Just a small bar of metal dropped and stuck in the wrong place.
According to CSB investigation this was the origin of the catastrofic explosion of Valero’s Refinery in February 2007 that injured 19 people and led 50 milion dollars of losses.
Could this disaster be avoided? Let’s find it out.

After investigations CSB issued a final report and a 13 minutes video that describes what likely happened.
A foreign object barred the perfect closure of a valve, causing leak of propane in the low point of a dead leg. Because of some cold winter days, water in the propane froozed, cracking an inlet pipe elbow. Ice sealing the failed pipe from the process melted as the air temperature rose on the day of the incident, releasing 4,500 pounds per minute of liquid propane, which ignited.
“The rapidly expanding fire prevented field operators from closing manual isolation valves or reaching local pump controls to isolate the high-pressure propane being vented to the atmosphere. Control room operators were unable to shut off the flow of propane because remotely operable shut-off valves were not installed.”
The question is: what can we do to avoid similiar disaster?

• ROSOV (Remote Operaterd Shut-Off Valves). “API provides safety guidance for the use of ROSOVs in LPG storage installations, but does not address their use in refinery process units handling large quantities of flammable materials. Valero internal standards require the use of ROSOVs in such process units, but the McKee Refinery had not retrofitted them” in the unit where the accident occurred. Lack of ROSOVs “significantly increased the duration and size of the fire, resulting in extensive damage to the PDA, the main pipe rack, and an adjacent process unit.”
• Fire proofing. “API-recommended practices and Valero standards for fireproofing do not provide sufficiently protective guidance for fireproofing distance for pipe racks near process units containing high-pressure flammables. Flame impingement on a non-fireproofed structural support caused a pipe rack to collapse, significantly increasing the size and duration of the fire, and led to the evacuation and extended shutdown of the refinery.”
• Freeze protection. Unfrequently used piping or equipment subject to freezing should be indentified, protected by establishing freeze protection written program and specific approaches to eliminate freeze hazards.
• Jet fire scenarios. “API-recommended practices do not require the evaluation of hazards posed by adjacent process units when specifying the design, operation, or location of firewater deluge valves”. Three one-ton chlorine containers and a butan storage sphere were exposed to the radiant heating from the fire. This led to the release of approximately 2.5 tons of highly toxic chlorine,7 which was used as a biocide in an adjacent cooling tower. Biocides that are inherently safer than chlorine are available.  The manual firewater deluge valve for the butane sphere was located too close to the PDA unit and could not be opened during the fire.

U.S. Chemical Safety and Hazard Investigation Board
Final investigation report