Radiation Emergency Preparedness and Response - Background (2024)

Background

This page defines radiation and radiation emergencies and provides examples of the types of incidents that workers and employers may encounter. It also introduces workers and employers to hazard assessment and radiation measurement and describes health effects associated with exposure to radiation.

On this page…for general businesses:

• What is Radiation?
• What is a Radiation Emergency?
• Examples of Devices that Can Cause Intentional Radiation Exposure
• How is Radiation Measured?
• How are Workers Exposed to Radiation?
• What are the Health Effects of Radiation Exposure?
• Occurrence of Radiation-Related Health Effects
• What other Adverse Effects Might Workers Experience During and After Radiation Emergencies?

What is Radiation?

Atoms are the basic building blocks of all matter, and atoms of many different types of elements occur naturally on the earth. Some of these atoms are unstable and give off energy to become more stable. In this context, an unstable atom is said to be "radioactive," and the energy it releases is referred to as "radiation." When the radiation has enough energy to ionize other atoms in its path (i.e., remove negatively charged particles called "electrons" from them), it is referred to as "ionizing radiation." Types of ionizing radiation include alpha, beta, and neutron particles; gamma rays; and x-rays. Ionizing radiation is usually the type of radiation of concern during a radiation emergency. In contrast, non-ionizing radiation has a lower energy that is not capable of ionizing other atoms. Examples include radio waves, microwaves, and infrared radiation. The spectrum below includes several examples of different kinds of non-ionizing radiation (on the left) and ionizing radiation (on the right).

While this webpage explains many of the important concepts necessary to understand radiation protection - both for emergency response workers and employers as well as workers and employers who are not emergency responders but may be affected by radiation emergencies - readers can also familiarize themselves with radiation by consulting the:

• OSHA Ionizing Radiation Safety and Health Topicspage.
• Centers for Disease Control and Prevention (CDC) Ionizing Radiationpage.
• Nuclear Regulatory Commission Radiation Basicspage.

What is a Radiation Emergency?

A radiation emergency refers to a non-routine situation in which there is a release of radiation or other risk of exposure to radiation. As is the case with all emergencies, prompt action is required to mitigate the hazard and adverse consequences for human health and safety, quality of life, property, or the environment. Radiation emergencies include nuclear and radiological events in which there is, or is perceived to be, a hazard due to a nuclear explosion, release of radioactive material, or unintended exposure to some other type of radioactive source.

A radiation emergency can result from an accidental or deliberate cause.

Accidental causes include:

• Releases from a fixed nuclear facility (e.g., a power plant or research or test nuclear reactor).
• Releases from non-nuclear facilities (e.g., laboratories and hospitals using radioactive materials).
• Lost, found, or orphan(i.e., no longer under proper control) sources of radioactive material (e.g., nuclear fuel sources, medical imaging devices).
• Transportation incidents.
• Nuclear weapons accidents.

Deliberate causes include:

• Improvised nuclear or radiological dispersal devices (described in greater detail, below).
• Sabotage or intentional releases at a fixed nuclear facility.
• Nuclear attacks by other nations (i.e., warfare using a nuclear weapon), either on the U.S. or elsewhere.

Depending on the source, size (power or amount of radiation released), location, timing, and other parameters of a radiological or nuclear event, such emergencies can affect areas ranging from a single room in a building to many square miles in catastrophic nuclear incidents. In rare cases, radiation emergencies can result in many illnesses, injuries, and fatalities and can cause substantial radioactive contamination and infrastructure damage. A non-nuclear radiation release may pose exposure hazards for workers near the release as well as workers responding to the emergency. Similarly, the initial blast wave and radioactive fallout - residual radioactive material, or radioactive particles in the air - from a nuclear detonation may expose workers in the area and emergency response workers to harmful levels of radiation. The blast and heat released from a nuclear detonation can also cause burns, flash blindness, disorientation, injuries to hollow organs and body cavities, blunt trauma, penetrating shrapnel wounds, and other injuries. Although this page does not provide guidance for long-term recovery, employers should keep in mind that some types of radiation emergencies could also pose hazards for recovery workers for years once sites are contaminated.

