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Last month I mountain biked Cotopaxi.

I mounted the saddle at 15,000 feet. Thin air for pushing pedals – everything feels like uphill, until it is, then it feels like something worse – but I like to think it might have prepared me somewhat for the oxygen deprivation of my recent respirator trials. Integrating some sort of hypoxic training into a PT regime may be worth considering.


Respirator Considerations

Another year, and California is burning.

I’ve taken advantage of the recent fires to perform more respirator trials. I use the respirators when getting around town on my bicycle, which provides a good analog for any aerobic activity, allowing me to evaluate things like breathability, humidity within the respirator, and how well the seal performs when contaminated air is being blown over the respirator at high speeds. I’ve found there are certain characteristics that I desire in a respirator.


The standard respirators that are most worth considering are N95. The “N” designates that it is not resistant to oil. The “95” designates that it filters 95% of particles 0.3 microns or larger.

After the BP oil spill in 2010 I purchased a P100 respirator. These respirators filter 99.97% of particles, and are “strongly resistant” to oil. They are large, bulky cartridge respirators that are great to keep at home, but you are not going to carry them around.

Recently I purchased a box of R95 respirators. These are more similar to the N95 than the P100, but are “somewhat resistant” to oil. They have a service life of 8 hours in environments with airborne oil particles, which is long enough for me to get to my P100 respirator. Unfortunately the R95 respirators are quite a bit thicker than the N95. They could be easily carried in a bag, but they are too thick to fit in my PPE kits (without moving to a larger aLOKSAK). I’m splitting the R95 respirators between home and work, but will continue to carry N95 respirators in my kits.

Back in 2007, when I first started researching respirators, I came across an adhoc study comparing these ratings against common household materials:

I recently assisted in a study to determine how available materials compared to P-100 respirator cartridges. Cartridges were opened, the contents removed, and a series of different materials were attached to the cartridges. The cartridges were installed onto standard North full-face respirators. A Certified Industrial Hygenist performed fit testing on the mask assembly using a standard quantitative fit testing machine, the one that compares particle counts inside the mask to ambient air particulate counts.

The materials tested were:

  • coffee filters, 1 layer;
  • t-shirt fabric (knitted fabric), folded into 8 layers, wet, dry, and oiled with petroleum jelly;
  • bandanas(woven fabric), folded into 8 layers, wet, dry, and oiled with petroleum jelly;
  • a HEPA vacuum cleaner filter, dry.

We boiled the cloth to shrink it before testing.

The performance of the coffee filter, HEPA filter, and the dry fabric was terrible. Abysmal. Worthless. Bad.

The wet fabrics were a bit better, but still bad. Why firefighters use wet bandanas to filter smoke is beyond me. They are practically worthless.

The HEPA filter was so moisture-resistant that the mask fogged up to where you couldn’t see out. And it didn’t perform that well. Perhaps its stiffness made the seal leak, it really should have done much better.

But the 8-layer oiled bandana and oiled t-shirt performed about 80% as well as the P-100 filter, and in fact passed about half the tests. This makes it equivalent to about a N-90, which is 90% as good as a N-95 filter. It was nothing short of amazing how well the oiled fabric filtered air.

Now it’s interesting that there is a report (page 1, page 2) from WW1 that a doctor on a troop ship made everyone wear oiled gauze masks, and did not lose a single person on the trip across the Atlantic.

Using an old-style cloth surgical mask and oiling it with petroleum jelly increases its filtration efficiency something like 1000 times. And oiled cloth filters actually filter better the dirtier they get, until they clog up. They are used in high-perforance cars.

Oh, and I suppose I ought to admit it was my kid’s science fair project.


Most respirators either have a single continuous harness that goes around the crown of the head and back of the neck, or two separate straps. I’ve not noticed a significant difference between these two options, though the single continuous harness can easily be adjusted for smaller heads with a single knot.

The two-piece harness is usually attached to the respirator via staples, the penetration of which may reduce the efficacy of the respirator, but only if the puncture results in a tear.

