It appears that hydrogen sulfide, or H2S, is here for the long haul. This deadly gas has been around for centuries before you and I ever arrived and it will most likely be here long after we're gone. We have learned to regard H2S with cautious respect, and we are able to work in H2Scontaminated atmospheres as long as we adhere to specific safe work practices.
To refresh our memory bank about hydrogen sulfide, this gas most often occurs naturally and is a product of putrefaction or decay of organic materials. It frequently is an undesirable constituent of our oil and gas exploration and refining operations.
The gas itself has a disagreeable odor similar to that of rotten eggs at concentrations below 1 part per million (ppm). Continued exposure to H2S without proper protective equipment will produce a temporary loss of the sense of smell at concentrations above 100 ppm in 3 to 5 minutes. Concentrations above about 500 ppm will render you unconscious almost immediately, and death will soon follow if you are not immediately removed to fresh air and revived. At concentrations above 1000 ppm, one breath is all that it takes to kill you in an instant.
The gas is about 20% heavier than air and will accumulate and concentrate in low-lying places and confined spaces. An uncontrolled flow of a seemingly-safe level of H2S below the threshold limit value (TLV) of 10 ppm has the ability to displace air and create a toxic environment within a very short period of time. As diligent as we are in our efforts to provide a safe working environment, we still continue to lose a significant number of workers to this deadly gas every year. In fact, it is the leading cause of industrial sudden death syndrome. Hydrogen sulfide is a treacherous gas and is not to be trifled with. Utilizing proper engineering controls, personal protective equipment and comprehensive training can enable us to work safely within the realm of H2S's potentially-hazardous threat.
During the analyses of numerous hydrogen sulfide-related fatalities in the early 1980s, a common thread appeared consistent in all cases. That thread was the inconsistency of the H2S safety training that had been conducted in those work environments:
There were apparent deficiencies and variations in the course content and conduct;
The length of the training events varied widely from one course provider to another;
Some instructors, while possessing good presentation skills, failed miserably at conveying the important technical aspects related to H2S;
It was even possible to purchase an annual training certificate without even attending the course!