Fine dust respirator by repurposing a CPAP machine

[Bob Hammond]

Hi, I've been getting serious about dust control, in part because it's a matter of overall safety, and my personal safety because I think I'm developing allergies to wood dust. I've always wanted one of the powered helmet-style faceshield respirators with an air filter, but the price seemed a bit steep.

But now that I've replaced my existing CPAP machine, I think I'm going to repurpose it as a shop respirator. I'll enclose it in a box that is fitted with large HEPA filters, because the tiny ones that come with the CPAP machine are way too expensive to replace for shop use. The maximum recommended hose length is 6 feet, but if necessary I'm sure it could go 9-12 feet. It will supply plenty of cool air and won't be fatiguing to use, unlike N95 dust masks.

I see that used CPAP machines & gear go for about ~$50-200 on Craigslist or other trading sites. They are very durable machines (mine has given 25,000 hrs of use and still runs OK). You can wash out the masks and tubing and I think it would be safe (like buying used scuba gear), but you might talk with your doctor and explain what you want to do (I have) and ask him/her to write a prescription for the mask & tubing. I think the doc will recognize that it's a good idea.

And now for a Public Service Announcement from me, a cardiovascular physiologist: In case you don't know what a CPAP machine is, it creates Continuous Positive Airway Pressure, and is used for the treatment of obstructive sleep apnea (OSA -- when breathing stops for long periods during sleep, due to airway blockage by relaxation of the throat muscles). The estimates are that about 25% of the US population has it, and about half of them are completely unaware. OSA has serious longterm heath consequences -- excessive daytime sleepiness, foggy thinking, impotence, high blood pressure leading to heart disease, kidney failure, strokes -- in short OSA makes you old way before your time. and it can cut years off your life. It's like have nano-strokes many times each night, and they add up over time.

[Bob Hammond]

Now that I think about it more, this idea might be extended for another important purpose.

It wouldn't be too difficult to make an additional accessory fitting, a mounting plate for filter cartridges that absorb noxious fumes, e.g. organic solvents from paints & varnishes. It wouldn't be OSHA-approved, but I think it would work very well and be practical for me and my liver and other useful visceral organs. You can make up your own mind about that, I'm sure.

[Bob Gramann]

Why not run a hose from the outdoors to the pump inlet and avoid having to buy any expensive filters or cartridges?

[Bob Hammond]

Hmm, that's a thought worth consideration.

A limitation might be a matter of the conductance of airflow through the tubings, which is a function of the tubing diameter and length, and the pressure difference between the ends of the tube (Poiseuille's Law) The standard CPAP hose diameter is 20mm (same as an operating room anesthesia machine), and as I imperfectly recall the max possible airflow is about 20 l/m through the air intake at the machine with the standard filters. I would suppose that a large intake tube (~3" or greater) that supplied air from the great outdoors (assuming that air is clean too) would probably be ok, for a rude guess of about 10-20 feet. In cold climates, I doubt that would effect any change in air temperature within the shop, but it would be refreshing to breathe.

[Randy Roberts]

Bob,

I like you're inventiveness with repurposing the Cpap. (Might have to give you an honorary verterinary degree <g>).

When I had to replace the garage door on my "shop", I had them put one of the 4" ports through it down in the corner, like auto garages use to vent car exhaust when the door is closed. I use it to with a portable air conditioner /dehumidifier in the summer. I* don't remember it costing much. Perhaps one of those would work as a large bore fresh air source for your Cpap. Just hope the wife doesn't come home unexpected and push the button on the garage door opener and leave you hanging from the ceiling.

[Bob Hammond]

Randy, I'm subterranean. It's too cold here in the winter for working in the garage. I still need to pack the garage shop up so that I can get at least one car inside.

[Randy Roberts]

Too cold here too. But I'm putting in heat tomorrow...WoooHoooooo!

[Bob Hammond]

Randy, good for you. Are you installing it yourself? A neighbor gave me a 40K BTU garage heater (a ceiling-hung Reznor), and I'm wondering how much it might cost to have a plumber run the gas line.

[Barry Daniels]

I have a powered air purifying respirator that has both particulate filters for dust, as well as organic vapor cartridges suitable for spraying finishes.