When staple punctures tear holes in the filter medium, the concentration of particles leaking through those openings is considerable and resembles face seal leakage… The findings of this study suggest that stapling head straps directly onto the filtering material of a respirator has the potential to create leaks in amounts similar to that of face seal leaks.

I look for a textile harness. Cheaper respirators use thin rubber bands. For single use these are adequate, but they snap if you are frequently donning and doffing the respirator.


A valve to vent exhalation is critical. Non-vented respirators are useless to me. Even if all you’re doing is sitting around not moving, the non-vented respirator will build up humidity over time, making long-term wear quite uncomfortable. Add in any physical activity and the process is accelerated.

At a minimum the vent should be closed at the top of the respirator. This prevents the warm, humid air from moving directly up and fogging your eyewear. On some respirators, the vent is closed on both the top and sides, forcing the exhaled air to escape downwards only. This is desirable.

Non-vented respirators are appropriate in healthcare environments when sterility needs to be maintained. That is to say: where you are concerned about your exhalation impacting the sterility outside the respirator, not the other way around. Vented respirators meet the same protection requirements as their non-vented counterparts.

If you’re worried about keeping your operating theater sterile, get a respirator without a valve and embrace the suck. Otherwise don’t.


I want to carry the respirator, which means I need to be able to fold it flat. There are two variants of fold-flat respirators: those that fold vertically along the center, and those that fold horizontally.

A center fold respirator provides more volume across the front of the face. When a respirator fits properly and provides a good seal, it should collapse slightly due to suction when inhaling during aerobic activity. When wearing a center fold respirator, this collapse happens along the cheek area. I find I tend not to notice it. With a horizontal fold respirator the collapse is more likely to happen across the front. The respirator touches my lips with each heavy inhalation, so I constantly notice it. I do not think there is a functional difference here, but it is a factor in long-term comfort.

A horizontal fold respirator can be more comfortably pulled down below the chin. A center fold respirator can not (unless perhaps you have an unusually long neck). If you need to temporarily remove the respirator – perhaps to take a drink – it can still be pushed down, such that the nose clip rides on the chin. I find this uncomfortable for more than a brief period of time. When the air quality index (AQI) is red or worse (151+), I generally want to wear the respirator whenever I’m outdoors. When the AQI is orange (101-150), I don’t feel I need a respirator if I’m just walking or standing outdoors, but I do want it when I’m breathing heavily. It’s in these conditions that I appreciate the ability to wear a horizontal fold respirator pulled down on my neck. I can easily (and quickly) pull it up when I begin breathing more heavily (ie, when I get on the bike). With a center fold respirator I’m more likely to temporarily store the unused respirator in a pocket, increasing the time requirement to don it.

Horizontal fold respirators place the valve in the center. On center fold respirators, the valve is offset to one side. When using horizontal fold respirators, I find that close-fitting eyewear is more likely to fog if I’m not moving (when moving more than a few miles per hour, air flow across the eyewear eliminates any fogging). I experience less fogging with center fold respirators. I’m not sure if this is due to the position of the valve – perhaps the offset valve encourages the warm, moist exhalations to be vented to the side, rather than immediately up to the lenses – or due to the seal. A center fold respirator, I find, provides a superior seal across the top of the face because the respirator naturally wants to pinch the bridge of the nose and hug the cheeks.


Most disposable respirators are white. Some come in gray. The fashion market offers respirators in dark colors and patterns. These look cool, but I prefer white. White shows dirt, encouraging me to replace the respirator more frequently than I probably otherwise would. Despite the lack of a NIOSH standard for respirator reuse (including those labeled “single use” by the manufacturer), particle build up on the surface of the respirator will increase pressure, which will increase leaks. If you’re using the respirator out of concern of influenza or flu, the color of the respirator is probably irrelevant. For smoke and other pollutants that leave visible residue, white may be better.


