Common Questions about Basic H2S Training

Hydrogen Sulphide (H2S) gas is an extremely flammable, explosive gas and can cause possible life-threatening situations.


3/28/2023 2:12:34 AM

What is Hydrogen Sulphide (H2S)

When you're working in an environment with a potential for a high level of H2S, you need to be cautious, understand the risk of H2S exposure, and know what to do in the event of an H2S emergency. 

What is H2S and why does one need to be cautious?

Hydrogen Sulphide is one of the most dangerous gases to be found in the oil and gas industry. It is an extremely toxic, colourless, flammable, corrosive gas that affects the body's nervous and respiratory systems.

At low concentrations, hydrogen sulphide (also known as H2S, sewer gas, swamp gas, stink damp, and sour damp) emits a pungent "rotten egg" odour. It's extremely flammable and toxic.

Our sense of smell is paralysed at high concentrations (above 100 ppm). This means that the gas can be present at dangerously high concentrations, but we won't smell anything.

It should be noted that H2S is a toxic gas that can be lethal in high concentrations. Numerous industries have safety protocols in place to manage and control its release, and workers in areas where H2S is present may be required to wear personal protective equipment.

Sources of Hydrogen Sulphide

Health Hazards of H2S Exposure

H2S Exposure Limits and Thresholds

Emergency Response and First Aid for H2S Exposure

H2S Training and requirement

Where to register for H2S Training?

Where can H2S be found?

H2S occurs naturally in crude petroleum, natural gas, volcanic gases and hot springs. It can also result from bacterial breakdown of organic matter or industrial activities such as food processing, coke ovens, paper mills, tanneries and petroleum refineries. It is possible that an oil or gas field can start to produce H2S at any time, particularly where water injection is concerned, or it may well produce H2S from when it is first drilled.


Wherever a large volume of seawater is kept in storage tanks for an extended period of time, H2S can be detected.


Even while some have the technology for sparging installed as standard, the legs of concrete platforms or other such enclosed spaces may still represent a serious risk. Sparging is the technique of forcing air through seawater that has been held to release H2S so that it can be drawn into an air-purifying procedure. This significantly lowers the possibility of seawater being retained and producing H2S while people are working on the leg.


Because H2S is heavier than air, it can build up in small amounts in low places where there is little to no air circulation, like drains or sumps.



Health hazards of H2S Exposure

Exposure to H2S can be extremely hazardous to human health, as it is a toxic gas that can cause a variety of health effects depending on the concentration and duration of exposure. H2S can irritate the eyes, nose, and throat at low concentrations, as well as induce coughing and breathing problems. Long-term exposure to low levels of H2S might result in nausea, headaches, and dizziness. 

Nonetheless, H2S exposure at high levels can be fatal. Concentrations above 100 ppm (parts per million) can cause immediate respiratory paralysis and death, while lower concentrations can cause unconsciousness and other serious health effects.

In addition to its acute health effects, exposure to H2S can also have long-term health consequences. Chronic exposure to low levels of H2S can cause a range of health problems, including neurological symptoms such as memory loss and mood changes, as well as respiratory, cardiovascular, and digestive issues. It is important to note that the health effects of H2S exposure can vary depending on the individual, as well as other factors such as age, pre-existing medical conditions, and exposure history. As such, workers must be trained to recognize the signs and symptoms of H2S exposure and that appropriate measures are taken to prevent exposure in the workplace.


Properties of Hydrogen Sulphide

  • It is extremely hazardous to your health, even in small concentrations
  • It is extremely corrosive, causing severe stress cracking of steel and other metals
  • It burns with a blue flame to form sulphur dioxide, which is also a toxic gas
  • It is heavier than air and tends to collect in low-lying areas and confined spaces
  • It is easily dispersed by wind or air currents
  • It is soluble in water, crude oil or petroleum fractions


Learn more detail about H2S with our e-learning by clicking here

H2S Exposure Limits and Thresholds

Maximum Occupational Exposure Limits

Industrial hygiene guidance establishes Maximum Occupational Exposure Limits or MELs, as follows:

  • Long-term exposure limit: Over an 8-hour reference period, of 5 ppm
  • Short-term exposure limit: Over a 15-minute reference period, of 10 ppm
  • 800ppm is the generally accepted lethal concentration for 50% of an exposed human population for 5 minutes of exposure

It's crucial to keep in mind that even if the short-term exposure limit is 10 ppm, irritation of the eyes and respiratory system might occur after just a few minutes of exposure. If you have any of these symptoms, cease what you're doing right away and leave the area.

