h2s in the oilfield eng

8/11/2019 H2S in the Oilfield Eng

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H2S in the Oilfield Fact Sheet

Introduction to H2S

Hydrogen Sulfide, or H2S, is an ever-increasingproblem for workers involved in oil and gasexploration and production.H2S, however, is not just an oil field problem.This gas is found in many areas unrelated to the oilfield, such as landfills, sewers, waste treatmentplants, and septic systems.

Where does H2S come from?

H2S is formed in the process of the natural decompositionof organic matter. This is the reason that it shows up inmany different locations. Another source of HydrogenSulfide is as a by-product during a reaction between anyacid and any sulfur compound.

Hazards of H2S

The hazards of Hydrogen Sulfide gas can be controlled through: Receiving adequate training Pre-job planning Emergency response planning Controlling hazards

Following safe work procedures Using breathing apparatus

All of these activities are designed to ensure your safety when working in an area whereH2S may be present.


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Operations involving H2S

Many oilfield operations expose workers to HydrogenSulfide.

H2S can be found in the following type operations: Well Servicing Drilling Water Hauling Well Stimulation Production Operations Plant Operations

Sources of H2S

Oilfield workers can expect to find H2S at several specific locations involving different

types of operations.Here are some examples of the specific locations where youcould expect to find H2S:

Confined spaces Tank Batteries Shale shakers & mud pits Circulating tanks Wellheads Produced water

Liquids and H2S

Hydrogen Sulfide may be dissolved in liquids and thenreleased if agitated, depressurized, or heated.This means that gas in the liquids is released when theyare circulated, pumped, flowed or swabbed into tanks.This also applies to H2S in well bore fluids that areagitated by these activities. Thats another reason whyyou would expect to find Hydrogen Sulfide at the top ofopen tanks, gauge hatches and vent lines.


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Characteristic of H2S

It is important that you know the characteristics of H2S.

Knowing these Hydrogen Sulfide characteristics are valuable when you have toevaluate a potential H2S hazard at your work location.

The characteristics of Hydrogen Sulfide are: It is Colorless H2S cannot be seen as a gas.

It can have a Rotten Egg Smell Due to its sulfurcontent, H2S has a distinctive smell.

o This smell is only apparent in lowconcentrations.

o The olfactory nerve suffers fatigue at higher

concentrations, and the sense of smell is lost.

H2S is also Flammable H2S has a flammable rangeof 4.3% to 46% in air, and an ignition temperature of500F. By comparison, the temperature of the tip of alit cigarette is over 700 F.

H2S is Heavier than Air H2S has a vapor density of approximately 1.19, whichmakes it slightly heavier than air (1.00). This is why H2S settles in low areas.

H2S is Water Soluble H2S will mix into a solution with water, and will be carriedto the surface in produced water and drilling mud.

It is also Corrosive When H2S mixes with water, a weak hydrosulfonic acid isformed. This acid will deteriorate metals with high iron content, creating IronSulfide Scale. Also, this causes irritation of the eyes, nose, and throat areas of theexposed person.

And most important, H2S is Toxic Hydrogen Sulfide ranks as the second mostdeadly naturally occurring gas, behind Hydrogen Cyanide.

o H2S kills by paralyzing the nervous system area that controls theinvoluntary function of breathing. The result is lack of oxygen to the brain,followed by death in minutes.


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Toxicity of H2S

As has been emphasized, H2S is extremely poisonous. Below is toxicity information forH2S. It contains important information concerning H2S at different concentrations.

At 1 ppm there is a detectable rotten egg odor At 10 ppm, that is the maximum allowable

exposure level and the alarm set point forpersonal monitors.

A concentration of 20 ppm will result in irritationof the eyes, nose and throat areas.

50 ppm of H2S causes a loss of the sense ofsmell, headache, and dizziness from lack ofoxygen.

