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I have heard in various situations people use a wet fabric to breathe better in situations where a lot of fire-based smoke is present (like near wildfires). I wanted to know if there was any truth to this, specifically with regard to wet fabric vs dry fabric.

A quick Google search brought me to this website from FEMA where it says that dry material works better for aerosols and particulates, but it seems the primary focus of the article is chemical attacks, and I can't really find any other sources to back this up; almost ubiquitously across my searches, it seems that everyone is inclined to think that wet fabrics do better.

So my question is that: do wet or dry fabrics work better for filtering smoke? I would greatly appreciate sources when possible, seeing as this seems like an empirically determined fact.

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    $\begingroup$ Wet is good for cooling the air you breathe through the fabric. You don’t want to burn your lungs. $\endgroup$
    – Jon Custer
    Commented Dec 28, 2022 at 15:05
  • $\begingroup$ @JonCuster That is an excellent point; while I’m still interested in the answer here, it definitely seems there would be many instances where that benefit outweighs possible loss of filtering efficiency. $\endgroup$
    – Justin T
    Commented Dec 28, 2022 at 18:49
  • $\begingroup$ some possible information here though not sourced: physics.stackexchange.com/questions/685455/… $\endgroup$
    – Andrew
    Commented Dec 30, 2022 at 13:18

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The composition of smoke is not well-defined. On the one hand, some smokes could be considered aerosols of solid particles or liquid droplets only (no gaseous material worth considering). These smokes, as well as other aerosols (e.g., sneezes) can be filtered well enough by using fine weave fabrics (e.g., K95 medical masks). There does not seem to be any suggestion that wetting these masks improves their performance, perhaps because the fine weave would be blocked too much, even by a thin film of water or by swelling of the fabric material.

On the other hand, it might seem that a wet mask could trap liquid aerosol droplets (assuming they are aqueous, not oily) more easily, and this might prove advantageous if the mask is less protective or efficient than a K95 mask. Such a less effective mask probably wouldn't close down so much if it became wet.

On the other hand (if you have one), the gases in a fire combustion smoke may include NO2, SO2, HCN, H2S, Cl2 (from PVC), dioxins, methanol, and many others (Ref 1). These might well be trapped better by a wet mask because they won't be "trapped" at all by a dry one.

Smoke inhalation is the primary cause of death in victims of indoor fires. Particulate inhalation could certainly cause death, but I think the gases would cause incapacitation faster (choking, gasping, collapsing) than suspended particulates.

The graph below shows chemical compositions of volatile organic compounds in smokes from various fuels (Ref 1). The prevalence of oxygenates is obvious; these would likely be better absorbed by a wet mask.

enter image description here

In a reverse sense, wet masks seem to prevent transmission of large aerosol droplets outward better than dry masks (Ref 2). But for COVID protection, dry masks are preferable (Ref 3). But, wet or dry is better than nothing (Ref 4). And cotton exposed to humidity shows an improvement in filtering, whereas synthetic fabrics do not (Ref 5).

In general, specific testing, against the specific smoke (or its likely composition), of the exact mask or cloth/towel/etc., would be needed to determine what would "help you breathe better". In the short run, helping you get out of the smoke would be best; perfect elimination of contaminants with overly restricted airflow isn't the best solution. Perhaps every situation is unique.

Ref 1. https://en.wikipedia.org/wiki/Smoke

Ref 2. https://www.sciencedaily.com/releases/2021/11/211122135517.htm

Ref 3. https://www.wusa9.com/article/news/verify/does-a-wet-mask-make-a-difference-or-am-i-safe-wet-mask-efficiancy-vs-dry-masks/65-5d760229-9e3e-4649-b420-969c74f219cb

Ref 4. https://www.popsci.com/science/wet-masks-covid-protection/

Ref 5. https://www.nist.gov/news-events/news/2021/03/study-indicates-humidity-breath-makes-cotton-masks-more-effective-slowing

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  • $\begingroup$ Exactly what I was looking for, thank you! $\endgroup$
    – Justin T
    Commented Dec 31, 2022 at 17:22
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    $\begingroup$ Good answer, the great problem is that the science of air purifiying respirators is complex. I know that in charcoals that while water adsorption normally reduces their ability to protect against gases / vapors in the case of phosgene the water can increases the ability of the charcoal to remove the toxic gas from air. $\endgroup$ Commented Jan 1, 2023 at 10:36

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