Failed to provide an adequate bund to prevent molten metal coming into contact with water under the Anode Casting Wheel."
5 An Agreed Statement of Facts, tendered by Mr Docking, of counsel, appearing for the prosecutor, and an affidavit of Drew Glen Winning relied upon by the defendant, represented by Ms McDonald, of counsel, revealed the operation of the furnaces and the systems in place at the smelter to identify and rectify problems at the time of the offences. It is necessary to repeat, in some detail, the operation of the furnaces, and the systems in place in order to understand the sequence of events leading up to the accident on 8 June.
6 The east anode furnace could rotate through 360 degrees in either direction. A clockwise rotation rotated the furnace towards the casting side. This facilitated the pouring of copper through the casting opening, which is approximately 125mm in diameter, into an adjacent launder system, from where it was directed into copper moulds on an anode casting wheel and cooled with water. An anticlockwise rotation rotated the furnace towards the refining or processing side. This enabled the deposit or charge of scrap copper into the furnace by means of a charging boat into another opening (the scrap opening) in the furnace which is approximately two metres in diameter. The scrap opening was also used to remove impurities known as "slag" from the copper in the furnace.
7 The east anode furnace was operated by three drives or motors. The main drive, an electric motor, rotated the furnace during the refining or processing operation. A second electric motor, the casting drive, rotated the furnace during the casting operation. An air motor, or pneumatic motor, acted as a back up system to the main drive and was generally activated in the event of an electrical failure. If the furnace was rotated past either -2.5 degrees (the casting side) or +2.5 degrees (the refining side), the air motor was automatically activated. Both the main drive and the air drive had emergency air roll-out functions. In the event of an emergency, these functions were designed to rotate or roll-out the furnace to a position of 0 degrees (the "all ports free" position), and hence prevent the escape of molten copper from the furnace. A component of the air drive was a double solenoid pilot valve in which the air drive rotated the furnace. This was the valve which malfunctioned on 8 June 2002.
8 A furnace control room (the "dog box") housed one set of controls for the east anode furnace. The furnace could also be controlled outside the dog box by means of joy sticks. One joy stick operated the main drive to rotate the furnace into the refining position. The second joy stick operated the air motor. A separate set of joy sticks operated the furnace during the casting process and were located in the casting control room. The furnace was also equipped with a braking mechanism which was automatically activated whenever the furnace stopped rotating.
9 A computerised system known as the distributive control system (DCS) controlled both anode furnaces. It allowed technicians to view operations taking place in several areas on screen. The DCS was programmed to identify errors or inconsistencies in the operation of the furnaces. When an error was detected, the programme was designed to disengage the main drive operating the east anode furnace and therefore prevent further rotation until the error was investigated and rectified. The air drive was designed to operate as a "stand alone" system independent of the DCS. It overrode the DCS if the DCS halted the rotation of the furnace at a point which might allow copper to escape or if the DCS was no longer able to control the rotation (for example, in the event of a power failure).
10 The emergency air roll-out function, when activated, was operated by the air drive. This function could either be activated automatically if the power to the main drive was interrupted or shut down; or, activated by a technician using one of the anode furnace control panels, by pressing a button for either the main drive or the air drive. The emergency air roll-out function was designed so that, once activated, the air motor could not be disabled while it was returning the furnace to the "all ports free" position. It could only be manually disabled by isolating its air supply.
11 Water was an important element used during the copper casting process. It was sprayed on top of the molten copper which was poured into 24 moulds on the anode casting wheel located next to the furnaces in order to cool the copper and accelerate its solidification. Excess water from this activity fell into a sump by means of a series of drains located below the casting wheel. The water could, at times, reach a depth of 600mm in the sump. One of the risks, which was known to the defendant prior to the offences on 8 June 2002, of working with water in the smelting operation was, as earlier mentioned, the risk of steam or phreatic explosion. The risk only arose when water was trapped underneath the molten copper. There was no risk of a phreatic explosion when water was applied on top of the molten copper. According to Mr Winning, who gave evidence during the sentence proceedings, it did not require a "great" quantity of water to give rise to the risk of an explosion. This was because the conversion of water to steam resulted in a "significant increase" in volume for a small volume of water.
12 About six months prior to the offences (in December 2001), approximately 20 tonnes of molten copper spilled out of the east anode furnace onto the ground. One of the recommendations arising from an investigation by the defendant into that incident resulted in increasing the depth or holding capacity of the bund located underneath the anode furnaces. At that time, the defendant did not identify as a possible risk the overflow of molten copper from the ladles and launder facilities into the area outside the bund thereby causing the molten copper to come into contact with the water in the sump.
13 On 8 June 2002, Jason Stirling Koster and Marcos Sergio Miranda, both smelter technicians employed by the defendant, were operating the east anode furnace. Some time after 4pm, the furnace was rotated towards the casting side to an angle of approximately -13 degrees. Later, Mr Koster attempted to rotate the furnace from -13 degrees to 0 degrees in order to effect some repairs. Either he or Mr Miranda used the main drive joystick but the furnace did not respond. Since the furnace had rotated to a position in excess of -2.5 degrees on the casting side, in the normal course of events, the air drive would be automatically activated. In this instance, however, unknown to the workers, the double solenoid valve which, once the air motor was activated, moved a shuttle valve that in turn controlled the direction of rotation, malfunctioned. As a result of the malfunction, the shuttle valve could not move to the appropriate position (towards the casting side).
14 The DCS detected that a fault had occurred by displaying a yellow flashing "Fault" on the screen. In response, the DCS disengaged the electric drives, including the main drive which prevented the furnace from further movement. Neither Mr Koster, nor Mr Miranda, were trained to operate the DCS. Mr Koster notified Evan Rodney Wilson, a shift system support officer (SSSO). The SSSO was trained to verify the currency and accuracy of the DCS code as it applied to the operation of equipment or processes. The SSSO was not trained to diagnose and correct faults identified on the DCS. Mr Wilson made several attempts to rectify the error without success. These attempts were undertaken, according to a report compiled by the defendant of the incident (annexed to Mr Winning's affidavit), between about 4.10pm and about 5.50pm. During training, the SSSO was made aware that if he or she required assistance or was unable to correct a fault identified on the DCS then a process control engineer should be contacted. These engineers were on call 24 hours a day under a roster system. Mr Wilson also gave evidence during the sentence proceedings. In a statement tendered into evidence Mr Wilson said: