Technical Guidance On The Use Of Gaseous Ozone Against COVID-19 Virus

1. Introduction

Ozone is a strong oxidiser which can kill microorganisms and viruses effectively. It has been used for treatment of water and wastewater since the early 1900s,¹ though the use of ozone for disinfection of surfaces and air is less established. In recent years, some ozone generators have been promoted as air cleaners for use in occupied spaces.² However scientific evidence shows that ozone concentrations that are within safe health limits are likely to be ineffective for disinfection³ and the use of any effective ozone concentrations must preclude the presence of people and pets, including fish.

This document aims to provide a general overview of gaseous ozone as a disinfection method as well as the considerations for its safe and effective use.

2. Physical and chemical properties

Ozone is an inorganic gas with chemical formula O₃. Ozone has a distinctly pungent smell reminiscent of chlorine, with odour threshold between 7 – 20 ppb.³ Ozone is denser than air and therefore will settle close to the ground in the absence of ventilation.

Ozone is a strong oxidiser which makes it effective for the inactivation of bacteria and viruses. However, this same property also makes ozone a hazard to human health at concentrations as low as 60 ppb. An important consideration in the use of gaseous ozone for disinfection of premises is the half-life of ozone, which will affect its effectiveness and safety protocol. Its half-life ranges from several hours in a sealed plexiglass cylinder (Table 1)⁵ to 11 mins in an office environment with recirculating air and temperature between 21 – 27 °C and relative humidity of 26 – 50%.⁶

Table 1. Half-life of ozone in a sealed plexiglass cylinder under different conditions

3. Disinfection efficacy of gaseous zone

The antimicrobial (anti-bacterial and anti-viral) properties of the gaseous form of ozone have been well documented, and have been shown to inactivate different microbes with varying degree of effectiveness (Table 2). The efficacy of gaseous ozone against enveloped viruses (e.g. coronavirus, influenza virus, mumps virus) was consistently effective (≥ 3 log reduction) at concentration that ranges from 10 ppm to 120 ppm and time of contact between 1 min and 480 min. However, the efficacy of disinfection is more varied for non-enveloped viruses (e.g. calicivirus, HepA virus, etc.). Together, the data shows the inter-dependence of time and dose, and emphasises the importance of verifying antiviral efficacy against specific pathogens of concerns. Importantly, the effectiveness of gaseous ozone against coronavirus is supported.

Table 2. Disinfection efficacy of gaseous ozone on different pathogens.

4. Health effects associated with exposure to ozone

Exposure to ozone can cause adverse health effects to the nose, throat and airways, with more severe health effects observed at higher levels. Exposure of 300 ppb of ozone may cause tightness in chest and throat as well as irritation of lung and throat within 30 min.¹⁴ Exposure of healthy individuals to 80 – 120 ppb of ozone over 6.6 hours has been associated with loss of lung function with cough and chest pain on deep inhalation, inflammatory responses associated with cellular and biochemical changes, and increased airway responsiveness to allergens and irritants¹⁵. A study indicated a decrement in lung function of children when exposed to ozone concentration as low as 60 ppb in the ambient air during a 4-week summer camp in Pennsylvania, US ¹⁶. Chronic exposure has been shown to cause irreversible obstructive airway disease in animals, while some studies showed similar effects to humans. There is no evidence that ozone is a lung carcinogen in human.

5. Air quality guidelines and occupational safety limits

Table 3 shows the air quality guidelines and occupational limits for ozone. As ozone concentrations used in a typical disinfection process can be an order of magnitude above both air quality guidelines and occupational safety limits, care must be taken to ensure that operators and passers-by are not exposed to elevated levels of ozone. According to the Occupational Safety and Health Administration (OSHA), USA, ozone concentration of 5,000 ppb and above would pose an immediate threat to life, cause irreversible adverse health effects or impair an individual’s ability to escape.

Table 3. Guidelines / Limits for ozone concentration

6. Material compatibility with ozone

Ozone has been known to damage plants, fabrics and building materials such as paint, walls and flooring.¹⁷ In particular, ozone can cause significant damage to rubber products.¹⁸ Table 4 provides some reference on the reported compatibility of ozone with various materials.¹⁹ The compatibility of the materials with ozone within the premises should be considered before commencement of disinfection. In particular, checks should be conducted to ensure that safety systems are not compromised due to material degradation from the use of ozone gas.

