Oil and gas well drilling and servicing activities involve the use and production of potentially hazardous materials. OSHA, the National Institute for Occupational Safety and Health (NIOSH), and industry and safety groups continue to evaluate the type and extent of chemical and other health hazards across the industry.
Health hazards on a drilling site include all of the following:
Silica is a mineral that is found in stone, soil and sand. The amount of silica in soil and rock may vary widely depending on the local geology. Breathing in silica dust can cause silicosis, a serious lung disease. Using rock-drilling rigs mounted on trucks, crawlers, or other vehicles to drill into rock, soil, or concrete may expose workers to hazardous levels of airborne silica. The small particles easily become suspended in the air and, when inhaled, penetrate deep into workers’ lungs.
There are three main methods used to control silica dust during earth and rock drilling. OSHA recommends that drill operators always use a combination of these dust-control techniques.
The three methods are:
Dust Collection Systems: Best practices when using dust-collecting equipment for rock drills include using a movable duct attached to a shroud, a flexible rubber skirt that encloses the drill hole opening and captures cuttings that come through the hole. Equipment without these controls can be retrofitted by the manufacturer or a mechanical shop.
Dusty air is pulled from inside the deck shroud through a flexible duct to primary and secondary filter media. The primary filter or dust separator often includes a self-cleaning back-pulse feature that dumps the collected particles to the ground. Secondary release of particles to the air is minimized by a dump shroud.
Wet Methods: The proper use of wet methods requires a trained and skilled operator. In wet drilling, too much water can create mud slurry at the bottom of the hole that can trap the bit, coupling and steel extensions. Too little water will not effectively control escaping dust.
Operator Isolation: Drill operators using rigs with enclosed cabs can reduce their silica exposure by staying inside the cab as much as possible during drilling. To be effective, the cab must be well-sealed and well-ventilated. Ensure that door jambs, window grooves, powerline entries and other joints are tightly sealed.
Where control methods do not reduce silica exposures to OSHA’s permissible exposure limit, respirators are required, and employers must have a written respiratory protection program in accord with OSHA’s Respiratory Protection standard.
Hydrogen Sulfide, or sour gas (H2S), is a highly toxic, colorless gas. It is a very insidious industrial hazard for two reasons:
Hydrogen sulfide has been identified by NIOSH as a leading cause of sudden workplace death. At concentrations up to 30 parts per million (ppm), it has an odor of rotten eggs. However, at more deadly concentrations (100 ppm), hydrogen sulfide rapidly fatigues the olfactory nerves. A person may momentarily smell the gas but think little of it when the odor is no longer detectable. If exposure is sufficiently, intense, unconsciousness and respiratory failure may occur without warning symptoms. The gas is 1.2 times denser than air, and at high concentrations will tend to accumulate in low spots. Mixed with air in concentrations of 4.3-45.5%, hydrogen sulfide is explosive. It may also burn with the production of toxic sulfur dioxide.
During oil and gas well drilling operations, H2S is first released to the atmosphere at the shale shaker area and later at the circulation fluid treatment areas. It may also be released during tripping procedures in the immediate area around the drilling operation. Typically, however, only nominal amounts of H2S are released during normal drilling operations.
With the exception of exploratory or "wildcat" wells, drilling operations take place in oil fields where the hydrogen sulfide locations and formation pressures likely to be encountered are known. With the demand for hydrocarbons increasing, formations historically deemed too dangerous to produce are now being developed. In some instances, there is frequent to nearly continuous employee exposure to hydrogen sulfide at concentrations from 10 ppm (OSHA 8-hour permissible exposure limit (PEL)) to life-threatening levels requiring the wearing of self-contained breathing apparatus. Innovative technologies, alarm systems, and respiratory protective equipment and programs are being employed without uniform Federal regulation.
The effect of hydrogen sulfide on metals, known variously as metal fatigue, hydrogen embrittlement, and sulfide stress cracking, can cause failure of the drill string during a well control situation. Such failure can result in the release of hazardous concentrations of H2S in the drilling area. Careful selection of resistant metals and chemical treatment of drilling fluids can effectively guard against such failure.
Iron sulfide is a byproduct of many production operations and may spontaneously combust with air. Flaring operations associated with H2S production will generate Sulfur Dioxide (S02), another toxic gas.
Active monitoring for hydrogen sulfide gas and good planning and training programs for workers are the best ways to prevent injury and death.
All well drilling sites should be classified into areas of potential and/or actual exposure to hydrogen sulfide by the definitions outlined below. The safety recommendations made are a minimum. The American Petroleum Institute (API) has published "RP 49: Recommended Practice for Safe Drilling of Wells Containing Hydrogen Sulfide" which details recommendations in more depth and should be followed in all medium and high exposure areas. Below are OSHA and API definitions for each hazard area:
No Hazard Area – Any well that will not penetrate a known hydrogen sulfide formation. No special hydrogen sulfide equipment is needed (OSHA) (API).
API Condition I - Low Hazard Area – Work locations where atmospheric concentrations of H2S are less than 10ppm (OSHA). This includes any well that will penetrate a formation containing hydrogen sulfide that could result in atmospheric concentration of 10 ppm or less and/or in which the hydrogen sulfide zone has been effectively sealed off by casing/cementing and/or cementing method (API). For low-hazard areas, a 30-minute, self-contained breathing apparatus for emergency escape from the contaminated area only is recommended.
API Condition II - Medium Hazard Area - Work locations where atmospheric concentrations of H2S are greater than 10ppm and less than 30ppm (OSHA). Any well that will penetrate a formation containing hydrogen sulfide and is not defined as a low or no hazard area, including all exploratory (wildcat) well sites (API).
The following are recommended for medium hazard areas:
API Condition III - High Hazard Area - Work locations where atmospheric concentrations of H2S are greater than 30ppm (OSHA). Any operation expected to bring free hydrogen sulfide gas to the surface. The following are recommended for work in high hazard areas:
The recommendations and employee instruction will vary depending on the type of area.
Employees present at all medium and high hazard wells should be instructed in the use of the safety equipment provided onsite. Hydrogen sulfide instruction should be given by a qualified person(s). The instruction of personnel should include, as a minimum, the following elements:
Other suspected health hazards, that have not yet been quantified, may include exposure to:
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