Hydrogen sulfi de (H2S) gas can cause nausea, headaches, unconsciousness, and death. Industries struggle to detect this deadly substance before it harms workers or communities. Safety system manufacturers have developed detectors that sense the H2S quickly and accurately.
This paper illustrates, in general terms, considerations in effective placement of H2S detectors: applications where the gas might exist and environmental conditions to think about. In addition, the paper reviews limits, strengths, and applications of the H2S gas detection sensor technologies: electrochemical, metal oxide semiconductor (MOS), and optical.
In high concentrations, hydrogen sulfi de gas can cause unconsciousness and death very quickly. Still dangerous in lower concentrations, side effects of the gas include nausea, headaches, and skin and eye irritation. The oil and gas industry worldwide grapples with strategies to detect this deadly substance before it harms workers or communities. Safety system manufacturers strive toward the same goal by developing detectors that sense the H2S quickly and accurately.
The primary function here is to save lives, so the speed of response is vital. The average person takes 12 breaths per minute, or one breath every fi ve seconds. A solid detection plan is key to personnel survivability.
This paper covers the following topics:
- Health dangers posed by H2S gas
- General guidelines for determining placement of H2S detectors
- Conditions affecting gas-detector performance
- Fixed-detector technologies, existing and future, that effectively detect H2S
- General characteristics of detectors
Deadliness of Hydrogen Sulfide
H2S is a flammable gas that attacks the central nervous system. Although it is flammable, the toxicity of H2S is so high that its flammable level is not reached before it begins to kill people. In addition, when used in areas of H2S exposure, catalytic sensors (a standard in detecting flammable gases) life expectancy is reduced making them unreliable.
Trace amounts of H2S are recognized by a distinctive odor of rotten eggs. Although the odor threshold of H2S is very low, continued exposure results in an individual losing the ability to smell it.
According to the Occupational Safety & Health Administration (U.S. Department of Labor), the acceptable concentration limit for exposure to H2S is 20 ppm for an 8-hour period. The maximum peak exposure is 50 ppm for 10 minutes.
H2S Locations and General Placement of Fixed Detectors
Acknowledging the importance of H2S detection to life safety, one must consider the locations and the consequences of its presence.
A common byproduct of fuel development, sour gas (or H2S) can be generated in a variety of ways. It is formed from the decomposition of organic matter and as a byproduct of various chemical reactions. And, for example, it can result from mixing a sulfi de (such as sodium sulfi de) and an acid.
The possibility of toxic H2S levels exists in many industrial applications including farming, wastewater, stagnant cellars/sumps disposal, chemical, and, of course, oil and gas exploration and production. Specifi c to oil and gas production, these are some potential hazard areas:
- Drilling sites pose leak and blowout hazards.
- Consider gas detection near the driller stand, the shale shaker, and the bell nipple.
- Analyzer buildings take in gases to be analyzed. In these enclosed buildings, leaks of gases, which can include combustible, nitrogen, and H2S, create dangerous hazards.
- Mud return line receiver tank
- Crude oil storage tanks, pipes, flanges, and valves require gas detection.
- Remote well sites require detection at the well heads, the storage tanks, and flare stacks.
In each situation, review drawings to analyze the probable sources of leaks. In addition, remember that H2S is heavier than air and will sink to the lowest lying area.
Most importantly, place detectors on HVAC air vents of accommodation buildings and personnel areas.
Consider assigning a team from the loss-prevention and project-management groups to survey the facility. They should decide the number and location of LEL and H2S sensors. Typically, sensors will be placed next to potential release points. In addition, install sensors around the boundaries of each area to supplement the point detectors.