Health Effects of Hydrogen Sulfide

Hydrogen sulfide (H2S) is an extremely hazardous, toxic compound.  It is a colorless, flammable gas that can be identified in relatively low concentrations, by a characteristic rotten egg odor. The gas occurs naturally in coal pits, sulfur springs, gas wells, and as a product of decaying sulfur-containing organic matter, particularly under low oxygen conditions. It is therefore commonly encountered in places such as sewers, sewage treatment plants (H2S is often called sewer gas), and mines Industrial sources of hydrogen sulfide include pulp and paper manufacturing, rayon textile production, leather tanning, chemical manufacturing, and petroleum refining.

Hydrogen sulfide has a very low odor threshold, with its smell being easily perceptible at concentrations well below 1 part per million (ppm) in air. The odor increases as the gas becomes more concentrated, with the strong rotten egg smell recognizable up to 30 ppm. Above this level, the gas is reported to have a sickeningly sweet odor up to around 100 ppm. However, at concentrations above 100 ppm, a person’s ability to detect the gas is affected by rapid temporary paralysis of the olfactory nerves in the nose, leading to a loss of the sense of smell. This means that the gas can be present at dangerously high concentrations, with no perceivable odor.  Prolonged exposure to lower concentrations can also result in similar effects of olfactory fatigue. This unusual property of hydrogen sulfide makes it extremely dangerous to rely totally on the sense of smell to warn of the presence of the gas.

Key Points for Personal H2S Monitors

• Everyone wears a personal H2S monitor
• Wear your personal H2S monitor on your outer layer of clothing within the breathing zone (the hemisphere forward of the shoulder line and within a 9 inch radius of the nose)
• Test your monitor daily by pushing the blue button
• Treat all alarms as real and evacuate the area immediately
  • Notify the Unit Operator when your personal monitor alarms
  • Have your personal meter read for exposure concentrations and durations to determine your ability to return to work that shift
• Never attempt to assist a coworker that you believe has been overcome by H2S on your own