Food Processing Equipment Disinfection

Chlorine dioxide treatment for food processing is often used for microbial decontamination on food processing equipment as well as entire food processing plants. Many food processors utilize a chlorine dioxide treatment after new construction to reset the microbial environment and assure a clean start-up. Other uses in the food industry include specific applications for fruit and vegetable, cheese & milk products, bakery and meat processing as a disinfectant spray, for packaging and container disinfection, a-septic filler disinfection, piping disinfection, ductwork disinfection, clean in place applications (CIP), disinfection treatments for the recycling of process water, treatment of source water, carcass wash, and flume disinfection.

PureLine - Food Beverage

The food industry relies heavily on chlorine dioxide for many treatment applications. Approved by the EPA for potable water applications and by the FDA for use as a disinfectant in the processing of foods and beverages, chlorine dioxide is the perfect solution to many of the problems food and beverage companies encounter on equipment, in drains and floor areas and in their air and water supplies. PureLine Solutions patented equipment options and pre-cursor chemicals are also NSF certified.

The unique properties of chlorine dioxide, including it being extremely effective without affecting taste and the ability to immediately resume plant operations upon cessation of a gas or aqueous phase sterilization process, are just a couple reasons that chlorine dioxide is the preferred choice for multiple applications in the food and beverage processing industry. PureLine Solutions makes chlorine dioxide an even better choice with their patented chlorine dioxide generation systems, producing a 99.5% pure, pH neutral solution with no reaction by-products passed through to your air and water systems.

With experienced, expert engineers, chemists, and technicians, PureLine Solutions stands ready to assist you with plant decontamination needs, resetting of your environment upon completion of new construction, and assisting you and/or your existing water treatment partner in every aspect of the evaluation, design, implementation, and long-term support of your custom chlorine dioxide solutions.

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The Food Processing Industry

Chlorine Dioxide (ClO2) in the food industry is important for many critical processes that include baked goods, fruit and vegetable, milk and cheese, and meat processing. Applications include gas and aqueous disinfection, disinfectant sprays, packaging and container disinfection, a-septic filler disinfection, piping disinfection, ductwork disinfection, clean in place applications (CIP), disinfection treatments for the recycling of process water, treatment of source water, carcass wash, and flume disinfection.

The food industry relies heavily on chlorine dioxide for many treatment applications. Approved by the US Environmental Protection Agency (EPA) and by the US Food and Drug Administration (FDA) for use as a disinfectant in the processing of foods and beverages, chlorine dioxide is the perfect solution to many of the problems food and beverage companies encounter on equipment, in drains and floor areas and in their air and water supplies. PureLine Solutions’ patented equipment options and precursor chemicals are also NSF certified.

The unique properties of chlorine dioxide, including it being extremely effective without affecting taste and the ability to immediately resume plant operations upon cessation of a gas or aqueous phase sterilization process, are just a couple reasons that chlorine dioxide is the preferred choice for multiple applications in the food and beverage processing industry. PureLine Solutions makes chlorine dioxide an even better choice with their patented chlorine dioxide generation systems, producing a 99.5% pure, pH neutral solution with no reaction by-products passed through to your air and water systems.

Physical Properties

Size of chlorine dioxide molecule

At 124 picometers (0.000124 micrometers), a chlorine dioxide gas molecule is much smaller than any microorganism. Chlorine dioxide is a real gas and by definition expands and conforms to the shape of the area in which it is held and acquires a uniform density inside that area, even in the presence of gravity and also regardless of the amount of equipment in the area.  This property of chlorine dioxide gas allows it to easily penetrate and disinfect locations where other fumigant applications such as dry fog is not able to effectively reach.

Chemical Properties

Chlorine dioxide is a visible yellow-green gas with a swimming pool-like odor allowing it to be detected well below its 8-hour human habitation ‘safety’ level of 0.1 parts-per-million. Chlorine dioxide is a strong, yet selective oxidizing agent that does not produce harmful or environmentally hazardous by-products. When reacting with other substances, chlorine dioxide is selective, allowing it to be a more efficient and effective sterilizer than many other options. Chlorine dioxide is not a carcinogen nor is it a poisonous gas. Furthermore, chlorine dioxide does not leave any residues and there is no need for post-application clean up prior to resuming plant operations. Once the gas has dissipated to a safe level of < 0.1 ppm, typically within 60 minutes of cessation of gas generation, personnel may enter the area and plant operations can resume normal processing immediately.

