Oliver pulled the mask and pressurized bottle of breathing gas from his bag. Besides the risk of hypothermia imparted by the cold salt water, the dive that Oliver and Jeanne were about to undertake would descend to such a depth that a standard SCUBA compressed air mix would be rendered toxic by the pressure.
The human body is designed to operate at a particular range of air pressure and temperature. The mix of gasses commonly referred to as ‘air’ includes dozens of elements, primarily nitrogen and oxygen. While both oxygen and nitrogen are essential for the human body to function under normal atmospheric pressure, they become deadly poisons when the increased pressure of a deep water dive causes them to dissolve into the tissues of the human body. At a depth of only 90 feet, nitrogen dissolves into the blood and travels to the brain, where it acts as a powerful narcotic. While Oliver enjoyed the buzz of a couple beers on occasion, he certainly did not want to experience the similar effects of nitrogen narcosis while deep underwater. Even more dangerous than nitrogen was oxygen. At 50 meters, which they would certainly reach as they descended the flooded shafts towards the salt dome, the pressure would cause oxygen to dissolve out of the blood and into body tissues. While oxygen is essential for human life, the body is designed to make use of a limited quantity. If too much oxygen became trapped in their blood and tissue, then Oliver and Jeanne might find themselves experiencing sudden muscle spasms, and even full body seizures, without any warning.
“Checking… checking…” Jeanne’s voice crackled out of the radio in Oliver’s rebreather mask.
Oliver pressed the mask over his face and said, “I can hear you. Can you hear me?”
“I got you too, buddy,” Ray called in.
“Good. Let us know if we start to fade out, Ray.”
Oliver removed his mask and turned back to Jeanne. She was already wearing her full face mask, which sealed around her face and over her ears. Her hair was pulled back into a tight bun, which bulged at the back of her suit hood. He raised the mask to his face and said, “Turn around. I’ll check your rebreather.”
Jeanne gave him a thumbs up and turned her back towards him. Oliver ran his gloved fingers over the tubes leading from her mask to the compact plastic unit strapped between her shoulders, checking that the seals on the mask were secure, the insulated tubes were free of kinks, and the connections to the recycling unit were tight. Oliver gave Jeanne a pat on the shoulder and, when she turned around, gave her a thumbs up.
He put on his own mask and said, “Check me now.”
“Sure,” Jeanne said. Oliver felt her patting at his neck, shoulders, and back, then she came around the front and gave him a thumbs-up. “You’re good.”