U.S. Team Blames Carbon Dioxide for Cameroon Toll

The victims of a volcanic gas leak in northwestern Cameroon were asphyxiated by a cloud of carbon dioxide and sulfur compounds that emerged from a crater lake and filled the valley, a U.S. medical team said Monday.

“Basically, the gas cloud replaced the air that they ordinarily breathe,” said Navy Cmdr. Michael A. Clark, chief of forensic pathology at the Armed Forces Institute of Pathology in Washington and a member of the team.

The team’s conclusions, which were labeled preliminary, were arrived at after autopsies on human and animal victims, visits to the stricken area around Lake Nios and interviews with 19 hospitalized survivors. Additional laboratory tests are planned for later in Washington.

On the night of Aug. 21, a geyser of gas shot out of Lake Nios, about 150 miles northwest of Yaounde, and settled in the nearby valley, which is dotted with mud-block houses and grass huts. Officials estimate that 1,500 to 2,000 people died. A more accurate count is not possible because so many were buried in mass graves by volunteers from neighboring villages.

“All victims became unconscious within seconds of gas exposure, dying shortly thereafter of respiratory or cardiac failure,” the medical team said in its report.

Some of the injured residents were unconscious for up to 36 hours after being overwhelmed by the high concentration of carbon dioxide, the report said. Their symptoms--painful rapid breathing, confusion and weakness before fainting and burning eyes, joint pains and stomach upset after awakening--were consistent with lack of oxygen, the doctors said.

The chemical burns suffered by some survivors were caused by “acid formed in the reaction of sulfur compounds with water droplets in the air or ground water,” according to the report prepared by the four-person team.

The experts believe that the hydrogen sulfide that emerged from beneath Lake Nios changed as it moved through the valley.

‘Turned Into Stronger Acid’

“We think the hydrogen sulfide turned into a stronger acid as it became oxidized, turning into sulfur dioxide or even perhaps sulfur trioxide, which is sulfuric acid,” Clark said.

That conclusion was based on the types of injuries suffered at varying distances from the lake. In Nios, only a mile from the lake, where virtually the entire population was wiped out, there were few burns. But as the gas cloud moved farther from the lake, people suffered increasingly severe burns.

The team said it found no evidence that carbon monoxide or hydrogen cyanide were involved in the deaths or injuries.

Clark stressed that the conclusions are tentative and that the results of laboratory analysis could give researchers a clearer picture of the types of gases that were present.

Lake Still Being Studied

Meanwhile, a U.S. scientific team and specialists from other countries continued to study the murky crater lake. They say the incident apparently occurred when the carbon dioxide and perhaps other gases that had collected in a pocket beneath the lake--perhaps for a century or more--were suddenly released.

What actually triggered the release of that bubble, however, remains a mystery, and scientific tests of the lake continue.

Among the possible explanations is that an earth tremor shook the trapped gas and “like a bottle of champagne that’s been shaken up” it burst out, said an Italian volcanologist. So far, however, researchers have found no evidence of seismic activity in the area that night.

Another possibility, scientists say, is that a fissure from deep within the Earth’s crust released the gas. Others suggest that the moment arrived when more carbon dioxide was being added than the pocket, which was under the pressure of hundreds of feet of water, could hold.

Lake 20 Degrees Warmer

The lake, now tranquil and the color of cocoa, is still more than 20 degrees warmer than other crater lakes in the area.

Haroun Tazieff, a French volcanologist, said there is no immediate danger of another such gas leak, “but we shouldn’t let people go back until we have fully analyzed the situation.”

Two years ago, escaping gases from another volcanic lake in the same general area killed 37 people.

A French team is studying other lakes in the area, including Lake Wum, adjacent to a community of 25,000 people about 15 miles from Nios.

“In the future, perhaps we can monitor these lakes and forecast a possible disaster,” Tazieff said.