Decontamination Foggers

Decontamination Foggers and Liquids – Droplet Evaporation

In the Sanitizing and Decontamination Fogger market, fog droplet diameter has been the primary focus over the last two years with the understanding that the smaller the droplet diameter in the output of a fogger, the more effective the fogger is at introducing enough aerosol droplets to the local airflow. Devices emitting 35-micron and larger droplets operate as sprayers, while fogger devices emitting liquid droplets less than 35 micron in diameter are foggers; and devices emitting droplets with 10 micron or less diameter are referred to as dry foggers. Sanitizing foggers are designed to emit droplets that have time to evaporate in the airflow to form a larger vapor gas cloud in which molecules of the sanitizing liquid encounter and kill unwanted bio-organisms. The intent is to convert a sanitizing / decontaminating liquid into small enough droplets that evaporate into the airflow and not land on the ground creating a wet surface. The objective is to convert as close to 100% of the available decontamination liquid into a suspended vapor with the desired vapor density in the airflow to efficiently kill bio-organisms that are dangerous to humans, food and dairy animals and food plant growth. Unwanted bio-organisms include spores, molds, fungi, viruses such as COVID-19 and Coronavirus, Rhinovirus and Candida auris fungus, which attacks the lungs and brain.

Sauter Limit

Many people think the spherical diameter of suspended liquid droplets into an airflow should be around 5 microns. Using water droplets as the standard carrier of a decontamination liquid, a 10 micron or less droplet meets the dynamics of the Sauter Limit. This is a reference to ≤ 10-micron droplet diameter of water droplets that begin to float in 1 atmospheric pressure, low droplet velocity and standard humidity of 40%. In nearly all sanitizing equipment discussions, the Sauter Limit is the single focus for Marketing and Sales of the sanitizing foggers, i.e., “if our products produce a sanitizing fog droplet under the Sauter Limit, then we have a good sanitizing fogger product”.

But this singular focal point on very small fog droplets is not correct, for example a 5 micron fog droplet is under the Sauter Limit. Smaller droplets are emitted at very low velocity in the airflow. The airflow velocity around the droplet, or conversely the velocity of the droplet in a slow airflow is essential and more beneficial. Airflow around the droplet is critical to evaporation of the droplet, converting the liquid source into an exponentially larger vapor cloud (a gas), enabling the disinfectant solution in the water droplet to turn into a vapor as the water droplets evaporate, allowing the disinfectant molecules to contact and kill the dangerous pathogens in the airflow and the immediate physical surface areas. The converse to airflow velocity around a droplet of sanitizing liquid is droplet velocity injected into the airflow at the output of a fogger, where airflow velocity is the speed of the airflow in feet or meters per second, which flows around droplets in the airflow. If you control droplet size and droplet velocity through a relatively slow airflow, the decontamination fogger can be far more effective to decontaminate your objective. Decontamination foggers are most effective by operating at 15 microns, so as to get much more volume of disinfectant vapor into the airflow.

If you inject small diameter droplets into a slow-moving airflow, the concentration of droplets in the airflow is equally low without getting a significant movement of that airflow, other than the existing airflow velocity. However, if you inject larger diameter droplets at a controlled velocity into the airflow, you achieve airflow movement, increased decontaminate surface area contact in the airflow, resulting in increased evaporation, which in turn accelerates the decontaminating vapor volume outward in the airflow and increases the volume of the decontaminate vapor cloud to sanitize a larger volumetric area.

PathAway Decontaminate to kill Pathogens in Cattle and Olive Tree growth. Our PBF-48 with PathAway Solution from YesAnalysis eliminated pink eye and hairy foot wart.

