An aerial view of the disaster. - Photos by Yuisa Rios / FEMA

An aerial view of the disaster.

Photos by Yuisa Rios / FEMA

Equipment to determine liquid levels in storage tanks at the Caribbean Petroleum (CAPECO) terminal facility near San Juan, Puerto Rico was poorly maintained and frequently not working prior to a devastating vapor cloud explosion in 2009 triggered by a gasoline tank overfill, a draft investigation report released by the U.S. Chemical Safety Board (CSB) states.

The facility primarily measured tank levels using simple mechanical devices consisting of a float and automatic measuring tape, the report states. An electronic transmitter card was supposed to send the liquid level measurements to the control room. But the transmitter card on overfilled tank 409 was out of service, so operators were required to manually record the hourly tank level readings.

Investigator Vidisha Parasram said the ‘float and tape’ measuring system was the only control system CAPECO used to avoid overfilling a tank.

“When that system failed, the facility did not have additional layers of protection in place to prevent an incident,” Parasram said. “The investigation concluded that if multiple layers of protection such as an independent high level alarm or an automatic overfill prevention system had been present this massive release most likely would have been prevented.”

The draft report includes proposed recommendations for addressing regulatory gaps in safety oversight of petroleum storage facilities by the Occupational Safety and Health Administration (OSHA) and Environmental Protection Agency (EPA).

The draft report was discussed at a CSB public meeting June 10 in Washington, D.C. The meeting was webcast and public comments were accepted. At the meeting, the CSB previewed an excerpt from the upcoming video on the CAPECO incident entitled, “Filling Blind.”

The 2009 incident occurred when gasoline overflowed and sprayed out from a large aboveground storage tank, forming a 107-acre vapor cloud that ignited. While there were no fatalities, the explosion damaged approximately 300 nearby homes and businesses and petroleum leaked into the surrounding soil, waterways and wetlands. Flames from the explosion could be seen from as far as eight miles away.

Outgoing CSB board member Mark Griffon said the CSB’s investigation indicates that there are a number of shortcomings in regulations that cover petroleum storage facilities.

“Facilities such as CAPECO, which store large quantities of gasoline and other flammables, are not required to conduct a risk assessment of potential dangers to the nearby community from their operations,” Griffon said.

On Oct. 21, 2009, CAPECO began a routine transfer of more than ten million gallons of unleaded gasoline from a tanker vessel docked two and a half miles from the facility. The only storage tank that was large enough to hold a full shipment of gasoline was already in use. As a result, CAPECO planned to distribute the gasoline among four smaller storage tanks. This operation would take more than 24 hours to complete. During transfer operations, one CAPECO operator was stationed at the dock, while another monitored valves controlling gasoline delivery at the terminal.

By noon the next day, October 22, two of the tanks were filled with gasoline. The operators then diverted the gasoline into two other tanks – tanks 409 and 411. At 10 p.m. that night, as tank 411 reached maximum capacity, operators fully opened the valve to tank 409. According to witness interviews, the supervisor on duty estimated that tank 409 would be full at 1 a.m. But shortly before midnight, tank 409 started to overflow. Gasoline sprayed from the vents forming a vapor cloud and a pool of liquid in the tank’s containment dike.

The CSB report further explains that an independent high level alarm could have detected and alerted operators to the danger of an overfill, even if the primary system for measuring the tank level fails, as it did at CAPECO. An automatic overfill prevention system goes even further, and can shut off or divert the flow into a tank when the tank level is critically high. These additional layers of protection, however, were not used at CAPECO.

Investigators found that existing process safety regulations exempt atmospheric storage tanks of gasoline and similar flammable liquids. Additionally, the report concludes current regulations only require a single layer of protection against a catastrophic tank overfill – thereby putting workers and nearby communities at potential risk.

The draft report recommends that EPA adopt new regulations for facilities like CAPECO to require that flammable storage tanks are equipped with automatic overfill protection systems and to require regular testing, inspection and risk assessments. The CSB is also recommending similar regulations to OSHA, the American Petroleum Institute, and two key fire code organizations. The proposed regulatory changes would affect the EPA’s Risk Management Program; Spill Prevention, Control, and Countermeasure (SPCC) rules; and/or OSHA’s Flammable and Combustible Liquids standard.

A final vote on the draft report was postponed due to the lack of a quorum at the board meeting.

The CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency’s board members are appointed by the U.S. president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards and safety management systems.

The CSB does not issue fines but does make recommendations to plants, labor groups and regulatory agencies.