H2S (Hydrogen Sulfide) Training

H₂S is a colorless, flammable gas that can be naturally present in most fossil fuels. It occurs as a byproduct of the production and processing of oil and natural gas. We often characterize our crude oil and gas fields as “sweet” or “sour” depending on the concentration of H₂S. H₂S can also be produced during metal refining, pulp and paper production, mining, and sewage and wastewater treatment.

Who is at Risk?

Anyone who works or lives around:

•      Drilling rigs, Pipelines, Refineries,Gas plants

    Gas-oil separation plants (GOSPs)

    Sewers and wastewater treatment operations

What are the Hazards of H2S?

Toxic, Invisible, Heavier than air, Flammable and explosive, Corrosive and reactive

1. Toxic

H2S is toxic and can affect several different systems in the body. When inhaled it goes from the lungs into the bloodstream immediately, where it can rapidly paralyze the respiratory center in the brain and cause the lungs to cease to function, with death from asphyxiation (suffocation) following in minutes.

Concentration and Effects
0.10 ppm	Foul, rotten egg smells noticeable.
10 ppm	TLV-TWA; eye irritation; use SCBA.
15 ppm	Short-term exposure limit (STEL) for 15 minutes.
50 ppm	Maximum peak exposure (MPE).
100 ppm	IDLH; severe eye irritation, coughing, loss of sense of  Smell in 1 to 5 minutes.
250 ppm	Pulmonary edema; gastrointestinal disturbance.
500 ppm	Dizziness; loss of consciousness within 30 minutes.
1,000 ppm	Death within minutes.

Above Table shows the toxic effects of the gas at different concentrations. The permissible exposure limit (PEL) for H2S at 10 ppm. This is the maximum H2S concentration a person is allowed to be exposed to over an average 8-hour day during a typical 40-hour workweek, also called the threshold limit value-time weighted average (TLV-TWA). When H2S concentration is suspected to be at 10 ppm, appropriate respiratory protection must be used. The short-term exposure limit (STEL) for H2S is 15 ppm for 15 minutes. Note that at 100 ppm, H2S is considered immediately dangerous to life and health (IDLH) and no work is allowed. Appropriate respiratory protection is a full-face respirator connected to either an auxiliary air supply or self-contained breathing apparatus (SCBA).

2. Invisible

H2S gas cannot be seen. H2S is colorless at room temperature so it cannot be detected with the naked eye. Low concentrations of the gas — even as low as 5 parts per billion — have a foul, rotten egg smell, but higher concentrations can quickly deaden your sense of smell — your nose becomes overpowered by the gas and stops sensing it completely. Never rely on the sense of smell to detect the presence of H2S.

3. Heavier than air

H2S is heavier than air. With poor ventilation, it tends to accumulate in low lying areas around drilling rig platforms, pipeline trenches, sewers, sumps and excavations. In confined spaces, H2S settles at the bottom, forming a deadly gas layer.

4. Flammable and explosive

H2S forms explosive mixtures with air and can ignite. H2S is extremely flammable and explosive over a wide range of concentrations in air. Its lower explosive limit (LEL) is 4.3% and its upper explosive limit (UEL) 46%. 

When H2S burns, it produces sulfur dioxide (SO2), which is a colorless and toxic gas that can severely irritate the eyes, nose, throat and respiratory system.

5. Corrosive and reactive

When H2S is combined with moisture in the air, it forms a corrosive acid called sulfuric acid that irritates the eyes and mucous membranes. It can also corrode metal, causing dangerous leaks in pipes, valves, tanks and other metal equipment. When H2S reacts with steel in pipes and other equipment it forms iron sulfide, which is pyrophoric — meaning it can ignite when dry and exposed to air.

Controlling the Hazards of H2S

We take all the reasonable precautions necessary to protect everyone from harmful exposure to H2S. The three basic approaches to controlling hazards are:

•      Engineering controls

•      Administrative controls

•      Personal protective equipment (PPE)

1. Engineering controls

4 Safe and effective design, construction, operation and maintenance of drilling, work over, process, transportation and storage equipment.

4 Ventilation (using exhaust fans, air pumps).

4 Flaring systems (safely burn remaining gas).

Engineering controls offer the first line of defence against H2S hazards. Engineering controls or efforts to keep H2S away from people are by far the most effective controls for hazardous exposure to H2S. Some examples include safe design, construction and maintenance of drilling, work over, process, transportation and storage equipment. Additional engineering controls for H2S during routine equipment maintenance and process upsets include ventilation and gas flaring.

Ventilation systems are engineered to provide either local exhaust or dilution ventilation. Mechanical ventilation is a widely used engineering control for diluting H2S concentrations to safe levels. The idea behind dilution ventilation is to provide the means to reduce concentrations of H2S below the threshold levels for both toxicity and the lower flammable/explosive limits to simply avoid these types of hazards. Local exhaust is just what the term suggests — using ventilation for the remaining unwanted gases or fumes and safely transporting them somewhere elsewhere so they won’t pose a hazard. Proper ventilation prevents the accumulation of hazardous levels of H2S. Common forms of ventilation are natural winds, powered air-blower systems and powered air-exhaust systems.

