Ag United News

Use of hydrogen sulfide analyzer takes knowledge

September 11, 2005 Sioux Falls Argus Leader

READER'S FORUM
Steve Dick, 44, is the executive director of Ag United for South Dakota in Sioux Falls.

A recent Argus Leader article, "Feedlot opponents travel to test odors," discussed the use of a hydrogen sulfide analyzer near livestock operations in South Dakota. Although involved with South Dakota's agricultural production, even I had questions about the testing process.

Information from South Dakota State University professors Dick Nicolai and Steve Pohl from the Agricultural Engineering department helped to answer the questions I had about this process.

Hydrogen sulfide is a colorless gas, formed as the result of the breakdown of organic matter (in this case, animal waste) in the absence of oxygen. In high concentrations, it has the possibility of affecting health, which is why some states monitor levels in the air.

The professors said it is critical to understand that hydrogen sulfide analyzers measure all reduced sulfur in the air, not just hydrogen sulfide. While hydrogen sulfide makes up the majority of reduced sulfur, the analyzer cannot separate it from other sulfur sources.

They also were able to explain how the analyzer works. A handheld hydrogen sulfide analyzer takes an air sample and filters it across a gold film. The film attracts the sulfur in the sample, changing the film's electrical resistance. The change can be measured and converted to reflect the level of hydrogen sulfide in the air at that place in that moment. It's called a "grab sample."

They explained that a handheld hydrogen sulfide analyzer can measure and detect levels down to 1 ppb. At that level, most analyzers have an accuracy of plus or minus 5 percent, but the accuracy increases with the concentration of hydrogen sulfide in the air.

To maintain the accuracy of the analyzer, they said, it must be sent to the manufacturer annually for calibration. It also must be cleaned, or regenerated, after daily use. The regeneration process cleans the gold film of any remaining sulfur. Failure to properly maintain the instrument can cause sulfur buildup on the gold film that can corrupt future readings.

The professors at SDSU also were able to explain more about the Minnesota regulations cited in the article related to hydrogen sulfide levels. Testing is done on a complaint basis, and a violation does not occur from a single grab sample. State law requires the levels be measured continuously to establish an average for a 30-minute period. A violation occurs when a half-hour average of 30 ppb is exceeded twice in one week, or a half-hour average of 50 ppb is exceeded twice in one year.

As with any scientific data, I have learned it is important to understand the conditions of the environment where hydrogen sulfide levels were tested and how those results are presented.

Hydrogen sulfide analyzers are complex instruments, and the most accurate results will come from people trained in when, where and how to use and maintain them.

For more information, see: www.argusleader.com/apps/pbcs.dll/article?AID=/20050911/OPINION03/509110314/1006/ARCHIVE