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.

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.

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.