log reduction reduces all microbes by 10 times or 90 percent, whereas a 2-log reduction reduces all microbes by 100 times or 99 percent. Therefore, a 6-log reduction reduces all microbes by 1,000,000 times or eliminates 99.9999 percent of all microbes. Of course the population of organisms associated with the BI must be sufficient enough to support its efficacy. For example, a decontaminating agent cannot demonstrate a 6-log reduction by inactivating a BI with a population of less than 1,000,000 microbes.

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