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Oleum release caused by pump power supply lacking safeguards

06 October 2009

The cause of the uncontrolled oleum release from INDSPEC Chemical Corporation in Petrolia, Pennsylvania, which forced the evacuation of three surrounding towns in October 2008 has been disclosed by the Chemical Safety Board (CSB).

Use of pump power supply that lacked safeguards caused Oleum release
Use of pump power supply that lacked safeguards caused Oleum release

In the report the CSB encouraged companies that handle hazardous chemicals to follow proper management-of-change procedures, monitor deviations from written operating procedures, and implement appropriate safeguards to mitigate human errors.

The accident that took place on Saturday, October 11, 2008, forced over two thousand residents of Petrolia, Bruin, and Fairview, to evacuate or to shelter-in-place for approximately eight hours. Oleum, also known as fuming sulphuric acid, was released when a tank transfer operation was left unattended during weekend operations and an oleum storage tank overflowed. The oleum formed a toxic sulphur trioxide gas, which mixed with moisture in the air to form a dense, corrosive, sulphuric acid cloud that threatened the neighbouring towns.

CSB Chairman John Bresland said: “The managers of companies that handle highly hazardous substances, such as oleum, need to exercise special care that appropriate process safeguards are in place. In this accident, the CSB found that for many years, operators had been using an auxiliary pump power supply that lacked safety interlocks to prevent tank overfilling.”

Owned by the Occidental Petroleum Corporation and located approximately 50 miles northeast of Pittsburgh, the INDSPEC facility produces resorcinol, a chemical used for making tires and other products. The CSB report noted that three operators were involved in bulk liquid loading and unloading work from Monday to Friday. However, to maintain operations on a continuous, seven-day-per-week schedule, an operator would regularly perform work on weekends, transferring oleum from pressure vessels to storage tanks used to supply the resorcinol manufacturing process.

The CSB investigation determined that the normal power supply for the three oleum transfer pumps was equipped with a safety interlock, which would automatically shut off the flow of oleum when the receiving tank was full, preventing a dangerous overflow. However, the oleum storage building also had an auxiliary or “emergency” power supply that had been installed in the late 1970s. It was originally intended as a temporary way to keep the pumps functioning during interruptions of the normal power supply but eventually the emergency power supply became a permanent fixture. Facility management never installed interlocks for the emergency power and written operating procedures did not address how or when the emergency power supply should be used.

The CSB found that to save time on weekends, operators typically ran two oleum transfer pumps simultaneously, using both the normal (interlocked) and emergency (non-interlocked) power supplies. Current managers and engineers stated they were unfamiliar with the practice. The practice had not been considered or described in process hazard analyses or operating procedures for the transfer operations.

On the day of the accident, an operator began transferring oleum at about 11:45 a.m. using two pumps and both power supplies. Although he shut down one of the pumps, he evidently did not shut down the other pump, which was connected to the non-interlocked emergency power supply, before departing the facility at 2:15 p.m. One of the storage tanks began overfilling with oleum; about an hour later acid mist began escaping from a vent, and by 4:30 p.m. the mist was flowing from the building. Facility personnel were unable to control the release, and both the facility and the surrounding towns were evacuated.

“By installing the emergency power supply without the same safety devices as the normal power supply, former facility managers traded safety for efficiency,” said CSB Investigator Jeff Wanko, P.E., C.S.P., who led the investigation. “Facilities should evaluate changes, even those considered to be temporary, to determine their potential to cause an accident. That which is temporary can easily become permanent.”

The CSB case study report identified four key safety lessons for companies: thoroughly evaluating temporary process changes, ensuring uniform safeguards for different modes of operation, monitoring deviations from operating procedures, and ensuring hazard analysis teams have complete information to perform their tasks.

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