Health Physics Questions and Answers - Question 26
Question 26 (a): There has been some confusion about the revised Part 20 requirements with respect to controlled areas and when individuals are receiving a public or an occupational dose. Before asking questions involving specific exposure scenarios (in parts b, c, and d of this question), does the NRC staff have any general guidance on these topics?
Answer: Anyone attempting to answer questions about which dose limits apply in a particular situation should be familiar with the requirements of 10 CFR 20.1201, 10 CFR 20.1207, 10 CFR 20.1208, and 10 CFR 20.1301, and with the definitions of the following terms in 10 CFR 20.1003: occupational dose, public dose, member of the public, restricted area, controlled area, and unrestricted area.
Occupational Dose vs. Public Dose
By definition, and with the exceptions given in the definitions of "occupational dose", any dose received by any individual in a "restricted area" is an "occupational dose." No one in a restricted area is a "member of the public." Outside "restricted areas" (i.e., in "controlled areas" or in "unrestricted areas"), whether the dose to an individual is an "occupational dose" or a "public dose" depends on whether the dose received by the individual is (as specified in the definition of "occupational dose") a dose received "in the course of employment in which the individual's assigned duties involve exposure to radiation and to radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee or other person." In other words, outside "restricted areas", whether the dose to an individual is an "occupational dose" or a "public dose" (and whether the occupational dose limits or the public dose limits apply to the individual) depends on what the individual is doing and not on what area (controlled or unrestricted area) the individual is in when the dose is received.
Different understandings of the meaning of the second part of the definition of "occupational dose" (which begins ". . . or in the course of employment . . .") has been a source of much of the confusion with respect to applicable dose limits. Generally, this part of the definition does not mean that any dose received by an individual while working, regardless of the type of work, is an "occupational dose." Doses received by an individual while working outside a restricted area (in a controlled or unrestricted area) usually would be categorized as public dose when the dose received is within the public dose limit (and is not likely to exceed that limit) and the work being done is not closely connected (i.e., is only casually connected) to the licensed activity.
The regulations (revised Part 20) allow licensees a certain amount of discretion in developing a radiation protection program that is suitable and practical to implement at the licensee's location and for the licensee's particular set of working conditions. For example, licensees are permitted by the regulations to select the boundaries for restricted areas and controlled areas. (Because licensees are not required by 10 CFR Part 20 to have controlled areas they may choose whether or not to have controlled areas.) When an individual is to work in a controlled area or an unrestricted area, the licensee should evaluate the individual's assigned duties and determine whether a dose would be categorized as a public dose or an occupational dose in accordance with the definitions of these terms in 10 CFR 20.1003.
The following criteria that include both regulatory requirements and basic radiation protection philosophy will be used in the NRC inspection program.
When an area satisfies both the definition of a restricted area in Part 20 and the definition of a protected area in Part 73, it is considered to be a restricted area for purposes of compliance with 10 CFR Part 20.
Boundaries of restricted areas may be selected by licensees but being selected, they should be documented (recorded) (good practice).
Access to restricted areas must be controlled, e.g., by barriers, signs, or guards (§20.1003). Note: Areas that can have personnel access controlled but that are not being controlled (e.g., because the radiation source has been removed) are not restricted areas.
Posting of a restricted area as a restricted area is not required although other posting may be required within the area (§20.1902).
Doses received by all individuals in restricted areas are occupational doses (§20.1003).
Individuals working in or frequenting a restricted area must be provided training, as appropriate (§19.12).
Individuals entering a restricted area must be informed that they are subject to occupational dose limits.
Effort must be made to maintain all doses ALARA (§20.1101).
A decision must be made as to whether monitoring is required (§20.1502).
Controlled areas are not required (§20.1003).
As indicated in the preceding section, an area that satisfies both the definition of a restricted area and the definition of a controlled area is considered to be a restricted area for purposes of compliance with 10 CFR Part 20.
Boundaries of controlled areas may be selected by licensees but should be documented (recorded) (good practice).
Posting of a controlled area as a controlled area is not required (§20.1902).
Doses received in controlled areas may be occupational doses or public doses. Generally doses will be public doses except when the licensee determines that an individual receives exposure to radiation "in the course of employment . . . ." [§20.1003, §§20.1301 (b)].
Doses are to be categorized as public doses (i.e., public dose limits apply) whenever reasonable and practical (good practice) (except for occupational doses).
In determining whether an individual in a controlled area is to be categorized as an individual who receives an occupational dose or as a member of the general public, the more difficult decisions concern individuals who may be occasionally exposed or whose assigned duties are not closely connected to the licensed activity. Such individuals include messengers, delivery men and women, custodial workers, secretaries, clerical workers, hospital volunteers, etc. Usually, such individuals are considered to be members of the public and the doses they receive are well within the limits for members of the public. However, if the assigned duties of these individuals are closely and frequently connected to the licensed activity, and their doses may approach or exceed the limits for members of the public, the doses such individuals receive are better treated as occupational doses. Only when doses are to be categorized as occupational doses (i.e., occupational dose limits apply) do the following conditions apply: - A decision must be made as to whether monitoring is required (§20.1502).
