Hydrogen sulfide: a silent killer

NEEPAWA, Man. Ñ A farmer enters a manure pit located inside a hog barn to clear a clogged pipe. He collapses and his brother, who is standing at the entrance to the pit, goes in to rescue him. Both are later found dead.

In another case, a worker enters a hog barn first thing in the morning, but for some reason stops before opening the door that leads to a room housing pigs. He instead looks through a window and sees that all the hogs appear dead.

In a third scenario, a worker at a hog barn goes into the washroom to clean the toilet and immediately feels dizzy. The worker collapses while trying to leave the washroom. A co-worker sees her and drags her to safety.

None of these stories is fictitious. All have happened at hog barns in Western Canada in the past few years and all were attributed to hydrogen sulfide, a gas known as the silent killer.

Mary Petersen can cite several similar incidents and tragedies related to hydrogen sulfide. Her goal is to prevent more of them.

“Everybody needs to have some awareness of that gas when they work in a hog barn,” Petersen said.

“You don’t want anybody to be knocked down and die of this gas.”

Petersen works at Assiniboine Community College in Brandon and is co-ordinator of training programs for Manitoba’s hog industry.

She held workshops at five communities this month to talk about hydrogen sulfide, how it affects people and ways to prevent serious exposure. The workshops were supported by the Manitoba Pork Council and the Canadian Agricultural Safety Association.

Hydrogen sulfide is considered the most dangerous of the gases commonly created in hog manure storage facilities. The two other common ones are ammonia and methane.

Hydrogen sulfide is created during the breakdown of organic material under anaerobic conditions, meaning there is no oxygen present. Liquid in the slurry keeps oxygen from getting to the organic material, which in the case of hog barns means manure and wasted feed.

Deadly properties

Unlike many other gases, hydrogen sulfide doesn’t bubble off, Petersen said. It remains in the hog barn slurry until the slurry is disturbed. The gas also is heavier than air, so it will stay near the floor or ground if there is no wind or ventilation to disturb it.

During a workshop at Neepawa, Petersen cited the places and circumstances at a hog operation where people are most likely to be exposed to the potentially lethal gas.

The danger arises when the slurry is agitated, such as when the plugs are pulled to release the slurry from pits underneath the pens in hog barns.

“That is one of the most dangerous things,” said Petersen. “Research is saying: pull the plug and get the heck out of there. Don’t stay.”

Other areas of greatest risk are lagoons, pumping stations and separator rooms where solids and liquids are separated. People need to be cautious in those areas, Petersen said, especially when the slurry has been agitated and there is a lack of ventilation or air movement.

She described the manholes leading into pumping stations as “very, very high risk areas.”

With above-ground lagoons, exposure usually occurs when the slurry is pumped into a bulk container tank and a person, for whatever reason, lifts the lid on the tank.

Because the gas tends to stay close to the ground, it is wise to avoid areas downwind of a lagoon when it is being pumped out, especially if it is low-lying ground sheltered from wind by trees or fencing.

“Outside, the gas will go to the low-lying areas,” Petersen said. “If there is no wind, it will just hover there.”

The most common scale for measuring hydrogen sulfide is in parts of gas per million parts of air. Devices can measure hydrogen sulfide in the air and sound an alarm at dangerous levels.

Generally, ongoing exposure to the gas at no more than 10 ppm over the course of an eight-hour work day is considered acceptable for workplace safety, Petersen said.

Once the level of hydrogen sulfide reaches 15 ppm, a person should not be exposed more than 15 minutes. A variety of symptoms can appear, depending on the level of exposure.

At 100 ppm, the gas poses an immediate danger to people.

At 1,000 ppm, a person can be knocked unconscious immediately. Death or permanent brain damage likely will occur if the person isn’t pulled to safety right away, according to Petersen.

One of the perils with hydrogen sulfide is that it typically has the smell of rotten eggs at low levels, but it causes a temporary loss of smell in higher levels. It is colourless so it cannot be seen.

Petersen said hog barn owners and managers need to assess their operations and identify the risks.

Understanding how ventilation affects air movement in the barns is important. It is also critical to identify the “dead air” spaces in a barn where hydrogen sulfide could accumulate.

She noted that an understanding of the overall plumbing could be valuable, as well. For example, some barns are designed so the toilets for humans are linked through plumbing to the pits holding the hog barn slurry. It has happened that the gas backs up through the plumbing and into staff washrooms.

Precautions needed

Precautions should be developed to offset the risks and everyone in the barns needs to know those.

A response plan should be established so people know how to react if someone is exposed.

Several issues need to be covered when developing an emergency response plan. For example, how would one get an affected person out of a place with high levels of hydrogen sulfide without putting other lives in jeopardy?

Would equipment, such as breathing apparatus with an air tank, be needed? Where should that equipment be kept so that it is easily accessible? Should everyone who manages or works at the barns be trained on how to resuscitate someone who has quit breathing or whose heart has stopped?

Will there always be a telephone handy to call for an ambulance or other emergency services?

Having an emergency response plan and backing it up with training could save lives.

“Our natural reaction is to go in and respond and deal with it, especially when a family member goes down,” said Petersen, explaining why exposure to dangerous levels of hydrogen sulfide can result in multiple deaths.

“They aren’t thinking rationally at that point.”

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