Decontaminating Fogger Technology

Sanitizing foggers are typically the tool used to introduce sterilant droplets into the airflow, and these foggers come in three primary technical designs:

  • Dry Fogger – Using positive pressure from an external, filtered air compressor with air pressure applied into a liquid volume, which is directed to a specifically designed nozzle to emit a controlled droplet diameter of 7.5 microns, using a positive pressure to directly push the liquid into the nozzle or using positive pressure to create a venturi affect to pull the liquid thru the nozzle, both applications producing the desired liquid droplet diameter output of 10 microns or less in diameter; in this case 7.5 microns;
  • Vapor Generator – Using electrical power to an electrode to convert the liquid to a vapor droplet, which is then evaporated to a desired droplet diameter by controlling electrode current, heat and a slight positive pressure, producing the desired liquid droplet diameter output of 10 microns or less in diameter, typically 5 microns;
  • Ultrasonic Generator – Using ultrasonic piezo technology and an internal fan, 8 to10 micron droplets are generated and pushed into the local airflow at a typical 36-90 CFM;
  • Fog Generator – Using positive pressure from an internal (onboard) air generator with air pressure applied into a liquid volume, which is directed to a specifically designed nozzle to emit controlled droplet diameter ranges at a nominal 15 microns, 30 microns or 50 microns, using a positive pressure to directly push the liquid into the nozzle or using positive pressure to create a venturi affect to pull the liquid thru the nozzle, both applications producing the desired liquid droplet diameter output of 15 microns or larger, based on Nozzle selected.

Each fogger design has advantages in use and application. Dry Foggers are most often used in large inside areas to sanitize unwanted pathogens within volumetric areas of 7500 cubic feet to 30,000 cubic feet per cycle, also contacting the accessible surfaces within the volumetric area. Driven by an external dry air compressor, the dry fogger introduces outward movement of the sanitized airflow. Vapor Generators introduce a smaller diameter droplet at low exit velocity, thus evaporate quickly but require a moving airflow for best results, such as HVAC, small volume tunnels, etc. Ultrasonic Foggers do not require an external compressor and produce a steady volume of liquid to a typical 10 micron or less droplet diameter. Fog Generators have wider applications, since they can be provided with small, medium or large droplets, depending on the sanitizing applications required. In addition, Fog Generators provide higher velocity output, can introduce more droplets in the airflow at higher velocity, thereby providing increased evaporation rates due to increased surface contact, and higher concentration of decontaminant in the airflow.


Using the typical liquid volumes in the respective foggers discussed above, one can estimate the number of droplets produced in a given liquid volume at a given droplet diameter. This then describes the evaporative surface area contact per minute and in total volume. One way to understand droplet evaporation is to visualize how a droplet evaporates in angstrom thick layers, i.e., each moment as the air passes by the droplet, evaporation of that liquid boundary to a vapor occurs; steadily decreasing the diameter of the liquid droplet to zero, while expanding the decontaminating vapor volume from that liquid droplet.

At a specified given liquid volume, you can have trillions of 5-micron droplets or billions of 15-micron droplets. If you have for example 10 liters of liquid volume, whether converted to 5-micron droplets or 15-micron droplets, evaporation of the ten liters of liquid will still produce the same volumetric size vapor gas cloud if the droplet is allowed to evaporate in the airflow.

The analogy is if you poured the 10 liters of water out on an infinite flat surface, the molecules of water at the air/liquid boundary will quickly begin to evaporate to a gas state. The large puddle shrinking to a small puddle, eventually disappearing. Whether you have a flat evaporate surface, a 5-micron or 15-micron spherical surface, the volume of water will evaporate at the surface to the same gas volume. Water molecules of liquid are a typical 5 to 10 angstoms in diameter. When combining decontaminate liquid chemistries with water, the decontaminate molecules will be larger than a water molecule. Since we are discussing decontamination, evaporation of the decontaminate liquid occurs at the liquid surface boundary in contact with the airflow at any given moment. Airflow over the droplet surface and electrical charges in the airflow and within the liquid droplet controls the conversion of the droplet to an aerosol decontaminate gas. The fogger difference being the size of the droplet emitted and the velocity at which the droplet is emitted as it flows thru the surrounding airflow.

A 5-micron droplet evaporates in a short distance; thus, can be injected into smaller volumetric areas, such as HVAC systems, allowing the small micron droplets to quickly convert from a sanitizing liquid to a larger sanitizing vapor. As the droplet diameter decreases in foggers, technology limitations typically reduce the number of droplets per second generated and, in most cases, the smaller droplet size puts limitations on exit velocity of the droplet. Conversely, as the droplet diameter increases, dynamic limitations begin to disappear enabling droplet volume to increase and allowing exit velocity of the droplet to increase.

