We don't know how safe is enough which is why we should allow as little as possible.
We do know what is safe enough in most, if not all, cases. The EPA and OSHA, along with the CPSC, go for 'zero tolerance' instead. For example, the EPA during the Clinton administration lowered the allowable arsenic in drinking water limit from 50 ppb (parts per billion) to 10 ppb. The only--ONLY--reason they did that was there was now equipment that could accurately measure 10 ppb in a sample.
50 ppb had been the limit for decades and nobody was dying or whatever from consuming water with 50 ppb or less arsenic in it. Now, at 50 ppm (parts per million) or the like, arsenic becomes a danger to human health over several decades of consumption. In places like Bangladesh you find those levels in drinking water commonly. People there often get health issues after 20 to 30 years of consumption of water with upwards of 50 ppm (a thousand times what the US limit was).
So, at the cost of billions spent per year in new filtration equipment, testing on far more expensive equipment, the EPA succeeded in raising many people's water bill by 2 to 5 times what it was before they lowered the limit
FOR NO APPRECIABLE HEALTH OR SAFETY BENEFIT.
Or, the EPA wants to lower allowable ozone pollution from the current 75 ppb to 70 ppb at an annual estimated cost of about $100 billion dollars. That's a reduction of 5 ppb or literally nothing. The EPA claims this will result in over $100 billion in health benefits through reduction of asthma and other breathing issues. When Congress confronted the EPA on their claims on this and demanded the EPA turn over their research and records that prove that the EPA adamantly REFUSED TO DO SO. They didn't want their bullshit research questioned in the least. So, the limit is still at 75 ppb even though the EPA is still trying to lower it.
At one point, the CPSC wanted to put little crossed plastic sticks on 5 gallon buckets to keep small children from falling in and drowning. 10 to 15 children a year fall in these buckets headfirst and drown. The bucket makers said this would cost over $1 billion a year to do and increase inflation by about 1%. End users of these buckets told the CPSC in many, even most, cases they'd simply bash these sticks out to make the bucket usable by them. The CPSC said they'd make that a crime to stop it.
The backlash was so severe that the CPSC settled on putting a warning label on the side of these buckets at a small increase in price.
Today in the US 10 to 15 children fall into one of these buckets and drowns. The warning label is useless and you can't fix stupid.
There are literally thousands, possibly tens of thousands, of regulations on the books from federal agencies that are similarly worthless or utterly stupid. But they're there. Not all regulations are useless or stupid, but a good percentage are and that percentage is increasing because the reasonable and sensible regulations are already taken. All that's left for bureaucrats to do in many cases is produce unreasonable, stupid regulations because their job is at risk if they don't produce regulations.
Here's a book, written for humor, highlights how insane the federal bureaucracy has become:
Here's another:
https://www.amazon.com/Three-Felonies-Day-Target-Innocent/dp/1594035229