The Occupational Health and Safety Act(s) states that the employer must take all reasonable precautions in the circumstance to protect a worker. A component of this duty includes risk assessments of hazards and processes used in the workplace. A risk assessment must be completed by the employer, in consultation with the (Joint/Workplace) Health and Safety Committee, before implementing a program to disinfect the workplace using a fine spray, misting or fogging.

Multiple CUPE workplaces have introduced or are planning to introduce the use of fine spray devices to disinfect surfaces potentially contaminated with the COVID-19. CUPE has concerns about the effectiveness of this practice and the effect on the health and safety of workers and others when a chemical is sprayed in the workplace.

Moreover, the World Health Organization (WHO) and the U.S. Centers for Disease Control (CDC) do not support this method of disinfection.

According to the WHO:

In indoor spaces, routine application of disinfectants to environmental surfaces by spraying or fogging (also known as fumigation or misting) is not recommended for COVID-19. One study has shown that spraying as a primary disinfection strategy is ineffective in removing contaminants outside of direct spray zones. Moreover, spraying disinfectants can result in risks to the eyes, respiratory or skin irritation and the resulting health effects. Spraying or fogging of certain chemicals, such as formaldehyde, chlorine-based agents or quaternary ammonium compounds, is not recommended due to adverse health effects on workers in facilities where these methods have been used. Spraying environmental surfaces in both health-care and non-health care settings such as patient households with disinfectants may not be effective in removing organic material and may miss surfaces shielded by objects, folded fabrics or surfaces with intricate designs. If disinfectants are to be applied, this should be done with a cloth or wipe that has been soaked in disinfectant[i] [emphasis added]

According to the CDC:

Disinfectant spray-fog techniques for antimicrobial control in hospital rooms has been used. This technique of spraying of disinfectants is an unsatisfactory method of decontaminating air and surfaces and is not recommended for general infection control in routine patient-care areas.[ii] [emphasis added]

Wiping vs Spraying

The mechanical action of wiping down a surface is more effective at killing a virus on a surface rather than spraying. As such, CUPE recommends either a) using a rag soaked with disinfectant to wipe surfaces, or coarse spray the surface with a pump bottle with disinfectant and then wiping with a rag. 

Wiping is also beneficial as the cleaner can ensure that all of the surface has the chemical actually applied to it, because the cleaner actually touches each surface.  Though more effective, properly cleaning with the wiping techniques will take longer than the less effective spraying, which is why many employers have pushed to adopt the practice (rather than hire additional cleaning staff).

While sometimes spraying can be effective on flat, clean and horizontal surfaces, when compared to wiping down surfaces, spraying:

  • often leads to overuse of chemical products (more is needed to ensure coverage than wiping)
  • requires more PPE than simply wiping down a surface
  • can cause chemical damage to floor finish, furniture, electrical equipment and other items(books, paper) in the room
  • increases the risk of slip and falls
  • requires surfaces to be clean before using disinfectant[iii] as bacteria can be hidden in the soiled surfaces.

Effectiveness of the disinfection method

The effectiveness of a disinfection process consists of four elements; chemistry, concentration, contact time and coverage. Before starting the process, as decrided above, it is necessary to ensure that the surfaces are not dirty. The process is then dependent on the following:

1. Chemistry - The product must be effective in killing the virus that cuases COVID-19 in question. No assumption should be made that the product used in the sprayer will work just because a product states that it can “kill germs.” Health Canada maintains a list of all products approved for rendering COVID-19 inert[iv].

2. Concentration - The level at which a product is diluted in water. Too much or too little product in a cleaning solution can cause problems (see below on dilution and decanting).

3. Contact time - The time it takes for a disinfectant to be on a surface before a specific germ is inactivated. If the product is not in contact with the germ for the required amount of time, then you will not get complete disinfection.

4. Coverage - The amount of surface the product covers after application. Ideally, coverage is 100%. Spraying usually only gets the tops of surfaces, while wiping ensures the worker will touch each surface.

Health and Safety Considerations

In Canada, if a workplace uses a hazardous product, there must be a WHMIS program in place. Workers must be educated and trained so they understand the hazards, and know how to work safely with hazardous products. Training must include:

  • how to read product labels and Safety Data Sheets
  • safe use, handling and disposal of a hazardous product
  • the procedure to follow if the hazardous product may be present in the air and a worker may be exposed
  • all procedures to be followed in an emergency that involves the hazardous product

The method to disinfect surfaces in most workplaces involves applying the product on a surface using a cloth, mop or coarse sprayer for a set amount of time. In some cases, surfaces must be rinsed with water afterwards to remove any leftover product (residue).

