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I replaced the hepa filter and put a new bag in my shop vac a couple of weeks ago, just before I had to use it to pick up the debris from the cleanup of a moldy area. Obviously, the last thing I want to happen is the growth of pathogens inside the shop vac, but, if possible, I would like to avoid replacing a still new filter and bag. Since my vac is dry/wet, I have been mulling over the idea of sanitizing its innards by pouring a small amount of liquid disinfectant in a cup and vacuuming it up: is it reasonable or completely insane? (the inability of a google search to find any suggestion in that direction might suggest the latter).
The idea relies on my intuition that the suction mechanism would distribute the disinfectant in an efficient way to kill all the mold that was vacuumed.

As a disinfectant, my first choices would be either hydrogen peroxide or isopropyl alcohol, both effective against mold and relatively safe in breathing terms, but both present some question marks.
Without having done any computation with the actual numbers, I can see the possibility that hydrogen peroxide might be rendered inactive by this process: if the kinetic energy provided by the vac shop is enough to detach the weakly bonded extra oxygen atom, only ineffective water (which is already 97% of the liquid commercially available) will arrive to contact the mold inside.

With alcohol, of course, there is always the obvious flammability concern to consider whenever electricity is involved. Would it be crazy to try that?

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  • 4
    Vinegar is good mold killer, bleach is better
    – Traveler
    Feb 23, 2023 at 0:58
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    vaporized alcohol, internal motor spark, where's the kaboom?
    – fred_dot_u
    Feb 23, 2023 at 1:18
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    @Ruskes, thanks vinegar is an excellent suggestion!
    – MarcoD
    Feb 23, 2023 at 7:44
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    Do you regularly vacuum up wet/damp stuff or store it in a damp place or anything? If you can just keep the inside of the shop vac dry then mold isn't going to multiply anyway. Feb 23, 2023 at 14:31
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    I’m voting to close this question because small appliance questions are off topic per the help center.
    – isherwood
    Jan 22 at 15:12

3 Answers 3

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My home was flooded last month by a combination of cyclone-related storm water and overflow of the city sewer network (turns out rain gets into the sewer, mixes with wastewater in there, and in extreme weather events like the one we just had, causes overflows and massive mess

Once I ripped out all the carpet and wall lining, a friend lent me his "green machine" (similar to https://www.godfreys.co.nz/bissell-little-green-portable-carpet-cleaner ) . This machine is obviously designed a little more towards the "wet" end of the wet'n'dry cleaner spectrum, but the instructions I was given for sanitising the machine after it was used to suck up water and contaminants, was to mix up a bucket with a half-gallon of 10% bleach and suck that through the cleaner, empty the receptacle and repeat a couple of times. The guy who owned it has been doing that for about a year having bought this machine to deal with the requirement to frequently clean up after his elderly, incontinent, pet cat, and it seems to be doing the job.

In your situation, I'd think about removing the dry filter, running some bleach solution (or your other sanitising agent of choice, as discussed already) to take care of the hose and "wet-friendly" parts of your shopvac, let it dry and return your dry filter to the machine. As long as you haven't gotten it too wet, the HEPA filter nature of your dry filter means its probaly already OK, and as long as you don't promote mould growth by keeping it too moist, I'd expect you'll be fine.

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    How good is it to lend something to a friend, who respects it, and returns it in at least the condition it went out in!?
    – Tim
    Feb 24, 2023 at 10:56
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Either you trust the HEPA rating or you don't. If you do, you can continue to use the vac until you are ready to swap that filter media out, and then decide whether you want to sanitize. If you don't, dispose of the filter material and then sanitize by direct application of/immersion in a disinfectant. I don't think just sucking in disinfectant is going to hit all the surfaces.

Or decide that mold spores are everywhere and, unless you know it's an especially toxic variety and they are given both a medium they can eat and moisture, they really aren't going to do much to cause a problem.

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    Thanks, I guess trusting the hepa filter is indeed the most rational approach. I was probably overthinking when I saw the drywall dust coating the interior of the hose and assumed it might be mixed with anything more dangerous than what's left in the air.
    – MarcoD
    Feb 23, 2023 at 7:52
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    @MarcoD both the news media and product manufacturers have a vested interest in generating the most amount of fear possible in you. The more afraid you are, the more money they make. They don't like it when you stop to think rationally and question what they say.
    – FreeMan
    Feb 23, 2023 at 14:07
  • I think this is the best answer. If anything, bleach, hydrogen peroxide, or any other liquid can potentially be turned into an aerosol when it gets sucked up by the vacuum. That was stated in the question with alcohol, but no one is really thinking about how bad bleach can be in the air. Nathan's answer flat out hurts my lungs thinking about how they clean out that "green machine".
    – Blerg
    Feb 24, 2023 at 6:39
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If yours is a commercial model then it probably uses the venturi effect or compressed air to cause suction. This means that the sucked-up material does not touch any internal moving parts. If it is a lower-end model then the material goes past the impeller/fan, possibly touching it briefly.

Being a dry and wet one, it probably has two collection compartments, which again tells you that a liquid will not touch all parts of the cleaner.

  1. Industrial vacuum cleaners use compressed air - Venturi effect
  2. There is some information here on How Vacuum Cleaners Work

I would suggest that sucking up disinfectant will not actually disinfect all parts of the cleaner. It may be better to spray the moldy area first, wait a few hours and then suck it up.

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  • Thanks, for the info on the Venturi effect. I have a simple Workshop vac (workshopvacs.emerson.com/documents/ws0301va-en-us-198254.pdf). It is dry and wet, but with a single collection compartment. When used as a full wet vac, I need to replace the hepa filter with a wet filter. However it can be used with the dry hepa filter with small amounts of liquid, which is what I was thinking. The idea was to quickly sanitize the hose and the parts that might have come in contact with the mold before it ended up inside the collection bag. Probaby not a real need.
    – MarcoD
    Feb 23, 2023 at 8:08
  • I think that mention of larger vacuum cleaners using compressed air refers to units that are powered by an external supply of reticulated compressed air, carried from a central compressor(s) to various loads by piping. I don't think it's referring to shop-vacs. Feb 28, 2023 at 7:18

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