Revision 0
January, 1983





"Orders requiring furnishing bioassay services" (WAC 402-24-080) indicates that the department may incorporate into a license provisions requiring a specific program of bioassay measurements as necessary or desirable to aid in determining the extent of an individual's exposure to concentrations of radioactive material.

This guide provides criteria acceptable to the department for the development and implementation of a bioassay program for any licensee handling or processing Tritium. It further provides guidance to such licensees regarding the selection of workers who should participate in a program to detect and measure possible internal radiation exposure. THE GUIDE IS PROGRAMMATIC IN NATURE AND DOES NOT DEAL WITH MEASUREMENT TECHNIQUES AND PROCEDURES.

The topics treated in this guide include determination of (1) whether bioassay should be performed, (2) frequencies of bioassay, (3) who should participate, (4) the actions to take based on bioassay results, and (5) the particular results that should initiate such actions.
FOR THE USER's convenience, the following terms are presented with their definitions as used in this guide:

Bioassay: The determination of the kind, quantity or concentration of radioactive material in the human body by urinalysis.

Intake: The total quantity of radioactive material entering the body.

1. Conditions Requiring Bioassay

A. Routine bioassay is required when quantities processed by an individual at any one time, or total amount processed per month, exceed those for the respective forms of tritium as shown in the attached Table I.
B. Above 0.1 of, but less than, the levels in Table I, routine bioassay is required unless a written justification is submitted for not performing bioassay.
C. Except as stated in 1.D below,bioassay is not required for process quantities less than 0.1 of those in Table I.
D.Special bioassay measurements should be performed to verify the effectiveness of respiratory protection devices and other protective clothing. If an individual wearing a respiratory protective device or protective clothing is subjected to a concentration of tritium in air (in any form) such that his or her intake with no protection would have exceeded that which would result from exposure for 40 hours per week for 13 weeks a t uniform concentrations of tritium in air as specified in WAC 402-24-220 Appendix A, Table I,* Column 1, bioassay should be performed to determine the resulting actual tritium intake. These special bioassay procedures should also be conducted, for personnel wearing respirators, if for any reason the average tritium concentration in air and the duration of exposure are unknown.

2. Who Should Participate

All workers involved in the processing of tritium under conditions specified in 1 above, or sufficiently close that intake is possible , should participate.

3. What Types of Bioassay Should be Performed

A.Baseline (including Pre-employment, or Pre-operational Urinalysis, not more than one month prior to beginning work with tritium requiring bioassay under Section 1 above).
B. Routine Urinalysis.
C.Post-operational. Within one month of last possible exposure to tritium
D.Diagnostic. Within one week of any sample exceeding levels given as action points in Section 5 below. See 5.A(2)(d).

4. How Often

A. Initial Routine Samples

Within 48 hours following entry of an individual into an area where operations require bioassay according to Section 1.A and B above, and then every two weeks or more frequently thereafter as long as the individual is working with tritium.

B. After 3 Months

The sampling frequency selected in accordance with Section 4.A above may be changed to quarterly if, after 3 months, the following 3 conditions are met:

(1) The average urinary tritium concentration form specimens obtained during the 3-month period does not exceed 3 µCi/liter.
(2) Where measurements of the concentration of tritium in air are required as a condition of the license, the quarterly average concentration (µCi/ml) to which workers are exposed, multiplied by the factor 6.3X108 ml does not exceed 0.8 mCi, and

(3) The working conditions during the 3-month period, with respect to the potential for tritium exposure, are representative of working conditions during the period in which a quarterly urinalysis frequency is employed, and there is no reasonable expectation that the criteria given in (1) and (2) above will be exceeded.

5. Action Points and Corresponding actions

A. Bi-weekly or More Frequent Sampling

(1) If urinary excretion rates exceed 5 µCi/liter, but are less than 50 µCi/liter, the following course of action should be taken:

(a)A survey of the operations involved, including air and area monitoring, should be carried out to determine the cause(s) of exposure and evaluate potential for further larger exposures.
(b)Implement any reasonable corrective actions indicated in the survey that may lower the potential for further exposures.
(c) A repeat urine sample should be taken within one week of the previous sample and should be evaluated within a week after collection.
(d) Any evidence from (a) and (b) indicating that further work in the area might result in an employee receiving a dose commitment in excess of the limits established in WAC 402-24-020 should serve as cause to remove the employee from work in this operation until the source of exposure is discovered and corrected.

(2) If urinary excretion rates exceed 50µCi/liter, the following course of action should be taken:

(a) Carry out all step in (1)(a) to (d) above.
(b) If the projected dose commitment exceeds 5 rems, report the incident to the department in accordance with WAC 402-24-190.
(c) Refer the case to appropriate medical/health physics consultation for recommendations regarding therapeutic procedures that may be carried out to accelerate removal of tritium from the body and reduce the dose as low as reasonably achievable.
(d) Carry out repeated sampling (urine collections of at least 100 ml each) at approximately one-week intervals, at least until samples show an excretion rate less than 5 µCi/liter. If the tritium is in a form such that there is a possibility of longer-term tritium exposure to certain body organs, continue sampling as long as necessary to ensure that appreciable exposures to these organs do not go undetected.

B. Quarterly Sampling

Carry out actions at levels as indicated under A. above, and if the excretion rate continues to exceed 5µCi/liter, also reinstitute biweekly (or more frequent) sampling for at least the next 6-month period, even when urinary excretion falls below 5 µCi/liter.

*Multiplying the concentration given in WAC 402-24-220, Appendix A, 5X10-6 µCi/ml, by 6.3X108 ml gives the corresponding quarterly intake of tritium by inhalation. This is assumed equal to the uptake of tritium (as HTO) by absorption through the skin unless the form of tritium in the air can be demonstrated to have lower uptakes. The total uptake, including skin absorption, would be assumed to be about 6.3 mCi, which delivers a dose commitment of about 1.25 rems to standard man.


(and other forms other than those in right-hand column)

HT or T2 GAS
In sealed process vessels


Nucleotide Precursors


HTO mixed with more than 10 kg of inert H2O or other substances (Ci/Kg)

In Open Room or bench, with possible escape of tritium from process vessels





With possible escape of tritium, carried out within a fume hood of adequate design, face velocity, and performance reliability





Carried out within gloveboxes, ordinarily closed, but with possible release of tritium from process and occasional exposure to contaminated box and box leakage





Table I

Table I


Quantities present (<10 Kg) may be considered either the amount processed by an individual at any one time (when accidental intake is more likely), or the amount of activity entered in process (throughout) during any one month (when routine handling of repeated batches is the more likely source of exposure). Concentrations in the right-hand column may be used when activity in process is always diluted in more than 10 Kg of other reagents, as in nuclear reactor coolant systems.