Question Alcohol evaporators are: Answers Illegal. Used to add alcohol to braking systems to prevent items from freezing. Only allowed on vehicles carrying hazardous materials. Explanation Some air brake systems include an alcohol evaporator. The evaporator introduces alcohol into the braking system to prevent the formation of ice, which can cause damage. This questions appears in the following tests: Arizona Double Arizona Air Brakes Arkansas Air Brakes Idaho Double Idaho Air Brakes Louisiana Double Louisiana Air Brakes Maryland Air Brakes Mississippi Class B Knowledge Test Oklahoma Air Brakes South Dakota Air Brakes