hellium

At one point, however, the city hired a crew of near-permanent deep-sea divers to fight these leaks: specifically, New York "enlisted six deep-sea divers who are living for more than a month in a sealed 24-foot tubular pressurized tank complete with showers, a television and a Nerf basketball hoop, breathing air that is 97.5 percent helium and 2.5 percent oxygen, so their high-pitched squeals are all but unintelligible."