Hydrogen sulfide the invisible killer in hog manure

Kevin.Schulz, senior content specialist

September 18, 2015

5 Min Read
Hydrogen sulfide the invisible killer in hog manure

An invisible killer lurks in hog barns and producers need to step up their defense against it. Harsh reminders in the form of news reports this summer of an Iowa father and son falling victim to manure pit gases reinforce the need for producers to be vigilant about safety around manure pits.

According to news reports, the son went into the pit to retrieve a piece of equipment that had fallen into the manure. After noticing the son had become overcome by gases, the father came to the rescue. He also was overcome by gases. Both men died. That report came on the heels of another father and son, these from Wisconsin, who met the same fate. 

A number of gases are created in a manure pit – ammonia, carbon dioxide, carbon monoxide, methane – but hydrogen sulfide is by far the deadliest. Though it does give off an intense rotten-egg small, it doesn’t take much of it to overcome a human, and the matter is only getting worse.

Daniel Andersen, Iowa State University assistant professor in the College of Engineering and College of Agriculture and Life Sciences, says the sulfur levels in hog manure have increased due to hog farmers becoming better at water conservation, thus not as much manure is being created, but he points to a larger culprit in the introduction of dried distillers grain into swine diets.

About 10 years ago, manure had about 3 pounds of sulfur in 1,000 gallons of manure; now that number is pushing 9 pounds. Andersen says processing of the corn in ethanol plants increases the sulfur level in DDGS two to two-and-a-half times compared to the sulfur levels in corn. “So when you substitute corn for DDGS in the swine diet, you are going to end up with higher sulfur content,” Andersen says. In the ethanol milling process as carbon is removed, the sulfur remains, but in a more concentrated level, “so there isn’t a lot that we can do” to abate the situation, Andersen says.

Caution when agitating

Hydrogen sulfide is heavier than air so it hovers near the manure surface, so Andersen says that for the most part producers and pigs are safe to be in the barns. The problem arises when a producer needs to work near the surface of the manure, or when the manure is agitated. “If a producer has to do some maintenance near the manure level, then we need to take special precautions,” Andersen says, such as having the barn’s ventilation fans turned to maximum air flow or having the luxury of a breezy day for a natural-ventilated barn. Andersen also warns hog producers with lagoon manure storage to not get lax with safety, as hydrogen sulfide still exists and can be just as deadly.

Pigs are just as susceptible to hydrogen sulfide as humans, and Andersen suggests that producers closely monitor the pigs during the manure agitation process, if it is impractical to move the pigs out of the barn. “I’ve heard the death loss of pigs during manure agitation is something like 1%,” he says, but admits it may be an all-or-nothing situation – some barns will have total loss, while other barns will have no losses. “Producers need to monitor the pigs in the barn during manure agitation,” he says. Since producers should not enter barns during agitation, they need to rely on their ears. “If the pigs start squealing more they may be in stress, or if they stop squealing, they may be under stress due to hydrogen sulfide.”

To help minimize hydrogen sulfide release, Andersen suggests that producers be sure that the agitation nozzle is below the manure’s surface, and to adjust accordingly as the manure level lowers as the pit, or lagoon, is emptied.

Naturally ventilated barns and barns with good fan ventilation can improve the situation, by diluting the concentration of the noxious gas. Andersen says an 8 to 10 mph wind is best, but, of course, one cannot always rely on Mother Nature to assist when pits are being pumped.

Andersen recommends producers invest in, and wear, personal hydrogen sulfide detectors. “These can be worn, best on the collar, so it’s close to where you would be breathing the gases,” he says. These detectors can be set to go off when the gas reaches the 10 to 50 ppm levels, but Andersen says hydrogen sulfide levels can be 500 to 1,000 ppm at the manure surface. At those higher levels, only a breath or two can be fatal. A personal detector worn on the producer is recommended versus a detector mounted somewhere in the barn, since the hydrogen sulfide levels will not be consistent throughout the building and at various heights.

Andersen says the only acceptable air mask when working in a hydrogen sulfide environment is a properly fitting self-contained breathing apparatus, and not to trust anything less than that.

Danger outside barns

Danger from hydrogen sulfide is not isolated to inside the barns, as ventilation fans do their part to remove the gas while the manure is being agitated, so Andersen warns producers to be aware of where they are walking near their barns, and to avoid walking too close to these fans. He also recommends avoiding the downwind side of the barn or “dead-air zones” between barns when pit manure is being agitated.

As mentioned before, hydrogen sulfide hovers near the manure surface and is released during the agitation process, thus Andersen suggests to allow at least a foot to foot-and-a-half of head space between the manure surface and the pigs before starting agitation. “If you don’t have that amount of space, just straight pump out the manure before you start to agitate the manure,” he says.

Neutralizing hydrogen sulfide

So, is there anything a producer can do to eliminate or at least reduce the amount of hydrogen sulfide in their hogs’ manure? Andersen says there are some put additive products claiming to reduce hydrogen sulfide levels in manure, but he isn’t confident to endorse any of them. That may soon change as he and some ISU colleagues will begin studying some of these products this fall with results anticipated by next spring.

In the meantime, he says some producers have reported good luck with adding tannins (a natural enzyme in plants) or sodium borate to their pits to remove hydrogen sulfide. 

Andersen addresses the issue in his July 28 Manure Scoop blog. 

Access the National Pork Board's "safe Manure Removal Policies" fact sheet by clicking here.

About the Author(s)


senior content specialist, National Hog Farmer

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