At first glance, Person 3 seems like the obvious smartest choice: the fire extinguisher is specifically designed to fight fires, while a blanket or water may be ineffective against a burning gas cylinder. For LPG or other flammable-gas fires, dry-chemical extinguishers are commonly used for fire protection.

But there’s a catch: putting out a gas fire without stopping the gas supply can actually make the situation more dangerous. If gas continues escaping after the flame disappears, it can accumulate and potentially ignite explosively. Fire-safety guidance therefore emphasizes shutting off the gas supply when it can be done safely; if that isn’t possible, people should evacuate and leave the emergency to professionals.

That means the puzzle’s three choices aren’t quite as simple as “extinguisher = smartest.” Water generally won’t stop the gas leak, while a blanket isn’t a reliable solution for a pressurized gas fire. An appropriate extinguisher may control the flames, but only when used safely and in circumstances where the gas source can also be controlled. In a real emergency, approaching a burning cylinder can expose you to fire, escaping gas and potentially a dangerous cylinder rupture.

So if the puzzle asks you to choose only among the three visible actions, Person 3 is the best answer. But the truly smartest response in real life is not trying to be a hero: get people away, shut off the gas only if it is safe, and call emergency services. Gas-safety authorities also warn against operating electrical switches where escaping gas may be present because a spark can ignite it.