It's a truism to say healthy people are healthier than unhealthy people. Of course they are. The point isn't that healthy people can work more than unhealthy people, it's that all people - even healthy people, even young people, even experts - have a much lower tolerance for stress and fatigue than they think they do, and their performance at the limit degrades quickly.
The issue is that the limit is in a different place for different people. One person's performance is degraded by hour 6 as much as another's is by hour 10, so it makes no sense to limit them both to 8 hours -- the first presumably shouldn't even be working 6.
There is also the question of where to stop. Suppose that the average person's performance is degraded by 5% after 4 hours. Should everyone stop after 4 hours then? They're not at peak performance anymore. But 95% is often good enough. And maybe 90% is good enough. Maybe 80% is good enough. Maybe 75% is good enough and one person is at 75% after 8 hours. Maybe only 90% is good enough but it's a different kind of work and then the same person is still at 90% after 14 hours. Maybe you're at 85% after 8 hours but get back to 90% with a cup of coffee.
It's not necessary to think that one size fits all to think that 12 hours is too long. There is plenty of evidence that long shifts affect cognitive functioning[1] and so it could well be reasonable to say we don't know where the safe threshold is for each person so there may be some individuals who might otherwise safely work with no impairment but in the interest of safety for users of the cars we can set some cap at less than 12 hours.
Secondly, even if someone was to show that some workers are still able to function well, make good decisions and not make manufacturing errors that would likely impact safety after 12 hours it might still be reasonable to not have such long shifts because the length for some workers would tend to compell all workers (including some for whom that shift length would be too much) to work the long shift if they want to keep their job. There is lots of research associating long shifts with chronic health problems[2] and poor wellbeing for example[3] .
> There is plenty of evidence that long shifts affect cognitive functioning[1]
That study attributes much of the deficit to interrupting circadian rhythms, which is the thing that isn't required with 12 hour shifts, because the other 12 hours a day can contain a consistent 8 hour block for sleeping at night. Whereas the alternative where you bring on a second shift with different workers does exactly that, because now the second shift is e.g 5PM-1AM and by the time those workers go home, eat a meal and get ready for bed, they're sleeping in the daylight. Or if the business is one that operates 24 hours, using 8 hours shifts causes there to be two night shifts instead of one.
> Secondly, even if someone was to show that some workers are still able to function well, make good decisions and not make manufacturing errors that would likely impact safety after 12 hours it might still be reasonable to not have such long shifts because the length for some workers would tend to compell all workers (including some for whom that shift length would be too much) to work the long shift if they want to keep their job.
This is a fully generic argument. Maybe some workers have heart disease and shouldn't do a job that involves lifting. Does that mean no one should be able to do it? People over 65 disproportionately suffer from various forms of dementia. Should they be prohibited from working if they want to, even the ones who are healthy?
Most jobs don't use 12 hour shifts because they don't want to pay overtime, so it's hard to see how anyone who prefers a job with 8 hour shifts could be forced to take one of those instead of the majority of other jobs that use 8 hour shifts.
> There is lots of research associating long shifts with chronic health problems[2] and poor wellbeing for example[3] .
We need to be extremely careful with correlational studies. There is evidence that all kinds of negative outcomes are associated with poverty, and the people working long hours are typically doing it because they don't have enough money. What happens when you say they can't work that much and make them even poorer?
