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This question was inspired by this one, which brought up the concept that a lot of the issues with a sword that created toxic fumes would also kill the user (that question also has one of the best answers I've seen on the site, check it out if you have the time)

So here's the question: Using only technology that was available in the Medieval Era, but knowledge of how air filtration works on a modern level, is it possible to create a working Gas Mask?

As for which part of the "Medieval Era"? That's up to you. As early as possible is preferred, but feel free to go as far as 1492 if you feel like you need to.

To count, the Gas Mask must:

  • Be light enough to be wearable (around the same weight as a full suit of armor at the time)
  • Be portable (no air hoses leading off the body or anything similar
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    $\begingroup$ The Manga Dr Stone does this very thing. readms.net/r/dr_stone/031/4623/19 $\endgroup$ – John Jul 17 '18 at 15:00
  • $\begingroup$ It should be noted that chemical (Gas) weapons aren't as effective as many people would believe: youtube.com/watch?v=l6uLUaqgWY0 Rather, it is effective in certain contexts (Underground/sealed space). $\endgroup$ – Sarah Szabo Jul 18 '18 at 2:12
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Yes it's possible.

How?

The mask body would be made out of leather. In order to make it airtight I would take one layer of leather, then a layer of pitch (which was also used to seal ships) and another layer of leather. With leather straps you could fix this mask to the head.

You could even fit glasses in there - medieval glass was not as good as today's but it would be enough to see through and protect your eyes.

For a breathing filter I would use activated carbon, perfectly doable with medieval technology. I'd either make a leather or a metal tube, that I'd fill with activated carbon. A cloth on each side would hold the carbon in place while letting air pass through. Fix the tube to a hole in the mask body and seal the edges with pitch. As ironduke97 already stated urine-soaked clothes were also used, so you could make different kind of filters by adding such a cloth to the filter.

It would probably not be as comfortable or easily usable as modern masks. You'd need a second person to help you with putting it on and fitting it to your head in an airtight way, but it would do its job.

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    $\begingroup$ Welcome to Worldbuilding! You seem to have made your first post one of quality. Good job! $\endgroup$ – ArtificialSoul Jul 17 '18 at 6:38
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    $\begingroup$ @ChrisH Steel doesn't really do anything to protect from gas, and unless it's a very thin layer of steel - which would be fairly brittle - the weight would make putting the mask on and wearing it more difficult. $\endgroup$ – Cubic Jul 17 '18 at 9:46
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    $\begingroup$ @Cubic I think he meant the steel would be useful for other threats like someone hitting you with a sword, for instance. $\endgroup$ – Sydney Sleeper Jul 17 '18 at 10:14
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    $\begingroup$ Was it known at the time that carbon could be used in this manner? $\endgroup$ – levelonehuman Jul 17 '18 at 13:54
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    $\begingroup$ @levelonehuman The question says we can use modern knowledge of how air filtration works. I'd say that includes the knowledge that charcoal's good at absorbing stuff. $\endgroup$ – David Richerby Jul 18 '18 at 16:29
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A full-faced gas mask has two features that prevent us from inhaling potentially toxic contaminants in the air. Then it has to be sealed against the face, preferably to skin (so no beards), and then, if needed, have glass eye protection. It's the filter that causes the issues...

  1. The first is a particle filter which removes any bacteria/dust in the inhaled air. There is essentially no chemistry involved here, just a physical barrier that forms a field between the toxins and the face. When a particle is inhaled, it hits the fibers on the filter and becomes tangled before it ever has the chance to reach the nose or mouth and move down to the lungs. This is very replicatable in medieval times. They had the ability to weave silk etc. to very fine levels, and simply having the material be dampened increases its effectiveness considerably.

Asbestos could be used which would aid this as well, as they were using it in Roman times for various items, but alas as we know, it tends to causes a lot of issues in the long run, especially if it was being breathed through. The crazy thing is even the Romans knew that asbestos causes lung damage, but no other material came close to what was needed at the time, and even now, asbestos still beats almost anything else, which is why it is still used in nuclear reactors etc., but that's a tangent... back on track.

  1. The second element is based on a chemical process called adsorption, and removes toxic molecules like the nerve gas sarin. Through adsorption, a solid or a liquid can trap particles on its surface — analogous to the way a cigarette filter reduces the amount of toxins a person inhales when smoking.

To filter out harmful chemicals, most gas mask filters are made with activated charcoal, or oxidized charcoal. When charcoal is activated with oxygen, it becomes ripped with tons of "sticky" holes in each molecular structure just like chicken wire. Any toxins that pass through the charcoal become bonded to these holes, and are prevented from moving into the gas mask. while there are other chemicals used nowadays, activated charcoal is the best solution for most toxic gases.

So - could a medieval society make activated charcoal?

Rough process for making activated carbon

  • Make charcoal.
  • Powder the charcoal.
  • Make a 25% solution (by weight) of calcium chloride.
  • Make a paste with the calcium chloride solution and your powdered charcoal.
  • Spread the paste to dry.
  • Rinse with clean water.
  • Bake at 225 degrees F for 30 minutes.

