Ozone cleaning: hazards and protective equipment

If we hear a lot about ozone pollution peaks or about the ozone layer protecting the planet from UV rays, one aspect of this gas is very little known: ozone cleaning. This disinfection and cleaning technique is increasingly being practiced by professionals, especially since the beginning of the Covid-19 crisis. Let’s review the ozone cleaning technique, the dangers of exposure to this gas and protection means available to exposed workers.

Ozone (O3) cleaning is a simple technique: it consists of applying this gas in a room, a closed place or a vehicle via an ozone generator (or ozonator) and letting it act until it degrades into oxygen (O2). Thanks to its oxidizing power, O3 disinfects by eradicating viruses, bacteria, parasites and fungi that are present on all surfaces of a room and suspended in the air.

To be effective, the ozone cleaning process requires a 10 to 20 ppm ozone concentration in the ambient air of the concerned enclosed environment. This concentration level creates a lethal danger to anyone in the concerned room. This operation must therefore be carried out in a space without any occupant throughout the duration of the treatment. After this operation site ventilation or air recycling must be carried out to ensure safety of future occupants.

Despite these requirements, the sprayed ozone or ozonated water cleaning technique has developed in hospitals and is now present in various fields (vehicle cleaning, office cleaning, hotel rooms, etc. etc.). This practice is growing in popularity because it avoids the use of toxic and polluting products, it is easy to perform and it destroys odors quickly. Today it is even possible to use this technique at home with a home ozone generator.

The coronavirus health crisis has developed the practice of ozone cleaning. The technique is particularly popular because it makes it possible to easily carry out a complete decontamination of complex places to disinfect such as offices, public reception areas or even public transportation.

While there are many alternatives for disinfecting COVID-19 potentially contaminated places (virucides, dry steam, UV rays, cold plasma, aerosol cans), ozone cleaning has certain advantages:

• O3 destroys microorganisms of all kinds (bacteria, viruses, spores) and sanitizes all surfaces as well as ambient air contaminated by the coronavirus.
• Ozonators are available at affordable prices for all businesses and public organizations.
• Ozone cleaning can be done by one person.
• It is a non-polluting technique.

Ozone, or trioxygen (CAS number 10028-15-6) is a chemical made up of 3 oxygen atoms that quickly breaks down into oxygen (dioxygen, O2) in ambient air. In gaseous, liquid or diluted water form, ozone is a toxic, corrosive and potentially oxidising substance. In its gaseous form, O3 is a colorless or slightly bluish (when pure) gas that gives off an odor resembling bleach or chlorine and can be detected by human smell as low as 0.01 ppm.

Ozone is one of the chemical substances with the greatest oxidizing power (52% more effective than chlorine (Cl2) for example with a much faster cleaning effect). The oxidizing power of trioxygen makes it a particularly efficient microbial agent with a very wide action spectrum. Recognized for its oxidizing and disinfectant qualities, it is used in drinking water disinfection, wastewater treatment, in medicine wounds treatment (antiseptic and bactericidal properties), swimming pool water treatment (disinfectant), laundry cleaning, in the paper industry (bleaching agent), in the food industry (equipment and food products disinfection and cleaning), or in agriculture (pest control action on grain stocks).

The oxidizing power exploited by the ozone cleaning process represents a real health danger. In fact, exposure to certain ozone concentrations can have health effects on workers performing the cleaning, or on people in the treated area that was poorly ventilated following the process.

Ozone exposure mainly passes through the respiratory tract, but can also affect the skin, mucous membranes, and eyes resulting in eye irritation, causing pulmonary edema and also damage to respiratory organs. Depending on the gas concentration in ambient air, people present may be prone to breathing difficulty, cough, dyspnea, chest pain, bronchial hypersecretion or shortness of breath for up to 48 hours after exposure. When the trioxygen concentration in ambient air reaches 5 ppm, it represents an immediate danger to life or health.

In addition, chronic exposure to ozone used during cleaning processes can cause harmful pulmonary respiratory effects (atrophy of the alveolar walls, fibrosis, bronchopathies, dyspnea) and can affect the neurological system (headaches, memory problems, neuromuscular impairment).

To avoid these dangers related to ozone cleaning, in France the INRS indicatively sets the occupational exposure limit values (OEL) for trioxygen as follows: 0.1 ppm for the TWA (threshold limit value Time Weighted Average over an 8-hour workday) and 0.2 ppm for the STEL (Short-term Exposure limit value for a 15 minutes period).

Responders performing ozone cleaning may be chronically and / or highly exposed to particularly dangerous ozone concentrations. This is why it is necessary for these people to have adequate protective equipment: respiratory protection and an ozone detector.

When faced with polluted ambient air during or after an ozone cleaning process, wearing a respiratory protection mask helps to ensure the safety of workers performing the task.

The use of a full face gas mask (completely covering the face) is recommended to help with eye irritation. This air purifying protection must be used with ABEK2 Hg CO P3 or ABEK2 NO P3 filter cartridges. These combined filters for gas masks offer protection against organic, inorganic and acid gases and vapors, ammonia and its organic derivatives, vapors, compounds and derivatives of mercury, carbon monoxide (CO), solid particles, liquids, radioactive, toxic and microorganisms.

It is common practice to equip workers performing ozone cleanings with air purifying respiratory protection (gas masks) providing a certain level of protection. However, it is necessary to note that ozone, by its oxidizing and corrosive properties, reacts with the activated carbon and the hopcalite generally composing the filtering medium in gas masks cartridges. Contacting ozone and these components causes their oxidation and therefore reduces the filter capacity faster than under normal use conditions. A filter cartridge used for respiratory protection during ozone cleanings will therefore have a faster breakdown time and will need to be changed more often.

In addition, regardless of the respiratory protective equipment used, an inspection of the gas mask or the SCBA should be carried out after each use in this kind of situation. In fact ozone exposure on some materials might degrade those by oxidation. For example, at high concentrations, rubber, neoprene, polyamide and polypropylene are not resistant to O3 in gaseous or diluted form. Inspection and maintenance of respiratory protective equipment will monitor the potential degradation of certain elements due to ozone exposure and ensure user safety.

The ozone odor is perceptible by human smell, however smell perception does not replace a clear measurement of the gas concentration in a room or an enclosed environment. To preserve workers’ health during all phases of ozone cleaning, it is therefore necessary to have equipment able to precisely measure trioxygen presence in the air.