100 parts per million is the IDLH or ImmediatelyDangerous to Life and Health level for H2S. No

work is allowed without the use of the buddy-system. 200 ppm causes severe eye, nose, throat irritation, headaches, dizziness, and

nausea. When the concentration reaches 500 parts per million, unconsciousness occurs

within a few minutes along with respiratory paralysis, followed by death. At 1000 ppm the victim becomes unconsciousness immediately. Death results in

4-6 minutes, if not rescued promptly..

Corrosivity of H2S

Hydrogen Sulfide is highly corrosive. This may cause problems such as IronSulfide Scale production, which is dangerous when disturbed.H2S can be released back into the environment in dangerous quantitiesduring the removal of this scale.Iron Sulfide Scale can also burst into flames if allowed to contact oxygen.Hydrogen stress fractures can occur due to Hydrogen embrittlement, whichcan cause failures of the metal components.


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Detection Equipement

Many facilities will use some form of fixed monitoring devices to detect and alertworkers to the presence of Hydrogen Sulfide.

If a release occurs, the sensors will detect it, an alarm willsound, and a light will usually flash.These devices are placed with the sensors in the areas arelease is likely to occur, and the lights and alarms whereworkers will be able to see and hear them.The monitors commonly have alarm set points at 10 ppm(low) and 15 or 20 ppm (high).

At times, it will be necessary to use personal monitors.These devices are preset to alarm at 10 ppm, andfrequently come equipped with a light that flashes, abeeping alarm, and a vibration alarm.

These are to be worn on the personal body, and outside allclothing. It is recommended that they be placed up high onthe body, preferably within 18 inches of the nose andmouth.

Respiratory Protection

When it is necessary to perform work in areas where the H2Sconcentration is greater than 10 ppm, a positive pressurerespirator will be required. Negative pressure respirators shallnot be used in H2S environments.Once a fit-test has been performed, it is necessary not to allowthe seal to be impaired by facial hair or glasses. Many locationswill not allow persons entry with improper facial hair.


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Respiratory Equipment

One type of positive pressure respirator is the Air Lineor Cascade unit.

This device will provide the wearer with a clean airsource from compressed air cylinders and hoseassembly.The benefits of this unit are that it will give the wearera steady supply of air for a long period of time.

An attendant will be required to monitor the airavailable in the cylinders, and alert the wearer whenair reaches too low a level.Problems with this type of unit include the hosebecoming tangled or kinked, and the need for possibleescape in a direction away from air supply, requiring a 5-minute escape bottle.

Another type of positive pressure respirator is the SCBA or Self-Contained Breathing Apparatus. These units are more compact thanthe Air Line units, and do not have the hose problems. However, theyare limited to a smaller air supply, which results in a shorter amountof time available to the wearer. SCBAs are usually rated for 30min or45min, yet the actual time will vary with the wearers physical exertionand conditioning levels. These units are equipped with an alarm toalert the wearer when the air cylinder pressure is too low.

Emergency Response

Medical experts tell us that, without a continuous supplyof oxygen, the brain can only survive four (4) to six (6)minutes. That is the reason it is so important to get theH2S victim to a safe area as soon as possible.

At the pre-job safety meeting, the designated safe areasshould be established and a rescue plan be designed toget the victim or victims to fresh air and resuscitate them

within 3 minutes.


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If someone is overcome by H2S, leave the areaimmediately, utilizing an escape mask, ifprovided. Evacuate upwind or crosswind andreport to a pre-determined safe area.Make your emergency notification according toyour Emergency Action Plan. Details must begiven to ensure a timely response by EMSpersonnel. If available, send someone out tomeet them and bring them into the site.

Yell Man Down!! sound the emergency alarm or whatever means has beenestablished at your worksite. Notify someone, such as a dispatcher or supervisor, of thesituation so emergency assistance can be made available.

It is important to remain as calm as possible so you can determine the number ofvictims and to determine if any additional safety hazardous exist.

It is vital that you put on a breathing apparatus before attempting any rescue.The oilfield is full of stories about workers being fatally injured trying to rescue co-workers without respiratory protection.

h2s in the oilfield eng

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