Deadly Gases Hidden Hazards in Manure Pits

By Ron Johnson
Thursday, September 6, 2007 5:42 PM CDT

Dairy Editor

This past July, gas from a manure pit killed five people on a Virginia dairy farm. First, the farmer entered the pit to unplug a pipe. Next, his wife and two young daughters died when they tried to rescue him. Last, the gas killed a farm employee who tried to help.

Presentations on the hidden hazards of manure gases were part of the recent Upper Midwest Manure Handling Expo at Prairie du Sac. Cheryl Skjolaas, agricultural safety specialist with the UW Center for Agricultural Safety and Health, talked about methane, hydrogen sulfide, carbon dioxide and ammonia.

Methane, also known as CH4, is not a toxic gas, Skjolaas began. Still, it is an asphyxiant and can cause rapid breathing, dizziness and fatigue.

It’s also highly flammable, meaning a spark from equipment, poor wiring, or welding can set it off. Methane can’t be detected without specialized equipment, since it has no color and no smell. Even though methane is lighter than air, it can still replace the normal atmosphere in a confined space, such as a manure lagoon or pit.

By contrast, carbon dioxide (CO3) is heavier than air. It will also replace the oxygen in a confined space.

Breathing a large concentration of carbon dioxide can cause a headache and dizziness. If the concentration of carbon dioxide is great enough, it too, can kill, Skjolaas warned.

Ammonia, meanwhile, has what Skjolaas described as a “sharp, pungent” odor. It’s lighter than air and can irritate eyes and the respiratory tract.

What’s more, ammonia can permanently damage the lungs. At 1,000 parts per million or more, it can kill. Ammonia, the safety specialist noted, is usually highest in poultry manure.

The last of the frightening four manure gases is hydrogen sulfide (H2S). A manure pit or lagoon might not contain much hydrogen sulfide all the time, but agitating the manure can boost the H2S level a thousand times, Skjolaas said.

Hydrogen sulfide is “extremely toxic,” she warned. Three things make it especially dangerous.

First, hydrogen sulfide has no color, so it can’t be seen. Second, it’s heavier than air, meaning it sinks to the bottom of a manure storage structure, so a farmer or employee might enter and step down into the gas.

Third, hydrogen sulfide can kill in seconds if the concentration is high enough. Skjolaas said death can quickly occur if the gas is present at 1,000 parts per million.

Many people know hydrogen sulfide by its “rotten egg” smell. But people can’t detect the smell of hydrogen sulfide at higher concentrations.

But there can be other warning signs of the presence of hydrogen sulfide. They include a headache, eye and nose irritation, nausea, and dizziness.

False security

It can be easy to gain a false sense of security about manure pits. Sometimes there are no problems associated with entering them. Trouble is, the next time could prove deadly.

“The most serious problems with gases occur when manure is agitated or when ventilation systems fail,” Skjolaas said. “Gases are constantly being produced, so there is never a ‘safe’ time to enter a pit.”

To prevent deaths from manure pit gases, she offered several suggestions.

First, before agitating the manure in a pit, remove all the animals and people that are in the building that’s over it. Agitating, Skjolaas reminded, speeds the release of gases in the liquid manure.

Second, ventilate the pit when manure is being agitated or pumped. But don’t stop when pumping or agitating stops. Keep ventilating the pit several hours afterward.

Third, don’t smoke or use any other source of fire or ignition around a manure pit. A mix of methane and air can be highly explosive, and methane is more explosive when it’s under 10 parts per million.

If it’s “absolutely necessary to enter a pit,” follow these precautions, the safety specialist said.

First, ventilate the area thoroughly. Keep the ventilation going while people are working in the pit.

This ventilation should be by a “powered” air supply. That is, use fans or blowers to force fresh air into the pit.

It also needs to include an air exhaust - a way for the gases to escape from the pit. Remember to leave at least five feet between a manure pit’s opening and a gasoline-powered blower.

Next, wear self-contained breathing equipment. This means using equipment that includes an oxygen tank. Cartridge respirators and dust masks simply will not do the job.

Monitor conditions in the pit before anyone enters it. Use a “four-gas monitor” - one that can detect methane, hydrogen sulfide, ammonia and carbon dioxide.

Normal air contains 21 percent oxygen. But 19.5 percent is the minimum safe oxygen level. If a pit’s air contains less than 19.5 percent oxygen, judgment and coordination will be impaired.

Anyone who is going to enter a manure pit should wear a safety belt or harness that has a lifeline. Attach the lifeline to some sort of mechanical lifting device.

Finally, make sure at least one person stays out of the pit. This person should be in constant contact with the people in the pit.

What’s more, this extra person should be ready to lift out the people who are in the pit, or begin a rescue operation.

Don’t select just anyone for this standby position. His or her job is very important.

“This person should know the hazards and symptoms (of manure pit gases) and be aware of the behavioral effects of exposure,” Skjolaas said. “It’s important that this person be ready to summon rescue (assistance) but not try to rescue the worker. More than 50 percent of confined-space fatalities are to people who attempted to rescue someone.”

Think, don’t go in

With a manure pit or any confined space, apply this rule, said the safety specialist: “If someone is down, think. Call ‘9-1-1,’ but don’t go in.

Comments »

Comment on this story

Comments will be approved within 48 hours

Name:

Email: (optional)

Comments:

Image Verification: (Case sensitive)