Module 5 - External Dose Limits

Annual Radiation Dose Limits

The State of Washington Department of Health (DOH), Radiation Protection Division has established dose limits which are based on recommendations from national and international commissions.

The table below lists the limits set by DOH:

Organ

DOH Limit
(mrem/year)
(Sv/year)

University of Washington investigation level (mrem)

Comments

Total Effective Dose Equivalent (TEDE)
Whole Body

5000
0.05

500/month
1000/quarter

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 Dose Equivalent
Lens of the Eye

15,000
0.15

1,500/month
3,000/quarter

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

Extremities
Shallow Dose Equivalent

50,000
0.5

5,000/month
10,000/quarter

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

Skin
Shallow Dose Equivalent

50,000
0.5

5,000/month
10,000/quarter

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

Embryo/Fetus

500 (for the entire pregnancy)
0.0005

50

Applies only when a Declaration of Pregnancy has been submitted

Occupational exposure of a minor

10% of the limits above

Occupational exposure of a minor is not permitted at the UW

Applies to anyone under 18 years of age

Member of the general public

100
0.0001

50

 

Investigational Levels

The University has established investigational levels at doses considerably less than the dose limits. When a worker accumulates during any part of a year a dose at or above the investigational level, the Radiation Safety Office (RSO) will investigate to determine causes of the dose and to recommend practices to minimize radiation exposure in the future.

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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 NRC 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.

To keep doses ALARA, the University has established investigational dose levels and will investigate any dose exceeding these levels in an effort to address causes of unnecessary radiation exposure.

In addition there are a variety of practical steps that you can take while working with sealed sources to minimize your radiation exposure. These steps will be described in detail in the Using Sealed Sources Safely Module.

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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 Section 6 of the University of Washington Radiation Safety Manual.

The Washington State DOH'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 RSO. All inquiries will be kept in confidence. Radiation Safety will take the following steps:

  • Provide an opportunity to submit a Declaration of Pregnancy.  (A Declaration of Pregnancy form may be obtained from Radiation Safety.)
  • 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 the University of Washington, it is rarely necessary to recommend reassignment or changes to job duties.

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

Section 6 of the University of Washington Radiation Safety Manual provides detailed information about the University of Washington's Declared Pregnant Worker Program

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This is the end of the Dose Limit Module, which is the fifth of the seven Sealed Source Radiation Basics training modules.  The next module is the Dosimetry Module.

Dosimetry (Module 6)

Back to the Sealed Source Training Introduction Page