Ionizing Radiation

Hazard Recognition

This section provides information to help employers and workers recognize ionizing radiation hazards in the workplace.

The first two sections on this page describe two sources of ionizing radiation: naturally occurring radioactive material (NORM) and technologically enhanced naturally occurring radioactive material (TENORM). The NORM tab provides information on radon. The TENORM tab provides information on the oil and gas industry.

OSHA Ionizing Radiation Standards

OSHA's Ionizing Radiation standards protect workers in general industry (29 CFR 1910.1096), construction (29 CFR 1926.53), shipyard employment (29 CFR 1915.57 and, to the extent it applies, 29 CFR 1910.1096), marine terminals (29 CFR 1910.1096, to the extent it applies), and longshoring (29 CFR 1910.1096, to the extent it applies).

The construction standard for ionizing radiation (29 CFR 1926.53) incorporates by reference the provisions of the general industry standard (29 CFR 1910.1096), in addition to requiring a competent person to perform activities involving the use of radioactive materials or X-rays (see 29 CFR 1926.53(b)).

While some shipyard employment operations are covered by OSHA's Uses of Fissionable Material in Ship Repairing and Shipbuilding standard (29 CFR 1915.57), the general industry standard for ionizing radiation (29 CFR 1910.1096) also applies across the maritime sector to activities on vessels and on shore, including in shipyard employment, marine terminals (see 1910.1(a)(2)(vii)), and longshoring (see 29 CFR 1918.1(b)(5)).

The next two sections on this page provide a starting point for recognizing hazards from radiation-emitting equipment or devices.

OSHA's Ionizing Radiation Standard (29 CFR 1910.1096) requires employers to protect workers from exposure to ionizing radiation sources that are not regulated by other federal agencies (e.g., the U.S. Nuclear Regulatory Commission, NRC), such as X-ray equipment, some accelerators (i.e., accelerators that are operated to produce only particle beams and not radioactive materials), incidental accelerator-produced radioactive materials, ion implanters and some NORM. See the Standards page for more information about OSHA and NRC standards.

The Exposure Scenarios section on this page provides information about external exposure and internal exposure to sources of ionizing radiation. See the Control and Prevention page for information about control measures, including shielding and personal protective equipment (PPE), to reduce a worker's radiation dose from exposure to sources of ionizing radiation or prevent contamination.

Emergency response workers involved in a catastrophic radiological emergency might be exposed to different radiation hazards than other workers. Visit OSHA's Radiation Emergency Preparedness and Response page for information on protecting workers during radiological emergencies.

Naturally Occurring Radioactive Material (NORM)

Workers in some occupational settings can be exposed to ionizing radiation from radioactive materials that are naturally present in the environment (i.e., soil, rock, air, water). NORM is, by definition, naturally occurring (not man-made and not disturbed as a result of human activities). NORM can be found everywhere in the natural environment. Some common examples of NORM are listed below:

  • Radon (Rn-222), a naturally occurring radioactive gas, is found in soils, rock, and water throughout the United States. Radon gas can accumulate in below-ground areas (e.g., basements, tunnels) as well as in above-ground areas inside buildings, trenches, and excavations. The primary source of radon is uranium found in the earth. As illustrated in the natural uranium decay series, over time, uranium-238 decays into radium-226, which then decays into radon-222.
    USGS U238 Decay Series | Source: U.S. Geological Survey

    Source: U.S. Geological Survey

    The uranium-238 decay series (naturally-occurring) produces alpha, beta, and gamma radiation (not shown).

  • Radium (Ra-226 and Ra-228) may occur in water drawn from deep aquifers (groundwater sources).
  • Uranium (U-238 and U-235) or thorium (Th-232) and their decay products are present in granite, marble, limestone, or other materials used for stone work and in buildings. During stone cutting and polishing, granite with naturally high uranium or thorium may emit NORM that may be later considered TENORM for commercial products such as granite countertops.
  • Uranium (U) is in the ground before being mined and processed.
  • Carbon-14 (C-14) is taken up by all plants and animals and can be measured by scientists to determine the age of organic materials through "carbon dating."
  • Potassium-40 (K-40) occurs naturally and can be found in several foods, especially bananas.
  • Cosmic rays come from high-energy particles originating both within and outside our solar system, are associated with several different types of radiation (e.g., alpha, gamma, neutron, and x-ray), and contribute to the radiation doses airline crew members receive.