Examples of Devices that Can Cause Intentional Radiation Exposure

Radiological dispersal devices (RDDs), radiation exposure devices (REDs), and improvised nuclear devices (INDs) are examples of devices that could be used intentionally to expose people to radiation. The diagrams below illustrate examples of these types of devices. In an actual radiation emergency, the extent of damage, radiation contamination, potential for casualties, rescuers' ability to enter impacted areas, and other outcomes will vary greatly depending on many factors, including the type of device, source of the radiation, and atmospheric conditions at the time of deployment.

These diagrams are hypothetical and for illustrative purposes only. Scientists have developed much more realistic models of radiation emergencies, forecasted atmospheric conditions, and projected casualties. Examples of such modeling are included on the Additional Resourcespage.

Radiological dispersal device (RDD)

A RDD may use conventional explosives or mechanical means (e.g., a spraying mechanism) to disperse radioactive material in the area around the device. RDDs can be stationary or moving. In this example, a stationary RDD could disperse radioactive material in a hot zone around the device. The area in which people may be exposed to radiation may change depending on many factors, including environmental conditions (e.g., wind).

Radiation (or radiological) exposure device (RED)

A RED placed on a moving vehicle such as a bus could expose passengers, the vehicle driver, and others within a small radius around the vehicle’s path of travel. In other scenarios, a RED may be a stationary device that exposes individuals who are near it or pass by it.

Improvised nuclear device (IND)

A nuclear explosion from an IND could result in extensive loss of life, injury, and illness in the area around where the detonation occurred. Dangerous radioactive material in the air would pose a significant radiation hazard through radioactive fallout for hours to days after the explosion, depending on the size of the explosion, environmental conditions at the time of the incident, and other factors.

How is Radiation Measured?

Radiation is measured in a variety of ways using different units depending on whether radioactivity, exposure, absorbed dose, or dose equivalent (dose adjustedfor the radiation type's potential ability to damage the body) are being described. For many types of workers and employers without emergency response roles, a basic understanding of radiation measurement, exposure, and dose is sufficient. However, employers, workers, and other decision makers who are responsible for the health and safety of themselves or other emergency personnel involved in response and recovery operations may need a more in-depth knowledge of radiation measurement and units.

Basics of Radiation Measurement

In radiation emergencies and other scenarios where radiation exposure is a potential hazard, hand-held survey meters can be used to quantify (i.e., measure) radiation exposure. The traditional unit for radiation exposure in the U.S. is the Roentgen (R).

Workers receive a radiation dose as a result of being exposed to radiation. The traditional unit for radiation dose in the U.S. is the Radiation Absorbed Dose, or "rad."

Some specially trained first responders from local, state, and federal governments will be equipped with personal radiation dosimeters that measure the dose rate and total dose received. These meters, along with exposure monitoring and dosimetry for responders, are discussed in more detail in the Responsepage.

More about Radiation Exposure and Dose

The previous section offers a basic discussion of radiation exposure and dose. This section provides more information that may be useful to employers and workers who must make decisions to protect themselves and others during radiation emergencies. However, an understanding of exposure and dose should not be a substitute for the knowledge of a person with appropriate training in radiation dose monitoring, health physics, and other aspects of worker health and safety.

Two important units of radiation measurement - the Roentgen (R) and rad - were introduced in the previous section. These and some additional units are used differently depending on which of four important aspects of radiation measurement they describe:Radioactivity,Exposure,Absorbed dose, orDose equivalent ("READ"):

• Radioactivityis the number of energized particles or waves emitted by a source of radioactive material per unit of time (e.g., second) and is typically measured in curies (Ci) or Becquerel (Bq).
• Exposureis a defined amount of x-ray or gamma radiation that interacts in a volume of air and is measured by exposure monitoring equipment in roentgens (R) or coulombs per kilogram (C/kg).
• Absorbed doseis the amount of radiation energy absorbed per unit mass of an individual or object and is typically measured in rads or grays (Gy).
• Dose equivalentquantifies in units of Roentgen Equivalent Man (rem) or Sieverts (Sv) the amount of radiation absorbed by an individual, adjusting for the damaging potential of the type of radiation using weighting factors (W_R) (formerly called quality factors, or Q). For beta and gamma radiation, the dose equivalent is equal to the absorbed dose (i.e., 1 rad (0.01 Gy) absorbed dose = 1 rem (0.01 Sv) of equivalent dose). With alpha and neutron radiation, the dose equivalent is higher per unit of absorbed dose due to the damaging potential of these types of radiation.

