I had indicated I would try to test whether masks cause us to increase our CO2 intake so here are my results and thoughts.
I noticed when I am wearing a mask, I am re-breathing some of my exhaled air, simply by the fact that inhaled air in a mask is hotter than fresh air without a mask.
When a person breathes in air it is roughly 78 percent nitrogen, 21 percent oxygen and 0.04% CO2.
We exhale a mixture of compounds which is roughly 78 percent nitrogen, 16 percent oxygen, 0.09 percent argon, and 3-4 percent carbon dioxide. (4% is 40000 ppm)
If the inhaled air contains some of this exhaled CO2, then the intake concentration will be higher than the nominal 0.04%. This is likely the case even when not wearing a mask, but does wearing a mask increase this level above the level experienced with non-mask breathing?
First a quick refresher on what levels are considered unhealthy: The OSHA Permissible Exposure Limit (PEL) and ACGIH Threshold Limit Value (TLV) for 8-hour exposure is 5,000 ppm (0.5%).
Symptoms of different levels of Carbon Dioxide exposure:
10,000 ppm (1.0%) Typically no effects, possible drowsiness
15,000 ppm (1.5%) Mild respiratory stimulation for some people
30,000 ppm (3.0%) Moderate respiratory stimulation, increased heart rate and blood pressure,
40,000 ppm (4.0%) Immediately Dangerous to Life or Health according to ACGIH
50,000 ppm (5.0%) Strong respiratory stimulation, dizziness, confusion, headache, shortness of breath
80,000 ppm (8.0%) Dimmed sight, sweating, tremor, unconsciousness, and possible death
Note that as the percentage of CO2 goes up, the percentage of oxygen goes down, which is also not good for us.
How bad is the problem?
Clearly, the air we exhale has an unhealthy amount of CO2 in it and a diminished amount of oxygen, so we don't want to inhale the exact same air we exhaled. Of course we don't do this and even with a mask we don't inhale anything like the amount of CO2 we exhale.
The mask may trap a little exhaled air, which will become the first air inhaled, but this is usually a small fraction of the exhaled air.
The mask may slow down exhaled air so more of it remains close to the face which could also increase the concentration of CO2 being inhaled.
Masks have been deemed safe for CO2 levels by all medical associations, even the more restrictive N95 masks.
They are not recommended for long term usage (many hours) and should be removed when there is no danger of exhaled droplets spraying on other people.
What can we do to minimize CO2 intake with a mask on?
Note that these ideas are just my opinion based on engineering principles of fluid dynamics, they are not based on accurate measurement or any medical study.
Also note that these ideas may not be good for staying safer from a virus.
- use a mask with a smaller gap to trap exhaled air (tighter around the nostrils)
- take deeper breaths (the trapped air will be a smaller percentage of total air intake)
- design a mask that separates intake from outlet (breathe in through the nose and out through the mouth)
Having some fun with measurements
I have 3 CO2 sensors, so I wanted to see if they would tell me anything about my CO2 inhalation levels.
Here is a picture of what they look like with an intruder trying to influence the readings:
The sensor on the left is from my Invisible Hazards project.
The sensor on the right is from my Amphenol Advanced Sensors Road Test.
The instrument in the middle is a commercial air quality sensor.
The mask to the right is a double layer cloth mask made by my company.
It was very challenging to get all 3 displays to be readable in the same camera image because they are such completely different technologies.
The OLED display on the right was particularly difficult because it was refreshing at a rate where the camera was only catching part of the information.
I had to turn off the bright lights and take a long exposure to get all the info on the OLED display.
Here is a shot of ambient CO2 levels - you may need to click on the image to see the data more clearly:
Left sensor: 444 ppm, middle sensor 524 ppm, right sensor 644 ppm.
Note the sensors don't exactly match, but they all responded well to increasing CO2 levels. The actual sensors are in different locations - the one on the left is the black area under the display, the meter in the middle has a sensor on the back, and the sensor on the right is the gold rectangle in the middle of the case.
Also note the 3D printed stands with puck bases to at least stabilize all sensors at the same angle. This is important for the middle meter since its sensor wouldn't have good access to air if it were laid on its back.
I used the middle meter (only because it is easier to hold) to take readings close to my face - about 3 inches in away from my face, inline with the side of my face at mouth level. With and without the mask on.
Here is a shot of the meter right after about 30 seconds of exposure with no mask on:
Left sensor: 420 ppm, middle sensor 1325 ppm, right sensor 630 ppm.
Note the 2 meters that were not close stayed about the same and the middle meter has doubled from being close to my face.
Sensor positioning during readings.
Now here is a shot taken after the same exposure of the middle meter with the mask on:
Left sensor: 427 ppm, middle sensor 639 ppm, right sensor 635 ppm.
Again note the 2 meters that were not close stayed about the same.
But the middle meter is now reading half of what it read with no mask.
I found this surprising, but the result was repeatable.
I do not have a good explanation for this result, but that is what the data showed.
Presumably the mask was causing exhaled air to be channeled away from where the sensor was.
Perhaps this was due to some of the exhaled air squirting out the sides of the double layer mask - away from the sensor.
Perhaps the mask had a diffusing effect so that exhaled air was more rapidly mixed with ambient air.
My apparatus doesn't definitively show what is going on.
A couple of tentative conclusions might be that:
- In either case, the concentration of CO2 near my face was a lot less than the 4% expected in exhaled air, so it wasn't accumulating to dangerous levels (that is good)
- CO2 concentrations drop very quickly in exhaled air as it mixes with ambient air (also good)
These sensors are quite sensitive, but they are not instantaneous, and the sensing area is not going to do a great job of measuring swirling air of variable concentration.
They cannot measure total CO2 in an area, they just measure the concentration right at the sensor.
These factors make them not ideal for this type of experiment, but it was fun and surprising to see what they showed.
As sloppy as the testing was, it did provide some insight into CO2 concentrations around masks and faces and it alleviates any concern about dangerous buildups of CO2 with masks.
If you found all this boring....you aren't the only one.....
What a yawner project...
Provide your own caption for this picture in the comments below...