Performance standard for microwave and radio frequency emitting products

This report contains a review of the requirements contained in the Food and Drug Administration (FDA) Standard for Microwave and Radio Frequency Emitting Products. Details include information on power density levels, user and service instructions and labeling.

Introduction

The provisions of this standard are applicable to microwave ovens manufactured after October 6, 1971. In 2016, changes were published for Standard for Microwave and Radio Frequency Emitting Products. This report will synopsize the latest version. For complete details, see 21 CFR 1030. Standards on microwave and radio frequency products are administered by the Food and Drug Administration.

Definitions

• Microwave oven means a device designed to heat, cook or dry food through the application of electromagnetic energy at frequencies assigned by the Federal Communications Commission in the normal ISM heating bands ranging from 890 megahertz to 6,000 megahertz. As defined in this standard, "microwave ovens" are limited to those manufactured for use in homes, restaurants, food vending or service establishments, on interstate carriers, and in similar facilities.
• Cavity means that portion of the microwave oven in which food may be heated, cooked or dried.
• Door means the movable barrier which prevents access to the cavity during operation and whose function is to prevent emission of microwave energy from the passage or opening which provides access to the cavity.
• Safety interlock means a device or system of devices which is intended to prevent generation of microwave energy when access to the cavity is possible.
• Service adjustments or service procedures means those servicing methods prescribed by the manufacturer for a specific product model.
• Stirrer means that feature of a microwave oven which is intended to provide uniform heating of the load by constantly changing the standing wave pattern within the cavity or moving the load.
• External surface means the outside surface of the cabinet or enclosure provided by the manufacturer as part of the microwave oven, including doors, door handles, latches and control knobs.
• Equivalent plane-wave power density means the square of the root-mean-square (rms) electric field strength divided by the impedance of free space (377 ohms).

Requirements

The subject standard (21 CFR 1030) specifies several design features for microwave ovens. All parameters must be thoroughly tested by the manufacturer for conformance to the standard.

• Power density limit — The power density of the microwave radiation emitted by a microwave oven must not exceed one (1) milliwatt per square centimeter at any point 5 centimeters or more from the external surface of the oven.
• Safety interlocks — Microwave ovens must have a minimum of two operative safety interlocks. At least one operative safety interlock on a fully assembled microwave oven must not be operable by any part of the human body, or any object with a straight insertable length of 10 centimeters. Such interlock must also be concealed, unless its actuation is prevented when access to the interlock is possible. Any visible actuator or device to prevent actuation of this safety interlock must not be removable without disassembly of the oven or its door. A magnetically operated interlock is considered to be concealed, or its actuation is considered to be prevented, only if a test magnet held in place on the oven by gravity or its own attraction cannot operate the safety interlock.
  
  Failure of any single mechanical or electrical component of the microwave oven must not cause all safety interlocks to be inoperative.
  
  Service adjustments or service procedures on the microwave oven must not cause the safety interlocks to become inoperative or the microwave radiation emission to exceed the specified power density limits as a result of service adjustments or procedures.
  
  Microwave radiation emission in excess of the limits specified in paragraph (c)(1) of this section shall not be caused by insertion of an insulated wire through any opening in the external surfaces of a fully assembled oven into the cavity, waveguide, or other microwave-energy-containing spaces while the door is closed, provided the wire, when inserted, could consist of two straight segments forming an obtuse angle of not less than 170 degrees.
  
  One (the primary) required safety interlock shall prevent microwave radiation emission in excess of the requirement of paragraph (c)(1) of this section; the other (secondary) required safety interlock shall prevent microwave radiation emission in excess of five milliwatts per square centimeter at any point five centimeters or more from the external surface of the oven. The two required safety interlocks shall be designated as primary or secondary in the service instructions for the oven.
  
  A means of monitoring one or both of the required safety interlocks shall be provided which shall cause the oven to become inoperable and remain so until repaired if the required safety interlock(s) should fail to perform required functions as specified in this section. Interlock failures shall not disrupt the monitoring function.

Measurement and test conditions

Compliance with the power density limit in paragraph (c)(1) of this section shall be determined by measurement of the equivalent plane-wave power density made with an instrument which reaches 90 percent of its steady-state reading within three seconds, when the system is subjected to a step- function input signal. Tests for compliance shall account for all measurement errors and uncertainties to ensure that the equivalent plane-wave power density does not exceed the limit prescribed by paragraph (c)(1) of this section.

Microwave ovens shall be in compliance with the power density limits if the maximum reading obtained at the location of greatest microwave radiation emission, taking into account all measurement errors and uncertainties, does not exceed the limit specified in paragraph (c)(1) of this section, when the emission is measured through at least one stirrer cycle. As provided in 1010.13 of this chapter, a manufacturer may request alternative test procedures if, as a result of the stirrer characteristics of a microwave oven, such oven is not susceptible to testing by the procedures described in this paragraph.

