I'm not the one to do great events, I have other people for that, but uh maybe put 16x16 zones everywhere and um maybe this works?
Before exiting a room until you go outdoors,
1. O onplayerenterzone > client > bottomtext > <font:impact> <color:ffff00>WARNING! TOXIC GASES OUTSIDE, TAKE CAUTION!
2. O (delay 1) onplayerenterzone > self > cancelevents
3. O onminigamereset > self > toggleeventsenabled > 1 2
1. O (delay 1000?) onplayerenterzone > player > addhealth > -5 or sooo
2. O onplayerleavezone > self > cancelevents
3. O onplayerleavezone > self > toggleeventsenabled > 1 2 3 4
4. X onplayerleavezone > self > toggleeventsenabled > 1 2 3 4
3. O onminigamereset > self > toggleeventsenabled > 1 2 3 4
idk not the best way to do it but yknow. and maybe a way to ammend the gas mask is uhhhehh
name all toxic zones, place a brick somewhere that looks like a gas mask and then maybe cancel all the toxic zones events? idk if this were a linear thing it'd work.