As a society we have been able to establish limits for a blood alcohol content level that is considered unacceptable and you will be criminally charged if you drive while meeting or exceeding those limits. Yet different people react to alcohol differently and on different days, etc, not unlike the impairment resulting from narcosis. Different states and countries have chosen different blood alcohol contents but most have chosen them. (I think I recall Rarotonga chose .30 as theirs..........)
If no one else was at risk and you were not going to use limited resources (ambulances, hospitals, etc) then I could care less if you chose to drive while legally intoxicated. It is when you put others at risk that I have concerns, not unlike the instructor on trimix who takes his student to 150' on air. Now you are making a "judgement call" for someone else other than yourself.
I worked as a police officer while I attended college and I read the state wide BAC printouts every morning. At the time .01 was the legal limit. To put it in perspective, most people become severely impaired in terms fo both judgment and coordination at .15, are at risk of blacking out and passing out at .20, will be unconcious at .30 and will be at high risk of dying to to respiratory arrest at 40. However, it was common to see people with BAC's in the .30 to .50 range, who were not only awake but actually driving a car with at least some degree of success with BAC's that shoudl have killed them.
These were individuals who were seriously alcoholic and who functioned "normally" at BAC's that would leave a non drinker on the floor, and in fact when sober they were so neurologically impaired by DT's that they probably could not drive at all.
So in effect, if we want to insist on the alcohol impairment analogy, we have to be willing to accept the possibility that narcosis does not affect all divers equally, that some divers may have more resources than others to start with and can in effect stand to lose more to narcosis than other divers and still be effective to the required degree, and that divers who dive deep air a lot may in fact develop a degree of tolerance.
I'm not saying any of the above is neccesarily true or false, but I am saying if anyone wants to use alchol impairment as an analogy, they had better be willing to look at both sides of the issue.
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For long exposures, PO2's in the 1.2 to 1,4 range are preferred as the risks associated with them are very low. 1.6 is considered ok for deco by most agencies as the work load is quite low and the benefits offset the risks. But in the now distant past 1.6 was considered ok for bottom gas.
In effect, the higher the PO2, the shorter the allowable exposure time, but 1.6 is by no means the maximum that can be tolerated with a reasonable degree of safety - it is just that PO2;s above 1.6 are not considered acceptable for long exposures.
The US Navy developed short term O2 exposure charts that allow high PO2 for short periods of time - as in 2.0 and above for very short periods in the 5 to 10 minute range. Deep air records in the 400 ft range have also been done with what are considered to be very high PO2's (the 2.8 range) but on very short profiles with minimum time above 1.6.
During WWII the British did research on rebreathers and routinely had divers at 50' on 100% O2 for in excess of 10 minutes (PO2 of 2.5).
So in light of what's been done, an ascent from 150' to a 70' stop for the couple minutes it would take to get there poses no excessive concern for oxtox as the exposure is short. It is not ideal, but if it's all you got, it's all you got (which is a bigger issue you need to beat yourself for later.)
