What signal indicates that a firefighter is experiencing a life-threatening emergency?

The term "Mayday" is universally recognized in emergency services as a call for distress, indicating that a firefighter is in a life-threatening emergency situation. When a firefighter issues a Mayday, it alerts their team and incident command that immediate assistance is required due to circumstances that pose a severe risk to life or safety. This specific terminology is crucial because it conveys the urgency and seriousness of the situation without ambiguity.

While "Emergency Traffic," "Code Red," and "Urgent Call" are also used in various contexts within emergency communication, they do not carry the specific connotation of an imminent threat to a firefighter's life in the same way that Mayday does. "Emergency Traffic" might pertain to significant updates regarding a situation that requires attention, but it lacks the personal urgency of a Mayday call. "Code Red" can denote specific situations, often related to hazards or threats, but it is not standard for individual distress signals from firefighters. "Urgent Call" can imply a need for immediate attention but does not specifically denote a life-threatening scenario.

In summary, a Mayday clearly communicates a critical need for immediate rescue or assistance due to life-threatening conditions, making it the correct answer in this context.