Disinfection of Scuba Equipment and COVID-19

The novel coronavirus, also known as SARS-CoV-2, is the cause of the disease COVID-19. SARS-CoV-2 is part of the viral group known as “corona” (Latin for “crown” or “halo”) because of the pattern of proteins that stud its surface (2). It is estimated that this group of viruses is responsible for 15%-30% of acute respiratory infections each year (3). These numbers, however, are subject to rapid change as a result of the current pandemic.

COVID-19 spreads via respiratory secretions in a variety of ways including aerosolised droplets expelled by coughing or sneezing, touching surfaces contaminated with the virus, or close contact with someone who has the virus (2). The incubation period of the virus ranges from 2-14 days (2). One study identified the median incubation as 5.1 days with 97.5% of patients showing symptoms within 11.5 days (3).

Coronaviruses belong to a group of enveloped viruses, which means the virion (the form that the virus takes while outside the host cell) is protected by an oily lipid layer (4). As with most enveloped viruses, damaging or destroying this lipid layer will inactivate the virus. Studies of other coronaviruses have shown their infectivity can be reduced by heat, UV light and alkaline or acidic conditions (5). Because of this, and the fact that enveloped viruses are generally easily inactivated, surfaces can be disinfected using household cleaning products (6).

Because research into SARS-CoV-2 is ongoing, there is debate about how long it can survive on surfaces. Recent studies have shown that it can survive up to 3 hours in an aerosol droplet (such as from a sneeze), 4 hours on copper, 24 hours on cardboard, and 2-3 days on plastic and stainless steel (7). In water, however, it is unclear how long SARS-CoV-2 survives. Studies on the SARS virus, called SARS-CoV-1 and the cause of an epidemic in 2003, have shown that it remained infectious for long periods in surface water (lakes, rivers, wetlands, etc.) and previously pasteurized sewage at both low and ambient temperatures (8). In chlorinated or bromated pools and hot tubs, the CDC specifies that SARS-CoV-2 would be inactivated (9).

Heat

There is very little data on SARS-CoV-2, and much of it is preliminary. In times like these scientists will look to related but slightly harder-to-kill viruses. In the case of the novel coronavirus, some data reports are based on the SARS-CoV-1 virus because it is more difficult to kill than the novel coronavirus. One study found that the SARS-CoV-1 virus loses infectivity after being heated to 133°F (56°C) for 15 minutes (5), and the World Health Organization specifies this temperature and timing as well (10). Another study found that the SARS-CoV-1 virus remains stable between 40°F (4°C) and 98°F (37°C) and would lose infectivity after 30 minutes at 133°F (56°C) (11).

Divers Alert Network has received questions about the virus entering a scuba cylinder as a result of contaminated air being drawn into the compressor. During the process of compressing air, using the ideal gas equation T2 = T1 x (P2/P1)(n-1)/n we can calculate that a four-stage compressor with 1 ATA inlet pressure and an 80°F environment pumping air up to 29 ATA or around 4000 psi, would have an inter-stage temperature inside the cylinder of 224 °F. This calculation is very basic and does not account for anything outside of ideal conditions. However, it does indicate the instantaneous temperature at the moment of peak pressure.

In reality, the outlet valve temperature will likely be 170°F-190°F, and the gas temperature around 150°F, occurring during each stage of the compressor (i.e. four cycles for a four-stage compressor assuming each stage’s outlet temperature is the same). Because this is definitively hot enough to kill SARS-CoV-2, it is therefore unlikely that COVID-19 would survive this process should an infected individual cough into the compressor intake. It is important to note that infected droplets exhaled by a person can be as small as 0.5 micron; the filter systems alone would not remove these, but the virus should be dead at that stage.  

It should be noted, however, that if an individual carried the virus on their hands, either as a result of being infected or unknowingly touching an infected surface, and touches the cylinder valve or fill whip, the virus could potentially enter the cylinder through this route. It has been shown that some viruses are extremely pressure resistant — an order of magnitude above diving gas storage pressures. These studies, however, were conducted on noroviruses, a non-enveloped group of viruses that are generally harder to kill than enveloped viruses (12, 13). Other studies conducted on enveloped viruses such as the flu only explored the efficacy of high hydrostatic pressure at 289.6 MPa (42,003 PSI) (14). It is therefore very important to practice hand washing and disinfection of high-touch areas including cylinders and fill stations, as it is likely that a virus could survive at diving gas storage pressures.

Quaternary Ammonium Compounds

Quaternary ammonium compounds, or quats, are a group of chemicalsthat are exceedingly common as active ingredients in cleaning solutions. These agents are hydrophobic and as such are effective against enveloped viruses. Quats are thought to react with the viral envelope and “disorganize” it, leading to the contents of the virus leaking out and degrading. In addition, little evidence exists to support viral resistance against these compounds (15). Studies have shown that quats are effective against SARS-CoV-1 (16), and the World Health Organization (WHO) recommends the use of cleaning products containing these compounds in their laboratory biosafety guidance related to coronavirus disease 2019 (17).

