When used as a sampling system safety shutoff the HAT (Heat Actuated Trap), TV/HAT (Tube Valve Heat Actuated Trap), or HST (High Sample Temperature) valves will remain open as long as sample temperatures are under the set point. If the sample temperature increases, the valve will shut off, protecting analyzing equipment from damage due to high temperature.

In commercial aircraft, high temperature water can unexpectedly travel to the cold water lines. HAT valves on cold water lines will limit flow when excessive temperatures are detected, preventing scalding of passengers and crew.