Under Pressure

Pressure. We’re all under it, all the time. 1 ATA to be exact, a single atmosphere, 1 bar (or 14.5psi for those still in the imperial or standard systems). Every 10m down, give or take depending on your tables, another atmosphere of pressure is added to this, altering the effects of common breathing gases like oxygen and nitrogen on your physiology and mental abilities. This is a short post on the effects of pressure on you and your brain.

For starters, the standard mixture of air we enjoy on the surface gets increasingly unhealthy for you. Nitrogen builds up in your very real theoretical tissues, lending itself to potentially lethal irritations like the many forms of DCI and DCS. By 75m, 21% oxygen air becomes toxic to the system. Hence why commercial divers use HeliOx for deep work, and why technical divers use Tri-mix.

Next up, your brain stops working on all cylinders. Classically referred to as the Martini Effect, every atmosphere of pressure is the equivalent of a dry martini on an empty stomach. A more technically correct term is Nitrogen Narcosis. The worst part is that unless you’re sharp, you won’t notice it starting to happen, if at all. This is where it pays to have a switched on dive buddy.

The last point is a bit of trivia that’s fun to pull out around diving buddies. Back in the day, Jacques Cousteau picked the red toque as his headwear of choice as a diver. This was no mere fashionable accessory though. He choose it out of respect to the men who first worked in and suffered from the effects of pressure. Caisson workers. Labouring in pressurized, watertight structures, it wasn’t long before they began suffering from “Caisson Disease”, what we know today as DCI and DCS. To alert the local gendarmes that they needed medical attentional and not jail when they collapsed to the streets in spasms, they wore red toques.

Pressure is simply a fact of life and a controlled risk factor for divers. By carefully mitigating the risk by controlling bottom times, breathing gas mixtures and exertion before/during/after the dive, you can greatly reduce the effects of pressure. More details to follow on the weekend!

About the author

Graeme is a professional diver, qualified as a PADI and SDI Divemaster, DCBC 40m Unrestricted Commercial Scuba Diver, 30m Restricted Surface Supply diver, and CAUS Scientific Diver Lv.2. Graeme has an Associate Degree of Arts in Environmental Studies, where he focused on archaeology and physical geography, and an Advanced GIS certificate.