Chemical safely exploded

South Dunedin business evacuations and exploding unstable chemicals may be seen as a "dramatic response" by some, but emergency services insist it was worth it to ensure public safety.

A small package of hydrazine monohydrate was detonated in Glasgow St by the New Zealand Defence Force at 9.30am yesterday.

The chemical was found in an unstable condition by a laboratory manager at Dunedin probiotics manufacturer Blis Technologies on Thursday.

Emergency services were called that afternoon.

There were initial indications the situation was not significant but, in an unusual development, firefighters discovered safely disposing of the chemical meant exploding it.

The defence force was called in, which decided it was unsafe to work overnight, so started the procedure early yesterday.

A 100m cordon was set up around the detonation site, which involved the evacuation of businesses on Glasgow and King Edward Sts.

Explosive ordnance disposal specialists wearing heavily-armoured bomb disposal suits entered the building and carried the package outside. Sandbags were placed around the container and a team detonated it.

Fire and Emergency New Zealand Dunedin city station officer Chris Lind said all the processes and systems in place at the laboratory were as it would expect.

"They set a good example in lab cleanliness and management."

The substance had developed crystals which made it unstable.

If moved it could have had a toxic effect or the potential to be highly flammable, or explosive "at the extreme end of the scale".

The substance was in a diluted form. However, emergency services called for the unusual destruction measures to go "to the far end with our preparations for public safety".

Blis Technologies chief executive Brian Watson said his staff did all the right things, but the company would investigate whether it could learn from the experience.

"We had it in a specific storage cabinet to manufacturer recommendations, but we'll endeavour to learn from that.

"In its original packaging, they noticed some deterioration in the cap area and then rightly undertook some investigation into how to deal with that."

The laboratory was expected to be running again yesterday afternoon.

The destroyed 50ml package was the only hydrazine monohydrate the company carried.

He understood the inconvenience to surrounding businesses and would be "going around and apologising".

University of Otago microbiology emeritus professor and Blis founder John Tagg, who also works there as an adviser and consultant, said he had "no idea that there would be such a dramatic response" to finding the unstable chemical.

It was used only occasionally in testing associated with micro-organisms, but was "not something that's used in production".

Who Ate All The Pies operations manager Brian Taylor, whose business was within the cordon zone, said he arrived yesterday morning and "didn't know anything about" the dramatic scene.

He described the explosion as "more of a puff".

Phoenix Rigging and Scaffolding manager Marcus Doorbar said he was lucky the cordon tape was just before his company's boundaries or it "would have been a bit stuffed".

Staff climbed up the scaffolding yesterday morning to get a better look at the scene, he said.

- Additional reporting John Gibb