Recent research has shown that the COVID-19 disease is primarily caused by airborne transmission of the SARS-CoV-2 virus, but it is believed that the virus may also be transmitted via contact with contaminated surfaces (Pitol and Julian, 2021). Thus, routine cleaning and disinfection of potentially contaminated surfaces is recommended, among other infection control activities, to limit the spread of the disease. Business owners, school district leaders, and even mass transit leaders have needed to find ways to clean and disinfect large surface areas quickly and effectively that are frequently touched by many people. Thus, use of electrostatic sprayers (ESS) and foggers to rapidly apply disinfectants over large areas or complex, intricate surfaces has increased substantially with the COVID-19 outbreak. ESS have been used for many years in several other industries (e.g., efficient application of pesticides to crops), but recently they have grown in popularity as a technique to efficiently and rapidly apply disinfectants to surfaces, i.e., especially those that may be contaminated with the SARS-CoV-2 virus. These devices impart an electrostatic charge to the disinfectant spray droplets (most do so as the droplets exit the nozzle of the sprayer), with the goal of improving deposition of the droplets onto surfaces and thus promoting more efficient use of the disinfectant. This attribute may be both an advantage and disadvantage: an ESS may allow less disinfectant to be used to cover a surface area, but with less disinfectant applied, disinfection efficacy may diminish if the surface does not remain wet for the required contact time.
There are several ESS parameters that may impact the disinfectant’s ability to inactivate the virus on surfaces, notwithstanding that an ESS is only as effective as the disinfectant chemical being sprayed (only EPA-approved disinfectants should be used for the SARS-CoV-2 virus and in accordance with the disinfectant product’s label).
These include the following:
• The amount of disinfectant to apply to a surface, i.e., the deposition rate (e.g., fluid ounces of disinfectant per 1000 ft2), so that the surface remains wet for the required contact time to ensure inactivation of the virus.
• The electrostatic charge imparted to the spray, potentially affecting its ability to deposit onto surfaces, including surfaces not in the direct path of the spray (e.g., the ability to wrap around and adhere to complex surfaces).
• The amount of the disinfectant’s active ingredient lost to the air before reaching the surface. Loss of the active ingredient to the air will diminish the concentration of the active ingredient on the surface, thus potentially reducing disinfection efficacy.
Other parameters may introduce exposure concerns by creating inhalation hazards to the operator of the ESS or those occupying the space following disinfection. These include the following:
• The droplet size distribution of the spray and chemical composition of the droplets. Smaller droplets are more readily inhaled and deposited deeper in the respiratory tract.
• The loss of the active ingredient of the disinfectant to the vapor phase during the spray process. Some disinfectant active-ingredient chemicals, such as chlorine and hydrogen peroxide, may volatilize and become hazardous if in sufficiently high vapor concentrations. This is a concern for the ESS operator, as well as for occupants of the space following disinfection (if not properly aerated).
The purpose of this research is to evaluate spray parameters for several different types of sprayers and foggers. Specifically, we are evaluating six ESS, two foggers, and one hand-pumped garden sprayer (Table 1). The hand-pumped sprayer is the only manual sprayer evaluated. Two of the ESS we are evaluating use alternating current (i.e., they are plugged in), while the rest rely on battery power. The sprayers were selected for our study based on an initial assessment of commercial availability.
Sprayers are used to apply disinfectant directly to a surface (recommended spray distances vary from about 2 feet to 10 feet), whereas foggers may be used for disinfection of surfaces or volumes (i.e., disinfection of air, inactivation of aerosolized viral particles). Because the disinfectant chemical fog can fill a room, they are usually operated automatically with no operator present. The two foggers we are evaluating do not use electrostatic charging of their droplets.
One ESS came with two different nozzles, stated to produce different size droplets, and thus both are being evaluated in our study. Another ESS has the ability to turn the electrostatic charge on and off; both settings are being evaluated.
Both water and disinfectants are being tested in the sprayers. Only disinfectants are being used in tests to evaluate loss of active ingredient, and in efficacy testing. Finally, we note that some of the sprayers were malfunctioning at the time certain parameters were being evaluated, and so not all sprayers were tested for every parameter.