Most Q1 wireless chargers have heat sensors and will shut down if either the charger or the device being charged get too hot. Unfortunately finding out whether a particular charger is so equipped can be very difficult.
NOTE: I have seen test results on MacRumors, 9to5Mac, or Apple Insider (I don't remember which) that found the so called fast chargers are not significantly faster than the standard wireless chargers and by far the fastest way to charge an iPhone X is with the 12W power adaptor and a lightning cable. Even the 5W power adaptor with a lightning cable charges the iPhone faster than a wireless charger at any power level.
