In terms of how to display it, icons on the trail would work. Direct exposure could be a diamond with a vertical line in it, indirect exposure could be a square with a line that is initially more horizontal that then goes vertical.
I’m not opposed to using hazards for this, but natural=cliff doesn’t indicate if the trail is 3cm or 3m from a cliff edge (likewise ridge or arete). The closest value on hazard=* which exists is falling rocks which isn’t appropriate. It’d be better than the current use case where it’s impossible to extrapolate exposure since it is mixed in with technique.
https://wiki.openstreetmap.org/wiki/Key:hazard
I think there’s a few different cases that would need to be addressed:
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A brief moment of exposure on a trail seems totally appropriate for this (and should be used even if there is a separate exposure key for ways/paths). I think in this case being able to differentiate between direct and indirect exposure would be useful, so that would be two values at least. Short falls could probably be ignored in the sense of being called out on topo vs being metadata for a path.
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For longer stretches of exposure, how would hazards work? Would there be two tags that act as bookends (start/stop, open/close) or would it just be a hazard tag every 5-10m.
Knowing that 200m of trail is exposed is different than a 5m section. Having two hazard tags 200m apart could look like it’s just two brief spots but having 20-40 hazard tags seems messy.