This is the stumbling block, specifically chlorine. It is rarely found by itself in nature. According to google, chlorine was discovered and first isolated by Carl Wilhelm Scheele in 1774, and calcium chloride was first discovered in 1808, long after the time frame you're wanting.

So, would anything else do?

Well... Activation of charcoal is really a word to describe the process of driving condensed smoke from charcoal’s pores, and this can be done with a variety of chemicals, its just that calcium chloride gives the best results, so replacing it with even water and repeating the process several times would activate it a bit, but you'd still be breathing in smoke as the charcoal released it over time (not ideal) - you want to be able to get rid of as much smoke as possible. Coconut oil is filled with calcium but lacks the fat/cream that cows milk would wreck the whole process. So all you need is a coconut in a medieval setting. Perhaps it could have been carried by a swallow? Not a European swallow, obviously, and then again, African swallows are non-migratory... oops, another tangent.

But then, you did say with modern knowledge, so.

Making calcium chloride (wow this is getting long)

  • Place the limestone in the beaker. Use enough limestone the fill the beaker about 1/4 full.
  • Add a 1/4 of a beaker of hydrochloric acid to the limestone.
  • The hydrochloric acid will start to bubble as it dissolves the limestone. Gently swirl the beaker to mix the contents and make sure the reaction goes to completion. If all of the limestone dissolves, add a little bit more.
  • Once the solution stops bubbling, filter off the solids by pouring the solution through the filter paper into the second beaker. The calcium chloride is dissolved in the filtered solution.
  • Use the hot plate to gently heat the second beaker containing the calcium chloride solution. The solid left after the water evaporates is solid calcium chloride.

So the big one here is hydrochloric acid, which, according to google again, was discovered by the alchemist Jabir ibn Hayyan around the year 800 AD!!! That's really good.

So we finally got there. Would it have been possible in our timeline, without knowledge and understanding? No.

But with modern understanding but only medieval materials - YES

might take a while and it would be very expensive to get all the materials together, but... YES!

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The bird-beak shaped masks used by plague doctors in the 17th century were a type of gas mask. I'm pretty sure people in medieval times had access to the herbs that were stuffed inside said masks. So with some craftsmanship, they could make something similar.

Other types of rudimentary gas masks included urine soaked cloths (the ammonia present neutralized the chlorine that was a favorite of the Germans) and simple masks with layers of charcoal, which is good at absorbing dangerous gases.

So I'd say yes, it is entirely possible for folks of the medieval period to construct gas masks of their own with technology only available at that time.

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    $\begingroup$ Interesting, I hadn't thought about urine-soaked cloth. I guess that means the earliest that a proto-gas mask could be created would be 3400 B.C. $\endgroup$ – Sydney Sleeper Jul 17 '18 at 5:11
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    $\begingroup$ As long as they had pieces of cloth lying around, yeah probably. $\endgroup$ – ironduke97 Jul 17 '18 at 5:20
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    $\begingroup$ Well the beak masos were more about: if i can't smell it it can't infect me. But yeah $\endgroup$ – dot_Sp0T Jul 17 '18 at 5:32
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    $\begingroup$ The herbs weren't what made the plague masks work (or at least, not the herbs as such). What made them effective against plague was that all the material between the wearer and the outside air acted as a crude particulate filter. $\endgroup$ – Mark Jul 17 '18 at 22:59
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    $\begingroup$ FWIW, the urine wasn't what worked against the chlorine gas either. It was the moisture that helped, by soaking up some of the gas and trapping it. Urine was just easier to provide in a crisis than precious water stores, so they encouraged the rumor. $\endgroup$ – Sean Duggan Jul 18 '18 at 2:28
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It depends on exactly what the mask is supposed to filter out. Even modern gas masks are not all equal. The respirators they use when sand blasting for instance are only rated for particulates, not gases. This kind of mask is well within reach of a medieval society; really all you need is wet cloth for particulates. They will have a harder time dealing with poisonous gases. Not every kind of filter works on every kind of gas. A charcoal filter won't help you against carbon monoxide for instance. They did have access to asbestos in the middle ages, and many WW2 and Cold War era masks used asbestos filters. I don't know if they had the experience working with asbestos necessary to make these filters, but I don't think it's that big of a stretch. So they should be relatively safe from things like chlorine, phosgene, or mustard gas. It's still likely to burn their eyes since I doubt they will be able to get an effective seal without rubber, but they should survive.

They have no hope of making a full PPE suit, which is what is necessary to survive weaponized contact agents like VX nerve gas. VX will kill you in minutes if it touches any exposed skin. Without rubber and zippers you have no chance of making an air-tight suit. And even if you somehow manage that, you still need an oxygen tank since you can't use outside air at all. I would say if you have the pump technology to fill an oxygen tank, your society is decidedly not medieval.

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    $\begingroup$ I doubt we need to go as deep as VX since that was only discovered in the 1950s. $\endgroup$ – ironduke97 Jul 17 '18 at 5:28
  • $\begingroup$ @ironduke97 Cyanides and various other highly corrosive chemicals are well within reach of medeival alchemists though, and such things may still need full PPE. $\endgroup$ – Austin Hemmelgarn Jul 18 '18 at 0:12

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