When an avalanche strikes, it's a race against the clock to get into the air. 

In the French Alps, rescuers board a helicopter to head to the emergency site. And there is an important team member who joins the ride: a mountain rescue dog. 

This is only a training exercise, but dog and handler are lowered to the ground just as they would be in a real-life scenario. The canines can also be transported around the mountain by snowmobile and between skis, but going by helicopter means they can be in place in five to 10 minutes. 

Survival rates drop significantly after just three to five minutes, so it is crucial to know what to do if caught in an avalanche. 

"If you're in the avalanche, stay calm, don't move, try and make a cavity to breathe," advises Olivier Ducastel, head of the Ski Patrol Security in Tignes. "If you're able to move, get any snow out of your mouth. But mainly, stay calm, to avoid running out of breath and using up the oxygen that's around your mouth."

Today, the team members are practising what they would do next by carrying out simulated avalanches. Volunteers enter small igloos, dug out the previous day. A snow plough then seals the entrance to hide their location.

Now it's up to a six-year-old German Shepherd called Nitro to find the trapped person. His handler says dogs like Nitro are trained from a young age for this job - and they use dog toys to motivate their four-legged friends.

"We start by going into open holes," explains Baptiste Braun. "Then as they progress we close up the holes - we make 'letter boxes', a tiny gap so that the dog has its smell. And then we will start to completely close it up. It won't be the victim the dog is looking for really, but its toy - it's a game for him."

Nitro has a good sniff around the training area. And once he thinks he's caught the scent, he starts digging. It's not long before he discovers the avalanche victim, and with the help of Braun, pulls her to safety. And of course, he's rewarded with playtime and his much-loved toy.

In 2017, four people died when they were hit with a wall of snow in an off-piste area of the resort of Tignes. The rescuers urge skiers to do their research to avoid ending up in an avalanche situation.

"We are not in a Disney World," says volunteer Charlène Trenel. "We have to be really careful and just ask the snow patrol, ask everyone about the conditions. And go with someone who knows the mountains, who knows the resorts."

The ski patrol unit carries out 1,500 training exercises over the course of a year. And the team intervenes in around 10 real-life avalanche emergencies a year. Rewarding the rescue dog is crucial, even when treating the injured.

"As soon as we get the victim out, first we take care of them, administering first aid," says Braun. "But at the same time there will be another patrol person or someone else who will go back into the hole with the toy, for the reward for the dog."

Rescue dogs can expect to patrol the slopes for several years. But beyond the age of 10, it becomes harder for them to keep doing the job. Dipsy is 11 years old and will be retiring this year but will continue to be looked after by her handler, Marianne Desmons. Until then, she and the other dogs are on standby for the next time an avalanche hits Tignes.

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