Hydrogen Sulfide and Manure Safety

In the last month, we've had two tragic accidents related to manure and repairs in a barn. In both cases, a father and son were working on some repairs in the barn near the manure. One of the two either then passes out and falls in the manure or enters the manure and passes out. The other then dives in to attempt to pull the other to safety; neither survives. These are tragic reminders that on the farm we need to think about safety every day in all our activities, especially those dealing with manure.

The decomposition of organic matter in manure results in the release of several gases, ammonia, carbon dioxide, methane, and hydrogen sulfide among them. Although all are potentially dangerous, hydrogen sulfide tends to be the one of most concern in these cases. Hydrogen sulfide has an intense rotten egg smell, so it is relatively easy to detect its presences, even in very low concentrations. However, after breathing it for a short time your sense of smell will become fatigued and you lose the ability to detect it. Just as importantly, since we can smell it at such low levels, there is not a clear indication of when it reaches a potentially hazardous conditions that we can detect without the use of analytical instruments.

In many animal housing facilities, the manure pit is often located below the facility floor. Within these buildings these gases are generally detectable in low concentrations throughout the year; however, under some conditions, such as manure agitation, the gases can be released rapidly from the manure and reach potential toxic levels for people and animals. Even in other systems, where the manure is stored outdoors, toxic levels of hydrogen sulfide can result near and in the manure storage under certain conditions; mostly limited to periods of manure disturbance such as agitation.

Generally, we use the barns ventilation system to try to control the level of these gases within the barn. Barn ventilation systems can be relatively complex, they consist of a controller that monitors temperature (and potentially other variables) within the barn and  then turns on and off banks of fans,  raise or lower ventilation curtains, and control when heaters run. Although ventilation systems can run in numerous ways, a common system in the US is the use of pit fans to provide minimum ventilation requirements, end wall fans for more ventilation, and then sidewall curtains that can be brought up and down to let a breeze blow through the barn and facilitate greater air exchange.

Example of a typical swine barn in Iowa. You can see the barn has an end wall fan for ventilation and is curtain sided. Curtains are raised and lowered to control the barns ventilation. What you might not immediately notice is that underneath the curtain there are a series of pump-out ports (see the lower right of the picture).

The pit fans provide minimum ventilation requirements for the animals and run almost continuously to help draw ammonia, methane, carbon dioxide, and hydrogen sulfide produced by the manure within the barn.

In the last few years we have been seeing higher sulfur levels in our manure. For example, swine manures used to average about 3 lbs sulfur per 1000 gallons of manure, but recent sample collection from 70 farms within Iowa showed we are currently averaging closer to 9 lbs of sulfur per 1000 gallons. This means our potential for larger sulfur releases are higher and to keep everyone (and pig safe) we will have to put a greater focus on safety.