Page:NTSB - Railroad Accident Report - Derailment on May 25, 1989.djvu/40

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potentially dangerous situations to the railroad and its contractor, and to make certain that the stakes that had earlier been located over the pipeline remained in place. No concern was voiced by Calnev during the removal process.

Events Preceding the Pipeline Rupture

Calnev’s dispatch center at the Colton Pump Station is equipped with a monitoring system that scans and records, among other system parameters, pipeline pressures. When normal operations resumed on May 16, the pipeline pressure had increased to 1,667 psig. Between May 16 and May 23, the pipeline was operated at pressures ranging between 1,690 and 1,060 psig (normal operating ranges established by Calnev) and was subjected to various pressure changes during this time. Operations during the next couple of days showed only smooth pressure transitions until about 8:05 a.m.[1] on May 25, 1989.

Pipeline Rupture

Pipeline Operations on May 25, 1989.—During the early hours of May 25, 1989, the three 1,000 horsepower (hp) mainline pumps at the Colton Terminal were operating at maximum output (2,300 to 2,400 barrels per hour), and the pressure on the pipeline was relatively constant at 1,620 psig. About 4:03 a.m., with the completion of a product delivery at Daggett (see figure 1), a gradual increase in pressure to 1,680 psig occurred over an interval of about 17 minutes at which time the pressure decreased within 5 minutes to 1,669 psig. The pressure then remained relatively constant until 8:05 a.m.

At 8:05:25, based on a readout of the information recorded by the monitoring system, a low suction pressure (15.188 psig) alarm[2] and a low discharge pressure (257.644 psig) alarm were received in the dispatch center at Colton Pump Station on Calnev’s computer system. At 8:05:38, the three 1,000-hp mainline pumps were shut down by the computer system. At 8:05:39, the dispatcher acknowledged[3] the alarms. According to testimony of the dispatcher on duty at the time, when changes in operating conditions occur: (1) an audible alarm will be sounded, (2) the word "alarm" will appear and flash at the top of the dispatcher’s computer terminal screen, and (3) information regarding the specific condition (in this case, "low suction pressure" and "low discharge pressure") will be highlighted in a particular

  1. The monitoring system at the Colton Terminal scans various pipeline parameters, including pipeline pressure, at 13-second intervals. Thus, an event (in this case, a pressure reading) may have occurred up to 13 seconds earlier than the recorded time (and the time cited in this discussion).
  2. According to Calnev and OPS officials, the word "alarm" in the pipeline industry is not used to denote an emergency situation, but rather a change in operating conditions.
  3. The dispatcher acknowledges the alarm by pressing a key on his computer terminal keyboard.