What type of emergency requires the deployment of oxygen masks in the cabin?

The deployment of oxygen masks in the cabin is specifically required in the event of a sudden cabin depressurization. When the aircraft experiences a rapid loss of cabin pressure, the breathable air becomes insufficient, which poses a significant risk to passengers and crew. Oxygen masks provide supplemental oxygen to ensure that everyone can continue to breathe adequately until the aircraft can descend to a safer altitude or the issue is resolved.

In contrast, while severe turbulence might pose risks to safety and comfort, it does not typically necessitate the use of oxygen masks, as the cabin remains pressurized. Electrical failures can impact systems on board but do not directly affect cabin pressure; thus oxygen masks are not mandated. A fire in the cabin is a critical emergency that requires immediate action but does not inherently lead to the need for oxygen masks unless it creates conditions that result in depressurization or smoke inhalation issues. Therefore, sudden cabin depressurization is the only scenario that unequivocally requires the immediate deployment of oxygen masks for passenger safety.