(2) For exposures of the whole body to X or gamma rays up to 3 million electron volts (Mev), this condition may be assumed to be met if the "air dose" does not exceed 1.25 roentgens provided the dose to the gonads does not exceed 1.25 rem. "Air dose" means that the dose is measured by a properly calibrated appropriate instrument in air at or near the body surface in the region of highest dosage rate.

(b) Employees may receive doses to the whole body greater than those permitted under paragraph (a) of this section, provided:

(1) During any calendar quarter the dose to the whole body shall not exceed 3 rems; and

(2) The dose to the whole body, when added to the accumlated occupational dose (which includes exposure of an individual to radiation in the course of employment in which the individual's duties involve exposure to radiation) to the whole body, shall not exceed 5 (N-18) rems where "N" equals the individual's age in years at his last birthday; and

(3) The contractor maintains adequate past and current exposure records which show that the addition of such a dose will not cause the individual to exceed the amount authorized in 41 CFR 50-204.306(b) (2).

(c) No employer shall permit any employee who is under 18 years of age to receive in any period of one calendar quarter a dose in excess of 10 percent of the limits specified in the table in paragraph (a) of this section. (See also requirements of Hazardous Order No. 6 (29 CFR 4.57) issued pursuant to the Fair Labor Standards Act of 1938.)

(d) "Calendar quarter" means any period determined according to either of the following subdivisions:

(1) The first period of any year may begin on any date in January; provided that the second, third and fourth periods accordingly begin on the same date in April, July and October, respectively, and that the fourth period extends into January of the succeeding year, if necessary to complete a three-month quarter. During the first year of use of this method of determination, the first period of that year shall also include any additional days in January preceding the starting date for the first period.

(2) The first period in a calendar year of 13 complete, consecutive calendar weeks; the second period in a calendar year of 13 complete, consecutive calendar weeks; the third period in a calendar year of 13 complete, consecutive calendar weeks; the fourth period in a calendar year of 13 complete, consecutive calendar weeks. If at the end of a calendar year there are any days not falling within a complete calendar week of that year, such days shall be included (for purposes of this part) within the last complete calendar week of that year. If at the beginning of any calendar year there are days not falling within a complete calendar week of that year, such days shall be included (for purposes of this part) within the last complete calendar week of the previous year.

(3) Alternatively, the four periods may consist of the first 14 complete, consecutive calendar weeks; the next 12 complete, consecutive calendar weeks; the next 14 complete, consecutive calendar weeks; and the last 12 complete, consecutive calendar weeks. If at the end of a calendar year there are any days not falling within a complete calendar week of that year, such days shall be included (for purposes of this part) within the last complete calendar week of that year. If at the beginning of any calendar year there are days not falling within a complete calendar week of that year, such days shall be included (for purposes of this part) within the last complete calendar week of the previous year.

(4) No employer shall change the method observed by him of determining calendar quarters (for purposes of this part) except at the beginning of a calendar year.

[28 F.R. 8208, Aug. 9, 1963, as amended at 29 F.R. 1438, Jan. 29, 1964; 29 F.R. 1620, Jan. 31, 1964]