Amendments to the U.S. Department of Health, Education, and Welfare Microwave Oven Performance Standard*

Abstract

The inclusion of a safety interlock monitor is discussed. Additional safety provisions using an interlock monitor are required for ovens manufactured after August 7, 1974.The United States radiation safety performance standard for microwave ovens, which was issued under the authority of the Radiation Control for Health and Safety Act of 1968, is applicable to all microwave ovens manufactured on or after October 6, 1971. The standard was designed to protect the public from possible dangerous exposure to microwave energy originating in microwave ovens by regulating those performance characteristics which could lead to microwave leakage. It is important to note that the “Act” only authorizes regulation of performance and precludes regulation of design.While the standard contains a number of protective aspects, two are paramount: (1) the limitation of microwave emission from an operating oven, and (2) the requirement for two interlock devices which must terminate generation of microwave energy upon opening of the oven door, or in the words of the standard, “when access to the cavity is possible.”During the interval between publication and the effective date of the standard an event occurred which raised serious questions about the adequacy of the two interlocks. The resolution of these questions is the main topic of this paper. It is appropriate, however, to examine some of the evidence of the adequacy of the emission control aspects of the standard.Between October of 1971 and April of 1973, a total of 349 certified ovens had been examined in the field and emission data tabulated.(a) The standard requires that oven emission not exceed 1 mW/cm2 prior to acquisition by the customer. The requirement is relaxed to 5 mW/cm2 after acquisition and remains so for the life of the oven. The chart, Table 1, summarizes the emission findings.