Workers can be exposed to ionizing radiation from radon gas. Radon gas is invisible, odorless, and tasteless. Examples of occupational exposure to radon include:

Radon gas (radon-222) decays into several short-lived decay products: polonium-218, lead-214, bismuth-214, and polonium-214 (see decay series above). These decay products can attach to particles in the air and be inhaled. When inhaled, these particles deposit in the lungs and deliver a radiation dose to the lung tissue. Polonium-218 and polonium-214, in particular, emit highly energetic alpha particles. In 1999, the National Research Council's Committee on Health Risks of Exposure to Radon (Biological Effects of Ionizing Radiation (BEIR) VI) provided a summary of scientific data on indoor radon and concluded that exposure to radon in homes is expected to be a cause of lung cancer. The Committee's preferred risk models indicated indoor radon to be the second leading cause of lung cancer in the U.S. after cigarette smoking (see Executive Summary).

In 2010, the International Commission on Radiological Protection (ICRP), in its Publication 115, Lung Cancer Risk from Radon and Progeny and Statement on Radon, increased the lifetime absolute risk coefficient for radon-induced lung cancer, and recommended a more stringent method for the calculation of doses from radon for radiation protection.

As indicated in the above Standard Interpretation letters and a Memorandum, the OSHA Ionizing Radiation Standard requires employers to conduct surveys as may be necessary to comply with the provisions of the standard (29 CFR 1910.1096(d)(1)). There are multiple methods available for determining radon concentrations. These include short-term measurements (e.g., 2 – 7 days) to determine any areas with high radon concentrations, and long-term measurement (e.g., 90 days or longer) to determine long-term radon concentrations. The 2015 National Council on Radiation Protection and Measurements (NCRP) Report No. 97, Measurement of Radon and Radon Daughters in Air, describes updated measurement techniques appropriate for assessing radon.

Indoor areas with high radon concentrations can be successfully remediated by closing holes (e.g., around sump pumps, etc.) through which radon may be entering the structure, sealing floor and wall cracks, and increasing ventilation with a radon mitigation system. The U.S. Environmental Protection Agency (EPA) Find a Radon Test Kit or Measurement and Mitigation Professional webpage also provides guidance on radon mitigation.

For more information about health risks from exposure to alpha particles from inhaling (breathing in) radon, see internal exposure on the Exposure Scenarios section of this page. For examples of radon and NORM in the oil and gas industry, see the TENORM section of this page.

Mining Industry

The Mine Safety and Health Administration (MSHA) regulates miners' exposure to ionizing radiation from short-lived decay products (daughters) of radon gas and gamma radiation from radioactive ores in underground metal and nonmetal mines (30 CFR 57.5037-57.5047).

Technologically Enhanced Naturally Occurring Radioactive Material (TENORM)

Worker exposure to ionizing radiation also occurs when industrial processes or human activity modify or ‘‘technologically enhance'' NORM so that its radioactivity is concentrated (intentionally or unintentionally) to result in a man-made concentration higher than NORM.

Examples of technologically enhanced naturally occurring radioactive material (TENORM) include:

  • Oil and gas industry wastes, including hydraulic fracturing or "fracking" wastes, such as flow-back fluids, pipe scale, sludge, and sediments. More information about the oil and gas industry is provided below.
  • Fertilizer (phosphate) industry wastes, including phosphogypsum waste byproduct and phosphate slag that may contain radium (Ra-226) or uranium (U-238).
  • Commonly used phosphate fertilizer products, which contain naturally-occurring radium (Ra-226) found in phosphate ores.
  • Coal industry wastes, including fly ash and bottom ash that may contain radium (Ra-226, Ra-228), uranium (U-238), or thorium (Th-232).
  • Bauxite and alumina production wastes, including waste (red muds or sands) from alumina (an intermediate product used to produce aluminum) that can contain uranium (U-238), thorium (Th-232), or radium (Ra-226, Ra-228).
  • Water treatment plant wastes, including sludge or sediments and certain resin filtration systems that may contain radium (Ra-226, Ra-228), uranium (U-238), or thorium (Th-232).
  • Geothermal energy production, including brine residuals and scale that may contain radium (Ra-226), uranium (U-238), or thorium (Th-232).

