After the company ride engineer hung up the phone he had a thought. With the pumps running the hydraulic oil would pick up heat and get hotter. He checked the chart for the top temperature of the oil, the heat dissipation of the oil coolers and the amount of heat that the pumps would add in this mode. The oil would stabilize at less than 200 degrees even in outside temperature of 130 degrees. This was thirty degrees above the normal, hot but well within limits for the system components, the boiling point of the fluid and safety rules. And it wasn’t nearly that hot in California today so it would be even cooler. He put the thought out of his mind.

The ride was rented by the studio from a company in Oregon. When it was built the oil cooler had four radiators each about two times the size of a truck radiator. Each had a three quarter horsepower motor driving a fan that blew air over it and a quarter horsepower pump that circulated low pressure oil from tank through the radiator. The idea was redundancy. The unit could run safely with only two if these units running except on a very hot day, then three were needed. Failure of a small component would not disable the ride.

A year ago one of the pumps failed during a major county fair. The operator consulted the manual, shut down the pump and fan on the one radiator and continued to run the unit with three radiators. Then a second one failed a day later. They needed the ride operating so they rerouted the oil flow so that the oil from each operating pump split between two radiators and turned on the fans. They checked the oil temperature on a hot day. At the worst it only hit 205 degrees. The engineer at the company was not consulted about the modification. Even with this change the oil should have stabilized at less than 220 degrees, scalding hot but within the limits of the operating temperatures of the unit and below the oil’s boiling point.

The voltage fluctuations and heat took its toll in other components. One of the two remaining pump motors, abused by low voltage, got hot, tripped its thermal overload and stopped at 11:21. With four twenty five HP hydraulic pumps and four blowers running nearby, nobody noticed the puny but critical motor was not running. The unit was now running on one circulating pump with two radiators. Had the engineer known this he would have estimated the cooling at 1.5 of a cooling unit, far less than needed to cool it in the current mode. The oil would get very hot.

The pumps had now been on for nearly two hours when the four young people got into the bucket. They started the unit to move them through the cycle. The hot oil, now at over 320 degrees and near its boiling point coursed through the lines. The bucket was being rocked by a hydraulic motor. The two young people grabbed the bar in front of them to hang on. The cameras were about to start.

Jan Chapter 03: Ten Seconds to Disaster Mar 6, 2008

Jan Chapter 01: School Days Mar 6, 2008