Scientists at the University of Rhode Island (URI) have helped solve the mystery blast at Salty Brine beach. The likely source of the explosion was the combustion of hydrogen gas, which was produced by a disconnected copper cable underneath the beach. That cable, owned by the U.S. Coast Guard, used to power a navigational light at the end of the jetty.
The explosion didn’t leave behind any chemical residues, which told scientists to home in on clean-burning gases, such as methane or hydrogen.
URI's Art Spivack, a geochemist oceanographer involved with the investigation, explained how metal corrosion produces hydrogen to reporters at a news briefing at the Department of Environmental Management (DEM).
“If you put a piece of copper in salty water, it’ll corrode, just as if you put iron in salty water, it rusts,” said Spivack. “But if there is no oxygen there [in the environment],” the metal cable produces hydrogen gas, a process that Spivack also likened to the rusting of copper. A corroded copper cable not producing hydrogen gas creates a green patina, he said.
Investigators noted that the end of the disconnected cable closest to the site of the explosion did not have a green patina. The cable's copper color was intact, “which is what you expect on a piece of metal if it’s producing hydrogen,” said Spivack. “That cable has been in the water for more than 10 years. Normally, if you threw a penny in the ocean, you would expect it to be pretty corroded. You wouldn’t expect it to be bright copper after 10 years, unless it was protected chemically [by a gas].”
Spivack said test results from sand samples URI scientists collected a week ago showed pockets of extremely high hydrogen levels.
“Up to five percent of the air pressure was hydrogen,” he said. “That’s in the flammable range. And that’s—compared to natural levels that we would observe—that’s about 10,000 times higher than we would expect.”
Spivack said the hydrogen gas was produced deep in the sand, near the site of the blast. It became a combustible gas mixture when it bubbled up to the surface and mixed with air. He said methane levels were undetectable, which ruled out the hypothesis that decomposing seaweed may have produced methane gas.
State officials have not identified the source of ignition, because a hydrogen gas mixture alone would not cause an explosion. DEM Director Janet Coit said the woman who was injured during the blast had been smoking at the beach, but Coit cannot confirm her smoking as the source of ignition.
“First, our concerns are for her wellbeing and our thoughts are with her for a speedy recovery,” said Coit. “We know that she was smoking earlier and if she was smoking right before the incident—we don’t know that. I don’t know that there’s more to say about that.”
Spivack said a very small amount of energy, such as static, can ignite hydrogen. “In industrial hydrogen accidents, a very large number of them—many of them—we never identify the ignition source, because there are so many potential sources and it’s such a low level of ignition that can do it," he said.
Both Spivack and Coit stressed that another hydrogen combustion incident at the beach is very unlikely now that the disconnected cable has been removed.
Coit said state officials swept the beach three times today to look for any other cables and test for hydrogen gas.
“They took 10 samples,” said Coit. “None of them detected any hydrogen. These were machines that detect hydrogen to the .20 percent level. The beach has been trenched, dug, aerated, and we’ve got no concern for public safety.”
Coit said the U.S. Coast Guard typically leaves de-energized cables undisturbed under beaches as a standard practice. She said the state’s priority was to identify the cause of the blast for safety reasons.
The case is now closed, but Coit said state officials will continue to look into whether anyone is liable for the explosion.
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