Deep Diving: Definition and Limits.

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Choosing a depth to define “deep” is a bit like picking an altitude to define “high.”

Eighteen metres/60 feet may be “high” compared to standing on the ground, but compared to a satellite in orbit, it’s “low.”

Clearly, both “deep” and “high” are subjective terms, though physiology and physics make defining “deep” for recreational diving a bit less subjective.

In any case, you have to draw a line somewhere, if only to clearly discuss the subject.

PADI and most of the recreational diving community define a “deep” dive as 18 metres/60 feet or below, but no deeper than 40 metres/130 feet.

Depths below 40 metres/130 feet lie beyond recreational diving.

Given the limitations of recreational scuba equipment, the short no-stop dive times below 18 meters/60 feet

and the scope and intent of recreational diver training, these depth limits serve well and have a solid track record supporting their appropriateness.

Although 40 metres/130 feet has been set as the maximum, for general purposes, you probably want to treat

30 metres /100 feet as the optimal maximum limit, for four practical reasons:

First, the short no decompression limits and rapid air use below 30 metres/100 feet make deeper dives incredibly short.

Considering the time and effort to plan and make a deep dive,

the activity and objective of a 30 metre/100 foot dive has to be very satisfying to be worth only ten minutes dive time.

Second, nitrogen narcosis, the intoxicating effect of nitrogen as you go deeper,

begins to have a noticeable effect on most divers below about 30 metre/100 foot.

While susceptibility varies from person to person, this is an important consideration.

Third, dives to depths beyond 30 metres/100 feet tend to be more associated with decompression sickness,

particularly when making repetitive dives. Using a single tank of air, it’s possible to overstay the no decompression limits when you’re that deep,

and in any case, with short no-stop times dives tend to be closer to the limits.

Finally, in many dive environments deeper than 30 metres/100 feet it becomes very dim, or completely dark due to light absorption.

This means it’s not only difficult to see what’s around you, but difficult to read your gauges and use your equipment.

But they’re going Deeper…

The dive community accepts the 40 metre/130 foot limit for recreation divers virtually without exception,

yet invariably, you’ll see or read about technical divers who descend well below 40 metres/130 feet.

This doesn’t negate the limits for recreational divers, however.

On close inspection, you’ll see that technical divers each wear significantly more equipment –

often four to six cylinders, multiple regulators, etc. – and it is more elaborate.

Diving to depths below 40 metres/130 feet often requires special helium breathing gases, and an hour or more making stage decompression stops.

As you might imagine, this type of diving requires special training, and substantial experience in recreational diving before starting that training.

Even with the equipment, experience and training, technical diving by its nature entails significantly more risk than recreational diving.

When you think about it, technical divers validate the 40 metre/130 foot recreational limit with all the extra hardware,

special techniques and extensive training they require to manage the risk of going beyond.

Technical diving isn’t for everyone, nor is it a necessary step in your progress as a diver even after thousands of dives.

But, if this type of diving interests you, obtain the proper experience and training before attempting it.