[David King]

Cold air is a bummer after a while, at least it was in a supplied air hood. If the incoming pipe were metal and conducted the indoor heat to the chilly air you might get some heat exchange. Filters aren't expensive if you know where to buy them and you would hardly ever have to change them anyway. If you want to pull off any hydrocarbons you can buy a good-sized activated charcoal canister from one of the cannabis growing supply places on ebay or Amazon. You can also make your own with AC from an aquarium supply store.
A 225 CFM 6" dia model costs about $88. That should be way more than ample considering that CPAPs seem to run about 8cfm

You can buy an aftermarket HEPA filter for a hoover vacuum cleaner for $7. http://www.crucialvacuum.com/hoover-401 ... vQod3RQAzg
I use one these on the end of my electrolux "shop vac". All it pickup up is carbon coming off the motor brushes and that's fine by me.

[David King]

Bob, you may need a combined Electrical, Mechanical and Plumbing permit if you reside in a jurisdiction that requires permits. I'd consult your homeowners insurance agent to see what hoops they might want you to jump through. I did all my own gas plumbing in my house and it was quite easy for LP since you only need to hold 20PSI for 24 hours. Many places allow homeowners to pull permits as long as they aren't renting the space out. Of course threading black iron pipe isn't fun if you don't have a big box store to do it for you. In a small shop you might want to consider make up air for the combustion air if you aren't doing a direct vent system. You'll definitely want a CO monitor near the floor.

[Bob Hammond]

David, sometimes I think that you have more good technical advice than most people can make use of. But I'll tell you, that's a good thing that I appreciate.

I think that a CPAP machine and facemask is maybe the best shop respirator that could be found today. It is designed to work with the way that humans breathe at rest, and also it responds at moments of respiratory demand such as during mild to moderate exercise, i.e. moving and lifting objects of moderate weight during powertool operation and sanding/finishing. I think that for the purpose of workshop use, that It assists breathing rather than resisting breathing.

Now, about the garage heater: I'm going to inspect that thing to look for problems - cracks, loose joints, rusty exhaust vents. If it looks nasty, I'll ditch it. I grew up in a house with a coal furnace in western Pennsylvania that was installed about 1905-1920, and I remember firing it and cleaning out clinkers and ashes until I went to college in the early '70s. I know about such hazards, about how men got old by 45 y/o, from carbon monoxide, coal and wood dust, and why my uncles prevented me from getting a job in the steel mills.

[David King]

LOL Bob,
I'll take that as a compliment I had a coal furnace growing up too but it was located outside in an attached shed. The heat was hydronic. The best thing about it was being able to use it as an occasional forge. Getting it started if it went out on a cold morning was a nightmare. Glad you escaped the foundry life.

[Jason Rodgers]

Bob, I'm usually pretty good about remembering the year of an AL article, but I'd have to flip through a decade to find it: there was a gent who wrote an "It worked for me" article describing (if I remember correctly) exactly what you are proposing. The air source was an electric air mattress pump, attached to the wall outside his shop (still indoors), with a tube running through the wall.

[Bob Hammond]

Jason, somewhere I've got an airmattress pump-fan too. Maybe I'll dig it out and have a look at it. If it pushes enough air, it might work well with a much cheaper respiratory therapy mask. CPAP masks are much more comfortable and fit much better, but that comes at a price.

[Randy Roberts]

Bob,
My wife has been envious of the heated car seats that it seems everyone has except her, so I explained that I was installing this so that she would have warm seats in the morning in the winter. ( Going to have to get her an appointment with an ophthalmologist, her eyes always do this funny roll-back thing whenever I explain something to her)
I had a Lennox heater installed by a HVAC contractor. The combustion air and exhaust are both outdoor air. The 60 and 80 K BTU units were the same price, so I went with 80. Overkill for a 2 bay with 9 ft ceiling, and it may just mean it cycles more frequently, but there's no insulation in the walls or ceiling so I figured what the hey.

Neither gas nor electrical are things I'm comfortable messing with. Permits and inspections by both the city and the utility are required here, and although,like everywhere, those niceties are often ignored by homeowners, they do go with the house and the lack of them could create problems down the road when we kick the bucket and our son has to deal with selling the house (although probably not as big a problem as the two mounds in the back yard where he says is where he plans to plant us <g>)

Glad I went that route. we ran into a bunch of problems working with a 9 ft ceiling but low eaves that resulted in running the flue up through the roof instead of the wall to keep the unit up at the ceiling, problems with running the gas line, although here code allows a flexible rubber coated SS line for most of the run for gas. It took them from 9 in the morning until 8 last night to get it up and running (off an extension cord... the electrician failed to show) and it was way more work and aggravation than I would ever want. Ended up about 3500.00 for everything.

