You´ve made a good point here. Redundacy requires a thorough study of possible reasons for failure and dependencies. Sometimes having two identical items will be enough (if one lighter is empty it doesn´t effect an other one) sometimes it requires a different principle (like in your example with the stove).<br>One of my instructors once said: 'There isn´t such a thing like a little thing. There are only details. So take care of them.' . Well, taking care of the details saved my day more than once.