On a Saturday afternoon in May 1966, five men lost their lives, wives lost their husbands, and twenty children lost their fathers. Consider it a cautionary tale about the lethal danger of hydrogen sulfide. The confined space was a cistern fed by a 300-foot deep water well and the gas apparently occurred naturally in the ground.

The accident was reported as far away as Sidney, Australia via Associated Press wire service.
From the Ludington Daily News:

“The accident occurred shortly after 5 p.m., Saturday when Bowman, a maintenance worker, entered the cistern, used for storing water, to install a new float valve. He lowered himself to a platform about six feet below the two-foot opening at the top. Suddenly, he was enveloped in gas, apparently released from the sulfur water in the cistern. Forrest Anderson Jr., company manager, said he was inside the plant when James Howell, a man working on the surface with Bowman screamed.

Rumler, who was in the plant, heard the cry and ran to the manhole over the cistern. Seeing Bowman, he jumped down to the platform, was overcome by gas, and fell into the 12 feet of water at the cistern’s bottom.

The same fate befell Van Steenkiste.

Flores, who heard sirens from across the street, ran to help…Flores said “I can swim” and jumped into the cistern. He, too, was felled by the gas.

Fire Chief Filter, alerted by State Police in Blissfield, arrived at the scene and donned a gas mask. He descended into the hole with a rope. Gas apparently seeped into his mask and he “just went limp” when he reached the platform…

In trying to pull him up, the line slipped over the chief’s head, pulling off his mask…Other firemen pulled the bodies up with grappling hooks.

Anderson said he believed the gas was emitted from the cistern’s water, which he said contained high sulfur content

Riga, Michigan is a tiny village in Lenawee County, about 20-miles northwest of Toledo, OH. Geologically, there are glacial lacustrine sediments overlying fractured limestone and shale bedrock. Rural water wells are typically drilled into the bedrock and have slow yields. During summer, many of the wells run dry.

The nearby village of Blissfield, where I live, uses water from the River Raisin, and it is a common site to see rural residents hauling trailers with plastic tanks to fill up with town water.

“Rapidly acting systemic poison”
The Center for Disease Control describes the toxicity of hydrogen sulfide as “a rapidly acting systemic poison which causes respiratory paralysis with consequent asphyxia at high concentrations. Inhalation of high concentrations of hydrogen sulfide… may cause coma after a single breath and may be rapidly fatal.”

An insidious aspect of hydrogen sulfide poisoning, which smells like rotten eggs, is olfactory fatigue. Above a certain concentration, the gas knocks out the sense of smell. A victim might think they’ve moved out of the gas when, in fact, they’ve become engulfed by a higher concentration.

Hydrogen Sulfide is “heavier” than air
More correctly, hydrogen sulfide is more dense than air at a given temperature and pressure.

To compare the density of a gas to that of air, one needs to determine the molecular weight (mass) of the constituent elements of the gas compared to that of air, which is a mixture of mostly oxygen and nitrogen.

Molecular Formula of Hydrogen Sulfide =
2(H) + 1(S) = 2(1g) + 1(32g) = 34 grams per mole

To keep things simple, consider air to be a 21/79 percent mixture of oxygen/nitrogen, which are both diatomic:
Molecular weight of Air:
2(O) = 2(16g) X 0.21 = 6.72 grams per mole
2(N) = 2(14g) X 0.79 = 22.12 grams per mole
Molecular weight of air = 6.72 + 22.12 = 28.84 grams per mole (approximately).

Because of its higher density, hydrogen sulfide can collect in pits, tanks, and even topographic depressions when winds are calm. Hydrogen sulfide is produced by sulfur-reducing bacteria in sewers, wells, and manure pits. It is a common occurrence in oil and natural gas wells and many industrial processes.

This tragedy was devastating to the community, which I don’t think has fully recovered. In 1994, a group of citizens of Riga wrote and produced a “History of Riga, Michigan” to commemorate the town’s sesquicentennial. Not one word of the accident was included. I first heard of it from one of the surviving firemen who responded to the scene: “That was a bad night. It all happened so fast.”

Safety first.

For more information:
OSHA Confined Space Information

NIOSH Confined Space Information