Radiation Safety Training

  Initial Radiation Safety Training

Module 5: External & Internal Dose Limits
Overview of the Module

This module provides information about the following topics:

Annual Radiation Dose Limits

 The Ohio Department of Health (ODH) has established dose limits which are based on recommendations from national and international commissions.  The table below lists the limits set by the ODH:

Organ NRC Limit
Whole Body
Includes dose from both internal and external sources.  The Whole Body limit applies to exposure of the torso and head when the radiation is penetrating enough to irradiate tissues at a depth of  1 cm where the deeper blood-forming tissues are located. 
Lens of the Eye
The Lens of the Eye limit applies to exposure of the eye to radiation penetrating enough to irradiate the lens, at a depth of  0.3 cm. 
The extremities include the arm or leg below the elbow or knee.  The Extremities limit applies to exposure of the extremities when the radiation is penetrating enough to irradiate tissues at a depth of  1 cm. 
The Skin limit applies to dose deposited in the skin when the radiation is penetrating enough to irradiate tissues at a depth of  0.007 cm. 
500 (for the entire pregnancy)
Applies only when a Declaration of Pregnancy has been submitted 
Occupational exposure of a minor
10% of the limits above
Applies to anyone under 18
 years of age
Member of the general public



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As Low As Reasonably Achievable (ALARA)

Since the current model of radiation-induced cancer risk assumes that there is a risk no matter how low the radiation dose, it makes good sense to minimize radiation exposure. In fact, the University is required by ODH regulation to keep doses As Low As Reasonably Achievable (ALARA). This means that the University must work to keep doses as far below the dose limits as can reasonably be achieved.

There are a variety of practical steps that you can take while working in the lab to minimize your radiation exposure.  These steps will be described in detail in the Radiation Worker Safety Class.

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Annual Limits of Intake
Internal Exposure

Radiation exposure can occur both from radiation sources outside the body (external exposure) and from radiation sources within the body (internal exposure).  For example, internal exposure may occur through absorption through the skin when the skin becomes contaminated or when a volatile radioisotope, such as I-125, is inhaled.

Internal Dose Information for Common Radioisotopes

The ODH has defined a quantity, the Annual Limit of Intake (ALI), which is the amount of a specific radioisotope taken internally which will produce an annual Whole Body dose of 5000 millirems.  The following table below lists the ALIs for radioisotopes commonly used at Miami University:

Radioisotope ALI for Ingestion 
ALI for Inhalation
H-3 80 80
C-14 2 2
P-32 0.6 0.9
P-33 6 8
S-35 10 20
I-125 0.04 0.06

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Declared Pregnant Worker Program

This section provides a general overview of the Declared Pregnant Worker Program.  More detailed information about the program is available in the appendix of Miami University's Radiation Safety Manual.

The ODH's Fetal Dose Regulations apply only to a woman who has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.  The dose to the fetus resulting from occupational exposure of a declared pregnant woman may not exceed 500 mrem for the entire pregnancy.

Submitting a Declaration of Pregnancy

Any radiation worker who is pregnant or believes that she may be pregnant should contact the Radiation Safety Office. All inquiries will be kept in confidence.  The Radiation Safety Office will take the following steps:

  • Provide an opportunity to submit a Declaration of Pregnancy.  (A Declaration of Pregnancy form is included in the Radiation Safety Manual or may be obtained from the Radiation Safety Office.
  • Provide information concerning risk of fetal radiation exposure.
  • Evaluate the worker's dose history and exposure potential.
  • Make recommendations for reducing radiation exposure.
  • Monitor the worker's radiation dose with regard to worker and fetal dose limits.

For the type of radiation work performed at Miami University, it is rarely necessary to recommend reassignment or changes to job duties.

If a written declaration of pregnancy is not submitted to the Radiation Safety Office, then the worker's dose continues to be controlled under the normal dose limits for radiation workers.

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This is the end of the Dose Limit Module, which is the fifth of the six Radiation Basics modules.

Go to Module 6 (Radiation Monitoring Badges)

Miami University's Radiation Safety Office would like to thank Sue Dupre and Princeton University for the training materials used in this website.

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