- The licensee should have the ability to exercise positive control over the individual's activities in the controlled area.
- The licensee should provide appropriate instructions.
- The licensee should inform the individual that he/she is subject to occupational dose limits rather than public dose limits (§19.12-this is an implied requirement).
Individual Members of the Public
Individuals in controlled areas and unrestricted areas are members of the public unless they are receiving an occupational dose (§20.1003 & §20.1301). Licensees should apply lower dose limits (public dose limits) to non-workers whenever possible and reasonable (good practice). An individual is not a member of the public when they enter a restricted area (§20.1003).
Effort must be made to achieve doses that are ALARA (§20.1101).
Question 26 (b): Do occupational dose limits or public dose limits apply to the doses received by the individuals described in the following scenarios for nuclear power plants?
Assume an individual employed by a licensee working at a two-unit site (one nuclear plant and one fossil plant) is permanently employed at the fossil plant, which is inside the nuclear plant's controlled area. The individual does not enter any restricted areas. What dose limits apply to that individual while working at the fossil plant?
What dose limits apply to a pregnant taxi driver while she is picking up and discharging passengers within the controlled area (outside the restricted area) of a nuclear power plant?
What dose limits apply (a) to construction workers who are building a second nuclear power plant within the controlled area (outside the restricted area) of the first nuclear power plant at that site and (b) to secretaries in the administrative building within the controlled area (outside the restricted area)?
Answer: For scenarios #1, 2, and 3, the dose limits for members of the public apply. However, if turbine shine from the nuclear plant is such that the individuals in scenarios #1 (fossil plant workers) and #3 (construction workers and secretaries) are likely to exceed the dose limits for members of the public, the licensee should consider the individual doses to be occupational doses and meet the requirements for individuals who receive occupational doses.
Question 26 (c): Do occupational dose limits or public dose limits apply to the doses received by the individuals described in the following scenarios for a hospital?
A hospital has defined a controlled area as all areas within the main building. These areas can only be accessed by doors which open to the outside environment. In addition, they have designated the hot lab as a restricted area. The hot lab can only be accessed through the nuclear medicine department.
Individual A is a maintenance worker. He is employed by the hospital and has been assigned to repair ventilation ducts in the nuclear medicine (NM) department. The job must be performed during normal work hours; patient procedures will not be rescheduled. The ducts are not used to ventilate the hot lab.
Individual B is an emergency room nurse employed by the hospital. On frequent occasions she accompanies patients to the nuclear medicine department for emergency lung scans.
Individual C is not employed by the hospital but visits the hospital on a weekly basis for the purpose of performing preventive maintenance on the gamma cameras. He frequently observes the nuclear medicine technologist during patient studies to verify equipment operation.
Individual D is employed by the hospital as a caretaker. During the summer he routinely cuts the grass outside the hospital. Note: The hot lab has at least one outside wall.
Answer: Occupational dose limits apply to individuals B (emergency room nurse) and C (who maintains gamma cameras). The assigned duties of individuals B and C are closely and frequently connected to the licensed activities. Limits for members of the public apply to Individuals A (who repairs a ventilation duct) and D (caretaker who cuts grass). The assigned duties of Individuals A and D are only remotely (and, in the case of Individual A, infrequently), connected to the licensed activity and it is reasonable and practical to apply the public dose limits.
Question 26 (d): Do occupational doses limits or public dose limits apply to the doses received by the individuals described in the following scenarios for a radiography company?
A large radiography company performs radiography both in the field and in a hot cell within its plant. The hot cell is located in the delivery bay. The company shares its physical plant with an affiliated company. UPS deliveries for both companies come to the same bay area. The radiography company has defined its restricted area to be the hot cell and its controlled area to be the delivery bay.
Individual E is a secretary employed by the radiography company. Her desk, where she performs all administrative assignments, is located in the delivery bay, adjacent to the hot cell.
Individual F is a data entry clerk at the affiliated company. He is employed by a temporary agency on a 12-month assignment. He is responsible for picking up all UPS shipments (within the controlled area).
Individual G is a co-worker of Individual E. He frequently enters Individual E's office to use the telephone to make personal calls during the course of a normal work day.
Answer: Individual E (secretary): Assuming that the secretary's location near a hot cell is essential, the occupational dose limits apply.
Individual F (clerk): Limits for the general public apply. There is only a casual connection between the individual's assigned duties and the licensed activity that results in the individual's exposure.
Individual G (co-worker): This individual is subject to the dose limits for a member of the general public. He has not entered a restricted area and his assigned duties do not involve exposure to radiation and to radioactive material from licensed and unlicensed sources of radiation.
(Reference: 10 CFR 20.1003)