The men caught up in a Waihi mine fire had thought they were on a drill before they realised they were involved in a real emergency situation.
The 28 miners spent seven hours in refuge chambers inside the Trio underground mine at Newmont Waihi Gold yesterday.
It was the firstnon-drill event to occur at the Trio mine since it was established in 2006.
External affairs co-ordinator Kit Wilson said the significance of the refuge chambers at the mine was "huge" and this was reflected in the three drills held each year at the mine.
Mr Wilson said the drills were so regular, miners involved in yesterday's incident had thought they were involved in another one.
"This mining group had actually had their exercise just a month ago," Mr Wilson said.
"They happen regularly. The idea is that gold mines aren't dangerous but they are unforgiving."
The chambers are self-contained units, with three larger chambers described as like "shipping containers". Two smaller, portable chambers were introduced last year.
Each chamber is equipped with an oxygen cylinder, chemical toilet, water, a radio for communication, a siren and a pack of cards.
They are designed to provide a breathable atmosphere for up to 36 hours each and are required to be within 750m of anyone at work.
"The reason it's 36 hours is the maximum amount of time for a truck fire to burn out and a rescue team to come get you," Mr Wilson said.
The larger chambers hold 20 people each and the two smaller ones hold six in each. The chambers were designed to be used only if the way out was blocked or if there was a fire.
Miners were usually alerted to potential danger by radio or if they smelt stench gas - a rotten egg smell, pumped into the mine in an emergency.
