[vkou]

Generally safety is evaluated based on intended use.

The intended use of leaded gasoline is burning it and putting lead in the air.

The intended use of asbestos is as an inert fire-retardant layer. It's safe in that context. Where it's not safe is in all the work that goes into building, or tearing down that layer.

The intended use of BPA was putting it into 'microwave safe' plastic containers, where it leeched into food.

Bleach is safe to handle (carefully), but not safe to drink.

[lazide]

I’m not sure your examples make much sense?

It also requires a risk/reward assessment, as everything has tradeoffs. Without some sort of assessment of concrete risks, making tradeoffs is also a wild guess.

Using asbestos in oven mitts? Probably not worth it, safety wise. Plenty of good and safe alternatives, and nobody is going to die if it’s 25% more or less effective.

Using it in firefighter turnouts? Maybe, depending on shedding characteristics and effectiveness of alternatives.

Using it in encapsulated hard paneling for specialized industrial furnaces? Quite safe.

But only if you have some sort of stats on cancer rates vs exposure rates. But that takes a lot of time and exposure (for almost anything except FOOF anyway), and requires actually using it.

Or a lot of guessing and inconclusive/misleading lab tests anyway.

And if you can’t use something until you can prove it’s safe, the whole situation is a Catch 22.