Health, Safety, Security and Environment

H2S Gas and how to handle its Emergency

7 min read

Hydrogen sulfide ( H2S ) is a flammable and explosive gas, and can also be toxic when inhaled. It’s heavier than air, so it tends to collect in poorly ventilated, low-lying areas such as basements, wells, and sewer lines. Because of its inherent danger, it’s important to respond appropriately if your H2S monitor alerts you to the presence of this gas.

In the photo of today and articles, all personnel will be familiar with the hazardous nature of H2S, the safety concerns during production and maintenance operations performed onshore/offshore, and the precautionary measures, which are in place, and how to handle H2s during Emergency.

H2S poison Gas emergency

Hydrogen sulfide, H2S, is produced by the bacterial decomposition of vegetable and animal matter that contains sulfur. It is formed in some types of crude oil “sour crude” over many millions of years and often found in the production and refining of high sulfur petroleum and natural gases. Hydrogen sulfide is also found in stagnant waters, marshes, sewers, and mines.

At low concentrations, hydrogen sulfide has a strong and unpleasant odor of rotten eggs. A concentration as low as one part H2S is in a million parts of air may be smelt. At slightly higher concentrations H2S may have a sticky-sweet odor.

Hydrogen sulfide is also:

  • Colorless
    • Extremely toxic
    • Flammable
    • Heavier than air, specific gravity 1.19

There is, therefore, a major safety concern during production and maintenance operations performed onshore/offshore.

Nature and Effects of Hydrogen Sulfide:

When inhaled, hydrogen sulfide passes from the lungs into the bloodstream. In low doses, hydrogen sulfide is readily oxidized and the by-products excreted without any obvious or adverse health effects. As the concentration of hydrogen sulfide is increased, the intake of H2S is greater than the metabolism rate and adverse health effects commence.

Hydrogen sulfide is irritating to the eyes and respiratory tract and has a narcotic effect on the nervous system. Irritation to the eyes may cause severe pain and incapacitate the worker. At higher concentrations; hydrogen sulfide is odorless due to the phenomenon of olfactory fatigue, i.e., loss of sense of smell. Several fatalities have occurred due to respiratory paralysis following the erroneous belief that “no odor” means “no gas “.

Exposure to hazardous materials must be known and controlled or personnel may suffer a permanent health effect, possibly death. It is unacceptable to allow yourself or another person to be exposed to a concentration of hazardous material that may result in a permanent health effect. An unacceptable exposure to a hazardous material will occur if the exposure is not within the parameters determined by the exposure limits. These exposure limits are more commonly known as threshold limit values.

H2S Hazards and Symptoms

Extremely toxic (almost as toxic as Hydrogen Cyanide) and 5 to 6 times as toxic as Carbon Monoxide, H2S can be only smelt at low concentrations (1-50 ppm). Beyond 50 ppm, the sense of smell is lost after about 15 minutes of exposure.


H2S is irritating, asphyxiating, and very poisonous. It irritates the eyes and throat at low concentrations (30-150 ppm). At 500 ppm it causes dizziness and unconsciousness within 20 minutes.

Concentrations of 1,000 ppm of H2S cause immediate unconsciousness and death quickly follows unless artificial respiration and/or oxygen treatment is promptly applied (see table 1 of H2S toxicity). Death may occur even if the individual is removed to fresh air at once.

H2S poisoning is not cumulative like mercury, lead, or radioactivity. Repeated short exposures will not have the same effect as one lengthy exposure.

It must be noted that the values listed in Table 1 are approximate for the “average” person. Individual responses will vary according to:

  • Frequency of exposure
  • Duration of exposure
  • Intensity of exposure
  • Age
  • Fitness and health
  • Personal susceptibilities.

Consequently, these values should not be regarded as fixed but maxima .the principle when working with any hazardous material is the ALARA principles, AS LOW AS Reasonably Achievable. This does not mean trying to achieve “total safety” or ignoring the identifiable hazards, but a considered evaluation of the risk and implementing appropriate action to prevent any persons from suffering a health effect.

