Ballance Agri-Nutrients is facing a large fine after a toxic gas cloud from its fertiliser manufacturing plant wafted over a group of workers and two truck drivers.

Workers at the Ballance site described seeing a "huge gas cloud" , 20 to 30m wide, heading towards Mauao. Others described it as "a plume of black smoke coming towards us".

The gas cloud drifted from the roof of the manufacturing plant and across the Hewletts Rd site towards Totara St about 7.35am on May 22 last year.

Several people at the site and working nearby were exposed to the gas cloud. They experienced coughing, a "funny taste" in their mouths, irritation of the eyes and respiratory system, but their symptoms were relatively short-lived.

Advertisement

Two truck drivers employed by Winstone Transport were also treated and discharged from Tauranga Hospital after struggling to breathe.

One of the truck drivers was unable to attend work the following day due to dizziness.

In the Environment Court yesterday, the company's chief executive Wynne pleaded guilty to a charge of discharging a contaminant, sulphur dioxide and/or fluoride, into the air.

The summary of facts showed there was a breakdown in communication between controllers during a shift change, in regards to the conveyor speed processing product.

This resulted in a build-up of fumes and about 7.30am the cloud of fluoride and sulphur dioxide fumes bypassed the treatment systems and was released.

The new shift operator was unaware the fumes had been discharged.

People outside the plant tried to contact the controller on VHF radio but he did not respond, and the plant was shut down about 7.50am.

Victoria Brewer, the Bay of Plenty Regional Council's lawyer, told Judge David Kirkpatrick said the defendant had two prior convictions in 1999 and 2015 for similar offending.

The investigation revealed the offending was caused by a series of " fundamental errors" by operators at the fertiliser plant, she said.

This included a failure to properly communicate to the incoming acidulation controller the reason why the den floor speed processing product had been increased.

None of the personnel within the manufacturing plant noticed the severity or volume of the emissions from the acidulation den nor that fumes had discharged from the building.

It was a "systematic failure", she said, There were also errors in the communication in response to the incident and the emergency response system "did not occur", Brewer said.

She submitted a fine of $90,000 was appropriate as a starting point.

Ballance Agri-Nutrients lawyer Janette Campbell said this was not a deliberate discharge and the offending was not committed to gain profit.

The offending happened because of a "serious mistake" and was taken seriously by the company, she said.

Campbell said Ballance's two earlier convictions were unrelated to last year's discharge which happened at a different part of the site.

Ballance had taken significant remedial steps, including introducing a new computer system to add another level of control to prevent this from happening again, she said.

Judge Kirkpatrick reserved his decision.