If you plan on it being a DIY project, I'd recommend doing a lot of thought and planning first.

This thing is really cranking out heat, but the fan is sure noisier than I'd like. Anyone know if there is a way of varying fan speed, or do these garage units require a certain volume of airflow to prevent overheating of the unit, etc.?

Now it's spend the rest of the winter putting the shop back together.... but in warmth.

[Bob Hammond]

Randy, although the fans are not sophisticated objects (except in CPAP machines), I would let the heater's brain control the fan as it was designed to do.

I've run gas lines and run wiring. When I moved into this house (I looked at 40 houses in one weekend and bought this one), I discovered that there was no door from the attached garage into the house (no kidding), and so I sawed the bricks and smashed glassblocks, put a steel lintel and installed the door by myself. But I'm getting too young for that now, I'm inclined to have someone else do it. Here in Detroit, there is still an army of licensed tradesmen who are 'friends of friends', and if I ask around and be polite and offer a reasonable inducement then I can get it done properly, and the city building inspector will be happy too. I always do work to code, even if occasionally it seems irrational or a bit expensive.

About the cars, my seatheater has two settings - Warm and Skillet. I think I'm going to install a remote starter this year.

[David King]

The nicer heating units all seem to have VS brushless DC fans and a way to match fan speed and heat output to demand. Those fan motors cost between $400-1000 just for the motor and controller. Undoubtedly prices will come down and may have already. I'm a big fan (ouch) of hydronic heating systems that are ubiquitous in the rest of the developed world. They are much smaller, quieter, safer and cheaper to run. They don't kick up any dust and are easy to install. The downside for Americans is that we demand instant heat. A hydronic system needs a few hours to pump that out but if you keep regular shop hours and use a programmable thermostat you'll be happier with it in the long run.

[Bob Hammond]

David, one of the reasons that I bought the house that I live in (was solidly built in 1950, insulated), is the hydronic heating system, with solid copper piping and radiators, and a compact boiler (smaller than a dishwaher). It's toasty warm and quiet, and no drafty dust is blown out of ducts by a noisy fan. If electrical power goes down, it can operate by convection, but since the hotwater circulator pump only needs 75 watts, then I can power it with a small inverter in my truck, plus a few lamps too.

So far as energy efficiency is concerned, I don't think it's a big problem. Unlike cast-iron systems, it heats up and cools down quickly, But that said, I'd rather have a hydronic system with in-floor radiant heating, like a hot sidewalk on a cool summer night. That's what I like.

[Mark Fogleman]

Hi Bob,

I have been a Respiratory Therapist for 38 years, worked for Fisher & Paykel (NZ maker of CPAP equipment) for 14 years and wear a nasal mask connected to a CPAP machine every night. In the shop I wear a 3M 6000 half mask w/P100 filters when making dust with machines and use 2, 20" box fans fitted with 20X20 HEPA filters duct taped to the back arranged to blow away from me (think laminar flow hood) for powered and hand sanding/scraping on the bench. The filtered fans stay on continuously if I know I'll be in the shop the next day and do an excellent job of cleaning the air.

Your CPAP blower idea has one problem you need to be aware of. When there is a large leak in the pressurized CPAP circuit between the machine outlet and the mask or it is opened to the air, CPAP machines go to max blower mode to attempt to compensate for the leak to hit their CPAP target. The machines I know about from F&P, Philips-Respironics and Resmed aren't meant for max blower mode for long periods of time. They will die prematurely but will give you a few months (maybe) when used sporadically. Try to get a Face Tent which bathes the mouth and nose in a high flow stream of clean air. There are a few on Ebay. Search for this: cardinal health 001220 airlife face tent mask on Ebay. There is one seller listing them at $3.75 each. They are much less restrictive than other options:

It leaves your face open allowing protective eyewear. Extension tubing should not be a problem as long as the back pressure from airflow resistance doesn't get too high. You'll need some couplers. I'm not sure how long you can make it but I'm sure you can work it out with some math. Smoothbore tubing is preferable over disposable corrugated vinyl type tubing. The idea of building a HEPA
filter enclosure is excellent. I would leave the fiber filter on the machine just in case there is a leak.

I'm interested in how this works out for you.
Cheers!