Choke clearing incident

A senior maintenance member of a two-man crew, and another employee were working from an elevated work platform. The platform was mounted on the back of a trailer, which was mounted to an asphalt tank. The employees had begun bypassing the normal asphalt storage tank to prepare for its five-year to seven-year cleaning. They placed a bypass valve in position to route the asphalt from the permanent tank to the temporary, trailer-mounted tank. Most of the asphalt piping was heated with a steam jacket encircling the pipes. However, the piping that ran from the bypass valve to the temporary tank was encircled with tubing that was heated by steam. The employees complained that the steam tubing, also referred to as steam tracing, was not wrapped tight enough, thereby preventing the pipe from getting hot enough to turn the hardened asphalt back to its liquid (melted) state. The employees then attempted to repair the clogged pipe. As was reported to be the normal practice, they went to the end of the asphalt piping outlet and began heating the last bend of the piping with a propane torch. The piping outlet was located directly over the top of the manhole opening of the heated asphalt tank. The tank was reported to be 300 degrees to 400 degrees Fahrenheit, at that time. During the site visit, approximately five hours later, the tank temperature gauge read approximately 260 degrees Fahrenheit. After an undetermined amount of time that the employees were using the propane torch to heat the piping, an explosion occurred in the asphalt tank. A witness described the explosion as a flame which shot 30 feet above the manhole cover and quickly descended back into the tank. This witness also stated that he could no longer observe the employees standing on the platform. Employee #1 remained on the platform and suffered asphalt burns and fractures to his face, where an item impacted it during the explosion. Employee #2 fell from the work platform, approximately 9 feet 5 inches to the concrete surface. Employee #2 suffered asphalt burns to his body and face, in addition to a hip fracture. A radio call for emergency response was broadcast throughout the company. The company Emergency Response Team doused the flames and provided initial first aid to Employees #1 and Employee #2. Both employees were transported to the hospital.
Source:OSHA