Effective doseaccounts for the separate contributions to the total risk from each exposed body part. Tissue weighting factors are assigned to various body parts, based upon their sensitivity to ionizing radiation (i.e., radiosensitivity), for the risks of lethal cancer and serious prompt genetic effects. The effective dose is the sum of the tissue-weighted dose equivalents and gives an overall calculated dose as if the dose were to the whole body.

Note that while OSHA’s Ionizing Radiation standards (including 29 CFR 1910.1096in general industry and, to the extent it applies, shipyard employment, marine terminals, and longshoring; and 29 CFR 1926.53in construction) are based on limiting the dose to the most critically exposed part of the body, they do not use effective dose. See the definition of "dose" in paragraph (a)(5) of the general industry standard, which reflects the quantity of ionizing radiation absorbed, per unit of mass, by the body or by any portion of the body.

Because most radiation emergencies involve x-rays or gamma rays, this webpage considers 1 R = 1 rad (0.01 Gy) = 1 rem (0.01 Sv). For beta particles, 1 rad (0.01 Gy) also equals 1 rem (0.01 Sv). As mentioned previously, however, this equivalency does not apply to alpha or neutron particles. For alpha particles, 1 rad (0.01 Gy) = 20 rem (0.2 Sv). For neutron particles, the relationship (i.e., weighting factor) depends on the neutron energy.

The U.S. Department of Health and Human Services provides more information for understanding radiationin its Radiation Emergency Medical Managementtool.

How are Workers Exposed to Radiation?

Workers can be exposed to radiation in various ways. Everyone is exposed to low levels of radiation every day from what is known as "background radiation." Background radiation is constantly present in the environment, and exposure to it is part of everyday life. It is generally the result of ionizing radiation that is emitted from a variety of natural (e.g., radon, cosmic rays) and artificial (e.g., medical imaging equipment, tobacco products) sources. The average annual radiation dose to people in the U.S. is approximately 620 millirems (mrem) per year (yr) (6.2 mSv/yr). About half of this, or 310 mrem/yr (3.1 mSv/yr), comes from naturally-occurring background radiation.1The other half (i.e., artificial sources) comes from medical imaging (e.g., x-rays and computed tomography, or CT, scans).2For example, a chest x-ray gives a dose of about 6 mrem (0.06 mSv), depending on the view(s) captured during the procedure, and a conventional chest CT scan gives a dose of about 800 mrem (8 mSv).3

Radiation emergencies can result in worker exposure to radiation that is significantly higher than background radiation. During emergencies, doses to workers in the area of the emergency and to first responders responding to the emergency might exceed the normal occupational exposure limits for workers (e.g., those set by OSHA in its Ionizing Radiation standards, the U.S. Department of Energyfor workers in its own facilities, and the Nuclear Regulatory Commissionfor facilities operating under its licenses or authorities of its agreement states).

There are several ways in which a worker could be exposed to radiation during radiation emergencies, depending upon the type of incident. In general, radiation exposure occurs when a worker is in close proximity to an unshielded or partially shielded radiation source, contaminated surfaces, or radioactive materials, or if a worker has become contaminated with radioactive materials. A worker can be exposed to radiation and receive a dose without being contaminated with radioactive materials.

To understand the difference between radiation exposure and contamination with radioactive materials, consider two examples:

• Exposure:A worker uses an x-ray machine to examine the structural integrity of metal pipes. The machine is not working properly andexposesthe worker to radiation but not radioactive contamination.
• Contamination:A researcher in a lab spills a liquid that contains radioactive material. The liquid spills onto the researcher's hands, lab coat, and shoes. The spill results incontaminationof the worker's body and clothing and can also result in exposure to the radiation emitted by the material.

