Thunder Bay: Technical Diving

Many divers who visit the shipwrecks in the Thunder Bay National Marine Sanctuary use air in their SCUBA tanks. Air consists mostly of oxygen and nitrogen--you are breathing these gases right now. But did you know that oxygen and nitrogen affect a diver differently under water than above water? This is due to the pressure exerted on the diver by all the water around him or her. The deeper divers go, the more pressure they experience. Using air in your SCUBA tanks work great when diving wrecks up to about 40 m (130 ft) deep. Beyond that depth, divers use a mix of different gases to eliminate some of the safety hazards that oxygen and nitrogen can present during deep dives.

During their technical dives to the shipwreck Kyle Spangler, which rests in 55 m (180 ft) of water, divers filled the SCUBA tanks on their backs with helium, oxygen, and nitrogen. Helium helps to eliminate some of oxygen and nitrogen’s bad effects. Divers had to be very careful about making sure they had the right quantities of each gas in their tanks. By breathing this mixture of three gases, divers could stay at the wreck site longer and work more safely. Divers also carried extra tanks with high concentrations of oxygen in them. These tanks were strapped to the divers’ sides. As they slowly ascended to the surface after leaving the wreck site, the divers stopped and breathed from these tanks at certain depths. This is called decompression, and it makes sure that divers have the right balance of gases in their bloodstream before reaching the surface.