Toxic Gas Detection: Prevent Deadly H2S Hazards in the Workplace

If you think your nose and a pair of fast running shoes will protect you from the dangers of H2S on the job, you could be dead wrong in a hurry. That rotten egg smell that comes from Hydrogen Sulfide (H2S) gas can be quickly over-powering and immobilizing in less than a minute. In the worst situations, you’ll have precious little time to recognize the danger and even make the right decision to flee a contaminated work area. That’s why General Monitors continues to provide the industry’s most advanced line of reliable fixed H2S gas detectors, including detectors suitable for SIL applications.

Understanding H2S Gas
In nature, hydrogen sulfide is produced by decaying organic matter and is released from crude petroleum, sour gases, hot sulfur springs, salt mines and natural gas. It is a by-product of many industrial processes, including: petroleum refining, mining, paper mills, iron smelters, coke ovens, food processing plants and tanneries. H2S is a colorless, flammable, and highly toxic gas. It is shipped as a liquefied, compressed gas. It has a very noticeable rotten-egg odor. Inhalation is the major route of hydrogen sulfide exposure and can be deadly in high concentrations.

Standards and Guidelines
The various agencies have set the following H2S exposure standards:
OSHA Permissible Exposure Limit
  (PEL) = 20 ppm (if no other exposure occurs in an
  8-hour work shift)
NIOSH Recommended Exposure Limit
  (REL) = 10 ppm for 10 minutes
NIOSH Immediately Dangerous to Life or Health
  (IDLH) = 100 ppm
AIHA ERPG-2 (emergency response planning
  guideline) (maximum airborne concentration
  below which it is believed that nearly all
  individuals could be exposed for up to 1 hour
  without experiencing or developing irreversible or
  other serious health effects or symptoms which
  could impair an individual's ability to take
  protective action) = 30 ppm.

Exposure Symptoms
According to the U.S. Government’s Agency for Toxic Substances & Disease Registry, H2S gas is rapidly absorbed in the lungs. Hydrogen sulfide is slightly heavier than air and may accumulate in enclosed, poorly ventilated, and low-lying areas.

The odor threshold (0.5 ppb) is much lower than the OSHA ceiling (20 ppm). Although its strong odor is readily identified, olfactory fatigue occurs at high concentrations and at continuous low concentrations. The ability to smell H2S can begin to dull at 50 ppm and can be completely lost. For this reason, odor is not a reliable indicator of hydrogen sulfide's presence and may not provide adequate warning of hazardous concentrations.

H2S is a mucous membrane and respiratory tract irritant. Inhalation of high concentrations may cause respiratory paralysis, irregular heartbeat, collapse and death. Symptoms of acute exposure include nausea, headaches, delirium, dizziness, tremors, convulsions, and skin and eye irritation. Persons exposed to hydrogen sulfide pose no serious risks of secondary contamination to personnel outside the exposed area.

Preventing H2S Gas Accidents
In petrochemical plants, oil/gas production and wastewater treatment facilities, there is the potential for H2S accidents. Some common problem areas and gas monitoring applications include:
H2S Sludge De-Watering
   Sludge from waste treatment facilities may
   contain H2S and methane gas as well. The sludge
   is transported through a spiral conveyor into the
   dewater system where the water is removed.

Crude Oil Tank Storage
   Storage tank farms for crude oil and H2S require
   continuous monitoring for gas leaks. In addition to
   the tanks, common leak sources include pipes and
   valves, which require monitoring sensors.

Remote Oil / Gas Well Sites
   Remote automated oil/gas well production sites
   require protection against H2S gas leaks in and
   around the site. Common monitoring locations
   include the well heads, flare stacks and storage
   tanks.

Oil / Gas Drilling Sites
   Leaks, such as blowouts in oil drilling applications,
   release large quantities of H2S gas into areas
   around the site. Typical gas monitoring locations
   include the driller stand, bell nipple, shale shaker
   and mud tank.

To prevent H2S accidents, it is critical to audit processes and facilities for H2S gas hazards. This includes reviewing gas detectors and monitors in place to make sure they continue to provide the protection necessary. Facility expansions, upgrades and retrofits all have the potential to introduce new hazards or reduce the effectiveness of gas monitoring equipment that is already in place.

General Monitors’ H2S detectors are ideal for use in a wide range of demanding industries where the potential presence of dangerous H2S and other toxic gases are a threat to people, equipment and facilities. The S4000T / S4100T detectors are designed with a robust metal-oxide semiconductor (MOS) sensor, and the TS4000 / TS400 detectors feature a versatile electrochemical sensor. The highly intelligent S4000T / S4100T H2S Gas Detectors are available for Safety Integrity Level (SIL) 2/3 applications, and the TS4000 / TS400 Toxic Gas Detectors are designated for SIL 2 applications.

Visit our SIL Resource Center.