Out of a nuclear power plant, a combustion engine, a hydroelectric power plant, a wind turbine, and a fuel burning power plant, which is the worst energy source for a rescue team?

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?