The examples below illustrate the difference between radiation exposure and radioactive contamination.

A researcher could becomecontaminatedif she spills a liquid that contains radioactive material onto her body or clothing, such as a lab coat or shoes.

A worker could beexposedto radiation while working with faulty industrial radiography equipment (not pictured) if the machine emits excess or improperly controlled radiation. This type of exposure does not result in contamination.

The table below lists some types of radiation emergencies and the potential for worker exposure or contamination. Note that the examples are generalities only, as there are many additional considerations, such as the type of radiation involved, the activity, the proximity of the worker to an incident or radiation source, and environmental conditions that can impact a worker’s radiation dose in each situation.

Radiation emergencies with the potential for worker exposure and contamination

CDC provides additional information about the differences between radioactive contamination and radiation exposure on its Contamination vs. Exposurewebpage. The CDC page further breaks down internal and external contamination and radioactive contamination due to deposition of radioactive materials.

What are the Health Effects of Radiation Exposure?

The health effects of radiation exposure depend upon the dose a worker receives. Because ionizing radiation can cause cancer, there is assumed to be no safe level of exposure or safe dose. Thus, all radiation doses should be maintainedAsLowAsReasonablyAchievable (ALARA) - a balancing approach that optimizes the best result with the lowest dose possible.

Health effects can be grouped into two categories based on how dose affects their onset:

• The severity increases and/or time between when exposure occurs and symptoms begin decreases fordeterministichealth effects as a greater dose of radiation is absorbed. Deterministic health effects include sterility, hair loss, skin reddening/burns, and Acute Radiation Syndrome (ARS). (ARS is a collection of symptoms attributable to damage to bone marrow and the gastrointestinal, cardiovascular, and central nervous systems.) Effects with potentially rapid onset, such as death, are also considered deterministic since the time they take to develop or occur is linked to dose. Deterministic health effects often have a threshold dose below which they do not typically occur. Although it may not accurately describe all deterministic health effects, they are sometimes described as "short-term" health effects.
• The probability of symptoms ofstochastichealth effects increases with radiation dose, but dose does not increase the severity. Stochastic health effects include cancer and other genetic effects. Development of cancer, including leukemia and other malignancies, is possible at any dose, with increasing probability as the dose increases. These health effects may not appear until many years after exposure. Stochastic health effects generally do not have a threshold dose below which they do not occur. This is the reason that no level of radiation exposure is considered to be completely "safe" and why doses should always be kept ALARA. Although it may not accurately describe all stochastic health effects, they are sometimes described as "long-term" health effects.

Many factors may influence the outcomes of receiving a radiation dose, particularly a high dose. Each individual exposed to a particular dose of radiation may respond differently according to his or her unique characteristics, including age at time of exposure, various comorbidities (i.e., other medical conditions) and other factors related to the exposure itself, including:

CDC Radiation Hazard Scale

• Type of radiation (generally for stochastic effects only).
• Radiation source.
• Dose rate of exposure (which may vary by distance from a radiation source) and length of time exposed.
• Total dose (in non-technical terms, the amount of radiation absorbed by the body).
• Tissues/organs exposed to radiation source.
• Chemical form and particle size of any radionuclide(s).
• Control measures in place, including shielding and personal protective equipment (discussed further on the General Businesses, Preparedness, and Responsepages).
• In addition, route of exposure may also play a role in the development of health effects. For example, doses from external radiation may be more likely to result in development of ARS than would a dose from inhalation or ingestion of radioactive material.4

In general, higher radiation doses, particularly those well above the range of levels people are exposed to in everyday life, are more hazardous to worker health than lower doses. CDC has developed a radiation hazard scale for short-term exposures (e.g., up to a period spanning several days) during emergencies that provides a frame of reference for relative hazards of radiation and conveys meaning without using radiation measurements or units that are unfamiliar to most people. More information, including descriptions of the radiation hazard scale categories, is available on CDC’s Radiation Hazard Scalewebpage.

