From memory it was anything with an exposed heat source or high wattage- Toaster, hot plate, personal space heater, microwave, toaster oven, hair dryer, fondue fountain are what come from my memory. (At our desks mind you)

We had at least 3 microwaves in our floors break room, a few toasters, fridges, etc. Thinking about it, it was less about disturbing others or personal injury and more about fire hazards.