Understanding ozone disinfection technology with STERISAFE

Ozone disinfection technology has received increasing attention – but how do we separate the wheat from the chaff?

The current COVID-19 outbreak has prompted a growing interest in innovative disinfection technology. Notably, the potential benefits offered by disinfection technologies that use ozone are garnering attention.

This level of attention has contributed to creating an environment of opportunistic behaviour wherein multiple companies imply that their inexpensive and small ozone disinfection products can be used to remove bad odors, harmful pathogens, particles, bacteria, and in some cases, even SARS-CoV-2. However, these claims are at best debatable, if not erroneous. The efficacy when using ozone is highly dependent on several factors, including:

  • Ozone concentration
  • Contact time between ozone and targeted microorganisms
  • Relative humidity
  • The inherent resistance of the targeted microorganism.

In complex room settings, several other factors also play a significant role when it comes to efficacy. This includes air circulation and the homogenous distribution of the disinfecting agents.

Inexpensive solutions circulating the internet often do not live up to basic requirements or possess the adequate technology needed to make any thorough disinfection possible. When a global pandemic is roaring, individuals and organisations will attempt to reduce infection rates by following government guidelines. However, many wishes to go beyond those guidelines and expand safety protocols for the sake of customers, clients, employees, and themselves. These attempts could include the acquisition of simple and inexpensive ozone generators as these products position themselves as a remedy against unwanted viruses.

Only a narrow range of customers in possession of the appropriate knowledge are fully aware of their obligations when using ozone as a disinfection tool. However, the absence of any specific legislation or regulation regarding the sale of ozone disinfection technology enables rogue companies to target many potential uninformed customers and to sell them products that do not provide the promised results. Vague claims with no third-party verification can lead to improper use of ozone, create serious health hazards, and a dangerous illusion of protecting people from disease.

It is important to stress that the use of ozone should not be taken lightly. In developing and creating an ozone-based disinfection technology, STERISAFE has acquired expert-level knowledge regarding this subject. STERISAFE is a company located on the campus of the University of Copenhagen since 2014 and have developed a unique and patented technology to perform effectively, safe, and rapid automated room disinfection. From the very beginning, the mission has been to limit the increasing threats of Healthcare Acquired Infections (HAI). Nevertheless, the technology is now in use for infection prevention in several industries.

Recent tests by third-party laboratories confirmed, that STERISAFE’S disinfection robot: the STERISAFE PRO was affective against corona virus type, and since then, STERISAFE began a new journey trying to fight the global COVID-19 pandemic with ozone-based disinfection.

Since whole room disinfection is becoming an inevitable necessity in many settings, it is crucial to relay the current findings regarding the ineffective and, at times, dangerous products that are found when conducting a simple Google search. The distribution of disinfection technologies comes with a big responsibility towards clients and communities that rely on such technology to keep them safe.

Necessary features and abilities to consider when researching ozone disinfection units

Any ozone-based equipment should provide its customers with clear information on safety measures, the scope of usage, and adequately documented and proven claims. Unfortunately, many manufacturers fall far short of these requirements. Previous studies performed in particularly malodorous environments reported that ozone was only effective at removing part or selected groups of foul-smelling compounds at lower concentrations. It is suggested that a more significant reduction of smelling compounds would occur only at ozone levels higher than permissible exposure limits. Moreover, ozone can impair one’s sense of smell. The sensation of freshness after using a household ozone generator would be mostly due to a masking effect rather than actual removal of odor and virus.

From a technical standpoint, STERISAFE PRO is equipped with several components that ensure that every disinfection cycle is carried out effectively and, most importantly, safely. One of the critical aspects of STERISAFE’s Full-Depth Disinfection Cycle (FDDC) is its constant real-time monitoring of the ozone concentration in the sealed, disinfected room. This is important in order to validate that the room has been exposed to concentrations high enough to kill pathogens and why no one should be in contact with the ozone during the disinfection process. The STERISAFE PRO is equipped with an optic-based ozone monitor. It updates at regular intervals and ensures that the disinfection cycle is progressing under the proper conditions to warrant full efficacy.

A sensor feedback loop is used to monitor and control the humidity in the room at all times: a higher relative humidity allows for a better reactivity of ozone. This synergy makes both ozone concentration and relative humidity essential parameters for antimicrobial activity. While levels for both parameters are predetermined by extensive research regarding efficacy, a real-time monitoring and control function is imperative to guarantee that every cycle is conducted appropriately and without issue.

Even though ozone is a key player in disinfection technology, it is only useful and safe when integrated into a more extensive process

Equally essential to constant monitoring is the ability to produce ozone in a reliable manner and without by-products. The STERISAFE PRO uses an oxygen concentrator, which generates ozone from oxygen purified from ambient air. Having this intermediary step permits not only a stable, high throughput of ozone at approximately 40 g/h, but also removes naturally occurring nitrogen from the ozone production. This ensures that no harmful nitrogen oxide (NOx) gases – a family of common air pollutants – are released along with ozone, which is a common problem among inexpensive and simple air-fed ozone generators. The STERISAFE PRO has a powerful built-in fan that distributes the ozone homogeneously in all corners of the room. This ensures whole room disinfection, including all small cracks and corners.

