I guess I'll just have to rely on social distancing.
That video is so flawed it's LOL funny. The guy's a moron. A certified stone-cold idiot.
He's using an OSHA approved atmospheric monitor, which falls under 29 CFR 1910, and is specifically designed to monitor atmospheric gases in confined spaces. The one he's using is designed, and calibrated, specifically for firefighters to use at fire scenes.
A confined space is defined as a space
"large enough for a person to enter and perform assigned work in; it has limited or restricted ways to enter or exit the space; and it was not designed to be occupied continuously by a worker." I guarantee you that a restricted space immediately surrounding the exhaust pipe of a human being is not a confined space in which an atmospheric monitor's readings are even a little bit valid. He's essentially testing the atmospheric conditions inside a mechanic's 4-bay garage by inserting the detection tube up into the tail pipe of a running car, and than declaring the garage is not safe to enter.
If you want to test the oxygen level of a mask wearer, you don't test the carbon dioxide output level at the point of exhalation (or even the amount of oxygen present at the point of inhalation), you test the blood oxygen (oxygen saturation) level of the mask wearer. You do that with a Pulse Oximeter (that little thing they clamp onto your finger at the doctor's office). It ill also test your pulse rate, which will rise considerably to compensate if there is a lack of oxygen, in order to keep your blood oxygen saturation level consistent.
There are people who work in hospitals who wear masks ALL DAY LONG and none of them are dropping onto the floor because of low oxygen levels or high levels of carbon dioxide, nor are they experiencing higher pulse or heart rates, nor are they reporting headaches. There are construction workers and landscapers and industrial workers who wear masks ALL DAY LONG and none of them are dropping onto the ground because of low oxygen levels or high levels of carbon dioxide, nor are they experiencing higher pulse or heart rates, nor are they reporting headaches.
Get a pulse oximeter and test it yourself. 5 minutes is plenty, but test it for as long as you want. One with no mask, one with a surgical mask, one with an N95 mask, one with a vented N95 mask and then go crazy and test it with an N95 mask AND a surgical mask. You will find the same thing that countless doctors, nurses, hospitals and OSHA tests have found, that there is no significant change in you oxygen saturation (or pulse rate) in any scenario. There's a reason those masks are OSHA approved.
If your normal, at rest, without a mask, oxygen level is, say, 95, then in the worst case scenario, where you don both a surgical mask and an N95 mask, your blood oxygen level might drop as low as 90.
"Ninety!!! OMG!" you might say. But normal blood oxygen levels are between 75-100 (but ideally between 90-100). Below 75 is low, but headaches don't begin until actual hypoxemia sets in, which happens at or below 60. If your at-rest blood oxygen level (SpO2) is consistently below 90 for a prolonged period of time,like for weeks or months, especially if there is an objective cause, like COPD, lung damage, an illness, etc., then supplemental oxygen may be needed.
Construction workers and others who's mask becomes clogged (with dust or has gotten wet) to the point where it's difficult to breathe, their blood oxygen concentrations might drop by as much as 8% according to OSHA and CDC testing. Still safe, but OSHA and the CDC recommends swapping out a mask when it becomes too difficult to breathe.
As someone who over the last several weeks who has had more than my fair share of encounters with pulse oximeters, including wearing one for 24 hours a day for 6 days, I can tell you that I asked a lot of questions (to the point where I think I annoyed more than one person) and have done a lot of research, and I now know more about them and oxygen levels than any normal person should know. I can tell you that they are not as accurate as drawing blood directly from a vein and doing a ABG (Arterial Blood Gas) test, because dirty fingers and fingernail polish will affect the accuracy of the oximeter. The oximeter works by passing small beams of light pass through the blood in the finger (or toe, or even earlobe for someone with long and/or painted fingernails), measuring the amount of oxygen. It does this by measuring changes of light absorption in oxygenated or deoxygenated blood. But the accuracy of a pulse oximeter is close enough, within 2%. Meaning, if your oxygen saturation reads 92% on the pulse oximeter, it may be actually anywhere from 90 to 94%.
So to recap, the guy in the video is an idiot, and people who complain of headaches while wearing masks are whiny little children looking for an excuse not to wear a mask.