It was June, and the sunlight was still reasonably sufficient. The three felt a little stuffy in their wetsuits, but the stuffiness somehow disappeared the moment they entered the sea. As they dived deeper into the ocean, the temperature around them began to drop as well.
With a much higher thermal conductivity than air, a human would lose more heat in the water than on land. Fortunately, their diving suits helped them fight off the cold. Usually, casual divers like them would not dive too deep into the sea. Every ten meters deeper, the pressure would turn up a notch. After diving deeper than thirty meters, they risked suffering from nitrogen intoxication. The ordinary diving cylinder would typically be filled with compressed air consisting of 21% oxygen and 79% nitrogen. Under high pressure, nitrogen would enter the diver's body, and at the same time, breathing pure oxygen under a high-pressure environment for too long would cause oxygen poisoning.
