Hydrogen sulfide can also be encountered in voids containing decomposing organic materials. In order to work safely around hydrogen sulfide, you must be aware of its properties and characteristics. Hydrogen sulfide has a combination of properties and characteristics that make it a particularly difficult hazard to deal with. It is an extremely toxic gas that can lead to life-threatening conditions if the proper precautions are not taken. The signs and symptoms of exposure vary with the concentration.

Concentrations as low as 10 PPM, or .001% by volume, are considered unhealthy by the Occupational Safety and Health Administration.

Short term exposures to concentrations between 10 and 100 PPM can cause mild eye and respiratory tract irritation, headaches, and nausea. Short term exposure to concentrations between 100 PPM and 400 PPM can cause serious eye and respiratory tract irritation, headaches, severe nausea, and disorientation. 27 min.