In which scenario would a thermal detector be the least effective?

A thermal detector relies on the difference in temperature between the heat source (such as a fire) and its environment to function effectively. In an area with poor ventilation, the effectiveness of a thermal detector can be significantly reduced. Poor ventilation often leads to a build-up of heat and smoke, which can create a uniform temperature in the air rather than a distinguishable gradient. This uniformity can mask the thermal signature the detector is designed to sense.

In contrast, in high-heat environments, fluid spills, and situations involving rapid altitude changes, the functionality of a thermal detector may not be compromised to the same extent. High-heat environments could lead to quicker detection of extreme temperatures, while fluid spills might not interfere directly with the heat detection process. Rapid altitude changes primarily affect other aspects of aircraft operation but do not necessarily impede the temperature detection capabilities of the thermal sensors, provided conditions remain favorable for detecting temperature gradients.