3M has a large, sprawling product line that seems to have a lot of redundancy and overlapping offerings. The 3M Aura 9211+/37193 checks most the boxes and is the nicest horizontal fold respirator I’ve used. The material is about 1.5mm thick, and the valve sits about 15mm off the face of the respirator at its tallest point. The wings easily fold in, allowing the respirator to fit in a small aLOKSAK for one of my PPE kits. Because of how the respirator folds, when the wings are folded in, the thickest part of the respirator excluding the valve is 13mm. I feel the respirator is a bit loose around my chin and jaw, but the seal still seems effective. Condensation becomes visible on the outside of the valve, which shows you it is working. The material that makes up the upper portion of the respirator has a perforated layer between inner and outer shells, which I imagine contributes to the respirator’s breathability, but this upward facing exhaust causes the respirator to fog eyewear a bit more than it otherwise would. The center portion of the respirator has some sort of stiff interfacing that feels a bit like a thin foil. This stiffness seems to prevent the suction collapse I usually experience with horizontal fold respirators (although the perforated upper portion and the loose fit on the lower portion of the respirator could also contribute to this). The harness is two pieces, textile, and stapled.

Condensation on a 3M 9211+

The Dräger X-plore 1760 is a vented, center-fold R95 respirator. It is the highest quality respirator I’ve tried. Being an R95, it is too thick to fit into my PPE kits. The material is 3mm thick. Folding along the center line, and then folded again such that it would be the right dimensions to fit in my desired aLOKSAK, it ends up being 18mm thick (excluding valve), which doesn’t work. The valve sits about 11mm off the face of the respirator. If you want some oil resistance, and don’t need to fold the respirator more than once, this is an excellent option. I stay significantly more comfortable underneath this respirator than others. It has a tight seal on my face that provides good suction on inhalation, and you can hear and feel the valve flutter on exhalation. Condensation becomes visible on the outside of the valve, which shows you it is working. I have attempted to fog the lenses of my Rudy Rydons while wearing this respirator, and failed. They only fog when I break the seal of the respirator to adjust its placement. It has a single-piece, continuous, textile harness.

Condensation on a Drager X-plore 1760

After discovering how great the 1760 was, I purchased the Dräger X-plore 1750, hoping that it would be the same thing but thinner. That ended up being exactly what it is. This respirator is the N95 variant, which explains the difference in thickness. It is just under 2mm thick. Folded to fit in the aLOKSAK, the thickest part of the respirator excluding the valve is 7mm. I find myself leaning toward center fold respirators, and this is a perfect center fold N95. If you just want to buy a box of respirators and be done with, I’d recommend getting these.

Dräger also produces a version of the 1760 with activated carbon that I would like to try. If it isn’t any thicker than the standard 1750, the extra odor protection provided by the activated carbon could be a nice bonus. My respirator budget is depleted for now, and I have more than I need for a while, so you’ll have to wait until a future fire season for a review of that one.

My P100 respirator is a 3M 6391. It has not seen much use, as I’ve yet to be in an environment where it is needed. I’m as happy as I can be given the limited wear time I’ve logged with it over the past 8 years. You’ll have to wait until the next oil spill before I can give a meaningful review. One consideration worth keeping in mind when shopping for a respirator like this is that the height of the nose piece can interfere with some eyewear.

A Personal Air Filtration System

Another year, and California is burning.

After Napa burned to the ground last year I decided to invest in an air filter. I ended up with a Coway AP-1512HH, which seemed like the right size for my small apartment, and came with a good recommendation from The Wirecutter.

Coway AP-1512HH

The unit has three different filters: a pre-filter intended for large dust particles, hair, and the like; a carbon filter to remove odors; and a HEPA filter that does the heavy lifting.

The pre-filter I clean by vacuuming every 4-6 weeks (when I think of it). The carbon filter I’ve never attempted to clean. The HEPA filter has a 12-month lifespan. The air quality sensor is also supposed to be cleaned every couple months. I’ve cleaned this once, after about 8 months of service, when I noticed that the unit was constantly registering a high pollution level that I disagreed with. Cleaning the sensor immediately fixed the problem.

