Hydrogen sulfide stinks. Some describe its stench as reminiscent of “rotten eggs.” However, this odor is not the gas’s only characteristic. The odorless H2S is flammable and poisonous. In a mysterious blend of fortune and misfortune, the rotten egg odor of hydrogen sulfide goes away as its concentration heightens. Its subsiding smell, however, does not indicate a reduction of its hazards. For this reason, OSHA advises not to depend on your sense of smell for indicating the continuing presence of hydrogen sulfide gas.
Of course, standardization has long provided an alternative to depending on one’s insticts. The American National Standard ANSI/ASSP Z390.1-2017 sets forth accepted practices for hydrogen sulfide training programs. Please note that this document was formerly known as ANSI/ASSE Z390.1-2017, but, with the American Society of Safety Engineers changing its name to the American Society of Safety Professionals in June 2018, the document’s title has been updated.
In other words, ANSI/ASSP Z390.1-2017 and ANSI/ASSE Z390.1-2017 are the same thing.
Where Hydrogen Sulfide (H2S) Comes From
Naturally, hydrogen sulfide occurs in volcanic gases and hot springs, as well as in crude petroleum and natural gas. H2S results from the bacterial breakdown of organic matter. On a grander scale, hydrogen sulfide is a central participant in the sulfur cycle, the biogeochemical cycle of sulfur on Earth. As such, H2S arises from basically anywhere where elemental sulfur comes into contact with organic material, especially at high temperatures. It often can be found in places where bacteria break down organic matter in the absence of oxygen, such as swamps.
Hydrogen sulfide is found in industrial environments as well, resulting from food processing, coke ovens, kraft paper mills, tanneries, and petroleum refineries. In society, alongside the process of anaerobic digestion, hydrogen sulfide can be found in sewers. Because it is heavier than air, it tends to accumulate at the bottom of poorly ventilated areas.
The Effects of Hydrogen Sulfide (H2S) on the Human Body
Commonly known as hydrosulfuric acid, sewer gas, and stink damp because of its qualities, the health effects of exposure to H2S vary depending on the timeframe and intensity by which an individual is exposed to the hazardous gas.
At lower concentrations, during which the odor of rotten eggs is prevalent (the odor threshold is technically 0.01-1.5 ppm, but smell becomes more offensive around 3-5 ppm), those exposed can experience an irritation of eyes, nose, throat, or respiratory system. These effects can be delayed.
At moderate concentrations, the exposed can experience more severe eye and respiratory effects, as well as headaches, dizziness, nausea, coughing, vomiting, and difficulty breathing. Around concentrations of 50 ppm, slight conjunctivitis (“gas eye”) and respiratory tract irrigation can take place after one hour. These concentrations are also when the rotten eggs odor diminishes.
At high concentrations, the exposed are prone to shock, convulsions, the inability to breathe, coma, and even death. Of course, as concentrations increase, these effects become more rapid. Around 100 ppm, loss of smell (olfactory fatigue) can occur after 2-15 minutes, and death can occur after 48 hours of exposure. Around 500-700 ppm, the exposed can collapse within 5 minutes, serious damage to the eyes can occur within 30 minutes, and death can happen within less than one hour.
Around 1000-2000 ppm, the exposed will face nearly instant death.
The ANSI/ASSP Z390.1-2017 (ANSI/ASSP Z390.1-2017) American National Standard
There long existed a need to adequately prepare personnel for work environments in which the presence of hydrogen sulfide is probable. Historically, however, H2S training was addressed only by a handful of industries, and the criteria for these training programs varied between sectors.
ANSI/ASSP Z390.1-2017 has its origins in the early Nineties. It was purposed with offering criteria for hydrogen sulfide training programs that could apply to all industries.
The accepted practices set forth by this standard in instructing affected personnel include the minimum informational content of the course, recommended exercises and drills, properties and characteristics of H2S, sources of H2S and areas of potential exposure, typical site-specific safe work practices associated with H2S operations, detection methods for H2S, engineering/mitigation controls, safe work practices for sulfur dioxide (SO2), care of personal protective equipment suitable for atmospheres containing H2S concentrations above the applicable exposure limit, rescue techniques and first aid procedures for victims of H2S exposure, and H2S safety instructor qualifications.
Please note that this American National Standard features guidelines designed specifically to provide workers with the fundamental knowledge necessary to protect themselves from hydrogen sulfide exposure, and it does not include information necessary to providing respiratory protection for personnel.
Respiratory protection in the United States is legally required to comply with OSHA Respiratory Protection 29 CFR 1910.134. Further guidance can be found in the voluntary consensus American National Standard ANSI/ASSE Z88.2-2015: Practices for Respiratory Protection (otherwise known as ANSI/ASSP Z88.2-2015).
ANSI/ASSE Z390.1-2017: Accepted Practices for Hydrogen Sulfide (H2S) Training Programs is available on the ANSI Webstore.