Tips for Applying to Surfaces
Spraying Disinfectants
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A couple months ago, a colleague of ours received an email from a worker inquiring if their facility would spray employees with disinfectant as they enter the building. The worker was attending a training event at another facility, where entrants—after completing a health questionnaire and getting their temperature checked—were sprayed with a quaternary ammonium compound as a disinfectant. Since the COVID-19 pandemic began, some employers and contractors around the world have used sprayers to apply disinfectant to people entering their facilities. In one notorious instance from March 2020, migrants in India were doused with disinfectants and told to “close your mouth and eyes” as a safety precaution, according to a BBC report. Even today, many cleaning companies advertise the spraying of disinfectant on people as their “COVID cleaning package.”
While spraying is a great method for disinfecting surfaces, it was never intended for application to people. The U.S. EPA doesn’t recommend spraying people with disinfectant, and there is no data indicating that it’s an effective means of reducing the spread of COVID-19. As health and safety professionals, we should not allow intentional worker exposure to harmful chemicals, which would result from the release of disinfectants in the air (through fogging/fumigation) or directly on people. Social distancing and wearing a face covering are still the most effective means of reducing the spread of SARS-CoV-2 and other potentially infectious bioaerosols.
This article summarizes some of the common disinfectant chemicals used against SARS-CoV-2 and explains the equipment used to apply them to surfaces, with a focus on electrostatic spraying. Fogging and misting will not be discussed as they are more likely to lead to unintended worker exposure.
USING SPRAYERS TO DISINFECT SURFACES There are multiple ways to apply a disinfecting agent to a surface. The most basic and wasteful delivery method of all is to pour disinfectants from containers. More commonly, disinfectants are loaded into a delivery vessel, and a set amount is pumped onto a surface.
Many variations of this method exist. The vessel can be a simple, manually operated pump that forces the disinfectants in the container to a nozzle, from which they emerge as a stream of liquid or as mist. Manual pump-action sprayers are taxing on the user and may cause ergonomic issues if the disinfectants will be applied to a large surface area. Pressurized pump sprayers, which pressurize the container and release the disinfectant when the spray nozzle is opened, are more user friendly, but the stream tends to weaken as the pressure inside the container drops. Electrical pump sprayers mediate the variation in flow by using an electric motor to automatically draw the disinfectant and deliver a constant volume to the spray nozzle. A final option is electrostatic sprayers, which apply electrostatic charge to the liquid as it passes through the nozzle. The positively charged disinfectant is attracted to the negatively charged surfaces, thereby minimizing worker exposure by preventing the disinfectant from lingering in the air or drifting to other areas of the facility.
While traditional sprayers are the most common tools for applying disinfectants to surfaces, electrostatic sprayers are just as effective and greatly reduce the amount of disinfectant needed. Some electrostatic sprayers allow the user to adjust the droplet size. Selecting the larger size helps ensure the disinfectant coats the surface evenly and does not evaporate before the required contact time is reached. A droplet size of 5 microns or smaller increases the likelihood that the compound will stay suspended in the air for over 15 minutes, which increases risk to the user.
Of the many types of sprayers available, electrostatic sprayers are therefore the safest. If used properly, electrostatic sprayers consume fewer materials and provide better coverage in less time than other spraying equipment.
TYPES OF DISINFECTANTS EPA’s “List N” identifies products that are expected to kill SARS-CoV-2 when used according to the label directions. The information in List N includes the product name, active ingredient, manufacturer, and contact time. It is important to note that the products on List N are not approved to be used on humans; they are predominately for inanimate, hard, nonporous surfaces. To determine whether a product is on List N, locate the EPA registration number on the product’s label and enter the first two sets of numbers into the tool.
List N specifies each product’s formulation, which indicates the intended application method. For example, products specified as “dilutable” are liquids that can be diluted with water; “ready-to-use” products can be used off the shelf; “impregnated materials” have disinfectants built into them; and so on. The formulation also indicates products that can be used as fogs or mists, and those that can be applied with electrostatic sprayers. These include the following:
Quaternary ammonium compounds (for example, alkyl dimethyl benzyl ammonium chloride) are effective at inactivating SARS-CoV-2, but they can cause skin and respiratory irritation and exacerbate asthma symptoms. Approximately 37 percent of List N disinfectants are quaternary ammonium compounds. As reported by Chemical & Engineering News in August 2020, emerging evidence links quaternary ammonium compounds to reproductive and developmental issues in animals.