Chlorine dioxide is a selective oxidant and reacts with several components of microbial cells.  It breaks the molecular bonds in cell membranes and directly interferes with, and destroys the metabolic process, therefore permanently disabling and killing bacteria, virus and mold very quickly.  Because it is selective, the oxidizing action is retained longer than other treatment agents and therefore allowing for maximum kill.


In microbiology the probability that an object that has been subjected to a sterilization process may nevertheless remain nonsterile is called the sterility assurance level (SAL).  The SAL is used to measure the probability of microorganism survival and measured in orders of magnitude reduction, also called a “log” reduction.

The sanitization standard for contamination reduction of non-food contact surfaces is generally accepted as 99.9% (3-log reduction) and for food contact surfaces, as 99.999% (a 5-log reduction). For sterilization, the standard is generally accepted as 99.9999% (a 6-log reduction).

Chlorine dioxide, when applied correctly, provides for sterilization (6-log reduction).  Chlorine dioxide is therefore defined as a chemical sterilant and is a selective oxidant that effectively destroys several components of microbial cells. It destroys the DNA in cells and, therefore microorganisms such as bacteria, virus and mold are unable to build up a resistance. Because chlorine dioxide is selective, the oxidizing action is retained longer than other fumigation agents such as peracetic acid or hydrogen peroxide, therefore allowing for maximum kill.

Bacterial spores (available from several scientific sources) have long been considered the gold standard for proving an effective sterilization process.  Spores are extremely difficult to kill and therefore a sterilizing agent must be able to destroy spores and therefore considered as the most rigorous decontamination method. Although a 99.999% (5-log reduction) sanitation standard is accepted in the food industry, chlorine dioxide is classified as a sterilant and therefore much more powerful in the fight against presumptive or persistent pathogen problems.

Sterilization vs. Disinfection

Sterilization is defined as the process of all microbial life being eliminated, which may be accomplished by chemical or physical means.  A chemical sterilant must completely eliminate and inactivate spores, and therefore is verified to mean that it can eliminate and destroy all microbial life.  A 6-log reduction (99.9999%) is defined as the level required to achieve sterilization.  Sterilization is meant to convey an absolute, however; sometimes various commercial documents may make references to a ‘partial sterilizing’ agent.  To be clear, and based upon the definition of sterilization, a chemical or other decontamination method cannot ‘partially sterilize’ and can only be classified as a sterilant if it is proven to destroy spores and thus eliminate all microbial life.

Chlorine dioxide molecule

Disinfection is defined as the process of many or all pathogenic microorganisms being eliminated, except bacterial spores. In the food plant setting, floors and equipment are often routinely washed and cleaned by hand with various chemicals, with the goal of sanitizing food contact surfaces to eliminate pathogen contamination and meet the 5-log reduction (99.999%) sanitation standard for food contact surfaces and the 3-log (99.9%) standard for non-food contact surfaces, however; these methods seldom reach the level of disinfection.

Many factors influence the efficacy of disinfection and sterilization methods.  These include the frequency of routine equipment cleaning; organic load or inorganic load on surfaces; the type of microbial contaminants present; biofilm presence; temperature; ambient light, relative humidity and the level to which equipment has been designed and installed to meet accepted sanitary design standards.

Unlike sterilization, disinfection may sometimes, but does not always kill spores. A ‘high-level’ disinfectant is defined as the ability to kill all microorganisms except large numbers of bacterial spores. Intermediate-level disinfectants kill most vegetative bacteria, most viruses, and most fungi but are unlikely to kill bacterial spores. Low-level disinfectants can kill most vegetative bacteria, some fungi, and some viruses, but will not kill spores.

