A diver inspecting a massive water tower in Braintree, Mass., died Thursday when his air supply cut off and a spotter was unable to pull him out of the freezing waters, according to town officials, who said the man’s teenage son watched from the ground on a video feed.

The diver, who was not identified, was working in the 150-foot Lincoln Heights tank around 10 a.m., when he signaled he was losing air, the Boston Globe reported. Moments later, the diver lost communication with a spotter watching from atop the tank.

The spotter plunged in to save him, but also became trapped in the dark waters, which CBS reported were a frigid 45 degrees. Rescue workers rushed to the scene, hindered by 50 mph gusts of wind, extreme cold and ice forming on the top of the tank.

Officials said the spotter managed to grab hold of the diver, who had fallen unconscious, but he slipped away. Two firefighters eventually lifted the spotter out of the tank, and he emerged “completely soaked” with “no body strength at all,” Braintree Fire Chief James O’Brien told the Globe.

They were unable to save the diver, O’Brien said. As the tragedy unfolded, the diver’s 14-year-old son watched the harrowing sequence of events on a video feed on the ground, according to WCVB. Images from the scene show at least four rescue workers clinging to the narrow ladder leading up the tower to a hatch at the domed top.

Response crews spent Thursday draining 1 million gallons of water from the tank into a retention pond so that the diver’s body could be removed in a “dignified and respectful” manner, Braintree Mayor Joseph Sullivan told reporters at the scene.

“It’s a tragic day. It’s a difficult day for us,” Sullivan said. “That individual was providing valuable service to our community. We also saw the best of our fire department and others who stepped up and took the time to save a life.”

“None of this activity should be considered routine,” Sullivan added. “And obviously today we found out the difficulty of this work.”

The fire chief said the harsh weather made it too risky for rescue workers to climb through the two-foot hatch at the top of the tank to retrieve the body. The draining would take up to 14 hours, he told the Patriot Ledger, adding that the tower would be refilled in about five days.

Sullivan praised rescue workers, saying they risked their lives trying to pull the men out.

“There were incredibly difficult weather conditions,” he told the Globe. “You’re talking about a 150-foot tower. You’re talking about incredibly cold weather, with wind that was just gusting. Our firefighters responded in a very committed and heroic way.”

According to the Globe, Braintree hired Kentucky-based Pittsburg Tank & Tower Co. to inspect the tower, and the company subcontracted the work to T.K. Potable Diving, a commercial diving firm based in Texas. Town officials said the tank, one of five in the area, gets inspected every five years.

Pittsburg Tank & Tower president Ben Johnston said the company was investigating the accident.

“It’s a bad day and we’re just trying to get our arms around everything,” he told the Globe.

The Norfolk County district attorney has found no indications of foul play, the Globe reported, and officials said there was no threat to Braintree’s water supply.

Inspecting and repairing giant water towers is no easy task, and specialists in the commercial diving business tend to follow strict safety rules. One diver typically makes the plunge into the tank, while a spotter outside keeps watch. Both wear harnesses tethered to each other. On the ground, another crew usually monitors a video feed of the work.

Scuba Diving Magazine discussed water supply diving in a 2007 article on dangerous diving jobs, saying “someone has to dive the 150-foot-tall water towers on the blizzard-blown Kansas prairies where it’s gravity, not gas saturation, that will kill you.” The article profiled one commercial diver who compared the profession to rock climbing.

“There was a hell of a big difference between being 30 feet up on a rock face or roof, and being 150 feet on top of a round tower that is swaying in the wind,” the diver, Chad Campbell, told the magazine. “You’ve also got to be a mountaineer.”

A more recent article by Divers Institute of Technology, a commercial diving school, also warned of the risks involved in water tower inspections.

“Sometimes there is very limited space and poor weather conditions,” one of the institute’s graduates said. “If equipment isn’t secured properly, someone can get hurt or worse.”

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