(read more about hsseworld.com/hydrogen-sulfide-h2s/)

TWA and STEL Limit for H2S :

“Time Weighted Average” (TWA) up to 10 ppm = no more than 8 hours per day. (The refreshment time shall not be less than 16 hours)

“Short Term Exposure Limit” (STEL) up to 15 ppm = Max of 4 exposures per 8 hours, but not more than 15 minutes each. (the refreshment time shall not be less than 60 minutes between each exposure)

Things to remember:

  • Over 0.1 % in the air, unconsciousness at once with early cessation of respiration and death in few minutes. Death may occur even if the individual is removed to fresh air at once.
    • H2S poisoning is not cumulative like mercury, lead, or radioactivity. Repeated short exposures will not have the same effect as one lengthy exposure.
    • Low concentrations of H2S hinder the ability of an individual to think clearly by affecting the nervous system


Escape mask with H2S cartridges (Draeger Parat II type) will be provided for all personnel working in the area. A sufficient number of escape masks will be provided to allow personal issues for all workers. Escape masks should be used for evacuation only and not for search and rescue operations, nor for working in an H2S environment. Prior to any work being carried out in confined spaces and/or where the presence of H2S is possible, work permits and entry permits shall be obtained.

Evacuation equipment

  • Basic personnel equipment

Everybody entering a sour gas zone- potentially exposed to the possible presence of H2S or SO2 – should be equipped with an escape mask with H2S / SO2 cartridges.

Escape masks must be carried out at waists at any time during work in sites exposed to accidental H2S / SO2 gas release.

Escape masks should be used for evacuation only and not for search and rescue operations (SCBA), nor for working in an H2S environment (Cascade system).

For the maximum possible number of people on board, including visitors, 120% of escape masks nose clip type with filter and 120% of spare filters shall be provided.

Evacuation means

Exit ways:

Rapid evacuation routes will be provided from every working area to muster points. These routes will be maintained free from obstruction and properly marked

  • Exit way shall be specified with suitable signs and guides and adequate illuminations in order to readily and quickly of evacuation.
    • Periodic drills and maneuvers shall be programmed (scheduled) and executed in order to continuous preparedness of personnel and rescue worker.


An accurate wind forecast must be available at all times.

The wind direction must be shown by at least TWO VISIBLE WIND INDICATORS such as windsocks, pennants illuminated at night.

Muster point:

Designated muster points normally located outside the limits of the impacted area will be set up and suitably equipped with means of communication.

An accurate wind forecast must be available at all times. The wind direction shall be shown by VISIBLE WIND INDICATORS such as windsocks, illuminated at night.

Alarm system:

All sour gas installations will be provided with a dedicated general H2S alarm.

The first level of alarm should be set at 10 ppm. Explosion-proof horns and flashing lights will be provided.

These visible and audible H2S related alarms shall be distinct from the installation Fire & gas and Abandon alarms, to avoid any confusion and ensure that personnel immediately don the appropriate set of protection equipment.

How to Handle Hydrogen Sulfide Emergencies

Get out of the Area

The first thing to do when your H2S gas detector goes off is to get out of the area as quickly as possible. If you have safety gear, put it on at this time. Jobs with a higher risk of hydrogen sulfide exposure–such as water treatment plants and oil drilling operations–often have H2S safety gear and are required to teach their employees how to properly use it.

To get out of the reach of the gas, get upwind. If you can, it can also help to get up higher–remember, hydrogen sulfide tends to sink down to low, confined areas.

Account for All People

Once you’re safe, start checking to see if everyone else was able to get out of the area successfully. Hopefully, they all heard the H2S gas monitor alarm and were able to get out in a timely fashion. If you’re on the job, your training should include a protocol for where to meet and how to make sure everyone is accounted for. If you’re at home, make sure all members of your family know where to go in case of an emergency.

Notify the Authorities

After you’ve made sure that everyone is safe, call the local authorities to let them know of the hydrogen sulfide exposure. This will ensure that the site is properly evacuated, as well as nearby homes or businesses that may be affected as well. Also, inform the authorities if you weren’t able to account for everyone: they’ll need to send in rescuers with the appropriate training and gear for a hydrogen sulfide emergency.

Ventilate the Area

The final step to dealing with a hydrogen sulfide emergency is to ventilate the area to let the dangerous gas disperse safely. The authorities will take charge of this process so you won’t be at risk of exposure. You should also find out if there are steps you can take to prevent the problem from happening again.

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H2S Gas and how to handle its Emergency


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