If you control the droplet size and exit droplet velocity, then you are no longer controlled by the limitations of Sauter Limit of small droplets, which are low liquid volume conversion to vapor and low exit velocity. As the droplet size decreases it becomes increasingly difficult to convert large volumes of liquid per minute to droplets; thus, less droplets in the output with less liquid surface area, less evaporation, and a corresponding lower volume of decontaminating vapor cloud. As the droplet diameter increases, sterilant volume increases, as does droplet surface area contact within the airflow. As droplet diameter increases, droplet exit velocity needs to increase to enhance the required amount of evaporation necessary to convert the liquid to a gas.

Droplet Diameter Applications

What is the happy medium of droplet diameter and droplet velocity? In a smaller volumetric area, it is completely acceptable to use a 5-micron technology with the advantage of quick evaporation. A five-micron droplet is useful in tight dimensions, such as HVAC, to inject the desired decontaminating liquid into the tight constraints of HVAC airflow. 5-micron droplet technology introduces droplets at a smaller volume, thus in HVAC applications, a 5-micron technology would need to be used over a longer period to achieve a desired decontamination affect, especially if the HVAC output is in a large area recirculation.

As volumetric area increases, it is beneficial to go to a larger droplet to achieve the surface evaporation necessary to support volumes found in business offices, sterile pharmaceutical rooms, etc. 8 to10-micron droplets with a droplet velocity of 1 meter/second or more into the airflow is sufficient to allow evaporation of a liquid disinfectant to occur while producing ever increasing volumes of vapor cloud.

Large volumetric areas such as indoor conference centers, indoor stadiums and outdoor agricultural leaf plants (farmed tree food growth) would benefit best with 15 or 35-micron droplets, as long as the velocity of the aerosol droplets into the airflow is sufficient for droplet evaporation.

15-micron droplets from our Portable Backpack Fogger is about 3 meters/second exit velocity and will typically evaporate within 2-3 meters and provide increased concentration of decontamination vapor in the local area, excellent aerosol contact with unwanted pathogens in the airflow and very good surface contact on physical surfaces and plant surfaces at 5 meters distance. This fogger includes 15-micron, 35-micron and 50-micron output nozzles, so it can be adapted to a variety of portable applications in buildings, agricultural growth, and dairy and cattle applications. At 35-micron diameter the droplet velocity is about 5 meters/second exit velocity, which evaporates to a vapor at 8 to 10 meters and provides higher decontamination concentration in the local area. 35 micron droplets would primarily be used in farmed tree and plant growth. 15 micron droplets are excellent for use in agricultural growth, such as olive tree growth to kill unwanted pathogens during food growth to maximize tree fruit production. 15 micron decontamination droplets are very effective in the dairy and cattle applications to significantly reduce hairy foot wort, increasing dairy production and meat production. The droplets are allowed time to evaporate, allowing the decontaminate vapor to come in contact and kill unwanted pathogens in the airflow with superb kill contact on leaf plant surfaces and cattle at 5 meters distance. The Portable Backpack Foggers can be installed on ATVs and driven through rows of tree food growth to significantly reduce food pathogens while enabling very good increases to food production. The same technology is also available as a wall mounted or table mounted decontaminate fogger using 115 VAC or 220VAC, often used in tunnel decontamination applications for food package processing, dairy cattle, etc.

In summary, a 5-micron droplet technology has limitations of converting large amounts of liquid into a vapor in a short period of time but is quite useful in constricted airflow areas but requires longer periods of time to achieve decontamination goals due to lower efficiency of liquid conversion to vapor. 15-micron droplet foggers are very useful in volumetric areas such as office buildings, dairy tunnel applications and indoor leaf plant applications. 35-micron droplet foggers are quite effective in larger open areas of office buildings, as well as agricultural tree food growth applications.

As discussed above, it is not only droplet size that affects the disinfection goal. Droplet velocity in the airflow plays a larger role to produce a desired decontaminating vapor (gas) sufficiently large enough in volume to achieve the decontamination of an area in a shorter period of time.

