Fine dust respirator by repurposing a CPAP machine

[Bob Hammond]

Mark, thanks very much for your considered reply, and for presenting a workable alternative to using a CPAP machine. I like your ideas.

With respect to using the CPAP, I'm aware that they can burn out from overwork due to leakage. Above, I had suggested using the respiratory therapy mask with the air mattress fan, but I think your idea of two large box fans with filters is a much better idea even if it is somewhat large.

That said, as noted above, there's 25,000 hrs on the machine I intend to use (I'm replacing it prophylactically). I plan use a ResMed Swift nasal pillow mask, which is lightweight and very comfortable to wear, has a very low profile, and it doesn't obstruct vision or the use of spectacles. Also, since I enjoy roundwork (woodturning) as well as flatwork, with the nasal pillow mask, I can wear a logger's helmet with a mesh face shield, which I find much more comfortable than a regular plastic shield which can get hot and foggy (although the airstream from the CPAP would probably relieve that). I haven't said anything about the CPAP delivery pressure, and I don't think that that is an issue for this purpose, but I'll probably set it low at 5cm H2O.

In my present therapeutic setup, I've already constructed a box for a large HEPA filter and plumbed it into the CPAP machine's intake -- it's far less expensive than those dinky little filters that are standard for the machine. This same setup could work for the shop, but to protect the machine I think I'll put the entire thing into a box, and I'm wondering if I should include the humidifer too. This is probably unnecessary except during the winter months of dry heated air. Also, I think that I can still get 'disposable' 20mm respiratory hose in a cut-to-lenght 50ft roll, and this hose is actually better than the standard therapy hose because it has no crevices for mold to colonize.

Mark, I may PM you about repurposing myself -- as a respiratory therapist. Although my past primary professional life was/is in cardiovascular research, I've taught respiratory mechanics in a medical school. Now I'm thinking about moving to someplace that is not near in a major academic institution, and I'd like to work a few more years, probably part-time, and not sit at a desk. The idea of taking classes and exams is not appealing at all, but maybe I can escape some of that by having a Ph.D. and other relevant experience.

[Barry Daniels]

So the face tent is open at the top around the nose? If so, then it will not keep particulates out very well. Take a look at the hood provided for a PAPR (powered air purifying respirator). It has openings to allow the excess air to vent out, but is restrictive enough to keep contaminates from moving upstream into your breathing zone.

http://www.globalsafetyco.com/pperesp_northpapr.htm

[Mark Fogleman]

So the face tent is open at the top around the nose? If so, then it will not keep particulates out very well. Take a look at the hood provided for a PAPR (powered air purifying respirator). It has openings to allow the excess air to vent out, but is restrictive enough to keep contaminates from moving upstream into your breathing zone.

http://www.globalsafetyco.com/pperesp_northpapr.htm

The face tent is open from the top. With the mask snug against the chin (instead of down on the larynx as in the drawing) there is a high-velocity stream of clean air bathing the mouth and nares from below preventing or greatly reducing air from the room from being inhaled.

The North PA101 Primair Loose-Fitting Facepiece Assembly in the link above is a much better option if you have $50, a long length of wide bore tubing and can tolerate being enclosed. The pluses for me are the weight and the ability to wear glasses. It could be ventilated with any number of blowers inside Bob's HEPA enclosure filtering the air supply or rigging it so outside air gets entrained by the fan.

[Bob Hammond]

I think the Primair gear looks good. I agree with Mark that to work well with a boxfan system, that a large bore delivery tube would be necessary -- say a length of 1-1/4" (30mm) sump/pool pump tubing which would not be very expensive, and which I don't think it would howl (act as a whistle). According to a (near-careless) application of Poiseuille's Law, at a fixed length and pressure differential, ~20% increase in the tube radius will double the air flow.

This type of mask is much cheaper, about $5-10, but the suspension wouldn't be as comfortable.

[Barry Daniels]

I don't think you are placing enough importance on preventing outside contaminants from entering your breathing zone. Neither of those masks are designed to do that.

[Bob Hammond]

Barry, I understand what you mean. What would satisfy your concerns? Can you suggest a practical test?

If I asked around, then I could probably find a mechanical spirometer that would show if the air is flowing into the mask throughout the respiratory cycle, so that contaminants are excluded.

But I'll also tell you something else that I've learned, is that the enemy of 'good' is sometimes 'perfect' -- a good safety device is one that is convenient and so is used, and is not one that hangs on a hook nearby.

[Barry Daniels]

All people who wear respirators on the job must have a yearly fit test performed. They either do a qualitative test (consisting of exposing the person to banana oil and if they can smell it then they fail), or a quantitative test which compares the concentration outside to that inside the respirator (but this requires special computerized equipment. This is not rocket science and there are lots of good respirators on the market. I don't see the incentive for trying to reinvent the wheel here.

[Bob Hammond]

In the subject line, I've already stated what I intend to do, and I'm reasonably sure that it will work for me.

But ok, then let us talk about what is practical versus the ideal. Do you do the annual 'banana oil' test, or do you use your common sense? (No pun intentionally intended, but hey, considering that China has now outlawed puns...)

Another scent for sniff-testing could be methyl salicylate (pine/wintergreen scent -- e.g. 'PineSol' soap).

[Barry Daniels]

By law, we HAVE to perform annual fit testing and medical monitoring on every employee that wears a respirator more than a few hours for the year. I don't really want to argue this any further. I think you are being a bit cavalier on this issue, but you can do whatever you want. The banana oil is a special item which has a very strong smell. Another thing used for this test is a smoke bomb.

