If the person you care for is a smoker, make sure that they use a large, deep, non-tip ashtray.
Keep an eye on them if they are drinking and smoking, to make sure they don't fall asleep with a lit cigarette.
Empty ash trays often, wetting their contents before dumping them.
After an elderly smoker has left the room, make sure you check the cushions around where they were sitting for smouldering cigarette butts.