Liquid Chemistries

These fogger tools require a liquid decontaminant solution capable of killing unwanted spores, molds, fungi and viruses. There are a variety of sterilants that are quite potent against the pathogens used around the world today with high efficacy in the kill rate and short contact times. ‘6 Log kill rate On Contact’ is often discussed as the goal for killing unwanted pathogens. Many people, who buy sanitizing products, are naturally influenced by high kill rates, low equipment costs, low decontamination liquid costs and low operating costs. But they often do not have a working knowledge of the chemicals, affects of those chemicals in our environment, and affects to equipment preventive maintenance and downtime.

Sterilants using solutions of hydrogen peroxide with a paracetic acid are quite effective in killing unwanted pathogens at high kill rates and low contact times of 2-3 minutes. This type of sterilant uses a Paracetic Acid to break into the virus cell wall allowing the Hydrogen Peroxide vapor to kill the inner virus. Hydrogen Peroxide by itself is also effective but takes longer contact time to break into the cell wall and kill the virus. However in both cases, the sterilant vapor cannot be inhaled into the lungs. It needs to be introduced into the building atmosphere via remote control, or introduced into the airflow manually by hand with technicians suited in skin protection and 100% filtered, breathing apparatus. Hypochlorous Acid (HOCL) is a recent sterilant that has gained approval by various companies to battle coronavirus and COVID-19, as it appears to be less corrosive to the lungs, yet effective in efficacy with about 1 minute contact time to kill viruses. But even HOCL should not be inhaled into one’s lungs. Our customers often ask what they should use; and the question of “safer decontamination with kill on contact” comes up frequently.

Decontaminate Foggers using ‘Natural’ Decontaminate Liquids

Some people who buy sanitizing liquids and decontamination foggers have theoretical goals of 100% kill rates of unwanted pathogens and 6 log kill efficiency. In many cases the chemicals used are indeed effective at killing bio-organisms; but are also dangerous to human breathing. While high kill rates are technically sound, in the real world it is not logical to try and kill every pathogen, due to increased operating costs, increased preventive maintenance on equipment, equipment downtime; and increased chemical aerosol loads on the air we breathe. A more thoughtful approach is to use natural decontamination ingredients that are found in mother nature to be highly effective at killing spores, molds, fungi, and viruses, while reducing chemicals in the air we breathe.

In early 2021 Applied Physics began working with VPI Commercial of Alabama, who uses an alternative decontamination liquid called Path-Away®. It is described as a “Certified Organic Input, non-GMO, drug and alcohol free” decontamination liquid containing zero added chemicals, and is highly effective at killing pathogens on contact, such as, but not limited to spores, molds, fungi, Candida auris fungus and viruses such as COVID-19, Coronavirus and Rhinovirus. Pathway is quite effective at mitigating Hairy Foot Warts in cattle to significantly increase beef and dairy production by impacting the pathogens affecting cattle.

Path-Away® is produced from natural elements, not man-made with harsh chemicals, and Path-Away® would not be considered a sterilant. Most sterilants adversely affect our breathing. People do not normally choose to breathe sterilants. Path-Away has the pathogen killing advantages of sterilants and is safer to use. It has the benefits of a high efficacy in killing the unwanted pathogens on contact with minimal skin agitation when using the typical body wear while applying decontamination liquids.

Path-Away® is used to increase agricultural yields and bottom-line financial returns by significantly decreasing plant and soil pathogens. It is utilized in bovine applications to improve milk production and drastically reduce calf cough and pink eye by killing pathogens that cause harm to food and dairy cattle. It is found to be highly effective in food processing tunnels to kill unwanted pathogens on packaged, sealed foods. Decontamination tunnels are in the production phase and will be equally effective to safely sanitize airflow.

As people proceed through the tunnel to their group setting destination (sports stadium, school, church, mall, factory, subway, etc.), in the future it may be allowed to sanitize the air, allowing the circulation of the air around them to kill the pathogens on their clothing and skin that may be contacted in the airflow. Using Path-Away® in BackPack Foggers gives the flexibility to capture the effective anti-pathogenic qualities of Path-Away® in smaller areas such as taxi cabs, rental cars, buses, and private offices. The Wall Mounted Decontaminate Fogger can be installed to disburse Path-Away® throughout an entire HVAC system in buildings to create a safe environment for employees to work.

