Lake Nyos, Cameroon, surrounded by lush green vegetation
In 1986, Cameroon’s Lake Nyos released a cloud of carbon dioxide that killed over 1,700 people. Credit: iStock/Fabian Plock

Volcanoes belch out copious amounts of carbon dioxide, but gases linked to volcanic activity can also percolate up through the ground. And that can be disastrous: On the night of 21 August 1986, a cloud of carbon dioxide escaped from the waters of Lake Nyos, a crater lake in a notoriously volcanic region of Cameroon. The cloud engulfed a nearby village, suffocating over 1,700 people.

Researchers now have studied another case of poisoning from volcanic gases, this time at a country club near Rome, Italy. By measuring fluxes and concentrations of carbon dioxide and hydrogen sulfide, geoscientists have reconstructed the conditions of the accident, which killed one man and left another with permanent brain damage.

Out of Sight, Out of Mind

An environment composed of as little as 4% carbon dioxide is “immediately dangerous to life and health.” Such levels can easily be attained when volcanic gases travel upward through fissures in Earth and collect near the surface.

Carbon dioxide is an odorless, tasteless gas that makes up roughly 0.04% of the atmosphere. “It’s something you breathe out,” says Anna Hansell, an environmental epidemiologist at the University of Leicester in the United Kingdom not involved in the research. “You don’t really think about it too much.”

But higher levels can be lethal to humans: The National Institute for Occupational Safety and Health defines an environment composed of as little as 4% carbon dioxide as being “immediately dangerous to life and health.” Such levels can easily be attained when volcanic gases travel upward through fissures in Earth and collect near the surface.

Central Italy is punctuated with volcanic vents, calderas, and cones. “The Rome region is located right between two volcanoes,” said Franco Barberi, a volcanologist at Italy’s National Institute of Geophysics and Volcanology.

In 2005, a geological investigation of a country club located roughly 50 kilometers south of Rome revealed anomalously high fluxes and concentrations of soil-based carbon dioxide, hydrogen sulfide, and hydrogen gas. Despite the fluxes being far higher than could be explained by biological processes, no precautions were taken. The country club continued to operate uneventfully for 6 years, but that all changed in the fall of 2011.

Slumped to the Floor

In late August and early September of that year, the club drained its pool and adjoining balance tank—used to collect overflow water—for cleaning. On 5 September, four men descended into the basement balance tank, which had been closed to outside air for over 60 hours. The men immediately lost consciousness and slumped to the floor, where they remained until fire brigade personnel pulled them out about three quarters of an hour later. Two of the men recovered completely, one suffered brain damage affecting his movements and speech, and one died after being in a coma for nearly a year.

Barberi led a team of scientists who rushed to the scene of the accident to determine the geophysical conditions at the country club. “A few hours after the intervention, we were on site,” said Barberi. Working around the country club, the researchers made measurements of gas fluxes and concentrations. They found soil carbon dioxide fluxes in excess of 890 grams per square meter per day—roughly 25 times higher than what’s expected from microbial processes. Carbon dioxide concentrations in the soil, measured using a steel probe inserted to a depth of 50 centimeters, were as high as 92%.

The scientists also collected data from within the roughly 4- × 2- × 3-meter balance tank, which connects to the swimming pool via two tubes. To mimic the conditions of the accident, they closed the tank and found that concentrations of carbon dioxide and hydrogen sulfide increased over time to lethal levels. To determine from where the gas was entering the balance tank, they sealed the tubes leading from the pool. Bingo! The levels remained low.

But a mystery still remained: Where was the gas coming from before it entered the tubes?

From the Deep

To answer that question, Barberi and his collaborators measured gas concentrations near the country club’s empty swimming pool. They found that holes near the perimeter of the pool—which housed lights and boreholes anchoring the pool’s stairs—exhibited very high concentrations of carbon dioxide and hydrogen sulfide. These gases, originally emitted in magma chambers deep below Earth’s surface, were conveyed via the overflow channels flanking the pool’s longer sides, the researchers surmised. They were then transported into the balance tank via tubes, and dangerous levels built up when the tank was closed prior to cleaning, the team concluded.

These results were published this month in GeoHealth.

“Similar accidents will unfortunately occur again in the future.”

After remaining shuttered for over a year, the country club reopened in late October 2012. Safety measures, including the addition of a forced-air ventilation system and daily monitoring of carbon dioxide and hydrogen sulfide levels, were put in place. That same year, a regional decree was enacted requiring carbon dioxide fluxes and concentrations to be measured at new construction sites. That’s a step, said Barberi, but it’s not enough. “There are many buildings already erected in risk zones.”

This region is a hotbed of volcanic activity, and this incident isn’t likely to be the last, he added. “Similar accidents will unfortunately occur again in the future.”

—Katherine Kornei (@katherinekornei), Freelance Science Journalist


Kornei, K. (2019), Lethal volcanic gases at an Italian country club, Eos, 100, Published on 21 November 2019.

Text © 2019. The authors. CC BY-NC-ND 3.0
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