ToME: the Tales of Maj'Eyal

can this item save you from crush skill or suffocation in sandworm lair or it only works in breathing underwater? just to be safe

It won't save you from crushing damage.

It might mean that you don't start to suffocate after being crushed..

Sandworm suffocation won't kill you if you get away from it fast enough, and it's easy enough to test in relative safety if you can beat the monsters that live in level 1 one of the sandworm lair (as long as you're willing to rest afterwards). Why don't you check?

Eskatia wrote:can this item save you from crush skill or suffocation in sandworm lair or it only works in breathing underwater? just to be safe

As the amulet has 'can_breath = {water=1},', it would be a bug for it to work with sand... - it's the 'amulet of the fish', not 'amulet of the thing-that-doesn't-need-to-breathe-at-all'

Although maybe a higher-level amulet that does just that could be nice, could make the sandlair quite easier/less annoying. But an high-level amulet that ONLY does that feels a bit too...specific, so maybe...
'amulet of sustenance': no need to breathe, slight life and stamina regen bonus?

having a high-level amulet designed to make the sandworm lair a little easier seems a tch off to me - by the time you get it, you wouldn't need it anymore.