There are quaternary ammonium-containing products commonly used in the scuba industry to disinfect equipment. However, these compounds are harmful to the environment, so care must be taken in their use and disposal (18).

Bleach

Bleach, or sodium hypochlorite, has been studied in many different concentrations, and its effectiveness against viruses has been proven. It is a strong oxidant that works by damaging the viral genome (19). According to the WHO, the recommended bleach solution for general disinfection is a 1:100 dilution of 5% sodium hypochlorite. (Note that some brands of bleach have different concentrations of the active ingredient, such as those that are thickened and marketed to reduce splashing.) This dilution yields 0.05% or 500 ppm of the active ingredient and requires a soaking time of 30 minutes if objects are immersed in the solution or at least 10 minutes if sprayed onto a nonporous surface (20). In a study that examined SARS-CoV-2 specifically, it was found that a bleach concentration of 0.1% or 1,000 ppm was needed to reduce infectivity when sprayed onto a hard-non-porous surface (21). A second study on the same virus found that 0.1% sodium hypochlorite would inactivate the virus within 1 minute. A study on SARS-CoV-1 found that both 1:50 (0.1%) and 1:100 (0.05%) inactivated the virus after an immersion of 5 minutes (22).

When using bleach, the use of gloves, a mask, and eye protection is encouraged. Mix the solutions in well-ventilated areas, and use cold water, as hot water will decompose the active ingredient. It is important to never mix bleach with other chemicals and to remove all organic matter from items to be disinfected, as this too will inactivate the active ingredient (21). Items disinfected with bleach must be thoroughly rinsed with fresh water and allowed to dry before use, as it is corrosive to stainless steel (in higher concentrations) and irritating to mucous membranes, skin and eyes (20, 23). Highly concentrated bleach solutions have also been found to be harmful to life-support equipment, causing metal fatigue and in some cases hose failure during the Hart building anthrax attack. As such these solutions are not used by EPA units for dive equipment when effective alternatives exist.

Soap and Water

Washing hands and surfaces with soap and water is one of the most effective ways to protect against the virus. The type of soap used is not important. Washing with soap and water does not kill microorganisms but physically removes them from a surface. Running water by itself can be effective in removing some unwanted material from surfaces, however, soap will physically pull material from the skin and into the water (24).

Divers Alert Network was asked why soap and water will not work for scuba equipment if it is recommended for hands. Soap and water, as stated above, must be combined with mechanical action to be completely effective. Soaking scuba equipment in soapy water alone is not an effective disinfection method. If soapy water was combined with mechanical action, it would theoretically prove to be more efficient. However, there are some parts of scuba equipment that are not easily reached without disassembly, such as the inside of a regulator. Since an exhaled breath will travel through the inside of a regulator and make contact with the diaphragm, lever arm, and other internal surfaces, soaking the regulator in a disinfectant solution may be a better option.

EPA Guidelines

No matter the active ingredient or method of disinfecting scuba equipment, proven efficacy against the novel coronavirus is of utmost importance. The EPA’s “List N” is a compilation of products that have proven efficacy against SARS-CoV-1 and will therefore also work to kill SARS-CoV-2. Outside of the United States, local governing bodies may also have registered disinfectants. Following the directions for use for each individual product will ensure its efficacy.

When product manufacturers register their products with the EPA, they must submit a list of uses for the product. It is uncommon for registered products on List N to contain “scuba”; more likely to be listed are respirators or materials that scuba equipment is made of. When choosing a disinfectant solution from List N it is important to check that the product’s EPA registration specifies its use for the materials in question.

Some products commonly recommended by underwater breathing equipment manufacturers are classified as quaternary ammonium sanitizers registered with the EPA for use in food service only and are not currently on the EPA’s List N. The EPA does not consider them to be effective against SARS-CoV-2 when applied on those materials and surfaces. 

Best Practices

When selecting a disinfectant, it is of utmost importance to use a product that has proven efficacy against either SARS-CoV-2 or the harder-to-kill SARS-CoV-1. Consult your local governing body’s pesticide registration system for its list of registered disinfectants if the products specified in the EPA’s List N are unavailable in your area. When using these products, be sure to follow the directions and use the specified personal protective equipment (such as gloves or eye protection) when disinfecting. If registered products cannot be found, be sure to use disinfection protocols outlined by the CDC.

After disinfecting equipment, one must take care not to re-infect the equipment, such as by handling it when storing. Dive shop employees should take care to maintain good hygiene by washing hands frequently and regularly disinfecting high-touch areas, including fill stations (as outlined in the “heat” section of this article).

Finally, consider updating your existing emergency action plan to include a potential COVID-19 infection by staff or customers. Be sure to outline all disinfection protocols and ensure that they are being diligently followed by all staff. The most important consideration is the health and safety of your staff and customers.

If you have any questions, please email us at RiskMitigation@DAN.org.


References

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