What does the octagon symbol with a thermostat and "R/F" signify?

The octagon symbol featuring a thermostat and the "R/F" designation indicates a combination rise of rate and fixed heat detector. This type of detector is designed to provide two levels of protection: it will activate when a certain temperature is reached (the fixed heat threshold) and also when there is a rapid increase in temperature (the rise of rate component).

This dual functionality is particularly beneficial in environments where both fast heat generation, which could signify a fire, and consistent monitoring of ambient temperature are crucial for safety. In contrast, a fixed heat detector does not have the rapid response feature, while a rise of rate heat detector focuses primarily on detecting significant temperature increases. The combination aspect makes the indicated symbol an essential element in fire safety systems, as it enhances detection capabilities and reduces the likelihood of false alarms that could occur with singular-focused detectors such as a smoke detector.