H2S in the Oilfield – Fact Sheet

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

Where does H2S come from? H2S is formed in the process of the natural decomposition of organic matter. This is the reason that it shows up in many different locations. Another source of Hydrogen Sulfide is as a by-product during a reaction between any acid 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 where H2S may be present.

Operations involving H2S Many oilfield operations expose workers to Hydrogen Sulfide. 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 you could 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 then released if agitated, depressurized, or heated. This means that gas in the liquids is released when they are circulated, pumped, flowed or swabbed into tanks. This also applies to H2S in well bore fluids that are agitated by these activities. That’s another reason why you would expect to find Hydrogen Sulfide at the top of open tanks, gauge hatches and vent lines.

Characteristic of H2S It is important that you know the characteristics of H2S. Knowing these Hydrogen Sulfide characteristics are valuable when you have to evaluate 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 sulfur

content, H2S has a distinctive smell. o This smell is only apparent in low concentrations. o The olfactory nerve suffers fatigue at higher concentrations, and the sense of smell is lost. • H2S is also Flammable – H2S has a flammable range

of 4.3% to 46% in air, and an ignition temperature of 500°F. By comparison, the temperature of the tip of a lit cigarette is over 700° F. • H2S is Heavier than Air – H2S has a vapor density of approximately 1.19, which

makes 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 carried

to the surface in produced water and drilling mud. • It is also Corrosive – When H2S mixes with water, a weak hydrosulfonic acid is

formed. This acid will deteriorate metals with high iron content, creating Iron Sulfide Scale. Also, this causes irritation of the eyes, nose, and throat areas of the exposed person. • And most important, H2S is Toxic – Hydrogen Sulfide ranks as the second most

deadly naturally occurring gas, behind Hydrogen Cyanide. o H2S kills by paralyzing the nervous system area that controls the involuntary function of breathing. The result is lack of oxygen to the brain, followed by death in minutes.

Toxicity of H2S As has been emphasized, H2S is extremely poisonous. Below is toxicity information for H2S. 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 for personal monitors. • A concentration of 20 ppm will result in irritation of the eyes, nose and throat areas. • 50 ppm of H2S causes a loss of the sense of smell, headache, and dizziness from lack of oxygen. • 100 parts per million is the IDLH or Immediately Dangerous to Life and Health level for H2S. No work is allowed without the use of the buddysystem. • 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 Iron Sulfide Scale production, which is dangerous when disturbed. H2S can be released back into the environment in dangerous quantities during 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, which can cause failures of the metal components.

Detection Equipement Many facilities will use some form of fixed monitoring devices to detect and alert workers to the presence of Hydrogen Sulfide. If a release occurs, the sensors will detect it, an alarm will sound, and a light will usually flash. These devices are placed with the sensors in the areas a release is likely to occur, and the lights and alarms where workers 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, and frequently come equipped with a light that flashes, a beeping alarm, and a vibration alarm. These are to be worn on the personal body, and outside all clothing. It is recommended that they be placed up high on the body, preferably within 18 inches of the nose and mouth.

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

Respiratory Equipment One type of positive pressure respirator is the Air Line or Cascade unit. This device will provide the wearer with a clean air source from compressed air cylinders and hose assembly. The benefits of this unit are that it will give the wearer a steady supply of air for a long period of time. An attendant will be required to monitor the air available in the cylinders, and alert the wearer when air reaches too low a level. Problems with this type of unit include the hose becoming tangled or kinked, and the need for possible escape in a direction away from air supply, requiring a 5-minute escape bottle. Another type of positive pressure respirator is the SCBA or SelfContained Breathing Apparatus. These units are more compact than the Air Line units, and do not have the hose problems. However, they are limited to a smaller air supply, which results in a shorter amount of time available to the wearer. SCBA’s are usually rated for 30min or 45min, yet the actual time will vary with the wearer’s physical exertion and conditioning levels. These units are equipped with an alarm to alert the wearer when the air cylinder pressure is too low.

Emergency Response Medical experts tell us that, without a continuous supply of oxygen, the brain can only survive four (4) to six (6) minutes. That is the reason it is so important to get the H2S victim to a safe area as soon as possible. At the pre-job safety meeting, the designated safe areas should be established and a rescue plan be designed to get the victim or victims to fresh air and resuscitate them within 3 minutes.

If someone is overcome by H2S, leave the area immediately, utilizing an escape mask, if provided. Evacuate upwind or crosswind and report to a pre-determined safe area. Make your emergency notification according to your Emergency Action Plan. Details must be given to ensure a timely response by EMS personnel. If available, send someone out to meet them and bring them into the site.

Yell “Man Down!!” sound the emergency alarm or whatever means has been established at your worksite. Notify someone, such as a dispatcher or supervisor, of the situation so emergency assistance can be made available. It is important to remain as calm as possible so you can determine the number of victims 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 coworkers without respiratory protection.