Solubility in Water

Chlorine dioxide is used in many public drinking water supplies and in water supplies used for industrial settings such as water purification in pharmaceutical companies and oil well drilling.  Chlorine dioxide does not react with water and therefore retains its sterilization capabilities when dissolved in water. A 5-ppm chlorine dioxide solution is effective as a sanitizer (5-log or 99.999% reduction) with a contact time of at least 1 minute. Further, disinfection is achieved with 100 ppm using a contact time of 10 minutes. (Pfunter, 2011).  Pureline Solutions offers a unique chlorine dioxide floor wash service, that is often combined with a chlorine dioxide gas treatment to initially disinfect floors and drains and subsequently offering a complete sterilization process.

Safe for the Environment

Chlorine dioxide is an ideal choice to minimize impact on our environment.  It is often the preferred alternative to other options such as ozone, chlorine bleach, hydrogen peroxide and peracetic acid. Compared to these other options, a chlorine dioxide application is far less corrosive.  While many people may confuse the use of chlorine with chlorine dioxide, they are very different. As an example, when chlorine reacts with organic matter, undesirable pollutants such as dioxins and bio-accumulative toxic substances are produced. Chlorine dioxide eliminates the production of these pollutants and does not chlorinate organic material, eliminating the formation of trihalomethanes (THMs), halo acetic acids (HAAs) and other chlorinated organic compounds.

Chlorine Dioxide - Safe for the Environment


Chlorine dioxide is a widely used antimicrobial in drinking water, process water, swimming pools, and mouthwash preparations. It is frequently used to treat fruit and vegetables and to decontaminate equipment for the food and beverage processing industry and is widely used in pharmaceuticals and life science research laboratories. The health care industry uses chlorine dioxide to decontaminate rooms and for equipment and component sterilization. For years, chlorine dioxide has been used extensively in the paper-pulp, flour, leather, fats & oils, and textile sectors.


Over the past several years, the food and beverage industry has increasingly embraced chlorine dioxide as the preferred method for resetting the microbial environment and ensuring the safety of foods being prepared for humans and animals alike.  There has been confusion and sometimes conflicting information regarding its properties, behavior and capabilities. The following will further clarify why chlorine dioxide has become the choice for safe elimination of harmful bacteria and other microbial contaminants in the food and beverage industry.


Chlorine dioxide is classified as a sterilant.  Sterilants are defined by their ability to destroy bacterial spores, thus confirming that all other microbial life present in the treatment area has been eliminated. Chlorine dioxide works by penetrating the cell wall of microorganisms and disrupting the pathogen’s metabolic functions, thus immediately and permanently eliminating the problem at its source. It is a powerful biocide at concentrations as low as 0.1 parts-per-million over a wide pH range, does not produce hazardous by-products, and is more effective than hydrogen peroxide, peracetic acid, quaternary ammonia and sodium hypochlorite (chlorine bleach). Studies from the FDA and EPA show that chlorine dioxide is effective in eliminating over 20 of the most common harmful pathogens, including Salmonella, Listeria, E Coli, Clostridia, B anthracis (anthrax), and several species of fungal molds and yeasts.

Chlorine dioxide is a real gas at room temperature. As a real gas, it expands to uniformly fill the space it is contained within, regardless of the effect of gravity. This gives it the natural ability to contact all surfaces within a space in equal concentrations, guaranteeing an even level of kill throughout the space. Its small molecular size coupled with this distributive ability allows the gas to penetrate even the smallest cracks and crevices in walls and floors and reach all surfaces of food processing equipment.


Unlike some other fumigants such as hydrogen peroxide which leaves a residue and is also a human carcinogen, chlorine dioxide gas does not leave a residue, is not a carcinogen, nor is it a poisonous gas.

Some chemical fumigants are applied using a dry fog and/or vapor decontamination method which leave a residue, necessitating a post-treatment cleaning, and often requiring an extended period of time prior to resuming plant operations to allow the chemical concentrations to dissipate and reach levels safe for human habitation. This residue is attributed to the nature of these products and their composition.

Chlorine dioxide does not leave a residue and does not require post-treatment cleaning. Processing plants can immediately be re-occupied and begin production once gas levels have reached the safe human habitation level of 0.1 parts-per-million, typically within 60 minutes of gas cessation.


