The air temperature’s minus 11 and there’s thick ice underfoot: perfect conditions for a swim - if you’re a police diver, that is.
Members of the Police National Dive Squad recently spent five days at Lake Alta, at the top of the Remarkables ski field, training in some of the most inhospitable conditions winter can offer.
The winter training is a regular fixture on the squad’s calendar – but for six of the eight on the exercise it was a first time on - and particularly under - the ice.
There's a hole in the ice and police are looking into it.
Squad OC Senior Sergeant Bruce Adams says the exercise allows them to test safety procedures which can be applied to the range of high-risk environments they face in their work.
“The water was zero degrees, it got as cold as minus 11 topside and we had up to 90kmh winds,” says Bruce.
“But we got in a huge range of diving using different forms of equipment. There’s a lot of science and set-up behind it.
“We’re training in things that can be applied to diving in contaminated water, confined spaces, where there’s a risk of entrapment, deep diving.
“The exercise brings everything together without us having to actually dive into those conditions. And it means we can test everything at the same time.”
Staff have to be able to identify equipment faults and resolve them. Drills, pre-dive checks and actions under water have to be absolutely fit for purpose.
Masks are deliberately flooded “so they get used to the shock of the cold water. It’s going to happen for real at some stage,” says Bruce
“Stuff you take for granted, you just can’t in those conditions. Rubber hoses get stiff, you lose feeling in your hands because of the cold.
“It’s hard enough taking a good photo underwater - but when you’re hypothermic and have no feeling in your hands it’s even harder.
“It’s not just a case of jumping in for a splash-around and getting a bit cold.”
Three of the team started the training late after being diverted to Riverton to help search for a missing boatie.
Back at Lake Alta, team members had five dives of up to 30 minutes each. They were tethered to the surface with lines which include a hard-wired comms link, and were breathing a special oxygen-rich air mixture.
With safety to the fore, Bruce says the first task on arriving at the lake is to set up a shelter on the ice and equip it with safety gear.
An access hole for the divers is cut beneath the shelter, with another as a back-up 50 metres away. When the team leaves they fill in the holes and mark them with flags to prevent anyone falling in before they freeze over.
The team had help with the heavy lifting from the Royal New Zealand Air Force, though on day one white-out conditions meant the helicopter could not fly and they relied on ski field staff and snow groomers to get their gear up the mountain.
On the final day, the chopper dealt to their task with six lifts in 40 minutes. Not that the weather was perfect…
“Mother Nature kicked us in the bum on the last day,” says Bruce. “We’d packed up all the gear for the Air Force to pick up and were filling in the holes when 90kmh winds came through, shut down the ski field and blew our shelter across the ice.”
He says the squad is grateful to the Air Force, to Remarkables ski field staff, NIWA and others who provided equipment or other support.