The issue of the 'make up' air hit a button with me, because the NFPA codes are quire explicit, yet the 'common understanding' is quite different. This continues, even though NFPA 96 is pretty clear.
Clear, that is, only if you have seen hoods that had their own make-up air supplied to them. Since most hoods do not have this dedicated air supply, but draw from the kitchen in general, it is common for the kitchen air to be shut down. As I read NFPA 96, though, it's not actually required to do so.
This is more than just hair-splitting. When there is an "open" kitchen, as is often seen with the "mongolian grills' set in the eating area of restaurants (rather than back in the kitchen), there is no single unit that can be described as serving the hood; shut down one and the others will readily supply the air. While that air might 'feed the fire,' it will also help ensure that the occupants can escape.
Another detail sometimes asserted is that the exhaust fan must operate when the unit trips. Again, NFPA 96 goes to the extreme of explaining, in the text of the code itself, that there is no need for the fan to operate if all the cooking equipment has been shut off.
