Octobers massive blaze at the Caribbean Petroleum facility in Bayamon, near San Juan, Puerto Rico, was likely caused by a faulty monitoring system on a petrol tank.
A storage tank was being filled with petrol from a ship docked in San Juan harbour when the tank apparently overflowed, US Chemical Safety Board investigators comment.
Gasoline spilled from the tank without detection; as the material spilled, it vaporized and spread across the facility,
They estimate the vapour cloud spread to a 2,000-foot diameter until it reached an ignition source in the northwest section of the facility.
The liquid level in the tank could not be determined because the facility's computerised monitoring system was not fully operational.
Operators used a mechanical gauge on the tank's exterior wall to monitor the level in the tank, and as the petrol level in the tank rose and eventually overflowed, employees in the facility's control room were not aware of the situation.
The fire burned for three days. There were no fatalities, but thousands of residents were forced to evacuate to avoid the thick clouds of black smoke.
Caribbean Petroleum supplies a large volume of Puerto Rico's petroleum products. The facility includes a tank farm and refinery that was shut down in 2000. Before the fire, the tank farm stored petrol, diesel fuel, jet fuel and fuel oil in about 30 aboveground tanks.