Gas flare systems are engineered to burn any H2S gas that may be released through the process of venting pressure relief systems to mitigate otherwise serious personnel exposures. However, there is still risk from exposure to sulfur dioxide (SO2), produced when burning H2S.

2. Administrative controls

4 Assigning workers to work in areas with no potential for H2S exposure or limiting their work time in certain environments.

4 Substituting with less hazardous materials.

4 Implementing procedures to safely handle substances.

Administrative controls are next in the control hierarchy. Administrative controls include provisions, such as administratively preventing exposures by transferring employees to other work locations (i.e., areas without potential H2S exposure), limiting the time they work in certain environments (their maximum peak exposure time over an 8-hour shift), substituting less hazardous materials for more dangerous ones (to completely avoid the potential exposure), and establishing and implementing procedures for safely dealing with substances that are not reasonably controlled with engineering controls. Because of H2S’s high toxicity, using administrative controls to simply limit the length of exposure is generally not as effective.

Examples of procedures to be implemented include: Well control procedures to avoid blowouts or manage a kick; and procedures for detecting, monitoring and controlling potential personnel exposure to H2S while working in confined spaces and in low-lying (below grade) areas or equipment in sour service.

When persons are required to work inside confined spaces, such as excavations, tanks or vessels, and where concentrations are 10 ppm or greater, the appropriate respiratory protection must be used, and a standby man, fully trained in rescue methods and properly equipped to carry out rescue, must be present.

H2S detection

4 Fixed detection systems

4 Portable monitors

4 Personal monitors

The only reliable way to detect the presence of H2S is to measure its volume in air using either fixed and/or portable calibrated detectors. Fixed detectors are installed in areas where H2S may be present. They consist of a detector (sensing head), an indicator/beacon and an audible alarm. When the H2S levels exceed the preset limits, normally 10 ppm, an alarm sounds in the control room and locally in the vicinity of the detector.

To be effective, the detectors must be regularly checked, maintained and calibrated as per Standard.

3. Personal protective equipment (PPE)

4 Self-contained breathing apparatus (SCBA)

4 Supplied-air breathing apparatus (SABA)

When detection and monitoring systems indicate the presence of H2S at levels between 10 ppm to 100 ppm, while testing for H2S, and if there is an indication of equipment failure or product leak, personal protective equipment (PPE) must be used. PPE can also provide certain specific hazard protection when engineering and administrative controls are not feasible or in conjunction with these other control methods.

Because H2S is extremely toxic the first priority is to provide respiratory protection. When exposure to H2S is possible and only up to 100 ppm level, those in the area must wear one of two basic types of respiratory protective equipment appropriate for use around the gas. All work must be stopped at H2S levels above 100 ppm and all workers leave the affected area.

•          A self-contained breathing apparatus (SCBA) supplies compressed air from a cylinder worn on the user’s back to a sealed face piece. It provides air for up to 30 minutes.

•           A supplied-air breathing apparatus (SABA) supplies air through a hose from cylinders or a compressor in a location remote from the user. Although lighter than the SCBA, it restricts movement. A 5-minute escape bottle must also be worn in case of a problem with the main air supply.

Chemical gloves, coveralls and a face shield must always be worn when handling H2S to protect the eyes and exposed skin. An eyewash fountain and emergency shower must be provided and used as necessary.

Supplied Air Breathing Apparatus

•         Be fitted and receive training in its proper use.

•         Learn how to inspect and maintain the device.

•         Check the cylinders to make sure they are full.

•         Be trained in emergency rescue.

Before you use respiratory protection equipment, you must:

•         Be fitted for the specific device and trained in its proper use (i.e., how to put on the cylinder and harness, open and check the air supply, and adjust the mask for an airtight seal).

•         Know how to inspect and maintain the device. Check for cracks in the face seal, broken head straps and cracked or clogged hoses.

•         Check the cylinders to ensure that they are full and ready for use.

Be trained in emergency rescue if it’s part of your assigned responsibility.

Emergency Response Plans

Every operation where H₂S exposure may be possible must have an emergency response plan in place for H₂S release. Each facility has its own unique emergency plan depending on the nature of its operations. Should an uncontrolled H₂S release occur, follow your department’s emergency response plan. In general, take these steps:

1.      Stop work immediately and warn your co-workers (sound the alarm).

2.    Look for H₂S beacon to identify the location of the leak.

3.    Check wind direction. If you are near or downhill from the affected area, put on an SCBA immediately, if available.

4.    Evacuate to an area upwind if the release is downwind or crosswind if the release is upwind; and move to higher ground.

5.     Notify appropriate personnel/control room, providing all pertinent information (i.e., location and number of injured persons).

6.    If you are attempting a rescue, protect yourself first by wearing the appropriate respiratory protection.

7.     Move victim upwind or crosswind to a safe area.

8.    If properly trained, apply Basic Life Support (BLS) techniques.

Call for medical assistance if someone has been overcome or strongly affected by H₂S.

Summary comments:

•      Understand the hazards of H₂S.

•      Receive proper training in the use of SCBA and SABA.

•      Follow safe work practices.

Familiarize yourself with emergency response plans