Table 4. Compatibility chart for ozone (information from Cole Parmer’s chemical compatibility database)

Material	Compatibility	Material	Compatibility
ABS plastic	B	LDPE	C
Acetal (Delrin)	C	Natural rubber	D
Aluminium	B	Neoprene	C
Bronze	B	Nylon	D
Buna N (Nitrile)	D	Polycarbonate	A
Carbon steel	C	PEEK	A
ChemRaz (FFKM)	B	Polypropylene	B
Copper	A	Polyurethane	A
CPVC	A	PTFE	A
EPDM	A	PVC	B
Fluorocarbon (FKM)	A	PVDF (Kynar)	A
Hypalon	A	Silicone	A
Hytrel	C	Stainless steel 304	B
Kalrez	A	Stainless steel 316	A
Kel-F	A	Viton	A

Ratings – Chemical Effects
A – Excellent
B – Good: Minor Effect, slight corrosion or discolouration
C – Fair: Moderate Effect, not recommended for continuous use. Softening or loss of strength and swelling may occur.
D – Severe Effect. Not recommended for any use

7. Other concerns

Due to the reactive nature of ozone, it will also react with volatile organic compounds (such as terpenoids) in the air, giving rise to secondary organic aerosols (SOA). Such compounds may pose adverse health effects to exposed individuals. Monitoring ozone concentrations alone would not reveal the presence or magnitude of potentially harmful reactants that could have been produced during ozone treatment.

8. Safety guidelines for disinfection using gaseous ozone

A proper risk assessment, that considers potential health and material damages, must be conducted. All potential hazards should be identified and protective measures must be taken to minimise each hazard.

As a guide the following measures should minimally be taken:

• Operator of the ozone generating system should be trained in the following:
  • Use of appropriate personal protective equipment (PPE) appropriate for protection against gaseous hazardous chemicals
  • Health and safety topics related to exposure of ozone
  • Proper handling of the ozone generating system
  • First aid response
  
  
• Proper sealing of the premises during decontamination to prevent escape of ozone vapours.


• Minimise VOCs concentration in the premises by excluding the use of products that generate VOCs prior to decontamination. These include and are not limited to air freshners and disinfectants.


• Ensure no personnel in spaces where ozone is released or expected to be diffused to. A risk assessment should determine whether occupants in adjacent spaces may remain. Should there be occupants in these adjacent spaces, they should be alerted on the disinfection work, be advised on potential exposure risk and be provided with safe evacuation protocols.


• Provide monitoring devices that are able to continuously monitor ozone levels. If the levels in occupied spaces exceed 100 ppb (15 mins) or 50 ppb (8 hours), operators and/or occupants in these and adjacent spaces should be evacuated and ozone generation should be terminated.


• People with cardiac pacemakers or other electric implants are not permitted to enter premises with an ozone generation system.²⁰


• Operators should don respiratory protection such as self-contained breathing apparatus (SCBA) or filter apparatus with gas filters NO-P3 (colour code blue-white) or CO (colour code black) before entering the affected space with ozone levels above 100 ppb.²⁰


• Air purging/ increased ventilation shall be introduced in the treated spaces and the surrounding spaces after the disinfection process. A thorough check should be conducted to ensure ozone levels in affected spaces are less than 50 ppb before occupancy.

9. Efficacy guidelines for disinfection using gaseous ozone

Due to the varying efficacy results of ozone against bacteria and viruses at different concentration (Table 2), there is insufficient evidence to support any recommendation on  specific ozone concentration and treatment times for the disinfection of SARS-CoV-2 virus. Service providers must demostrate the efficacy of their product by providing efficacy test reports against various microbes. During the disinfection process, service providers must also monitor the ozone concentration in the treated spaces to ensure the appropriate concentration is maintained for the required period.

