If you work in fire protection , HVAC , or building safety , you may have come across the term "UL 242." This informative guide is available as a free e-book (kostenloses E-Book) to help professionals and students understand this important safety standard. What is UL 242? UL 242 is a safety standard developed by Underwriters Laboratories (UL). Its full title is: "Standard for Safety for Heat-Actuated Fire Damper Controls."