Tri Activ Disinfectant Spray
Chadwick Bosse
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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.
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.
This section briefly discusses the methods used to obtain data and information for the sprayer and fogger parameters presented in this data brief. The sprayer parameters evaluated and discussed in this brief include sprayer flow rate, recommended deposition rate, the droplet size distribution (DSD) of the spray, and the electrostatic charge of the spray. Note that other sprayer parameters will be evaluated as part of this study but presented in a future data release or in a final report.
This parameter is critical to ensure that sufficient disinfectant volume is applied to the surface such that it remains wet for the required contact time of the disinfectant, and thus ensures effective inactivation of the virus (and compliance with the EPA-required disinfectant label). This parameter was compiled from the sprayer user manuals, brochures, and distributer/manufacturer websites. Since ESSs are typically used for disinfection of large surface areas, the deposition rate is usually presented in units of fluid ounces of disinfectant per 1000 ft2. As previously discussed, foggers are primarily used for volumetric decontamination, and so no suggested surface coverage rate was provided for the two foggers we evaluated. This parameter is presented here to provide the user with an indication of the range in values as suggested by the manufacturers.
The droplet size distribution (DSD) of a spray is typically characterized in terms of the volumetric median diameter (VMD), which refers to the droplet size in which half the volume of the spray is in droplets less than, and half of the volume of the spray is in droplets greater than, the VMD. It is typically reported in units of microns. Results for the DSD may also be reported in terms of other percentages for which the volume of the spray is less than the specified diameter. Examples include the Dv10 or Dv90, which is the droplet diameter in which 10% or 90% of the volume of the spray is less than that droplet size, respectively. These measurements provide additional characterization of the size range of the spray droplets than the VMD alone.
The DSD of the sprayers was measured using deionized water as well as laboratory acquired tap water. For one of the ESS devices evaluated, the electrostatic charge function can be turned on and off, and so the DSD was measured for both settings. Another ESS came equipped with two different nozzle tips to adjust droplet size (a 40 micron and 80-micron VMD), and so the DSD was measured for both.
Following the tests with water, the DSD for one ESS was evaluated for three different water-based disinfectants to assess the impact the presence of the disinfectant solution might have on the DSD. The three disinfectants evaluated utilized an active ingredient of either chlorine, hydrogen peroxide, or quaternary ammonium. However, when testing the quat-based disinfectant, the spray penetrated the sheath air protecting the optics of the instrument and thus coated the lenses, rendering the data for this disinfectant unusable. The disinfectants were prepared according to the label directions.
The test apparatus used to measure spray charge consisted of an aluminum plate 20.1 in. by 11.4 in., mounted to plywood of similar dimensions using zinc screws at each corner. Two holes were bored at the top of the plate and rubber screen spline was used to suspend the plate 52 in. (to center point) from the floor in the center of the wind tunnel. The average wind tunnel temperature and RH measured approximately 23 C and 47.0%, respectively. A Keithley 4145 picoammeter was used to directly measure current generated from spraying the plate with electrostatically charged droplets and was connected to the top corner of the plate via positive lead with an alligator clip. The other lead was sent to ground via a ground plug to wall receptable.
Following the tests using water, the spray charge for one of the ESS was evaluated for the same three disinfectants used in the DSD tests to assess the impact the presence of the disinfectant might have on the charge. Lastly, the electrostatic charge was evaluated as a function of spray distance (1, 4, 6, and 8 ft), using the Clorox 360 device with deionized water.
This series of tests was conducted to qualitatively assess, and document with photographs, the ability of the spray (electrostatic or not) or fog to wrap around and deposit on the sides and back of a cylindrical object. We began this series of tests using a metal trash can (11 inch height, 8 inch diameter; purchased with a black matte finish), and then followed with a few additional tests to examine the spray deposition on objects with more complicated surfaces, such as a step ladder, a clip-on lamp, and fold-out chair.
The spray devices were filled with an aqueous solution of fluorescent dye (Blue aqueous tracer, T-900, Black Light World, Cub Run, KY), at a dilution of 1:25 in tap water. (For the Clorox 360 sprayer, we used both tap and DI water as the diluent in these tests, to evaluate whether the lack of ions in the water affected deposition.) In each test, the spray nozzle was placed at the same height as the center of the can. Each sprayer was evaluated using three replicate trash cans (i.e., each can was sprayed separately). A 3-inch by 3-inch square was marked on each can at 90-degree intervals using a UV-A fluorescent pen, and labeled as front, back, left and right. Approximately 8 mL were dispensed in each spray test. During each spray, the sprayer was moved back and forth, so that the spray cone fully enveloped the can.
Following each spray, the lights in the test chamber were turned off, and two, 24-inch long black lights were placed in front of the can to observe the deposition of the fluorescent aqueous mixture. Digital photographs were then taken of the front quadrant of the can, and then the can was rotated in 90-degree increments and photographs were taken for each quadrant. Prior to spraying the trash cans, photographs were taken of each can as described above, to serve as controls. Following each sprayer evaluation, the three trash cans were washed with a laboratory-grade detergent, and then further cleaned using a mixture of isopropyl alcohol and acetic acid.
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