What should be the first priority when handling a ruptured gas line onboard?

The first priority when handling a ruptured gas line onboard is to evacuate personnel and shut off the gas supply. This is crucial for ensuring the immediate safety of everyone on board. Gas leaks can create explosive and life-threatening environments, making it imperative to remove individuals from harm's way as quickly as possible.

After evacuation, shutting off the gas supply is vital to prevent further gas from escaping, which could escalate the situation and lead to an explosion or fire. Mitigating the risk is always the foremost concern in emergency situations, especially when dealing with hazardous materials like gas.

Once safety is ensured through evacuation and gas supply shutdown, other actions such as ventilation and repair can be considered. However, these are secondary to addressing the immediate danger posed by the leak and ensuring the safety of personnel.