At lower doses, particularly below 50 rem (0.5 Sv), radiation may cause short-term changes in blood chemistry, including the count, structure, and function of various types of blood cells. Other deterministic effects of lower-dose radiation exposure include:

• Birth defects at doses at or above about 10–20 rad (0.1–0.2 Gy) to the embryo/fetus.5
• Temporary sterility at doses at or above 15 rad (0.15 Gy) to the testes in a brief single exposure.6
• Detectable lens opacities (which, when they cause vision problems, are known as cataracts) at doses at or above 50 rad (0.5 Gy) to the lens of the eye.7

Although unlikely with most types of radiation emergencies, higher radiation doses to most of the body absorbed over a short period of time (i.e., several minutes) may result from an event such as a nuclear detonation (e.g., from an IND). Such highly concentrated doses may cause more serious, damaging health effects, including ARS-like symptoms. Damage to bone marrow and various body systems typically would be expected at doses around 70 rad (0.7 Gy), although mild symptoms may be observed with doses as low as 30 rad (0.3 Gy).8ARS manifests in four stages:

• During theprodromal stage(i.e., the period of early signs and symptoms), individuals may experience nausea, vomiting and diarrhea within minutes to days following exposure.
• During thelatent stage, individuals may look and feel healthy for a few hours or weeks before symptom onset.
• During themanifest illness stage, symptoms lasting a few hours to several months may depend on the specific syndrome and dose.
• Finally, individualsrecoverwithin several weeks to months after exposure, or they die from fatal doses.

CDC provides additional information about ARS, including fact sheets for the general publicand clinicians.

The tables below describe the health effects that may be associated with serious radiation emergencies, based on development over the short (immediate to days) and long (across many years) terms. The tables also discuss ARS, including at various risk levels by dose and time-to-onset by dose. Health effects associated with hazards other than radiation are described separately in the next section.

Risk of adverse health effects as a result of radiation exposure

Included in the table are estimates of excess lifetime risk of fatal cancer due to short-term radiation exposure. This excess lifetime risk of fatal cancer represents the risk of developing a fatal cancer sometime in the exposed individual's lifetime that is thought to be attributable to the radiation exposure, compared to the risk of developing such a fatal cancer among someone without the radiation exposure. Although the word "attributable" implies that the cancer is caused by the radiation exposure, it should not be interpreted as indicating that radiation exposure was determined to have caused cancer development. Rather, there is an association between being exposed to radiation and developing cancer; but many other factors, including other exposures, can also contribute to developing cancer.

Exposure or dose estimates producing certain health effects may vary, as radiation effects vary by exposure source, individual who is exposed, and other factors. The tables are provided for general reference, but should not be considered a definitive guide to health effects at certain discrete doses.

Occurrence of Radiation-Related Health Effects

Although scientists have more information about radiation-related health effects than about some toxic chemicals, data describing some types of deterministic and stochastic health effects and how often they occur are still limited. In some instances, information comes from major radiation events in history. The World Health Organization reports on thyroid disease, blood and solid organ cancers, deaths, and other health effects among individuals exposed to radiation from the 1986 Chernobyland 2011 f*ckushima Daiichinuclear power plant accidents, for example. A variety of studiesalso have explored similar outcomes among survivors of the atomic bombs detonated over Hiroshima and Nagasaki, Japan, in 1945 at the end of World War II.

What Other Adverse Effects Might Workers Experience During and After Radiation Emergencies?

Radiation is not the only hazard associated with radiation emergencies. For example, workers may face hazards such as slips, trips, and falls on uneven walking and working surfaces or falls from heights; heat, fire, or explosions from ruptured gas lines; downed electrical wires; structural collapse; hazards from trenches; run-over and roll-over injuries associated with heavy equipment; and air contaminants, such as silica or asbestos. Additionally, exposure to heat and blast energy from an explosion, particularly in the case of a nuclear detonation, may cause other adverse effects. The table below describes possible hazards and adverse effects beyond those associated directly with radiation exposure.

Other, non-radiation health effects

^{* Document or other resource available for a fee through the National Council on Radiation Protection and Measurements (NCRP), which was chartered by the U.S. Congress in 1964 to "collect, analyze, develop and disseminate in the public interest information and recommendations about protection against radiation."}