Dairy giant Fonterra has been given permission to sue the owners of the Tamahere coolstore that exploded in 2008 for $25 million worth of cheese that it lost in the blaze.

Fonterra has already filed papers against the lessee of the building, Waikato Coldstorage Ltd (formerly Icepak Coolstores Ltd), as well as Mobile Refrigeration Specialists Ltd, which carried out refrigeration work at the cool store.

Now Justice Rodney Hansen has allowed Fonterra to include the owners and lessors of the Tamahere plant, Icepak Group Ltd, as an additional defendant in the action.

A number of other parties, including other cheesemakers and insurers, are also involved in litigation as a result of the fire, which claimed the life of firefighter Derek Lovell and injured seven colleagues when the plant suddenly erupted into a fireball on April 5, 2008.

The judge said the explosion was believed to have been caused by the ignition of flammable gases used as a refrigerant.

"The plaintiffs' case is that the explosion resulted from the unlawful and unsafe operation of the coolstore," he said.

"They allege that there were defects in the plant installed and systems introduced when the coolstore was modified to introduce the refrigerant which caused the explosion."

Fonterra had initially proceeded on the basis that Icepak Coolstores was responsible for the installation of the plant and operation of the coolstore, Justice Hansen said.

It now said it had learned that Icepak Group, the parent company of Coolstores, was more involved in the installation of plant and development of associated systems than first thought.

"They now consider they have a cause of action against Icepak Group as owner of the site and plant, including refrigeration equipment," Justice Hansen said.

Fonterra claimed that Icepak Group had commissioned and paid for equipment and plant alleged to have been in breach of legislation, regulations, standards and other codes.

Icepak Group's position was that Coolstores was responsible for the decision to convert the refrigeration plant and to switch to the highly flammable refrigerant that caused the explosion.

It was argued that if group was added to the list of defendants, it would open up more claims and counterclaims involving various parties, significantly expanding the scope of the case and possibly causing an adjournment of the trial.

Justice Hansen said that was not a good enough reason not to allow group to be included in the action.

The interests of justice strongly favoured Icepak Group being joined in the action, he said.

The judge heard that a mediation hearing had been arranged for the end of November, but Fonterra had insisted on knowing Icepak Group's financial situation.

That was not acceptable to Icepak Group, though Coolstores had disclosed its financial position to Fonterra.

Coolstores and Icepak Group's lawyer told the judge that there had been contracts in place, with each of the parties having agreed how to allocate their respective risks.

- NZPA