I do one of the most dangerous jobs in the world – even though I've lost many colleagues and one mistake could cost me my life… this is what I love about it

“Most people look into the darkness of a cave and see only terrifying darkness. I see an undiscovered world of possibilities.'

This is what Canadian Jill Heinerth, a cave diver for thirty years, says in a fascinating new book Adventuress: Women who explore the wild (£30, Prestel), a book in which twenty 'extraordinary' women are profiled 'with a deep desire for adventure'.

Jill, a filmmaker and photographer, recognizes that her job is the most dangerous in the world and that one mistake could cost her her life.

But “despite the risks,” underwater caves pose “the ultimate challenge” for Jill and “make her feel like a kid in a candy store.”

She writes: 'People look at my work and suggest that documenting the world of underwater caves may be the most dangerous job there is.

Jill, a filmmaker and photographer, recognizes that her job is the most dangerous in the world and that one mistake could cost her her life. She is pictured above in a cave in Abaco, Bahamas

“I am burdened with the grief of the deaths of countless colleagues, some of whom made unwise choices in the darkness of underwater cave systems.

'Their names have been added to a long list of divers who ran out of air, got lost in a labyrinth or went too far in new explorations before returning.

'[But] for a filmmaker and photographer, underwater caves present the ultimate challenge: I create art while monitoring delicate life support equipment under task loads that push my body and mind to their limits. Despite the risk, I'm like a kid in a candy store, working with biologists discovering new species, physicists monitoring climate change, and hydrogeologists exploring our finite freshwater reserves. Exploring the planet's underground pathways.

“With training, preparation and dedication to proper safety procedures, I have been able to sustain a nearly 30-year career in research and science. It would be arrogant to say that I will never make a mistake or a bad choice that could ultimately cost me my life, but I believe that following the ultimate rule for survivors can help. Be willing to take risks. Be willing to push the limits of the razor's capabilities. Be courageous and confident in everything you undertake in life.'

Jill (above) says, “Be willing to take risks. Be willing to push the limits of the razor's capabilities. Be courageous and confident in everything you undertake in life'

LEFT: Jill is pictured here in Ginnie Springs, Florida. She reveals: 'I've lived here for over ten years and have done hundreds of dives in the caves on site.' RIGHT: A cave called 'The Pit' in Yucata, Mexico

The Explorers Club Fellow, who has dived everywhere from Egypt to Antarctica and Mexico, explains her rules of survival.

She writes, “Being trapped in a claustrophobic underwater cave in the darkness of total salinity, I must summon the calm necessary to take the next best step toward survival.

'When a rock holds me, I use logic to figure out how to free myself. If the safety guideline breaks, I methodically deploy my cave diver's reel and repair the broken guideline.

'I have to do all these things without panic. Every breath I take must be measured and calm. I need to keep my heart rate down and focus on the next best course of action.

Jill peers into an unusual waterhole in a hyper-saline lake in Egypt. She says, “With training, preparation and dedication to proper safety procedures, I have been able to sustain a career of nearly 30 years of research and scholarship.”

'Uncontrolled emotions do not help me in this life-threatening situation. They will only distract me from success and use up precious air.

'[And] when the hairs on the back of your neck stand up and warn you of danger, you must be willing to let go. As you reach for the alluring peak of the mountain or the new exploration in a virgin cave, remember that you must also get home safely.

“Knowing when to turn back is as essential as embracing fear.”

Adventuress: Women Exploring the Wilderness (Prestel) is available now and costs £30