Those warning labels on UTHs are so outdated and don't include some of the most important facts! Sigh.

- the UTH Must be controlled by a thermostat or rheostat as said. If plugged right into the wall they can reach up to 120 degrees.

- Substrate should never be so thick that the bottom is more than 3-4 degrees warmer than the surface.

The substrate would only catch fire if there was a spark from an uncontrolled UTH inside the enclosure. Since both of these things are what you should NEVER do with a heat source...fires are highly unlikely.