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Old 03-23-2020, 09:40 AM
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Join Date: Mar 1999
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A note on disinfection by SDStaff Hawk

Our old friend SDStaff Hawk (our resident expert on DNA and other science matters) has published this information on social media. We're happy to share it with you.

SDStaff Hawk says:

I've been sharing this info:

I did the math for you:

*Rubbing alcohol is available as 70% isopropanol, so it doesn't need dilution. It also comes as 91%, which means to dilute it down to 71%, you should take one cup of 91% rubbing alcohol and add 1/4 cup (it's actually 72.8%, but unless you have graduated cylinders at home like I do, it's close enough.) I keep mine in a spray bottle, apply lightly, and just let it evaporate. Be aware that isopropanol is a solvent and will cause a lot of inks and dyes to bleed, so test for steadfastness.

*Household bleach can range in concentration, so read the label. Here are the three most common concentrations that I've found on labels, with the appropriate dilutions:

*At 5.25% sodium hypochlorite, a 0.1% solution is equal to 1 tablespoon of bleach mixed with 3-1/3 cups of water.

*At 6.05% sodium hypochlorite, a 0.1% solution is equal to one tablespoon of bleach mixed with about 3-3/4 cups of water.

*At 8.25% sodium hypochlorite (a.k.a., concentrated bleach), a 0.1% solution is equal to one tablespoon of bleach mixed with about 5-1/4 cups of water (or one teaspoon of bleach mixed with about 1-3/4 cups of water).

**I don't know whether a 0.1% solution is strong enough to bleach fabric, so I don't recommend using it on clothing or furniture.

**Bleach is stabilized in the bottle, but becomes unstable when diluted and/or exposed to light, so (a) make small batches fresh daily, (b) put it in a spray bottle and apply sparingly to surfaces for one minute (I just let it dry on its own), and (c) if the bottle is transparent or translucent, just keep it in a dark place or cover the bottle with aluminum foil.

*Consumer-grade hydrogen peroxide solution is 3% hydrogen peroxide, so a 0.5% solution is equal to 1/2 cup of peroxide mixed with 2-1/2 cups of water. Please check the bottle to make sure that it's 3% hydrogen peroxide.

But there is a speedier option: research has shown that coronaviruses can be inactivated within a minute by disinfecting surfaces with 62-71% alcohol, or 0.5% hydrogen peroxide bleach or household bleach containing 0.1% sodium hypochlorite. Higher temperatures and humidity also tend to result in other coronaviruses dying quicker, although research has shown that a related coronavirus that causes Sars could be killed by temperatures above 56C or 132F (hotter than even a bath scalding enough to cause injury) at a rate of about 10,000 viral particles every 15 minutes.