What is a common sign indicating the need to call a 'mayday'?

The situation that calls for a 'mayday' signal is when a firefighter becomes trapped or lost. This is a critical and urgent scenario where immediate assistance is necessary to ensure the safety of the individual in distress. A mayday alerts the incident command and other firefighting teams that someone's life may be in danger due to an inability to escape a hazardous environment.

While limited visibility in smoke, equipment failure, and feeling fatigued are all serious concerns that could impact a firefighter's safety and effectiveness, they do not inherently mean that the individual is in an immediate life-threatening situation. A 'mayday' is specifically reserved for situations where the person cannot self-rescue and requires urgent help, such as being trapped under debris or unable to find their way back to safety. This distinction is crucial in emergency operations, as the appropriate response can make a significant difference in rescue efforts and outcomes.