[David King]

Try sawing up some camphor curl or imbuya if you want to know what is getting past yours or any mask <g>.

[Mark Fogleman]

Barry-
This is a whole different animal than what you are used to seeing. If the flow coming into the mask is greater than the inspiratory demand the result in this situation is no room air contaminants, sticks, stones and small furry animals going into the user's lungs. I would go one step further for insurance and insert 4 sections of 22mm disposable corrugated vinyl tubing into each side hole. In the hospital, we call them whiskers and use them for patients needing high flow 100% Oxygen and Helium/Oxygen mixtures. Each whisker will hold ~240mls to serve as a reservoir for the beginning of the inspiration. Seeing that most CPAP machines max their flow at around 80 liters per minute and normal ventilation is around 5 liters/min (500ml X 10 breaths/min) you can have a high degree of certainty that all is good.

Again, I would prefer the North loose fitting headgear you detailed above but if you could not get it or use it, Bob's setup with the whiskers would get the job done.

[David King]

Interesting to see that 80L/min is just under 3 CFM. I think my 1/3 Hp Gast rotary vane pump delivers 4.6 CFM free air and it's supposed to be enough to supply 2 masks/hoods.

[Bob Hammond]

Having thought about it overnight, I've decided that I'll buy a Primair hood and give it a try. I have several pump options, the CPAP machine, a pump such as David's, and a couple of Gast oil-less vacuum/compressor pumps that I picked from a hospital 'yardsale' of excess inventory.

Mark, I'd think that the standard resting respiratory values are a bit low for the relatively mild workload of woodworking activities associated with this craft. Do you have that information? I have limited online access to the medical literature now. I recently participated in a bicycle ergometry experiment at progressively graded workloads, and I have the respiratory and metabolic expenditure data for myself. (I'm in the upper-normal range of work and respiratory capacity for my age & body habitus).

[Barry Daniels]

Barry-
This is a whole different animal than what you are used to seeing. If the flow coming into the mask is greater than the inspiratory demand the result in this situation is no room air contaminants, sticks, stones and small furry animals going into the user's lungs.

Mark, this is no different that any powered air purifying respirator (PAPR) like the north unit I have shown links to. Air is forced into the mask and the excess keeps contaminants from flowing upstream. A PAPR is very different than an non-powered respirator where the user must take a breath before air enters the respirator and the fit of the respirator to the person's face is critical to prevent exposure.

The hood of a PAPR leaks the excess air out under the bottom skirt. For a contaminant to enter the mask it would have to travel upstream approximately a foot before it got to your face. That is the problem with the two face masks that were shown. There is insufficient travel distance for the air flow to prevent problems.

I am not pulling this information out of thin air, but from my 30 years of experience in environmental work.

Bob, good choice.

[Mark Fogleman]

This is more a "what if" discussion to me than a best practice discussion. I agree with the use of certified equipment and in each comment attempted to steer the decision toward that end. I am happy there is a lower cost option now than the last time I looked. I would never recommend a cobbled together solution like I've described if there was another better option. Not enough lawyers to defend that! But...the only effective personal protection equipment is the equipment that you actually wear and use correctly. Some people for whatever reason (and this is where Engineers stumble sometimes ) can't or won't wear it or insist in wearing/using it incorrectly.

[David King]

A thoughtful system is always going to concentrate on minimizing the production of dust at the source. A laminar flow of air away from the face towards the floor would be a good place to start. It needs to be quiet and efficient with a variable flow. Mario's wall filter is definitely on the right track.

I also wish we could come up with a comfortable band for the 3M P95 masks that most of us use. I'm a little tired of those deep lines across my cheeks my face at the end of every day.

[Bob Hammond]

David,

Efficient collection of dust at the site of production is extremely important, but your words about laminar flow hoods tweaked my imagination.

If you think about my other thread that is current -- a mini-cyclone with HEPA filtration, then you'd recognize that it is also a device that exhausts plenty of HEPA-clean air. Probably, it could power one of those fancy hoods, and with some air left over for imagineering a laminar-flow hood for my lathe too.

Hmm, Barry, how would one monitor the quality of the exhausted air of the cyclone?

[David King]

Who posted the particulate counter 6 months ago? http://www.iallergy.com/product1887/pro ... fgodWZoAHQ

Laminar flow is one thing but what about an invisible air shield using an air knife?

I'm seeing suspender clips and pacifier clips that might be useful ways of gripping the edge of the P95 masks and using a 1" wide elastic strap. Leakage would be a problem.

An better system would use double stick tape and an adjustable grip for the ends of the elastic strap.

[Bob Gramann]

I've been using that monitor since I originally posted. It warns me about my air when I wouldn't even suspect it was bad. I have checked the air coming from my dust collector (with a 1 micron Penn State cannister filter). The counter reads 70 next to the filter when it is reading in the 1000s away from it. The 3M "1900" furnace filter that I use with my fan box absolutely cleans the air according to the monitor--it will drop the counts to single digits. I am really pleased with the monitor. If it were to fail, I would definitely replace it.

[Barry Daniels]

Bob, It would be a really, really bad idea to use the exhaust of your dust collector as a source for breathing air. I don't care how efficient your dust collector is. There will be non-detectable particles smaller than one micron that can get down into your alveoli where they will stay.