TENORM can result from manufacturing processes, such as the production of materials and equipment from raw materials that contained NORM, and concentrations of NORM materials are sometimes increased as a result of these processes. Fertilizer manufacturing facilities may have potential for worker exposure to TENORM from uranium, thorium, radium (Ra-226), or potassium (K-40) associated with fertilizer production, along with TENORM concentrations in wastes, filters, products, or metal piping scales. Paint and pigment manufacturing facilities may have potential for worker exposure to thorium, uranium, or radium (Ra-226) in wastes from titanium ores.

Other examples of TENORM in manufacturing or processing facilities arise from increased concentrations of NORM materials in filters and the solid sludge if large quantities of water containing naturally occurring radionuclides (e.g., Ra-226, Ra-228) are used in some manufacturing processes, such as paper and pulp mills, or from water treatment systems used to supply drinking water. Workers who clean or change filters or handle sludge may be exposed to these increased concentrations. Water treatment facilities may have potential for worker exposure to TENORM from radium scale and sludge contamination in wastes and filters. Paper and pulp mills may have potential for worker exposure to TENORM from radium scale and sludge contamination in various areas of such facilities.

Zirconium, in the form of zircon, which is a form of TENORM, contains small amounts of radionuclides (U and Th) in the mineral matrix. Zircon can be ground into fine powder and is commonly applied to ceramics before firing to create a shiny glaze. Workers in ceramics manufacturing facilities may be exposed to zircon or uranium in wastes and molds.

In addition, commercial use of materials containing TENORM can result in worker exposure. For example, workers may be exposed to TENORM in phosphate fertilizers. They may also be exposed to TENORM-contaminated piping and metal in scrap metal recycling facilities.

Waste management and disposal of TENORM can also lead to occupational exposures. In December 2017, the Radiation Task Force of the Association of State and Territorial Solid Waste Management Officials (ASTSWMO) issued Waste Generation and Disposal: Awareness, Management, and Disposal Guidance for Solid Waste Containing Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) to increase awareness regarding TENORM waste generation, as well as the regulatory and radiological complexities surrounding appropriate and protective TENORM waste management methods. This guidance recommended developing a site-specific TENORM radiation protection program to protect disposal facility workers during receipt and, if applicable, waste disposal.

See the American National Standards Institute (ANSI)/Health Physics Society (HPS) Publication N13.53, Control and Release of Technologically Enhanced Naturally Occurring Radioactive Material (TENORM), for more information on the control of TENORM.

Oil and Gas Industry

Fracturing Flowback Operations
Courtesy of Universal Well Services

Flow-back operations that are part of hydraulic fracturing in oil and gas operations may be associated with worker exposure to ionizing radiation.

TENORM can be the byproduct or waste product of oil and gas production. Sludge, drilling mud, and pipe scales are examples of materials that often contain elevated levels of NORM, and the radioactive materials may be moved from site to site as equipment and materials are reused. OSHA's Oil and Gas Extraction Safety and Health Topics page provides more information about potential NORM exposure in oil and gas well drilling and servicing activities.

The Commonwealth of Pennsylvania TENORM study examined naturally occurring radioactivity levels associated with oil and natural gas development in that state, and provides additional information on this topic.

State Regulation

In April 2004, the Conference of Radiation Control Program Directors (CRCPD) issued its current model state regulations for control of TENORM, or Part N of CRCPD's Suggested State Regulations for Control of Radiation (SSRCR). The SSRCR Part N model regulations are intended to apply generally to all TENORM-containing materials. The SSRCR Part N: Regulation and Licensing of Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) includes protection of workers during operations through compliance with the occupational dose in standards for radiation protection in Parts D and J of SSRCR. Overall, states are given flexibility for implementing Part N consistent with their respective, unique circumstances.

Many states currently regulate TENORM under their general radiation provisions. Because of the increase in hydraulic fracturing, more state regulatory agencies are reviewing associated hazards and some states are regulating TENORM (and/or NORM) in the oil and gas industry specifically. For example, some states now regulate through defining, licensing, and enforcing permit or disposal requirements for TENORM and NORM.

How does an X-ray tube work?