Measurements shall be made with the microwave oven operating at its maximum output and containing a load of 275 +/-15 milliliters of tap water initially at 20 +/-5 deg. centigrade placed within the cavity at the center of the load-carrying surface provided by the manufacturer. The water container shall be a low form 600-milliliter beaker having an inside diameter of approximately 8.5 centimeters and made of an electrically nonconductive material, such as glass or plastic.

Measurements shall be made with the door fully closed as well as with the door fixed in any other position which allows the oven to operate.

User instructions

Manufacturers of microwave ovens are required to provide, with each oven, radiation safety instructions which:

• Occupy a separate section and are an integral part of the regularly supplied users' manual and cookbook, if supplied separately, and are located so as to elicit the attention of the reader.
• Are as legible and durable as other instructions with the title emphasized to elicit the attention of the reader by such means as bold-faced type, contrasting color, a heavy-lined border, or by similar means.

Microwave user instructions must include the following precautions to avoid possible exposure to excessive microwave energy:

• Do not attempt to operate this oven with the door open since open-door operation can result in harmful exposure to microwave energy. It is important not to defeat or tamper with the safety interlocks.
• Do not place any object between the oven front face and the door or allow soil or cleaner residue to accumulate on sealing surfaces.
• Do not operate the oven if it is damaged. It is particularly important that the oven door close properly and that there is no damage to the: (1) door (bent), (2) hinges and latches (broken or loosened), and (3) door seals and sealing surfaces.
• The oven should not be adjusted or repaired by anyone except properly qualified service personnel.
• Include additional radiation safety precautions or instructions which may be necessary for particular oven designs or models, as determined by the Director, Bureau of Radiological Health, or the manufacturer.

Service instructions

Manufacturers of microwave ovens must provide servicing dealers and distributors with adequate servicing and radiation safety instructions which:

• Occupy a separate section and are an integral part of the regularly supplied service manual and are located so as to elicit the attention of the reader.
• Are as legible and durable as other instructions with the title emphasized so as to elicit the attention of the reader by such means as bold- faced type, contrasting color, a heavy-lined border, or by similar means.

Microwave service instructions must include the following precautions to be observed before and during servicing to avoid possible exposure to excessive microwave energy:

• Do not operate or allow the oven to be operated with the door open.
• Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave source, and make repairs as necessary: (1) interlock operation, (2) proper door closing, (3) seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, and (5) evidence of dropping or abuse.
• Before turning on microwave power for any service test or inspection within the microwave generating compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment, integrity, and connections.
• Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual before the oven is released to the owner.
• A microwave leakage check to verify compliance with the federal performance standard should be performed on each oven prior to release to the owner.
• Include additional radiation safety precautions or instructions which may be necessary for particular oven designs or models, as determined by the Director, Bureau of Radiological Health, or the manufacturer.

Labels

Microwave ovens are required to have the following warning labels:

A label, permanently attached to or inscribed on the oven, which must be legible and readily viewable during normal oven use, and which must have the title emphasized and be so located as to elicit the attention of the user. The label must bear the following warning statement:

A label, permanently attached to or inscribed on the external surface of the oven, which must be legible and readily viewable during servicing, and which must have the word "Caution" emphasized and be so located as to elicit the attention of service personnel must bear the following warning statement:

CAUTION: This device is to be serviced only by properly qualified service personnel. Consult the service manual for proper service procedures to assure continued compliance with the federal performance standard for microwave ovens and for precautions to be taken to avoid possible exposure to excessive microwave energy.

Exemptions

Upon application by a manufacturer, the Director, Bureau of Radiological Health, Food and Drug Administration, may grant an exemption from one or more of the statements (radiation safety warnings) specified in the standard.

The exemption shall be based upon a determination by the director that the microwave oven model for which the exemption is sought should continue to comply with certain requirements under the adverse condition of use addressed by such precautionary statement(s). Copies of the written portion of the application, including supporting data and information, and the director's action on the application will be maintained for public review. The application shall include:

1. The specific microwave oven model(s) for which the exemption is sought.
2. The specific radiation safety warning(s) from which exemption is sought.
3. Data and information which clearly establish that one or more of the radiation safety warnings is not necessary for the specified microwave oven model(s).
4. Such other information and a sample of the applicable product if required by regulation or by the Director, Center for Devices and Radiological Health, to evaluate and act on the application.

References

1. Performance Standards for Microwave and Radio Frequency Emitting Products, 21 CFR § 1030 (2016). (Accessed 2/27/2017).

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