I need to use oxygen for a lung condition. is it safe to take an oxyen tank to a restaurant kitchen?

Oxygen: Yes it is. I have seen many people with this. I would let the restaurant know so that can seat you appropriately.

Avoid open flames: I think it is safe if there is no open flame nearby. Some restaurants have open kitchens and also serve a menu that includes dishes prepared at the table with an open flame, and these settings should be avoided. In addition, tables with candles should also be avoided.