The Effects of Humidity on H2S Sampling

Hydrogen sulfide, or H2S, is a toxic chemical asphyxiant that is very hazardous to those who come into contact with it. While colorless, small amounts of hydrogen sulfide can be identified by an odor that is similar to a rotten egg. A flammable gas, this compound also is known as sewer gas as it is found in sewage treatment plants, mines, manure stockpiles, sewers and hot springs. Due to the dangerous nature of this gas, it is necessary to sample areas where it is prevalent to ensure people are not exposed to hydrogen sulfide. When taking air samples to test for hydrogen sulfide, potential complications can arise depending upon the humidity levels in the air that are present during the sample.

Hydrogen Sulfide Exposure Complications

• There are three distinct levels of hydrogen sulfide exposure. Each of these levels has it's own health complications. Low exposure, which ranges from 0-10 parts per million (ppm) in the air, causes a person to have irritation in the throat, eyes and nose. Moderate exposure occurs when levels are in between 10-50 ppm. Symptoms of moderate hydrogen sulfide exposure include nausea, vomiting, dizziness, headache, labored breathing and coughing. High levels of hydrogen sulfide exposure range from 50-200 ppm. The effects of high exposure include shock, convulsions, coma, severe respiratory track infections, eye infections and death.

Sampling Procedure

• The Department of Labor's Occupational Safety & Health Administration designates the procedure for testing for hydrogen sulfide in the workplace. According to OSHA, testing for hydrogen sulfide in workplace air requires trained professionals to use specialized sampling pumps that are made with silver nitrate coated silica gel to draw samples. Any hydrogen sulfide present in the air will react to the silver nitrate in the sampling pump and form silver sulfide. Hydrogen peroxide is applied to these samples to form a sulfate. These samples are then reviewed through the scientific process of ion chromatography, which measures the concentrations of ionic species based upon their reaction with a specific resin. In the case of hydrogen sulfide, the silver nitrate layers within the pump is the resin that is test area the conductivity detector, otherwise known as the sampling pump.

Humidity and Sampling

• Humidity, or the amount of moisture in the air, can present challenges when attempting to take a sample of air to test for hydrogen sulfide. Problems can arise when hydrogen sulfide levels are high and the humidity levels in the air are low. During these conditions, the front section of the sampling pump has reduced capacity to take in outside air. The back section of the sampling pump must take on additional air. This has the potential to skew the results of the sample because the reading of the air that's taken is imbalanced within the pump itself. If the front section has reduced capacity, the air cannot properly flow through the sampling pump. This complication can cause discrepancies with test results.

Average Humidity Levels

• According to OSHA, the best humidity levels for hydrogen sulfide air testing is at 78 degrees. In addition to constant humidity levels, hydrogen sulfide testing is also most successful with the air is contaminant free. With minimal interferences, these samples will be the most accurate in checking the air quality of the area in question.