I think RBM hit the nail on the head. I have seen floor furnaces that
were not thermostatically controlled that didn't have any safety, but
they work about like a top burner on a gas stove, or a gas space heater.
You just turn the valve on and off, and adjust the size of the fire to
the amount of heat wanted. These furnaces were also antiques when I saw
them about 35 years ago. Some thermostatically controlled units had
mechanical safeties that worked with a bimetal that bowed when heated by
the pilot and opened a valve built into the burner to let gas through,
and closed it when the pilot was out. They were not 100% to begin with--
they did not stop the gas to the pilot-- but the valve would often stick
open, or partially oped, so they were not very safe at all. Larry