After turning on the electricity and applying a voltage, electrons are accelerated towards a heavy target such as tungsten, and then are either rapidly decelerated (leading to X-rays through Bremsstrahlung radiation) or knock out inner electrons of the target atoms (leading to characteristic X-rays as outer electrons fall to fill the inner electron vacancies).

An X-ray tube does not contain radioactive material, thus poses no ionizing radiation hazard when unplugged or turned off.

X-ray Equipment

Workers can be exposed to ionizing radiation from radiation-producing machines, such as X-ray equipment. X-ray equipment is used in various occupational settings, including security operations, healthcare, manufacturing and construction, and food and kindred products processing.

Security Operations

X-ray equipment for security purposes is used to check the contents of baggage, parcels, vehicles, cargo, and other items at airports, border crossings, seaports, postal facilities, building entries, public events, and parking facilities, among other places. Another use of ionizing radiation is to irradiate and kill biological agents sent through the mail and other delivery methods. Workers can be exposed to ionizing radiation when these types of equipment are not maintained or shielded properly.

Cabinet X-ray security systems are used primarily for creating an X-ray image of the inside of objects, without damaging or destroying the object being examined. That X-ray image is transmitted to a monitor. Closed X-ray systems are used, for example, for airport baggage security screening and cargo inspection of trucks crossing international borders. They are also used for industrial quality control to check for manufacturing defects and in medical and research laboratories.

Other X-ray systems, such as backscatter X-ray systems that use very low levels of X-rays, are used for security screening of people (e.g., at some prisons, for entry into some public buildings). These machines are no longer used at U.S. airports, which now use non-ionizing millimeter wave units for passenger security screening. The Interagency Steering Committee on Radiation Standards (ISCORS) developed interagency guidance to assist federal agencies in making consistent determinations about when the use of such X-ray security systems is justified. In July 2008, ISCORS published Guidance for Security Screening of Humans Using Ionizing Radiation (GSSHUIR), ISCORS Technical Report 2008-1, which includes basic information on how to set up an appropriate radiation safety program.

In 2009, ANSI published the current national consensus radiation safety standard for X-ray products used for security screening of people. Developed by Accredited Standards Committee N43, Equipment for Non-Medical Radiation Applications, administered by the Health Physics Society (HPS), ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation sets limits on dose to individuals being screened; sets limits on dose to bystanders, operators, and other workers; requires a variety of safety features; and establishes operational requirements for using these products.


Ionizing radiation is routinely used in medicine. OSHA's Hospital eTool provides information about protecting hospital workers from radiation exposure. OSHA has authority over non-NRC regulated medical uses, which are those that do not involve the use of radioactive materials (i.e., those involving radiation that does not come from NRC-regulated radiation sources), such as:

  • Diagnostic/Imaging techniques (e.g., radiography; computed tomography, or CT; fluoroscopy) used to locate fractures, growths, and tumors; determine the extent of an injury or disease; and determine the necessity for other medical procedures.
  • Interventional techniques (e.g., fluoroscopically-guided interventional procedures and angiography) used to guide treatments.
  • Radiotherapy used for treatment of diseases, such as cancer. Radiotherapy (also called radiation therapy) involves the use of high-energy ionizing radiation to kill cancer cells and shrink tumors. Non-NRC regulated radiotherapy includes the use of X-rays and some accelerators.

Many states also have state regulations addressing these uses.

Medical imaging includes many different technologies, of which selected examples are listed below:

Mobile C-arm Fluoroscopy Machine
WikimediaCommons/Ben Stephenson

A portable fluoroscopy machine can be used to guide cardiology, neurology, and other procedures.

