Hydrogen Sulfide (H2S) is an extremely toxic, flammable gas that may be encountered in the production of gas well gas, high-sulfide, high sulfur content crude oil, crude oil fractions, associated gas, and waters. Since hydrogen sulfide is heavier than air, it can collect in low places. H2S is a byproduct of the decay of protein-containing substances, H2S forms by bacterial reduction of sulfates in sedimentary rocks. H2S may also be anticipated in previously uncontaminated reservoirs into which sulfate-reducing bacteria were introduced through workover and completion fluids containing organic polymers, including starch, methyl cellulose and polysaccharide base additives. Flaring operations associated with H2S production will generate Sulfur Dioxide (S02), another toxic gas, which is corrosive and lethal. All well-drilling sites should be classified according to areas of potential and/or actual exposure to H2S.

Drilling Operations

  • Mud weight control to ensure that hydrostatic pressure exerted by the mud column overbalances the formation pressure and prevents influx of gas into the mud column
  • Continuous monitoring of drilling returns (mud and cuttings) for H2S
  • Addition of H2S scavengers (zinc carbonate and ironite sponge) in drilling and completion fluid formulations 
  • Negative pressure ventilation and air locks in mud-processing rooms 
  • Local exhaust ventilation over the shale shakers

Platform Design - Living Quarters

  • Positive pressure ventilation of living quarters, with H2S monitoring at the air intake linked to HVAC shutdown
  • Area monitoring system for H2S with strategically located sensors 
  • Supplied breathing air system in work areas and at muster/evacuation stations


  • Corrosion rings for pipe / tubular products
  • Specifying NACE standards in specifications (North American Corrosion Engineers)


  • Arrangements for emergency flaring when the well cannot be shut
  • Using dynamically positioned semisubmersible rigs (in preference to self-elevating or anchored      semisubmersible rigs), which can be oriented to the wind direction without disrupting rig operations, such that gases are blown away from living and work areas

At the Job Site

  • Conduct a Job Safety Analysis – Break down the steps of what to do and how to do it safely so that everyone is aware of the tasks. Pay special attention to note where H2S may be present. (Process tanks, well head, low lying areas etc.)
  • Make sure there is an emergency number available to call for trained rescue personnel. Know and follow the work site safety protocols
  • Make sure everyone has and is wearing a H2S monitor
  • Make sure that the monitors have been tested recently and are in good working order
  • Make sure respirators and other breathing equipment are the proper type for the level of H2S present
  • Make sure everyone knows what the H2S alarm sounds like
  • Establish the direction, location and process for evacuation in the event of an alarm
  • Everyone needs to know the wind direction as evacuation needs to be upwind and crosswind.  (Look at the wind sock).  Do not go to low lying areas
  • Ensure that no smoking is allowed