30 CFR §75.1101-16

1. (a)Each self-contained dry powder chemical system shall be equipped with sensing devices which shall be designed to activate the fire-control system, sound an alarm and stop the conveyor drive motor in the event of a rise in temperature, and provision shall be made to minimize contamination of the lens of any optical sensing device installed in such system.
2. (b)Where sensors are operated from the same power source as the belt drive, each sensor shall be equipped with a standby power source which shall be capable of remaining operative for at least 4 hours after a power cutoff.
3. (c)Sensor systems shall include a warning indicator (or test circuit) which shows it is operative.
4. (d)Each fire-suppression system shall be equipped with a manually operated control valve which shall be independent of the sensor.