10. References

1. Environmental Protection Agency, (2000). The history of drinking water treatment. EPA-816-F-00-006.
2. California Air Resources Board, (2006). Evaluation of ozone emissions from portable indoor “air cleaners” that intentionally generate ozone. Available at https://ww3.arb.ca.gov/research/indoor/o3g-rpt.pdf?_ga=2.20185208.15851615.1606897756-304392656.1606897756
3.  Dyas, A.; Boughton, B.J.; Das, B.C. (1983). Ozone killing action against bacterial and fungal species; microbiological testing of a domestic ozone generator. Journal of Clinical Pathology. 36, 1102-1104.
4. Cain, W. S.; Schmidt, R.; P. Wolkoff. (2007). Oflactory detection of ozone and d-limonene: reactants in indoor spaces. Indoor Air. 17, 337-347.
5. McClurkin, J. D.; Maier, D. E.; Ileleji, K. E. (2013). Half-life time of ozone as a function of air movement and conditions in a sealed container. Journal of Stored Products Research. 55, 41-47.
6. Mueller, F.X.; Leob, L.; Mapes, W. H. (1972). Decomposition rates of ozone in living areas. Environ. Sci. Technol. 7, 342-346
7. Selma, M.V.; Ibáñez, A.M.; Cantwell, M.; Suslow, T. (2008). Reduction by gaseous ozone of Salmonella and microbial flora associated with fresh-cut cantaloupe. Food Microbiology. 25, 558-565
8. Pekovic, D.D.; Kacimi, H. Efficacy of Ozone Gas against Mumps Virus under Experimental Environment Conditions. (2015) EC Microbiology. 1, 184-189Lee, J.; Bong, C.; Bae, P. K.; Abafogi, A. T.; Baek, S. H.; Shin, Y. B.; Bak, M. S.; Park, S.; (2020)
9. Lee, J.; Bong, C.; Bae, P. K.; Abafogi, A. T.; Baek, S. H.; Shin, Y. B.; Bak, M. S.; Park, S.; (2020) Fast and easy disinfection of coronavirus-contaminated face masks using ozone gas produced by a dielectric barrier discharge plasma generator. MedRxiv. Available at https://doi.org/10.1101/2020.04.26.20080317
10. Tanaka, H.; Sakurai, M.; Ishii, K.; Matsuzawa, K. (2009). Inactivation of influenza virus by ozone gas.  IHI Engineering Review. 42, 108-111
11. Hudson, J. B.; Sharma, M.; Petric, M. (2007). Inactivation of Norovirus by ozone gas in conditions relevant to healthcare. Journal of Hospital Infection. 66, 40-45
12. Brie, A.; Boudaud, N.; Mssihid, A.; Loutreul, J.; Bertrand, I.; Gantzer, C. (2018). Inactivation of murine norovirus and hepatitis A virus on fresh raspberries by gaseous ozone treatment. Food Microbiology. 70, 1-6
13. Dubuis, M. E.; Leblond, N.; Laliberte, C.; Veilette, M.; Turgeon, N.; Jean, J.; Duchaine, C. (2020) Ozone efficacy for the control of airborne viruses: Bacteriophage and norovirus models. PLOS ONE. Available at https://doi.org/10.1371/journal.pone.0231164
14.  Sittig, M. (2017). Handbook of toxic and hazardous chemicals and carcinogens , 7^th ed
15. Boeniger, M. F. (1995) Use of ozone generating devices to improve IAQ, Am. Ind. Hyg. Assoc. J. 56, 590-598
16. Spektor, Lippmann, Lioy, Thurston, Citak, James, Bock, Speizer, Hayes (1988) Effects of Ambient Ozone on Respiratory Function in Active, Normal Children. Am Rev Respir Dis 1988, 137:313-320
17. California Air Resources Board, (2008). Evaluation of ozone emissions from portable indoor air cleaners: electrostatic precipitators and ionizers. Available at https://ww3.arb.ca.gov/research/indoor/esp_report.pdf?_ga=2.6557170.¹⁵851615.1606897756-304392656.1606897756
18.  Lee, D. S.; Holland, M. R.; Falla, M. (1996). The potential impact of ozone on materials in the UK. Atmospheric Environment. 30, 1053-1065
19. Cole Parmer: Chemical Compatibility Database for Ozone. Available at https://www.coleparmer.com/chemical-resistance (accessed 31 Jan 2020)
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