  • Radiography (general X-rays) is typically conducted in a radiology department through either a central department or satellite facilities, but may also be performed in certain doctors’ offices (e.g., orthopedics). Radiographic equipment includes fixed and mobile radiographic systems. Most medical facilities use digital radiographic equipment that produces digital images instead of X-ray films, and this technology typically reduces the radiation dose workers and patients receive.
  • Computed tomography (CT), sometimes called "CAT scan," involves using one or more X-ray beams to acquire images of one or more body parts from many angles around a patient. Because they generally involve many scans, CT procedures are associated with higher radiation doses for the patient and higher radiation hazards for workers compared to general X-ray equipment. Patient dose from a CT scan depends on the part of the body examined and the CT protocol.
  • Fluoroscopy shows a continuous, real-time X-ray image, much like an X-ray movie, that can be used to monitor the movement of body parts, objects, or contrast agents through the body. It can be performed with fixed or portable fluoroscopy systems. Some fluoroscopically-guided interventional procedures have potential for high radiation doses, including most interventional radiology, interventional cardiology, and interventional neuroradiology procedures, as well as endovascular surgery. When fluoroscopy requires higher patient doses for long periods of time, it may result in increased risks of deterministic effects, including cutaneous (skin) radiation injury. Employers should ensure that fluoroscopy workers receive appropriate training and information about radiation hazards and the probability of deterministic and stochastic health effects. The U.S. Food and Drug Administration (FDA) also provides information about fluorscopy devices and their uses.
  • Cardiac angiography uses a specialized form of radiography (angiograms) for heart (cardiac) catheterizations, which may include angioplasty (procedure to open clogged arteries) and stent placement, and is often a fluoroscopically-guided interventional procedure. It involves radiography of blood vessels after injecting a special type of dye (contrast material) to enhance X-ray images. Cardiac angiography will include both a radiation dose from fluoroscopy and radiography.

Dental imaging uses special dental X-ray machines that produce either digital or film images and is typically performed in dental offices. A new technology, the cone-beam computed tomography (CBCT) scanner, may be used for more complex oral (mouth and teeth) and maxillofacial (jaws and face) imaging. Employers should ensure that protective measures, such as safely positioning the dental X-ray equipment operator relative to the X-ray equipment, are implemented to keep radiation doses for dental workers below regulatory limits and as low as reasonably achievable.

Veterinary imaging is performed using fixed or, occasionally, portable X-ray equipment. Workers in veterinary radiology operations may experience additional hazards from animal handling and behavior, depending on the animal’s distress and need for physical restraint. Employers can reduce such hazards by training veterinary workers on appropriate animal handling techniques and proper pain control, sedation, and anesthesia for animals. If it is not possible to position the animal through sedation or holding devices during the X-ray exam, employers should ensure a worker that restrains the animal is protected (e.g., aprons, gloves), and avoids the X-ray beam.

Manufacturing and Construction

There are many common uses of ionizing radiation in manufacturing and construction. For example, many precision measurement and nondestructive testing applications use radiography to inspect welds, measure the thickness of microelectronic wafers, develop polymers in the rubber and plastics industries, and measure and inspect the quantity and quality of goods produced during industrial quality control. Industrial radiography is also used in construction to determine ground densities for foundations; inspect concrete in buildings, bridges, and other structures; repair to inspect welds in shipbuilding and vessel maintenance; and in other settings to inspect other structural materials for fatigue. X-ray fluorescence (XRF), another technique involving ionizing radiation, is used to inspect paint for the presence and quantity of lead.

There are different types of industrial radiography devices1:

  • X-ray industrial radiography devices are powered by electricity. When the device is turned it, it produces X-rays; when it is turned off, it does not. X-ray industrial radiography devices generally create clear, detailed images that are used, for example, for testing automotive parts or aircraft parts. Because X-ray industrial radiography devices are large, they are often used in factories. OSHA and states have authority over these devices.
  • When gamma rays are used in industrial radiography, the ionizing radiation comes from radioactive material inside the device. Gamma ray devices do not need electricity. However, they cannot be turned off like an X-ray device because the radioactive material inside the device always produces gamma rays. The only way to "turn off" gamma rays emitted from an industrial radiography device is to interrupt the beam by covering the opening with a heavy metal plate. Because gamma ray industrial radiography devices are smaller than the X-ray devices, they are useful for checking inside pipes, ships, and other small spaces. They are also used as portable industrial radiography cameras for on-site inspections (e.g., testing concrete slabs). NRC and its Agreement States have authority over these devices.

Food and Kindred Products

In food safety applications, ionizing radiation (e.g., electron beams, X-rays) can kill microorganisms that cause food-borne illnesses—a process known as "irradiation." FDA is responsible for regulating the use of irradiation in the treatment of food and food packaging. The FDA regulations for irradiation in the Production, Processing and Handling of Food (21 CFR 179) do not include requirements to protect workers from ionizing radiation exposure. OSHA and States have authority to protect workers from electron beam linear accelerator and X-ray exposure during food irradiation. The NRC and its Agreement States are responsible for ensuring that radioactive materials (e.g., Cobalt-60) are used safely within irradiation facilities.


