The subject of CO toxicity in tank air is getting more coverage than ever before with expanded knowledge as well as available and affordable 21st century technology, but not nearly enough. Instructors, other professionals, and old-time divers aren’t saying much, but that’s either from their training or their habits from before current technologies became so available, I think.
DAN is finally taking some actions but really needs to do more in educating divers about the risks and solutions, and I’d be writing a much shorter post here. Padi and other agencies are doing little to nothing. I guess this is more important to some here who may have personally known a diver who died from a tainted tank, or in my case are simply insulted that most fill stations will not spend pennies per tank to prevent the risks, operators are not spending 50c/day to make tank testers available to customers, and a few personal exposures I have documented.
DAN does admit that they have no idea how many drownings are caused by CO hits, how many clinical hits are just not reported to them, how many subclinical hits are shrugged off as traveler's-flu, etc. The US standard has long been a 10 ppm max while some countries are requiring maxes of 3 or 5, in part because the effect multiplies when you breathe it at depth, in part because of the binding properties, and more - and I've found readings over 5 ppm to be pretty common actually. I fumbled with my early testing from a make-do unit and no one to tell me how at first so I only got testing proficient a few trips ago, but I have turned a boat when I found 17! My last trip was with the new Analox portable analyzer and that was so much easier. A buddy pair can easily share the costs on one for a little over $300, and it'll last at least 2 years without service - much longer if not used every day and kept in a pelican box or similar, or bite the bullet like me as a solo traveler usually and just get one.
For an operator to provide the units and charge an extra dollar/tank for testing was suggested in discussion recently, but that would fail. Testing every tank can be boring after a few days of a trip when the tests are clean but it is all too easy for one tank in a lot to be dangerous so I keep it up. Most divers haven't read as much and will take a very erroneous attitude of "if yours is clean then I'm sure mine is" and skip the extra charge optional testing. No, the suppliers need to spend pennies a tank to ensure their air is clean, and the operators need to 50c/day so customers can confirm that. How long is may take for these practices to become common even in the Caribbean and Mexico is anyone's guess.