Water which leaked through a valve, froze and cracked an out-of-service section of piping was the likely cause of a Feb. 16, 2007 fire at a Texas oil refinery, the US Chemical Safety Board said. The piping crack released high-pressure liquid propane which ignited, causing a massive fire which injured four workers and forced Valero Energy Corp. to shut down and evacuate its McKee Refinery in Sunray, Tex., CSB said as it issued its final investigation report of the incident. It also released a 13-minute safety video, including 3-D computer-generated animation depicting the accident scenario. CSB also asked the American Petroleum Institute to develop a new recommended practice to protect refinery equipment from freezing and to improve existing practices related to fireproofing, emergency isolation valves and water deluge systems.