The concentration at which chlorine dioxide gas is used for fumigation is more than 1,000 times less than the explosive threshold. This makes the risk of explosion ZERO as explosive concentrations cannot be achieved during the fumigation process. There is some truth to the notion that chlorine dioxide can be explosive. Chlorine dioxide, if compressed, may be explosive and this is the reason why it must be created at its point of use. Pureline creates pure chlorine dioxide gas on-site using two different and distinct safe methods and does not incorporate any compressed gasses in any form, in the fumigation process.


There is no evidence that chlorine dioxide is a carcinogen. Chlorine dioxide can be found in toothpastes and mouthwashes. It is used to treat municipal drinking water supplies and to rinse various fruits, vegetables, and meats. Both the EPA and FDA have approved the use of chlorine dioxide for use in these instances.


Chlorine dioxide does not react with water, has a neutral pH in water, and stays as chlorine dioxide within the water. This enables it to kill organisms within the water, as well as any on the surface beneath the water. This trait is unique to chlorine dioxide among decontaminating agents.

When mixed with water, chlorine bleach (sodium hypochlorite) forms hydrochloric acid.  Hydrogen peroxide, by contrast, will dilute in water and cannot kill organisms within or beneath the water.


Chlorine dioxide gas cannot be safely compressed and therefore it is required that it be produced on-site at the point of use.  There are several methods of producing chlorine dioxide.  PureLine Solutions uses methods that create a safe and effective 99.5% pure chlorine dioxide gas that DOES NOT require humidity controls and produces guaranteed sterilization results.

Some companies use methods that utilize highly corrosive chlorine gas in their process, requiring humidification of the area being treated.  The chlorine gas is filtered through a chemical matrix, which under humidity control of 65 – 75% will produce chlorine dioxide gas, however; if humidity is not high enough then highly corrosive chlorine gas may be present in the treatment area, increasing the possibility of corrosion on metals and other materials.

Material Compatibility

A typical chlorine dioxide decontamination treatment exposure is often in the range of 1,000 – 1,500 ppm-hours (concentrations of ~200 ppm for five to eight hours).  Pureline has performed rigorous testing of stainless-steel exposure to chlorine dioxide and has shown no signs of corrosion with concentrations as high as 900,000 ppm-hours (50,000 ppm for a period of 18 hours).  The exception to any evidence of corrosion on stainless-steel would be due to poorly passivated welds, and/or other deposits resident on the stainless steel which may show signs of oxidation.

Chlorine dioxide itself has been shown to be compatible with stainless steel and many other metals through exposure studies using the pure, gaseous form. The concern about chlorine dioxide corrosion is most likely due to confusing it with chlorine or chlorine gas. Also, some liquid chlorine dioxide solutions are produced by mixing a sodium chlorite base with an acid (most commonly citric acid) which creates a liquid acidified chlorine dioxide solution as well as chlorous acid and acidified sodium chlorite. It is these acidic by-products which can cause corrosion of metals. PureLine Solutions creates a 99.5% pure chlorine dioxide treatment with zero acidifcation or acidified by-products.

Commonly used food plant chemicals such as sodium hypochlorite, peracetic acid and hydrogen peroxide are much more corrosive than chlorine dioxide. The following chart illustrates that chlorine dioxide is far less corrosive than the other microbial fumigants listed below.

Other than unpainted mild steel, which may show signs of light oxidation, no other metals will be affected by chlorine dioxide.  Below are photographs of stainless steel exposed to 50,000 ppm over an 18-hour period (900,000 ppm-hours), and also unpainted mild steel exposed to a typical microbial treatment exposure of ~200 ppm over 8 hours (~1,600 ppm-hours).

Corrosion Bar Chart
Pureline Metal Exposure


PureLine - Food Beverage

Pureline uses a 99.5% pure chlorine dioxide gas, which is scientifically and statistically less corrosive than hydrogen peroxide, peracetic acid, ozone and sodium hypochlorite (bleach).

Chlorine dioxide gas is used safely every day to decontaminate rooms, suites, and other spaces. Hydrogen peroxide is most often injected as a vapor into the space being decontaminated. Unlike consumer use of 3% hydrogen peroxide, decontamination services using this chemical typically deploy a 35% hydrogen peroxide / 65% water composition. When the hydrogen peroxide vapor condenses, the condensate’s hydrogen peroxide concentration can increase from 35% to almost 80%. This increase in concentration adds to hydrogen peroxide’s corrosive nature, as noted in its incompatibility with some epoxy finishes on walls and flooring as well as other materials.