Disinfection processes release particulate matter (PM), which is also considered harmful due to the small size of by-product particles and the damage they can cause upon inhalation. These particles are also a common consequence of the reaction between ozone and volatile compounds. To address this issue, the STERISAFE PRO is equipped with an electrostatic precipitator (ESP), which role is to trap and collect such particles at the end of every cycle. Manufacturers typically ignore this issue, and lower-end ozone generators systematically cause a surge in airborne particle concentration.

After the disinfection cycle, the STERISAFE PRO reverses its process turning residual oxidants back into pure oxygen while also removing all particles and nano-particles. There are no remaining compounds or harmful by-products left behind by the end of this process, and it is then entirely safe to enter and use the room as usual.

Appropriate standards and testing, and why they are reliable

Only products that have gone through thorough quality testing and vetting by competent authorities should enter the market. Unfortunately, this is far from being the case. The NF T 72-281 standard is a protocol designed by the French standardisation body AFNOR. It is designed for airborne surface disinfection systems, and it is recognised for its particularly strict fulfillment conditions. NF T 72-281 defines a set of testing methods to challenge disinfectant products in real-life circumstances. The efficacy data of the product is obtained once tests have been conducted according to the intended manner of use.

AFNOR published the first version of NF T 72-281 in 1980 and has updated it several times since, with the latest iteration being in 2014 (NF T 27-281:2014). The necessity for this standard lies in the unsuitability of existing standardised test methods for biocidal materials delivered via air. Current European standards (EN) testing for the efficacy of disinfecting agents only test by direct application methods; meaning the allegedly biocidal product is in liquid form, and either submerged or directly entering in contact with target microorganisms. Those types of testing are usually considered type “Phase 1”; and while they are a good indicator of the tested substances’ biocidal nature, Phase 1 tests are not representative of the real-life usage of biocidal agents. This is a particularly important distinction in the case of airborne disinfectants. Active agents are delivered as gas, vapour, mist, or fog, and have completely different parameters of action (concentration, surface contact, and time).

Because regulatory bodies are aware of this issue, they currently use NF T 72-281 as the starting point for a new EN standard dedicated to airborne disinfection systems (EN 17272). Meanwhile, the Biocidal Products Regulation (BPR, Regulation (EU) 528/2012) only accepts the NF T 72-281 standard for airborne surface disinfection systems. When choosing an airborne disinfecting instrument, it is highly recommended to select a product that uses the NF T 72-281 standard for its efficacy claims. Manufacturers of airborne disinfecting materials that base their efficacy claims on unsuitable EN standards provide inapplicable figures, which can potentially put a health threat to the user and the environment.

As for all microbiology tests, NF T 72-281 measures efficacy against a logarithmic scale. Microorganisms are counted as numbers of colony-forming units (CFUs), and effectiveness is given as the difference between the CFU count before and after application of the disinfecting agent. The result is given as a number of ‘log-reduction’, where a log-reduction of one corresponds to a 10-fold reduction. For example, for a 106 initial CFU, a log-reduction of four would see a decrease of 102 CFU after treatment. This is typically marked on commercial packaging as a kill-rate percentage, where a log-two reduction corresponds to a 99% germicidal power, a log-three to 99.9%, and so forth.

NF T 72-281 is defined as a methodology for the “determination of bactericidal, fungicidal, yeasticidal, mycobactericidal, tuberculocidal sporicidal and viricidal activity, including bacteriophages”. The biocidal efficacy requirements depend on the target organisms:

  • Bacteria: > five-log reduction
  • Spores: > three-log reduction
  • Fungi & yeasts: > four-log reduction
  • Viruses incl. phages: > four-log reduction
  • Mycobacteria: > four-log reduction

Achieving results, safety, and protection

STERISAFE uses the NF T 72-281 standard for all its products and can guarantee their efficacy. Considering the test conditions, the high kill-level objectives it requires, and its extensive target range, the NF T 72-281 should be the only acceptable standard methodology for airborne disinfectant products’ efficacy claims. STERISAFE has been a pioneer in using this standard in the industry of the ozone-based disinfection systems and will continue to do so.

Ozone can be a remarkably useful component in a disinfection cycle. When ozone disinfection is conducted correctly and safely, there should not be any concerns connected to its use. However, potential users are strongly encouraged to question a disinfection product, which seems too good to be true. Excellent solutions, which fulfil both safety and efficacy requirements, are available on the market. The most crucial step is to research individual products and companies to ensure that their technology and data are adequate to the user’s specific needs. This information can function as a guideline for what to be attentive to in one’s search for disinfection technologies.

Special Report Author Details
Author: Amanda Johnsen & Sorivan Chhem-Kieth
Organisation: STERISAFE ApS
Email: info@sterisafe.eu
Website: Visit Website


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