How top cave diver Jill Heinerth keeps calm under pressure

It could be tempting to assume,after more than two decades in one of the riskiest jobs around, thatcave diverJill Heinerth is fearless.

In fact, the Ontario nativefeels fearevery time she descends into an underwater cavern and that`s a good thing.

"I enter the water scared,"said Heinerth, who last year was named the Royal Canadian Geographic Society's first explorer-in-residence.

"It's important for me to embrace that fear,because that tickling sensation on the back of my neck is self-preservation"

Heinerthhas been nearly trapped inside an iceberg in Antarctica, and travelled deeper into underwater caves than any other woman.

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Here's how Heinerth handles the fear to get out aliveand describes one terrifying night on land when she knew she had it in her.

What'sthe worst that can happen?

Inside a cave, whichHeinerthdescribes as"swimming through the veins of Mother Earth," many things can go wrong.

She could get lost, unable to see from silt clouding the water. She could get stuckor run out of air to breathe, several kilometres from escape.

Rather than ignore these risks,Heinerthsays she imagines every one before she dives.

"What's the worst that could happen today?" she asks herself, then runs through scenarioslike a checklist.

"I'm prepared.I have the technology.I know what to do," she tells herself.

"That way, when I actually enter the water ...I've sort of freed my mind of all of those negative thoughts."

What can I do next?

When something scary does happen, Heinerth says the first thing she does is try to control her stress response.

"Yourheart starts to race.You begin breathing faster, and that's the last thing that I can allow tohappen to me underwater with a limited gas supply," said Heinerth.

"I have to ... get control over my breathing, I have to take a deep breath and say to myself, 'Emotions, you won't serveme now'and I have to send them away.``

Then, she "works within the moment" as time seems to slow. Even if escape is uncertain,she looks for her next beststep.

Cave diver Jill Heinerth on learning to act despite fear

7 years ago

Duration 2:30

Heinerth describes a terrifying night she fought off a burglar and learned about staying calm under pressure

It's something Heinerth said she realized she could do after,as a university student in Toronto, someone broke into her apartment and came after her.

"I'm lying in bed, and my heart is jumping out of my chest," she recalled.

My rational brain ... said no, don't throw a brick at him because thenit's his brick- Jill Heinerth

"I need him to know there's someone in the house and I don't want to use my female voice to do that."

Instead, she began stomping around her room, making noise and looking for a weapon to defend herself.

She eyed a brick holding up her student bookshelf.

"Already, my rational brain was starting to act, and it said no, don't throw a brick at him because thenit's his brick."

She grabbed two X-Acto knives from her drafting tableand stood shaking, ready in case he came at her which he did.

She slashed him, and he laughed at her, then ran away.

"It's this tangle, this tug of warbetween the emotional brain and the pragmatic brain," said Heinerth.

"How long can you swallow that down in order to survive?That's what I learned that night and I've carried that with me ever since and into every cave that I've ever gone diving into."

Listen to the CBC Radio special Keep Calm on the science of business of handling stress, or read more in the series here: