Refrigeration manufacturers shall hereafter on each mechanical refrigerator and refrigeration plant which they manufacture and installation companies shall on each refrigeration plant which they install place a label designating the type of refrigerant the unit uses and, if the refrigerator has a refrigerating unit which contains more than 20 pounds of refrigerant and is of a type which can not readily be transported without disconnecting the piping or other part thereof containing refrigerant, shall label the control and diffusion valves of the unit, if any, so that any person in case of emergency will be able to turn off or shut down the plant or refrigerator quickly and expeditiously. Each violation of this section is a misdemeanor.