Building a powered air purifying respirator - Page 1
Forum section: electronics / general

author: engineheat
author_rank: Frequent Contributor
timestamp: February 23, 2022, 04:28:53 am
content: I'm interested in building a DIY powered air purifying respirator. I'm not going to use it for doing any hazardous work.I do plan to incorporate a HEPA filter and active carbon filter. Are there off the shelf sheets one can buy? As opposed to buying commercial filters that comes in fixed sizes and are designed for proprietary respirators/purifiers.I guess I will also need a battery pack and a portable impeller that can deliver high enough air pressure?Lastly, (and this is one powered respirators appeal to me so much), I heard you don't need to create a perfect seal with your face since the powered respirator will create a positive air pressure. Is that true?Any advice would be appreciated. thanks

author: thm_w
author_rank: Super Contributor
timestamp: February 23, 2022, 10:28:11 pm
content: I would consider off the shelf filters, they are not terribly expensive, you can use them with existing low cost respirator, and if you buy from a reputable supplier you'll know its genuine.https://www.3mcanada.ca/3M/en_CA/p/d/v101067018/Of course, if you want some large backpack mount unit, that would have better restriction than these small filters. But its really not clear what you are going to do.Even in that case I would try to find an off the shelf HEPA filter, eg Altec or Levoit 300. Carbon you can buy sheets or just buy the loose activated carbon pebbles, they are commonly used in aquariums.For the fan, you want one with high static pressure. Centrifugal style is generally good.

author: SmallCog
author_rank: Frequent Contributor
timestamp: February 24, 2022, 03:21:12 am
content: This video (although not for a mask) may be of interest to youWhilst googling for it I found this Reddit discussion that mentions a standard filter used in vacuum cleaners that may be worth looking intohttps://www.reddit.com/r/BigCliveDotCom/comments/mtam4i/easy_to_get_standardized_hepa_filters_for_diy/When I originally saw the BigClive video I was thinking that an automotive air filter from a very common vehicle (engine or cabin) may be a good option (although I've not looked into how good they filter) as they're readily available and unlikely to disappear from the marketplace like some random filter available on ebay might do.Example of a cabin filterhttps://www.rycofilters.com.au/N99-MicroShield

author: Rick Law
author_rank: Super Contributor
timestamp: February 24, 2022, 07:43:17 pm
content: One can get those large 30+ inch by 20+ inch HEPA filters for HVAC then cut it down to size. If say you just want 5x5 inches, a 30x20 will cut to 24 sheets 5x5's. Saves money too.

author: PaulAm
author_rank: Frequent Contributor
timestamp: February 24, 2022, 09:57:36 pm
content: If you are only concerned about dust, look for a 3M Air-Mate powered respirator. They're pretty cheap on the used market. I see one on Ebay for around $55 now.I used one with an open helmet + face shield when doing wood working. The air hose connected to the helmet and filtered air came down over your head. No restrictions and no breathing dust. The filters are HEPA rated. Worked great.You used to be able to find the power units for the 3M Breathe EZ respirators cheap and they used standard 3M cartridges, anything from HEPA to chemical hazard filters. That was all pre-Covid though. Finding the rest of the pieces affordably was a challenge.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: February 24, 2022, 10:55:41 pm
content: It is not true that a good seal is not necessary. That would only be true if the respirator blew enough air all the time to blow "outward" around the seal at all times even if you took a deep breath.Not all pos pressure air supply respirators do this, Some do.Studies done in firefighters who use air supply respirators (SCBA) with good air seals and professionally fit to them, have shown that even they have elevated carbon monoxide in their systems after a fire.Even external supplied air respirators with big hose, like the helmet design (which is a good idea and does not require a "fit") are not rated at the highest levelNone of these things are perfect.If you are going to use multiple filters like HEPA+Charcoal, air supply is a good idea because multiple filters do make it harder to inhale, even just a little bit is too much for some people to tolerate either physically or just psychologically(like me).

author: BrokenYugo
author_rank: Super Contributor
timestamp: February 24, 2022, 11:40:21 pm
content: I built my own as a proof of concept last winter when the covid outlook was a bit more uncertain.I used a generic 12V air mattress/pool toy inflation pump (centrifugal blower), pushing air (these pumps suck from both the inlet and a bit through the motor to cool it) into a chamber holding a surplus NATO thread CRBN gas mask filter, two military surplus gas mask hoses joined for more length feed clean air into a modified cheap snorkel mask, exhaust goes out through two slightly smaller hoses down my shirt (WARNING: outflow must be adequate to keep static pressure in the mask low!) just to be polite.For my pump 5V happened to give perfect flow (I forget the figure, there are recommended flow rates), tested by timing the inflating of a thin trash bag sitting in a 5 gallon bucket, this is supplied by a Anker power bank via short USB to 5.5mm barrel pigatil. The power bank has very little inrush capacity, so a fairly large 1R resistor was placed across the power switch in the pump to give a crude soft start feature, switch off, plug in to start, switch on for full power.Pump, filter, and power are kept in a small tool bag slung over my shoulder.This of course all comes with the disclaimer that deliberating pumping air into your body is dangerous, none of this post is to be construed as advice, you mess with this sort of stuff at your own risk, you get the idea.Pics can be provided, I just have to dig it out of storage.

author: engineheat
author_rank: Frequent Contributor
timestamp: February 26, 2022, 10:52:06 pm
content: Quote from: Wallace Gasiewicz on February 24, 2022, 10:55:41 pmThanks. Yes, ease of breathing is important for me, and I don't want to deal with needing a good seal all the time, which is why I think powered respirator is the way to go. Them being not perfect is okay, like I said, I'm not using this for a hazardous environment where I need extreme protection. This is more for environment that are "questionable" but not immediately dangerous, like a city with high air pollution, walking near major roads, preventing viruses, etc. So if whatever I build can get rid of 95%+ of contaminants, then I'm already better off than not having anything at all.The ones that you mentioned that blows enough air, do they have some kind of one-way exhaust valve to get rid of that excessive air if the air consumption rate (breathing rate) of the user is too low? I guess if there is no perfect seal then that's not necessary...Thanks

author: engineheat
author_rank: Frequent Contributor
timestamp: February 26, 2022, 10:55:05 pm
content: Quote from: thm_w on February 23, 2022, 10:28:11 pmCan you list a few reputable manufacturers of HEPA filters or carbon sheets other than 3M? Especially one that can be cut to size...thanks

author: Vgkid
author_rank: Super Contributor
timestamp: February 27, 2022, 09:19:44 am
content: We use the 3M versaflow at work , / 3m PAPR's , or air fed hoods...