INCIDENT: The Orica plant at Kooragang Island.ORICA will re-commence the start-up of its nitric acid and ammonium nitrate plants today after reviewing its operational procedures following Wednesday’s spill.
Nanjing Night Net

Orica said yesterday that a ‘‘failed computer card’’ led to the spill of ammonium nitrate solution. The incident – the fourth in a series that started with a hexavalent chromium discharge on August 8 – has led to further calls for the plant to shut.

But these have been countered by Stockton resident and Australian Workers Union official John Boyd, who says ‘‘the expert opinion is that Orica is safe’’.

An estimated 20,000 litres of 30per cent ammonium nitrate liquid escaped from a tank and over a restraining wall or ‘‘bund’’ about 2pm on Wednesday, two days after the EPA cleared Orica to restart part of its plant.

Site manager Sean Winstone said the spill happened ‘‘primarily as a result of a failed computer card in the computer control system’’.

Mr Winstone said Orica would report to the EPA but it believed it could resume restarting its ammonium nitrate and nitric acid plants. The ammonia plant remained shut under EPA orders after the August leak.

Mr Boyd said he was tired of people claiming to represent Stockton when they did not. He said most residents were happy with the plant.

‘‘[People] can trust the independent toxicologist, the EPA, the department of health, WorkCover and the independent specialist engineers, or can they trust the Stockton Community Action Group and the Greens,’’ Mr Boyd said.

But community group president Kate Johnson made no apologies for calling for Orica to close and said the group had more than 150 people on its mailing list.

Timeline of Orica incidents

October 19, 2010: Up to 12 tonnes of nitric acid were lost to the environment when a weld on a pipe failed at Kooragang Island site. Some turned to vapour, some was discharged into the Hunter River and some was discharged into groundwater. Prosecution being considered.

March 22, 2011: Ammonium nitrate was released into the air in a visible plume extending about four kilometres west of the Kooragang Island site. Initial investigations suggest the cause was a build-up of solid mmonium nitrate in a control valve. Investigation continuing.

June 17, 2011: A jackhammer ruptured an underground pipe, resulting in an emission of ammonia gas. 400 staff at Kooragang Island site were evacuated from ammonia plant.

August 8, 2011: Hexavalent chromium emitted into the air from a vent stack, resulting in the fallout of particles in Stockton and Kooragang Island.

August 19, 2011: Up to 1.2 megalitres of effluent containing concentrations of arsenic above the permissible limits released into the Hunter River.

September 27, 2011: Emission of mercury vapour that exceeded licence limits from Orica’s Botany plant in Sydney, detected by an on-site air monitor near a residential area.