The Coway is supposed to light an LED when the HEPA filter needs replacing. My unit has been in use for 12 months now, and that LED has never turned on. I’m not sure why that is, but since the replacement cycle is yearly, and the LED alert is nothing more intelligent than a timer, I simply offloaded the problem to taskwarrior.

$ task add project:air due:2018-12-15 recur:yearly wait:due-8weeks "replace Coway AP1512HH filter set (3304899)"

The filter detects pollution and, when placed in automatic mode, adjusts the fan speed appropriately. The current pollution level is indicated by a ridiculously bright LED that can light up a whole room. I’ve placed a piece of tape over this. This is necessary if the unit is in the same room that you sleep in.

Coway AP-1512HH Control Panel

I’ve enjoyed using the filter throughout the year. It takes care of cooking smells, so that I’m not smelling my dinner all night. I assume the copious dust I clean out of its pre-filter would otherwise end up in my lungs. At its lowest two settings it is quiet enough to leave on overnight, providing pleasant airflow even if I don’t need the filtering. During the cooler months when I don’t want the extra airflow, I keep the unit in “eco” mode, which disables the fan module when no pollution has been detected for 30 minutes.

However, I had not felt that the cost of the unit justified what I was getting out of it, until California caught fire again. Since last Thursday San Francisco has been inundated with smoke, requiring the use of a mask during outdoor activity. But I’ve had clean, clear air indoors. I tried turning the Coway off for a few hours when the Air Quality Index was in red. The difference was immediately noticeable. I don’t have any measurements to measure the efficacy of the unit on wildfire smoke, but in my qualitative experience, it makes a huge difference.

Living in an area where air quality can become tainted – which, given climate change, seems to be most areas of human habitation – I think a personal air filtration system is as important as water filtration and storage. It is the kind of thing you won’t spend much thought on until you need it, at which point its presence or absence can make a significant impact on quality of life.

I have not used any other air filter, so I’m not sure what the best option is, but I have no complaints about the Coway AP-1512HH beyond the LEDs. This past week has moved it from the would-not-purchase-again category firmly into my would-purchase-again-immediately category.

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PPE Kits

I began carrying an N95 respirator in my bag every day around 2007. The masks can be easily added to any first aid kit without much of a weight or size penalty, and offer respiratory protection far superior to that of a bandanna or a surgical mask. While useful during an influenza pandemic, my motivation for carrying the mask was centered more around urban disaster. Any time there are buildings coming down, I assume there will be asbestos, concrete dust, and similar contaminants in the air that I don’t in my lungs.

Most discussion of the extended use and reuse of respirators centers around contagions and the influenza use-case. While it seems safe enough to assume that the masks have an unlimited functional shelf life if stored properly, I’ve not found any information related to visual inspection of the masks for proper use. My own respirators get cycled every two or three years, but there is still a lot of room for abrasion in the pack, which I assume diminishes the protection the masks offer.

I had not thought much about this until last year. The respirator was something I carried but didn’t use. After a decade of carry, my first time actually needing to take the respirator out of my pack was this past October during the Napa and Sonoma fires.

After using the masks I had on hand during the fires (and unsuccessfully attempting to barter my surplus for chocolate), I began to better store the replacement batch for next time.


By keeping the respirator in a 5” x 4” aLOKSAK I’m ensured that no damage is done to during storage. The airtight seal offered by the bag means that the inside of the mask stays clean, at least until the first time I take it out in a contaminated setting. By added a pair of nitrile gloves to the bag, I create a compact, wallet-sized PPE kit. The same thing can be purchased, but all the prebuilt kits I’ve seen are too bulky for me to want to carry. My PPE kits can easily be slid in with the medical supplies in various my first aid and disaster kits. Pair that with EDC eye protection and you have a decently comprehensive solution.

The only appreciable thickness comes from the vent on the respirator, but I’ve found that vented respirators are key. A properly fitted respirator without a vent hampers my ability to perform physically, which isn’t a great trade-off in any situation where I find myself needing to wear a respirator.

PPE Kit with Every Day Carry

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