Chlorine dioxide has a 0.1 part-per-million (ppm) 8-hour safety level for human exposure. Chlorine dioxide gas has an odor similar to a swimming pool and can be sensed (smelled) below the 0.1ppm threshold, acting as an alert in case of a leak, as personnel are aware of the leak at very low levels below the safe human habitation level, allowing them to act upon it as they deem fit (either aborting the process or fixing the leak). By contrast, hydrogen peroxide is odorless, and any leakage cannot be easily identified by nearby personnel, allowing for leakage and exposure to personnel to continue and worsen.

A benefit of chlorine dioxide is that it is a real gas and therefore will expand to uniformly fill the space it is contained within, regardless of the effect of gravity.  This allows the gas to contact all surfaces within a space in equal concentrations, guaranteeing an even level of decontamination throughout.  It’s small molecular size coupled with this distributive property allows the gas to easily penetrate microscopic cracks and crevices. To contain the gas during treatment, the treatment area can be isolated from the HVAC system and from other non-treatment areas when sealed with common polyethylene plastic and tape.

Another property which aids in the safety of the chlorine dioxide process is its status as a real gas. Chlorine dioxide does not condense on surfaces; therefore, in case of emergency the gas can be aerated down to safe levels quickly. Hydrogen peroxide is a liquid at room temperature and therefore condenses on surfaces. This condensate takes much longer to dry and aerate from a space, needing hours if not overnight before it is safe for human habitation. This means that in the event of leakage, chlorine dioxide gas can be removed making the area safe quickly, while hydrogen peroxide may take until the next day.

Chlorine dioxide gas and chlorine dioxide aqueous solutions, when applied safely and effectively, are more effective in killing harmful bacteria, mold and spores and far less corrosive than most other microbial fumigants. Due to its nature as a gas that does not condense on surfaces, a plant can be re-occupied, and operations can resume immediately upon aeration and reducing gas level to the 8-hour safety level of 0.1 ppm or less, often within no more than a few hours of cessation of gas production.

A significant added value in using Pureline is our capability to safely and cost effectively deploy a chlorine dioxide decontamination engagement for areas ranging from small electric cabinets to entire plants up to several million cubic feet. Additionally, Pureline can train your operators in the safe deployment of PureVistaTM, our 99.5% pure chlorine dioxide product, for areas up to several thousand cubic feet, helping you cost-effectively manage your sanitation and decontamination needs.


Since the 1920s, chlorine dioxide has been known for its disinfecting properties. It was recognized as a chemo-sterilizing agent in 1984; and in 1988, it was registered with the US Environmental Protection Agency (US EPA) for use as a sterilant. The USDA has deemed chlorine dioxide as certified for organic use in crop production, as an algicide, disinfectant and sanitizer.  In addition, no corrosion is observed when using materials such as stainless steel, Lexan, and various other plastics such as Delrin, Teflon, and ultra-high molecular weight polyethylene (UHMWPE). With appropriate delivery equipment and care, chlorine dioxide is a safe and effective means of decontamination. A significant safety feature of chlorine dioxide is that it has a distinct odor much like a swimming pool, making even minor leaks self-alerting, well below the human habitation safety limit.

Both gaseous and aqueous phase chlorine dioxide has been proven to be an effective sterilizing agent that has broad and high biocidal effectiveness. Both forms of chlorine dioxide have been reported to effectively inactivate bacteria, including pathogens, viruses, bacterial spores, and algae.

Gaseous chlorine dioxide has proven to be an effective sterilant. Jeng and Woodworth (1990) reported the sporicidal activity of chlorine dioxide gas. Gaseous chlorine dioxide has successfully been used to decontaminate B. anthracis (anthrax) contaminated areas of the Hart Senate Office Building and the Brentwood postal sorting facility in Washington, DC.  Hans et al. also reported high efficacy of chlorine dioxide gas in reducing Bacillus spores on paper, plastic, epoxy-coated stainless steel and wood surfaces. Additionally, much research has demonstrated that chlorine dioxide gas is highly effective in eliminating foodborne pathogens such as E. coli, Listeria and Salmonella.

