Approved February 23, 1968
In November 1959 the National Committee on Radiation Protection and Measurements1 issued a statement designed to limit the exposure rate for radiation emitted by home television receivers.2 (The statement is set out in full in Annex 1 below.) The recommendation in that statement has since been used by most, if not all, manufacturers of television receivers with reasonable interpretation and understanding. It is as follows: “To insure that the television contribution to the population gonad dose will be only a small fraction of that due to natural background radiation, the NCRP recommends that the exposure dose rate3 at any readily accessible point 5 cm from the surface of any home television receiver shall not exceed 0.5 mr per hour under normal operating conditions.”
Recent events have indicated that some changes in television receiver design, function and manufacture have introduced conditions under which some of the sets, particularly color television, have not met the recommended limits. Also, some legitimate questions have been raised regarding measurements to assure compliance with the recommendation and regarding the meaning of some of the general terms used in the NCRP statement, e.g., “readily accessible point” and “normal operating conditions.” Accordingly, the Board of Directors of the Council has re-examined the statement. This was done at the regularly scheduled meetings of the Board held on June 16, 1967 and on December 15, 1967, and the basic intent of the statement of November 1959 was reaffirmed.
It is recognized that some aspects of the 1959 statement require clarification or explanation, but there is a need for additional positive and unambiguous data or information on which to base more detailed specificity. Any standard adopted now or in the foreseeable future will be based on, in addition to technical data, many value judgments and elements of practicability. Failure to realize this could, on the one hand, lead to an unjustified complacency about the use of a radiation-emitting device such as a television receiver in the home. On the other hand, insistence on the elimination of radiation beyond some reasonable point could result in unnecessary, and perhaps very costly, changes in home television sets; furthermore, it would be inconsistent with other principles of radiation protection.
The NCRP intends to give further study to the broad problems resulting from the use of radiation-emitting devices by the general public through its recently established Scientific Committee on Radiation Exposure from Consumer Products. This Committee will consider in detail the problem of home and other television receivers. In the meantime, judicious application of the performance standards outlined herein by industry, governmental agencies and individuals should assure adequate control of potential radiation exposure from home use of television receivers.
The judgment of the NCRP is that the use of television receivers in the home should not contribute to the annual genetically significant dose of the population in excess of about five percent of the average dose from natural background radiation (about 120 mrem in a year). For comparison, this amount is less than the difference in natural background radiation between some adjoining states, or even sections of many cities. It should be noted that, indirectly, such a limit assures that whole body exposure and exposure of other parts of the body will be suitably limited.
At the time of the 1959 statement, the principal source of x-ray emission was the front of the picture tube, from which the radiation is given off in a broad beam of nearly uniform spatial distribution. There is no significant difference between the maximum exposure rate at a point and the exposure rate averaged over an area comparable to that of the tube face. More recently other potential sources of x rays from television receivers, such as rectifiers and voltage regulators, have become of greater significance; the radiation from these components is sometimes emitted in relatively small beams.
For purposes of evaluation it is therefore necessary (1) to allow for the fact that the smaller the beam the less is the likelihood that the same area of an individual will be repeatedly or continuously exposed, and (2) to take into consideration the area of the radiation beam in relation to the area of coverage of the instrument used for measurement. The smaller the beam the greater is the ratio of the beam’s true exposure rate to the average as indicated by the instrument. It is considered that the basic intent of the NCRP recommendation will be met if the exposure rate, averaged over an area of 10 square centimeters, does not exceed the stated 0.5 mR in an hour at any external location 5 cm from the surface of the television receiver cabinet.
For practical purposes, instruments having sensitive areas on the order of 100 square centimeters are conventionally used to measure with acceptable accuracy the exposure rates in small beams; the instrument reading represents the average exposure rate over its effective sensitive area, and hence must be corrected for beam size.
The phrase, “under normal operating conditions,” as used in the 1959 statement, means that the potentially radiative components, and the set, shall operate within the specifications defined in accordance with accepted industry practices; it is intended that the specified radiation output should not be exceeded over that range of operating conditions within which the television receivers would be expected to operate and perform their function.
It should be realized that even a slight increase in potential on the picture, rectifier and/or voltage regulator tubes results in a great increase in exposure rate, e.g., increasing the potential on the picture tube from 25 to 30 kV may increase the exposure rate by 10 to 20 fold.
Special attention should be given to the possible exposure of television repairmen and other technicians in electronics fields; their previous training may not have alerted them to the possibility of x-ray emission from some components of television receivers. Individuals responsible for the training of electronics technicians, students and servicemen should be notified promptly of these problems, particularly as they apply to individuals under the age of 18.4
1Now the National Council on Radiation Protection and Measurements.
2Am. J. Roentgenology 84, 152 (1960) and Radiology 75, 122 (1960).
3Now referred to as exposure rate; see Radiation Quantities and Units, ICRU Report 10a (National Bureau of Standards Handbook 84, Washington, D.C., 1962). Also, the currently accepted symbol for roentgen is now R instead of r.
4See Radiation Protection in Educational Institutions, NCRP Report No. 32 (National Council on Radiation Protection and Measurements, Washington, D.C., 1966).
1959 NCRP Statement on Radiation from Television Receivers
At its meeting in November, 1959, the Executive Committee agreed that the NCRP should make a statement with regard to the maximum permissible dose from television receivers. Such a statement has been prepared and voted upon by the full committee.
The following position has been adopted by the NCRP:
During the past years, members of the NCRP have investigated the emission of x rays from television receivers. From a genetic point of view even sources of minute radiation are of significance if they affect a large number of people. X rays emitted by home television sets are, therefore, of interest because of the high percentage of the population involved. In order to insure that the television contribution to the population gonad dose will be only a small fraction of that due to natural background radiation, the NCRP recommends that the exposure dose rate at any readily accessible point 5 cm. from the surface of any home television receiver shall not exceed 0.5 mr per hour under normal operating conditions.
Laboratory and field measurements1 have shown that with this maximum permissible exposure level the television contribution to the gonad dose at the usual viewing distances will be considerably less than five percent of that due to the average natural background radiation. Most of the present television receivers already meet this requirement with a high factor of safety. In general, therefore, no changes in shielding of existing sets will be required. However, the recommended limit will insure that future television receivers, operating at higher voltages, will not contribute significantly to the population gonad dose.
1Braestrup, C.B. and Mooney, R.T. (1959). “X-ray emission from television sets,” Science, October 23, 1959, 130, 1071-1074.