What is typically involved in the flight attendant's signal for a "fire on board"?

The signal for a "fire on board" is a critical protocol in ensuring passenger and crew safety during an emergency. The correct answer highlights that there is usually a specific alarm followed by immediate response actions. This approach allows crew members to recognize the severity of the situation quickly and initiate the necessary emergency procedures without confusion.

Typically, the specific alarm is designed to convey urgency and differentiate it from other signals. Following the alarm, flight attendants are trained to respond immediately, which may include implementing firefighting measures, evacuating passengers if necessary, and informing the flight crew about the situation.

The other choices, while related to emergency protocols, do not capture the specificity and immediacy required in the context of a fire on board. For example, sounding the general alarm may signal various emergencies but does not specifically denote a fire situation. Waving a green flag is not a recognized procedure for indicating a fire, and simply announcing over the intercom lacks the immediacy required to deal with a fire emergency effectively. Hence, the selected answer accurately portrays the established protocol for addressing such a critical situation on board an aircraft.