Accelerators are special pieces of equipment used in research and materials analysis; medical therapy; non-invasive security assessment (e.g., inspecting cargo in trucks and shipping containers); and for production of radionuclides for medical, research, and industrial uses. Special purpose particle accelerators use electrostatic or electromagnetic fields to increase the speed of electrically charged atomic particles and direct those atomic particles to collide with each other or other pre-selected targets. In the medical field, accelerator-produced particle beams or X-rays are directed at cancerous tumors. Accelerators can target life-threatening growths within a patient’s body, but can also potentially cause serious radiation exposure hazards to operators if not used safely.

Because of the increasing use of special purpose particle accelerators, OSHA issued a Safety and Health Information Bulletin (SHIB) in 2009 to identify exposures to radiation hazards and other hazards (electrical hazards from high-voltage systems, arc-flash/blast hazards, and fires), and to provide information on the safe operation of these devices. See Special Purpose Particle Accelerators (SHIB 07-31-2009).

OSHA has authority over worker exposures to ionizing radiation from accelerators that are operated to produce only particle beams, such as linear accelerators used for medical treatment. The NRC has authority over accelerators that produce radioactive materials, except for incidental accelerator-produced radioactive materials generated by particle accelerators that emit only particle beams and not radioactive materials (see the MOU between OSHA and the NRC).

Exposure Scenarios

When an individual works near a radiation source or with radioactive material, there is potential for both external and internal radiation dose. In general terms, dose means the body has absorbed energy from radiation.

External Dose

External dose occurs when a person works near a radiation source (i.e., unshielded or partially shielded) or with radioactive material that emits radiation in a field that penetrates (goes into or through) the body. Standing in an X-ray field is one example of external exposure.

  • External exposure to radiation-producing machines, such as X-ray machines, stops once the field is deactivated.
  • External exposure to radiation sources, machines containing radiation sources, or radioactive materials is minimized once the source or material is appropriately shielded or once the person leaves the radiation field.

If a person comes near an X-ray machine in use (as in the photo at right) or near radioactive material, the energy from the ionizing radiation may go through the body, but there is no radioactive material either on or inside the body unless the person becomes contaminated.


Contamination occurs when a person comes into direct contact with radioactive materials (not just the radiation field) and gets them on or inside the body. For example, a researcher could become contaminated if she or he spills a liquid that contains radioactive material onto her or his body or clothing, such as a lab coat or shoes.

Note that a worker can be exposed to an external radiation field and receive an external dose without directly coming into contact and being contaminated with the radioactive material. If a radioactive material gets inside a person’s body, then she or he will receive internal dose.

For information on screening levels for the clearance of potentially contaminated items or materials, see ANSI/HPS N13.12, Surface and Volume Radioactivity Standards for Clearance. DOE also provides guidance values for fixed and removable surface contamination levels in 10 CFR 835 Appendix D. These guidance values for contamination can be used to determine posting requirements, release requirements, and PPE requirements for contaminated areas and equipment.

Internal Dose

Internal dose is received when a radioactive material enters the body through inhalation (breathing in), ingestion (swallowing), absorption through the skin or an open wound, or injection. Radioactive materials can accumulate in different body organs.

For example:

Some methods to control internal doses include:

  • Make sure all wounds or cuts (including scratches and scabs) are protected from potential radiation contamination sources.
  • Do not eat, drink, smoke, take medicine, or chew gum in areas where radioactive materials are used or stored, radiation areas, high radiation areas, or airborne radioactivity areas.
  • Be careful not to rub eyes, scratch exposed areas of skin, or touch hair.

All efforts should be taken to avoid internal doses from contamination with radioactive materials. For more information on controlling ionizing radiation hazards and preventing dose, see the Control & Prevention page.

The U.S. Department of Health and Human Services (HHS), Centers for Disease Control and Prevention (CDC) provides additional information about the differences between radiation exposure and radioactive contamination on its Contamination vs. Exposure webpage.

1 U.S. Environmental Protection Agency (EPA), Industrial Radiography