What is the safety rule regarding fueling a commercial passenger vehicle (such as a small bus) when passengers are on board?

1. You may fuel the vehicle with passengers on board as long as you keep the passenger door open
2. You must never fuel a commercial passenger vehicle while passengers are inside, unless there is an extreme emergency
3. Fueling is allowed with passengers on board only if the engine is kept running
4. Fueling is permitted with passengers on board only at commercial cardlock stations