There are several variables to determine usage amounts so, although we cannot provide an exact number, Human Touch® products are equipped with a thermal resetting protection device. This is an added safety feature to protect the product from overheating. If the product should suddenly stop and will not start, turn the main power switch, located on the back or side of the product, off and do not operate the product for at least 30 minutes. Failure to turn the product off may result in the product starting unexpectedly when the device cools.