Overview
Hydrogen sulfide is a colorless, flammable, extremely hazardous gas with a rotten egg smell. The gas occurs naturally in crude petroleum and natural gas and can be produced by the breakdown of organic matter and human/animal wastes such as sewage. The gas is heavier than air and can collect in low-lying, enclosed and poorly ventilated areas such as basements, manholes, sewer lines and underground telephone/electrical vaults
Detection by Smell
Can be smelled at low levels, but with continuous low level exposure or at higher concentrations you lose your ability to smell the gas even though it is still present.
At high concentrations, your ability to smell the gas can be lost instantly.
DO NOT depend on your sense of smell to detect the continuing presence of this gas or for warning of hazardous concentrations.
Safe Work Practices
Before Entering Areas With Possible Hydrogen Sulfide
The air needs to be tested for the presence and concentration of hydrogen sulfide by a qualified person using test equipment.
This individual also determines if fire/explosion precautions are necessary.
If gas is present, the space should be ventilated.
If the gas cannot be removed, use appropriate respiratory protection and any other necessary personal protective equipment, rescue and communication equipment.
Atmospheres containing high concentrations that are greater than 100 parts per million are considered immediately dangerous to life and health and a self-contained breathing apparatus is required.