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Comment by Mistletoe | Hacker News Reader

I was thinking yesterday how 70% ethanol is like the perfect disinfectant and we don’t use it. It’s what we used when working in sterile conditions when I was a scientist. You certainly wouldn’t use quat disinfectants to spray your gloves before working in a hood. You’d know it would probably get in your experiment and mess it up. Ethanol is perfect, it evaporates and leaves nothing. I assume we don’t use ethanol because people would drink it, or it costs too much. Both aren’t great reasons when safety is what you are throwing out.

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It evaporates too fast to fully penetrate all surfaces and isn't as effective against a bunch of biological vectors like spores that require prolonged contact to really kill. Quat disinfectants leave a residue behind that continues killing stuff and they're generally less irritating to skin and the respiratory system (though that's for people using the room after it was disinfected, not necessarily for the person doing the disinfecting).

What about suspending the ethanol like in alcohol gel? Could we find a gelling agent that is less irritating than the quat disinfectant residue?

That works fine for hand sanitizer but it becomes too viscous to spray as disinfectant, which is important for hospitals.

Well, we do use it in most hand-sanitizer solutions. I assume alcohol isn't a popular (home) cleaner because it is volatile and requires high concentrations (70%+) to be effective.

From a cost perspective, the Clorox Company no doubt prefers to add a few grams of a quat to multiple gallons of scented water, which means they're basically selling a spray bottle of a nearly-free solution that is 99.5% water for $5. Shipping 70% alcohol also brings with it a Flammability-3 (high) hazard label.

It should be illegal to sell such unconcentrated solutions, except perhaps in food (e.g., even milk is easily reconstituted). It would be much more efficient to sell the concentrated chemical and let consumers dilute them. Imagine the fuel savings, shelf space savings of not having to ship 99.9% water around the world.

I remember some medicines were dispensed like that in the 80s, and the patient had to reconstitute them before using.

You can usually get concentrated cleaning solutions, but they tend to be used more by industry/businesses. These quats are sold concentrated as dish sanitizer (mixed in a sink full of water) for restaurants, for example.

I think consumers would just rather have ready-to-use spray bottles in most cases. There's probably a surprising number of people that couldn't do the basic math of diluting based on a formula.

Personally I’m a fan of putting a mixture of salt, water, and vinegar through hydrolysis to get sodium hydroxide and hydrogen chloride.

Super cheap and effective cleaner, easy to make at home.

Only downside is it isn’t shelf stable, so you have to make a new batch every ~2 weeks.

Force of nature has a pretty neat kit that automates the chemistry.

You do what?

I’m afraid you have the reaction products wrong. This is the chloralkali process, and you get hydroxide, hydrogen, and chlorine gas. The latter is extremely nasty. If you do it right (which I can almost guarantee you are not doing), it will react with water to form hypochlorite (that’s your fairly safe disinfectant) and chloride (harmless).

But this reaction goes the other way in acidic conditions: hypochlorite will turn into chlorine gas.

DO NOT run the chloralkali process indoors. DO NOT run it near your face. DO NOT think you’re clever and run it in a closed container — not only is the chlorine toxic, but it can explode when mixed with hydrogen. DO NOT mix bleach-containing products with acids. Just buy plain bleach (the “sanitizing” kind), dilute it carefully with water, and use it in an appropriate concentration.

(You can safely do the chloralkali process in a cell with a high flow of salty swimming pool water, with safety measures to turn it off if the flow stops.)

Speaking of sanitising bleach, does it have a best-before date?

I have a bottle of it sitting around, but it’s quite old and I’m not sure if the date on it is when it was made or when it should be discarded.

Probably discard it. Hypochlorite is unstable, and it loses potency. Or, if you’re feeling adventurous, dilute it 1:20000 or so and measure it with a pool test kit. Also, one of the degradation products is chlorite, which is somewhat nasty.

You can find actual research from the swimming pool chemical industry. At higher concentrations (bleach sold for swimming pools is more concentrated), it’s less stable and apparently should ideally be used within 30 days in hot weather. The household stuff ought (good luck!) to be more stable, and you’re probably not storing it in a hot pool equipment room.

Even if concentrated (5%+), it will expire after about 1 year.

If it's diluted for use, it will expire in a few months.

The brand might document. For example: https://www.clorox.com/learn/how-to-tell-when-a-bleach-bottl...

I’m not sure what you’re going on about.

My lay understanding is that the process you’re describing happens at a different pH, same ingredients. Yes you can get bleach and toxic gases, but, like, don’t do that?

My understanding is that most large schools and hospitals have on-site synthesis of exactly this for disinfecting.

There are off-the-shelf products that do the same thing for the consumer market. This is the favorite I’ve found: https://www.forceofnatureclean.com/

My understanding is you get lye on the anode and hydrogen chloride on the cathode (might have those backwards?).

I think it’s one hydrogen one chlorine atom? Hydrogen chloride sounds right (but I’m not a chemist) I think it’s also called hypochlorite? My understanding is the vinegar controls the pH to get the water molecule and salt molecule to do its thing.

But I’m also under the impression that this is perfectly safe. I produce and use the cleaner daily, have been for a while!

Hypochlorous acid solutions for wound care and such are indeed a thing, and they are produced by companies that know what they're doing, and I assume they make a batch, purify it, measure and adjust the pH.

That "Force of Nature" site looks a bit sketchy. At least they claim to be using a controlled chemistry (although they can't actually control the tap water pH), and they are EPA registered. Their EPA registration claims that they produce 220 ppm "available chlorine" solution.

Hydrogen chloride is not hypochlorous acid. Hydrogen chloride dissolved in water is hydrochloric acid, aka muriatic acid or stomach acid (nasty stuff unless it's very dilute), and it will also kill bacteria if you concentrate it enough because it's very acidic. You can find it in a lot of toilet cleaners.

Here's an IMO mildly less sketchy product:

https://store.hocl.com/ecoone/

At least it ships with test strips.

If you DIY this and stick big electrodes in salt water (especially with added vinegar, especially if you get the pH below about or if you fail to capture the bubbles so they can dissolve fully) and connect a beefy power supply, you will regret it.

It's also very flammable, which is a bit of a problem.

My company’s product includes a piece of acrylic (PMMA). Ethanol would jellify it, quats are basically our only approved disinfectant.

One of the issues that I discovered during COVID is that alcohol isn’t a scheduled pesticide because it predates the regulation.

So applications that are regulated cannot use alcohol unless they can use a listed product, which is rare and expensive

Lots of stuff is resistent to 70% ethanol - norovirus for example.

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