The following chart illustrates the effectiveness of chlorine dioxide in the treatment of microbial growth problems.

Microbe Decon Chart

Chlorine dioxide is very reactive and completely destroys the cell by disrupting the DNA and thus microorganisms such as bacteria, mold, and viruses cannot build up a resistance.


Microbial Biofilms

Chlorine dioxide has been shown to be an effective antimicrobial agent capable of destroying biofilms. Biofilm forms when bacteria adhere to surfaces in moist environments by excreting a slimy, glue-like substance. Sites for biofilm formation include all kinds of surfaces and can be a major concern in food processing plants. Wherever you find a combination of moisture, nutrients, and a surface, you are likely to find biofilm.

Microbes like to grow on surfaces, whether natural or manmade. When it comes to industrial surfaces, bacteria are just doing “what comes naturally” by attaching to the surfaces with which they come into contact. However, their propensity for attachment may cause many problems for the food processing facility.

A biofilm community almost always consist of rich mixtures of many species of bacteria and other microorganisms. Biofilms are held together by a matrix of sugary molecular strands, collectively termed “extracellular polymeric substances” or “EPS.” The cells are held together by these strands, allowing them to develop complex three-dimensional, resilient, attached communities.

Cell to Cell Communication

Many studies have shown that the multicellular construction of biofilms affords protection for cells, making them less susceptible to antimicrobial agents. This protection is the result of intrinsic shifts in genetic expression when floating bacterial cells attach to surfaces and begin to form biofilms.

In biofilms, the matrix material (EPS) that holds cells in proximity allows concentrations of signal molecules to build up in enough quantity to effect changes in cellular behavior. Bacterial populations will activate some genes only when they are able to sense, via cell signaling, that their population is numerous enough to make it advantageous and/or “safe” to initiate that genetic activity. For example, some bacterial pathogens will not produce toxins until they sense that an adequate population has been established to survive host defenses.

Chlorine dioxide is effective at eradicating biofilms. In rigorous studies performed by Montana State University Center for Biofilm Engineering, chlorine dioxide gas concentrations of approximately 250 parts-per-million on a log 8 biofilm (108 CFU/cm2) resulted in a log 6 kill after 4 hours.  It should be noted that a log 8 biofilm is a substantial biofilm, that would be far in excess of what would be expected on a regularly cleaned surface or a partially wetted surface in any environment.

Environmental Testing to Prove Eficacy

For any cleaning process, it is important to quantify the results. PureLine Solutions utilizes three separate and distinct methodologies to measure microorganism presence to help you confirm a clean break has been achieved post chloride dioxide sanitization process. This three-pronged validation process provides you with the confidence of a clean break.

  1. ATP-based microbiologic monitoring methods were developed to monitor the cleaning and sanitization of equipment and materials, and immediately detect the presence or absence of organic material (live or dead) on solid surfaces. xvii, xix ATP monitoring systems are used in food production facilities, state health laboratories, and drug companies xx, xxi. PureLine Solutions uses the NEOGEN AccuPoint Advanced ATP detection device, which uses bioluminescence to indicate the level of residual ATP present on swabbed surfaces. The amount of ATP present on the surfaces tested are then quantified by the amount of light emitted during the enzymatic reaction (relative light units, RLU). The NEOGEN recommended scale is used in PureLine Solutions sanitization treatment processes: <150 = pass, 151 – 299 = caution/marginal, and > 300 = fail.
  2. Swab testing in the food industry has long been a standard process in measuring the level of micro-organisms present on surfaces. PureLine Solutions uses pre- and post- treatment sterile swabs which are cultured to quantify the number of colony forming units (CFUs/ml).
  3. Biological indicators; a spore forming bacterium that is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products, are used to determine log kill. The capability to form endospores makes these organisms resistant to extreme conditions such as pressure, extreme heat or cold, drought, starvation, biocides, and UV irradiationxxii (Moeller et al., 2008). Because the spores used in biological indicators are the most resistant spores to the chlorine dioxide sterilization process, a biological indicator that does not survive the treatment process indicates that other potential spores or bacteria in the sterilization load have also been killed. PureLine Solutions uses biological indicators affixed at each of several environmental test sites, which are incubated post-treatment, and used to determine effective log kill of micro-organisms in the treated facility to achieve a clean break.