If the label or Safety Data Sheet (SDS) does not describe fine spraying, misting, or fogging the product as a method used to disinfect a surface, then the product must not be used in that way. Using a fine spray will result in tiny particles being suspended in the air, which can be inhaled through the nose or mouth, or absorbed in the eyes or by the skin.

If a product is designed to be used with a fine sprayer, the manufacturer must describe:

  • the product’s safe work procedures (use, handling, storage, and disposal)
  • the surfaces upon which the product can be applied
  • requirements for ventilation, both when using the product and if there are lingering effects which require additional ventilation
  • requirements for personal protective equipment
  • the hazards associated with using the product
  • any other prescribed requirements under the WHMIS related regulation

According to the Government of Ontario3, there are some disinfectants specifically for use in electrostatic spray disinfection systems that have been approved by Health Canada for COVID-19. It should be noted that Health Canada only tests if the chemicial is effective against the virus, and does not provide guidance on the safe use of any of the chemicals it has appoved. The manufacturers of these disinfectants have provided evidence of disinfection efficacy while using the electrostatic spraying system to obtain approval from Health Canada.

Regardless of the system or chemical used, it is important to follow manufacturers’ instructions for safe use of the chemical, any sprayer system and utlize the personal protective equipment (PPE) recommended for the task.

Information to look for (and where to find it)

The safe use, storage and handling of most disinfecting/cleaning products are often described on the supplier label or the manufacturer’s website.  This information, along with the SDS’s (which frequently need to be read in conjunction with product lables on the container) will provide users with the relevant safety infomation. While the entire SDS provides important information, the following specific sections should be reviewed for the information as follows:



What to look for



The section should state what the product should be used for, and any restrictions. If the product is not identified (either on the SDS or the product label) for use in a fine mist or electrostatic sprayer it should not be used for spraying.


Hazard Identification

This section will provide information on the hazards of the product.



This section will provide ingredients and more importantly a ‘CAS number’ for the ingredients. These numbers can be used to perform additional research on the chemical.


Exposure Controls/PPE

This section will provide information on what personal protective equipment is required in order to use the product.

Decanting and Diluting

For ease of shipping, most cleaning chemicals sold for commercial use (i.e. not a consumer product packaging) will require a product to be diluted before use. Chemical producers have determined what the correct dilution is for the purpose of the product, and it is important that workers who use chemicals understand and use the correct dilution factor. Too much water and too little chemical will likely make the chemical ineffective (it will not properly ‘kill’ the COVID-19 virus partials). Using too much chemical and not enough water places the user at higher risk as they may be exposed to higher levels of a chemical and the manufacturer’s required PPE might not adequately protect the worker. Making the chemical concentration stronger may not actually increase the performance of the product and may cause unexpected results (e.x. too much bleach altering the color of a surface).

Consult the SDS if you have questions or concerns regarding the chemicals used in your workplace. The employer must make the SDS readily available for worker consultation and easily accessible in case of an emergency.

Additional Considerations

Spray Height.  If spraying is to be used, it should only be performed with the assistance of gravity. Spraying above waist level, or worse above the shoulders will increase the potential of inhalation by the user (and anyone else in the vicinity) and also increase contact with skin from either gravity or from pressurized “blow back”.

Clear workplace.  If spraying is used in a workplace, no other person should be present in the work area unless they have been provided with all the training and PPE required to perform the job safely.

Terms (for the purpose of this sheet- exact definitions vary)

Coarse sprayer – Device that sprays small liquid droplets without creating a majority of particles that are likely to be suspended in the air and inhaled.

Aerosol, fine or mists sprayer – Device that sprays liquids that create particles small enough that some will remain floating in the air long enough to be inhaled.

Electrostatic sprayers: Device that sprays disinfectant liquid in the form of an fine aerosol that is then electrically charged (i.e., cleaners, sanitizers, and disinfectants) as they pass through a sprayer nozzle. This generates charged droplets that repel one another and actively seek out environmental surfaces to stick to.  

Safety Data Sheets (SDSs): are summary documents that provide information about the hazards of a product and advice about safety precautions. SDSs are usually written by the manufacturer or supplier of the product.


[i] WHO Cleaning and disinfection of environmental surfaces in the context of COVID-19; Interim guidance 15 May 2020

[ii] CDC Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008(update May 2019)

[iii] Ontario Agency for Health Protection and Promotion (Public Health Ontario). COVID-19: frequently asked questions: electrostatic sprayer disinfection systems. Toronto, ON: Queen’s Printer for Ontario; 2020.