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Health Hazards in Drilling Operations



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
  • hydrogen sulfide
  • noise
  • diesel particulate matter
  • hazardous chemicals
  • naturally occurring radioactive material (NORM)
  • temperature extremes
  • fatigue

Exposure to Silica

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.

Control Methods for Silica Dust

silica dust

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.

Exposure to Asbestos and Refractory Ceramic fibers (RCFs)

silica dust

Asbestos is the name given to a group of naturally occurring minerals that are resistant to heat and corrosion. Asbestos has been used in products, such as insulation for pipes (steam lines for example), floor tiles, building materials, and in vehicle brakes and clutches. Oil field workers are among those at elevated risk for asbestos-related diseases such as asbestosis and mesothelioma.

Asbestos is added to drilling mud, which was used in the oil industry, for decades. Since the 1960s, such asbestos drilling has occurred both onshore and offshore. Drilling mud composition contains asbestos, which has caused mud engineers to be exposed to asbestos in drilling mud.

Asbestos fibers associated with these health risks are too small to be seen with the naked eye. Breathing asbestos fibers can cause a buildup of scar-like tissue in the lungs called asbestosis and result in loss of lung function that often progresses to disability and death.

There is no "safe" level of asbestos exposure for any type of asbestos fiber. However, OSHA limits exposure to asbestos to an 8-hour time-weighted-average (TWA) of .1 fiber per cubic centimeter (.1 f/cc). Asbestos exposures as short in duration as a few days have caused mesothelioma in humans.

Where there is exposure, employers are required to further protect workers by:

  • establishing regulated areas,
  • instituting engineering controls to reduce the airborne levels,
  • reducing exposure by using administrative controls and PPE, and
  • conducting medical monitoring where legal limits and exposure times are exceeded.

Refractory Ceramic fibers (RCFs)

Refractory Ceramic fibers are similar to asbestos fibers in size, shape, and long-term (months to years) exposure effects on humans. RCFs are amorphous synthetic fibers produced by the melting and blowing or spinning of calcined kaolin clay or a combination of alumina, silica, and other oxides. Oil and gas workers may be exposed to RCFs while installation and removal of RCF-containing insulation such as inside high-temperature furnaces.

RCFs, like asbestos, get into the body primarily by inhalation. The International Agency for Research on Cancer (IARC) and the American Conference of Governmental Industrial Hygienists (ACGIH) have classified RCFs as possibly carcinogenic to humans. OSHA has set an exposure limits for RCFs is.

To limit exposure proper ventilation and personal protective equipment should be used to limit the 8-Hour TWA to .2 fibers per cubic centimeter (.2 f/cc). Workers who may be exposed to RCFs should also be provided with information on the health effects and safe work practices related to RCFs. For more information, see the NIOSH Publication 2006-123, Occupational Exposure to Refractory Ceramic Fibers.

Exposure to Hydrogen Sulfide Gas

hydrogen sulfide
Courtesy- "Safety

Hydrogen Sulfide, or sour gas (H2S), is a highly toxic, colorless gas. It is a very insidious industrial hazard for two reasons:

  • unreliability of odor as a warning, and
  • sudden onset of incapacitation.

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.

Exposure on the Drilling Site

H2S sign

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.

Effects of H2S


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.

H2S Special Precautions

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:

  • NIOSH/MSHA approved manifold air masks with emergency escape cylinders for each employee
  • two NIOSH/MSHA approved, 30-minute, self-contained breathing apparatus for emergency escape from the contaminated area only
  • two wind socks and streamers
  • oxygen resuscitator
  • a properly calibrated, metered hydrogen sulfide detection instrument
  • audible and visual alarm system

H2S Special Precautions (Continued)

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:

  • Two NIOSH/MSHA approved, 30-minute, self-contained breathing apparatus for emergency escape from the contaminated area only.
  • The use of three wind socks and streamers.
  • The use of an oxygen resuscitator.
  • Two hydrogen sulfide detectors. One should be a properly calibrated, metered detection instrument, and the other should be a pump type with detector tubes.
  • The use of a separate audible and visual warning system.
  • Employees should not be permitted on location without hydrogen sulfide safety training. Employees may be permitted on location for specific hydrogen sulfide training purposes not to include general rig training.
  • Two means of egress at each location in a high hazard area should be provided.
  • A means of communication or instruction for emergency procedures should be established and maintained on location along with the names and telephone numbers of the person or persons to be informed in case of emergencies.
  • Signs should be posted 500 feet from the location on each road leading to the location warning of the hydrogen sulfide hazard.
  • All hydrogen sulfide safety equipment should be checked to ensure readiness before each tour change.

The recommendations and employee instruction will vary depending on the type of area.

Employee Hydrogen Sulfide Instruction

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:

  • the characteristics of hydrogen sulfide and its hazards
  • proper first-aid procedures to be used in a hydrogen sulfide
  • knockdown
  • use of personal protective equipment
  • use and operation of all hydrogen sulfide monitoring systems
  • corrective action and shutdown procedures

Other Health Hazards on the Drilling Site

Other suspected health hazards, that have not yet been quantified, may include exposure to:

  • Noise: Oil and gas workers can be exposed to harmful noise levels during equipment operation. Loud noise can also create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals.
  • Diesel Particulate Matter: Diesel engines power a variety of machinery, vehicles, and equipment on a drilling site. Workers might be exposed to harmful levels of diesel particulate matter during the operation of these engines.
  • Hazardous Chemicals: Workers, who use hazardous chemicals during work processes, especially during hydraulic fracturing, might be exposed to hazardous byproducts of oil and gas drilling. The degree of potential hazard depends on individual chemical properties and toxicity, but possible hazards include chemical burns from caustic substances and inhalation of toxic vapors. All employers with hazardous chemicals in their workplaces must have labels and safety data sheets for their exposed workers, and train them to handle the chemicals appropriately. Establishing effective engineering controls and work practices can reduce potential worker overexposures.

Other Health Hazards on the Drilling Site (Continued)

extreme temps
  • Naturally Occurring Radioactive Material (NORM): NORM might be released from oil and gas formations. Workers at risk of exposure include those who handle pipes and equipment that might have been contaminated with NORM. Sludge, drilling mud, and pipe scales, for example, often contain elevated levels of NORM, and the radioactive materials might be moved from site to site as equipment and materials are reused. Disposal, reuse, and recycling of NORM might cause worker exposures.
  • Temperature Extremes: Well-site workers are exposed to extreme temperatures and should take precautions to stay safe. Any worker exposed to hot and humid conditions is at risk of heat illness, especially those doing heavy work tasks or using bulky protective clothing and equipment. Anyone working in a cold environment may be at risk of cold stress. Oil and gas workers may be required to work outdoors in cold environments and for extended periods.
  • Fatigue: Workers might experience fatigue due to long shifts and when working multiple days in a row. Fatigue is a message to the body to rest. It is not a problem if the person can and does rest. However, if rest is not possible, fatigue can increase until it becomes distressing and eventually debilitating. The symptoms of fatigue, both mental and physical, vary and depend on the person and his or her degree of overexertion.



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Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

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1. Health hazards on a drilling site include all of the following, except _____.

2. 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 _____.

3. Why has hydrogen sulfide been called an insidious industrial hazard?

4. A well that will not penetrate a known hydrogen sulfide formation is designated by OSHA _____.

5. Work locations where concentrations of hydrogen sulfide are greater than 10 ppm and less than 30 ppm are designated by OSHA _____.

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