What alarm initiating device is activated by a rise in temperature of 12 degrees to 15 degrees in one minute?

A rate of rise heat detector is specifically designed to respond to a rapid increase in temperature within a short timeframe, typically set around 12 to 15 degrees Fahrenheit in one minute. This type of detector is sensitive to the quick changes in temperature that can indicate a fire, as it focuses on the rate at which heat is generated rather than simply reaching a system preset temperature.

In contrast, a bimetallic detector works on the principle of two different metals bonded together; as they heat up, they expand at different rates, leading to bending and leading to an alarm. However, this type does not necessarily focus on rapid temperature increases.

A fixed temperature heat detector activates once a specific temperature threshold is reached, meaning it does not consider how quickly that temperature is achieved, which is critical in identifying fast-developing fires.

A photoelectric smoke detector functions by detecting smoke particles rather than relying on temperature changes. It is useful in detecting smoldering fires but does not activate based on heat alone.

In this context, the rate of rise heat detector is the most appropriate choice for detecting a rapid increase in temperature characteristic of a developing fire.