Environmental test sites are prepared as follows:

4” x 4” sterile swab and ATP templates are placed on the floor at designated locations. Biological Indicators are placed in proximity to these templates.

A swab sample and ATP reading are taken for each site prior to, and immediately after the chlorine dioxide application(s). ATP readings are available immediately. Swab samples are sent to an accredited third-party lab and results reported in colony forming unit (CFU/ml). Biological Indicators are cultured for a specified time and results reported in “log kill”.

Hygiene and Sanitation
Bacterial Spore Test Strips


PureLine Research

During the disinfectant treatment, chlorine dioxide gas is exposed to varying environmental factors of light, temperature, and humidity which influence it’s disinfectant efficiency.

In several studies, including research by Lee et al.xxiv, the effect of UV-A and fluorescent lamp on chlorine dioxide gas degradation was observed. The degradation of gas under these conditions followed a first order reaction. In this research, gas degradation using a 40-Watt UV-A lamp was approximately four orders of magnitude larger than with a 34-Watt fluorescent lamp. In dark conditions, less than three percent degradation in gas was observed over a period of six hours. Therefore, while not a necessary requirement for chlorine dioxide treatment efficacy, a no-light or low-light environment is optimal.

In the same study, the effect of temperature on the degradation of chlorine dioxide gas was observed at 5°, 23°, and 40°C. In all cases, the effect of temperature was negligible indicating that treatment efficacy is not dependent on environmental temperature gradients in this range.  When treatments are performed in spiral freezers or other areas  that typically operate at  freezing or below temperatures, the cooling units should be shut off such that the  temperatures are at 5° C or higher during the treatment process.


During the disinfectant treatment, it is important to monitor chlorine dioxide gas concentrations to assure an effective dosage is being applied to the treatment area. PureLine Solutions utilizes concentration monitoring devices specifically designed and calibrated for chlorine dioxide gas. Monitors capable of reading concentrations between 0 and 1,000 parts-per-million (ppm) are used in the treatment areas to measure gas levels and report the total ppm-hours delivered. As a safety precaution, low level monitoring devices capable of detecting 0 – 2.0 ppm are placed in areas where no gas is expected to leak. The chart on page 14 identifies the various dosing requirements to effectively kill the varieties of bacteria and fungus most typically found in a food processing plant. The monitoring devices are placed in several locations within the treatment area prior to engagement of the gassing process and measurements are recorded throughout the process, including demarcation of when gas exhaust starts and when the “all clear” is given identifying the gas levels to be at or below the 0.1 ppm level when personnel are allowed to re-enter the area and respirators are no longer required to be worn.

60 Minutes After Start of Treatment
2 Hours After Start of Treatment

Concentration Calculations

When considering how to describe the efficacy of any fumigation treatment, the important treatment parameters are: temperature over the duration of the treatment; relative humidity over the duration of the treatment; the extent to which the target organisms were exposed to chlorine dioxide; and the concentration of exposure. The extent of exposure to the gas is described as “concentration over time” or CT. Usually the CT product is expressed in terms of hours of exposure multiplied by parts-per-million (ppm) or milligrams-per-liter (mg/l). The shorthand version of this calculation is ppm-hours or mg/l-hours. The concentration target for a chlorine dioxide treatment is in the range of 1,000-1,500 parts-per-million hours over a six to eight-hour exposure in a typical food processing plant treatment.

The formula given for use under leak proof conditions is:



Tn is the time the first reading was taken in hours.

Tn+1 is the time the second reading was taken in hours.

Cn is the concentration reading at Tn in ppm.

Cn+1 is the concentration reading at Tn+1 in ppm.

Ctn,n+1 is calculated CT product between Tn and Tn+1 in ppm.

Half the sum of two consecutive gives the average concentration between the two. These two formulae disregard the first rectangle (i.e. between the time of initial fumigant injection and the first reading due to the uncertainty of adequate mixing of the fumigant in the air surrounding the treated article and within the treated area).

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