Path-Away® Decontamination Liquid

FIFRA 25(b) EPA exemption allows use under The Emerging Viral Pathogen ruling due to its minimum risk of harm as per the January 29, 2020 notice, regarding The Emerging Viral Pathogen Guidance for Antimicrobial Pesticides

  • CDC approved lab has certified that Path-Away®+ kills SARS-CoV-2 and numerous other common bacteria and fungi in two (2) minutes or less.
  • FDA G.R.A.S. (Generally Regarded As Safe ingredients comprise the product content due to the fact that its ingredients are generally recognized, among qualified experts, as having been adequately shown to be safe

The US EPA has exempted certain pesticides that pose little to no risk to man or the environment from federal registration under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). These pesticides are known as FIFRA 25(b) exempt, or minimum risk, pesticides.


Most products have required the “N” listing by EPA which means:

EPA expects the products on List N to kill SARS-CoV-2, the coronavirus that causes COVID-19, because they:

  • Demonstrate efficacy against the coronavirus SARS-CoV-2 (COVID-19);
  • Demonstrate efficacy against a pathogen that is harder to kill than SARS-CoV-2 (COVID-19); or
  • Demonstrate efficacy against a different human coronavirus similar to SARS-CoV-2 (COVID-19).

EPA expects all products on List N to be effective against SARS-CoV-2 (COVID-19) when used according to label directions.

CDC – The Centers for Disease Control and Prevention (CDC) serves as the national focus for developing and applying disease prevention and control, environmental health, and health promotion and health education activities designed to improve the health of the people of the United States.

The CDC authorizes and recognizes only certain labs to conduct testing to verify products that “claim” to be instrumental in combating diseases.

MICROBAC is a CDC approved laboratory for testing of products that kill SARS-CoV-2 (COVID-19). Microbac tested Path-Away® August of 2020 and specifically verified that Path-Away® kills COVID-19 IN TWO (2) MINUTES OR LESS. In the spring of 2021 MicroChem, another CDC approved lab, tested Path-Away®+ (the enhanced version of Path-Away) on several common bacteria and fungi and Path-Away®+ passed all the certification requirements for an effective anti-pathogenic on these substances.

FDA – The Food and Drug Administration is responsible for protecting the public health by ensuring the safety, efficacy, and security of human and veterinary drugs, biological products, and medical devices; and by ensuring the safety of our nation’s food supply, cosmetics, and products that emit radiation.

Although FDA does not have premarket approval of food products, it has the authority to approve certain ingredients before they are used in foods. Those include food additives, such as substances added intentionally to food, and color additives. Companies that want to add new food additives to food are responsible for providing FDA with information demonstrating that the additives are safe. ONLY if Path-Away®+ becomes used in or on food, that people or animals ingest, will the FDA need to be involved for an approval.

However, Path-Away®+ IS recognized under the FDA G.R.A.S. program, which is “GRAS”, an acronym for the phrase Generally Recognized As Safe. Under sections 201(s) and 409 of the Federal Food, Drug, and Cosmetic Act (the Act), any substance that is intentionally added to food is a food additive, that is subject to premarket review and approval by FDA, unless the substance is generally recognized, among qualified experts, as having been adequately shown to be safe under the conditions of its intended use, or unless the use of the substance is otherwise excepted from the definition of a food additive.

Decontaminate Fogger Links and Applications

Portable BackPack Fogger, 48VDC: Decontaminating Pathogens on Food Trees; Leaf Plant growth; Large Office Decontamination Applications

Portable BackPack Fogger, 24VDC: Decontaminating Dairy Applications; Food Package Processing; Small Office Decontamination Applications

Wall Mounted Decontaminate Fogger, 110VAC or 220VAC; Decontaminating Tunnel Applications

Wireless Remote Control DryFogger, 110VAC or 220VAC: Office areas; Pharmaceutical

Remote Control, Dry Fogger, (requires Dry Air Compressor): Office Areas; Pharmaceutical