Off-the-shelf bleach contains approximately 5–10 percent sodium hypochlorite. Fourteen percent of the disinfectants on List N contain either bleach or sodium hypochlorite. When using bleach or sodium hypochlorite in electrostatic sprayers, it is important to make a fresh 10 percent bleach solution on the day of use since it degrades faster in diluted form. Bleach can cause skin and eye irritation as well as serious eye damage. Because bleach accelerates rusting in metal, it needs to be wiped down after the contact time has elapsed. The combination of bleach and ammonia creates toxic chlorine gas, so it is important for workers to ensure that bleach does not come into contact with ammonia-based disinfectants or cleaners.
No matter how effective a disinfectant is, it will treat the surface for only a short time.
Hydrogen peroxide is a strong oxidizer, but because it degrades into oxygen and water, it is a safer alternative to other disinfectants. As with all oxidizers, it will cause skin and eye irritation and can seriously damage the eyes.
Ethanol and isopropyl alcohol are two commonly used disinfectants that leave minimal residue. Both are effective against SARS-CoV-2, but they evaporate rather quickly. Reapplication on the surface might be needed to achieve the required contact time.
The contact time for List N products that contain hydrogen peroxide or alcohol ranges from 30 seconds to 30 minutes, depending on concentration.
CONSIDERATIONS FOR APPLICATION Concentration is an important health consideration. A chemical that can deactivate SARS-CoV-2 in the shortest contact time might need to be applied at a concentration that is unsafe for the user or damaging to the surface.
The compatibility of a chemical compound to the surface it is treating might be an important consideration. The chemical might discolor or corrode the surface or require a post-treatment rinse. For all List N disinfectants, pre-cleaning is required if the surface is visibly soiled. Pre-cleaning removes particles that will interfere with the disinfecting agent. Lightly soiled surfaces need only to be wiped with disposable paper towels. Grime or grease can be removed with detergent, surfactant, and paper towels.
Not all surfaces need to be clean before disinfectants are applied. Viral particles settle by gravitational force, and low-touch surfaces present low exposure potential. Therefore, cleaning behind a cabinet, underneath a desk, or similar areas might not be the most efficient approach.
Ensure that areas to be sprayed are vacated and the ventilation is closed off (isolated) from the rest of the building. To determine how long the area should remain vacated, refer to the product label or manufacturer specifications.
Workers who are applying disinfectant using a sprayer must be trained on proper cleaning methods for the surfaces they will be treating, correct use of the equipment, and required personal protective equipment. All workers tasked with spraying should understand the difference between cleaning and sanitizing. Once workers understand proper cleaning methods, they should be given the manufacturer’s specifications for the model of sprayer being used. Workers should follow the chemical manufacturer’s specifications and safety data sheets when choosing proper PPE, including but not limited to respiratory and skin protection. Workers must be a part of a respiratory protection program, which includes proper fit testing for all respiratory protection as required by OSHA. Training for handling hazardous materials should also be required.
SHORT-TIME CONTROL No matter how effective a disinfectant is, it will treat the surface for only a short time. If another virus carrier comes along, the surface will no longer be disinfected. Therefore, spraying shouldn’t be the first control option for COVID-19. Source control–social distancing and wearing face coverings—is the most effective method because it reduces the probability of exposure to the virus. Refer to guidelines available from CDC’s COVID-19 website for more source control information.
ASHLEY AUGSPURGER, PhD, CSP, is the biosafety officer and chemical hygiene officer for Corteva Agrisciences in Iowa. She is the president of the Nebraska-Western Iowa AIHA Local Section and secretary for the AIHA Biosafety and Environmental Microbiology Committee.
NANCY WILSON, CIH, works for Pennoni and Associates as a senior industrial hygienist. She works on all types of industrial hygiene projects including but not limited to employee exposure monitoring, chemical testing, lead, indoor air quality, mold, noise, and radiation monitoring. Prior to joining Pennoni, she worked for 27 years at a county health department as a hazardous materials response specialist.
KEE-HEAN ONG, PhD, MPH, CIH, CSP, is an EHS engineer working for a defense contractor in the D.C. metro area. He is also an adjunct professor teaching Environmental and Occupational Health at the University of North Texas Health Science Center. He is chair of the AIHA Biosafety and Environmental Microbiology Committee.
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BBC: “Coronavirus: Anger as Migrants Sprayed with Disinfectant in India” (March 2020).
Chemical & Engineering News: “Do We Know Enough About the Safety of Quat Disinfectants?” (August 2020).
EPA: “Electrostatic Sprayer Efficacy for Personal PPE Decontamination,” 10th U.S. EPA International Decontamination Research and Development Conference (PDF, presentation by John Archer and Madhura Karnik, May 2018).
EPA: “EPA Takes Action to Help Americans Disinfect Indoor Spaces Efficiently and Effectively” (July 2020).
EPA: “Evaluation of Electrostatic Sprayers for Use in a Personnel Decontamination Line Protocol for Biological Contamination Incident Response Operations” (October 2018).