A research team at Iowa State University (ISU) has developed a wireless hydrogen sulfide (H2S) detector that successfully detects the potentially fatal gas released from manure in deep-pit barns during slurry agitation and pumping events. This project was funded by the National Pork Board.

Lethal concentrations of H2S can develop rapidly and vary spatially in a swine barn during manure agitation and removal.

It is estimated the lost market value of 20 or more hogs to H2S poisoning during slurry agitation would pay for the new detection system in one year.

Personnel should never enter a swine barn during slurry agitation. The Occupational Safety and Health Administration's (OSHA) limit for immediate threat to life is 100 ppm of H2S. Field studies have shown that H2S concentrations can exceed this level quickly during slurry agitation with concentrations recorded as high as 1,300 ppm.

Researchers at ISU have the following objectives for this project to reduce the risk of human or animal fatalities from H2S gas:

1. Develop and test a wireless hydrogen sulfide detection system for use during hog manure agitation and removal;

2. Better establish building ventilation management strategies to increase human safety and maintain animal health during the manure agitation and removal process; and

3. Add to the knowledge base about the development of hazardous conditions due to H2S from manure.

Initially, six commercially available H2S sensors were tested in ISU's Agricultural Waste Management Laboratory.

The prototype consists of a sensor/transmitter and a handheld receiver. The sensor/transmitter is equipped with the H2S sensor, a wireless communication system and battery power. The unit is placed inside the swine barn before agitation begins. The receiver remains outside so the operator can safely monitor H2S gas levels inside the barn. Both an audible and visual alarm are activated when a predetermined H2S concentration is detected.

The prototype matched performance of a research grade H2S analyzer.

To better understand H2S burst formation and distribution in swine facilities, the prototype system was used to detect concentrations at various locations in a swine finishing facility. While using surface agitation with splashing (agitation that disturbs the slurry surface), measurements were collected simultaneously from the pit below the slats and just above the slats in the same location. The use of stir fans equalized H2S concentrations above and below the slotted floor. By using stir fans, the operator can obtain a representative sample of room gas levels using a single point detection system.

H2S gas levels from above and below the slats in the same location can be collected during subsurface agitation (no disturbance of the slurry surface). While H2S concentrations were detected below the slats, no measurable H2S concentrations were detected above the slats. These results suggest that subsurface agitation should be used whenever possible to minimize H2S burst releases.

In a third test, H2S gas data was collected simultaneously from different areas within the barn just above the slats. In less than 10 minutes after vigorous surface agitation, the H2S gas concentration had exceeded the maximum range of the gas detector (500 ppm), demonstrating the dangers of H2S gas emissions during slurry agitation.

Researchers: Ross Muhlbauer, Randy Swestka, Robert Burns, Hongwei Xin, Steve Hoff and Hong Li, all of Iowa State University. Contact Burns by phone (515) 294-4203, fax (515) 294-4250 or e-mail rburns@iastate.edu.