The toxicity levels of H2S, the symptoms and consequences of exposure to the body

The toxicity of H2S at:

  • 5 ppm is the long-term exposure limit (LEL)
  • 100 ppm causes loss of sense of smell
  • 500 ppm causes loss of consciousness and death
  • 1000 ppm causes rapid loss of consciousness and death

What to do in the event of H2S emergency?

The hydrogen sulphide sensor in your workplace has activated, alerting you to the presence of H2S. What do you do next? Regardless of whether you detect that particular foul odour, safety always comes first, thus presume H2S is present.

There are high-pressure air supplies for topping up breathing apparatus bottles in some high-risk H2S zones, while others have low-pressure air supplies called "cascade systems" that you can "plug into." In each case, you must be trained and assessed as competent to use the available safety equipment.

You can't overestimate the feeling of panic when an H2S alarm sounds and you know that you must don your breathing apparatus before taking your next breath. If you breathe in before properly wearing your breathing apparatus this could be your last breath!

1. Don your breathing apparatus

All breathing apparatus requires training in its use and a full understanding of its limitations. The breathing apparatus must have a pressurised mask or hood to ensure that no contaminated air from outside gets in. 

2. Reach a place of safety

If you're working in an area where H2S could be released, there should be flags or wind socks to show you which way the wind is blowing. Your aim is to head in the opposite direction right away. because the wind can blow and concentrate H2S into valleys or tree stands, the direction you head to is critical. When you reach a place of safety, don't remove your breathing apparatus yet as your clothes will be soaked with H2S which must be removed.

3. Count Heads

It may not be your stated responsibility to perform the final "head count," but safety is everyone's concern. Someone could have died from H2S before clearing the pad, or there could have been a faulty hydrogen sulphide monitor. Make it known if you find someone who is not at the muster site. Don't try to get them out of a dangerous situation, and don't go back into the area to find someone unless you've been trained and have the proper equipment.

4. Notify the authorities and ventilate the area

Call the local authorities to let them know of the hydrogen sulphide exposure. This will ensure that the site is properly evacuated and they can send trained rescuers and authorities to take charge of ventilating the area to let the dangerous gas disperse safely.

While it is critical to act quickly in an H2S emergency, taking these precautions will help keep you safe and in compliance with regulations. Finally, always maintain your monitor and replace it as necessary. It knows before you do when H2S levels are too high.

H2S Training

All employees entering work sites with a potential H2S hazard must be trained to understand the following:

  • The hazards of H2S
  • Warning signs related to H2S
  • How to use personal H2S detectors
  • Actions to be taken in the event of an emergency
  • What to do if a workmate is overcome by H2S
  • The escape routes to be used in an emergency

This training must be supplemented with practical training using the actual type of safety equipment you could potentially have to use onsite such as BA sets, smoke hoods, gas monitors and so on.

If you are going to work onsite with potentially high concentrations of H2S, you should expect to participate in frequent practical exercises to ensure that your capability of reacting well in an emergency is maintained.

Good quality training is the best means of reducing your stress levels, which directly relates to how much air you consume during an emergency escape, and thus the length of time that you have to make your escape.

Where to register for H2S Training?

Peninsular Malaysia

MSTS Pasir Gudang Training Centre
Oasis Complex, Johor Port,
81700 Pasir Gudang,
Tel: +607 252 2108

MSTS Cherating Training Centre
Lot 2014, Mukim Sungai Karang,
Cherating, 26100 Kuantan,
Pahang, Malaysia
Tel: +609 581 9049

Sabah and Sarawak

MSTS Miri Training Centre
Lot 960, Jalan Cattleya 3,
Piasau Industrial Estate,
98000 Miri, Sarawak, Malaysia
Tel: +608 5415 815



MSTS Singapore Training Centre
67, Tuas South Avenue 1,vSeatown Industrial Centre,
637579 Singapore
Tel: +65 6515 8193



RelyOn Nutec Thailand
919 Moo 2, Tamboon Taibaan,
Amphur Muang Samutprakarn,
Samutprakarn Province,
10280, Thailand
Tel: +66 2 703 9773