TO : All Microwave Oven Manufacturers 

SUBJECT: Incident of Open Door Microwave Oven Operation Caused by a 

Loose Connector 

An incident of excessive microwave exposure resulting from the use of a 

microwave oven capable of operation with its door open was recently 

reported to the Bureau of Radiological Health. Examination of the oven 

revealed that a bare snap-on connector became loose from its designated 

terminal, touched an adjacent terminal and became welded to it; an 

occurrence which caused all safety interlocks to be by-passed and the 

oven to be operable with its door open. The snap-on connector was 

attached to a wire leading to the primary side of the high voltage 

transformer while the adjacent terminal received its power through the 

timer directly from the input voltage line of the oven. 

Mter the manufacturer examined more than 2,500 unsold ovens, the Bureau 

( determined that the occurrence was an isolated incident. However, in 

view of the highly significant risk of injury manifested by this incident, 

vie urge you to examine your present and future microwave oven designs 

and production processes to determine if there are adequate safeguards 

to prevent similar occurrences. Please consider the following or similar 

methods and procedures: 

1. Use of plastic covers on all snap-on connectors so that 

if a connector became loose and touched another energized 

terminal, no transfer of electrical energy could be made. 

2. Securely anchor any wire near its snap-on connector so 

that if the connector becomes loose, no contact to another 

energized terminal within the radius of free movement of the 

wir.e could be made. 

3. Provide sufficient separation between one group of terminals 

that feed energy to points prior to the safety interlocks and 

those that receive energy through the safety interlocks so that 

any (snap-on) connector of one group within the free movement of 

its wire could not reach any terminal of the other group. 
Page 2 - A11 Microwave Oven Manufacturers 

4. Initiate quality control procedures to assure that snap-on 

connectors are securely mated to their designated terminals. 

The Bureau of Radiological Health will evaluate future oven designs to 

determine if a potential exists for a repetition of the subject incident. 

Sincerely yours, 

/.$&g&/&/~&. 

Robert G. Br-itain 

Director 

Division of Compliance 

Bureau of Radiological Health 
DEPARTMENT OF HEALTH. EDUCATION. AND WELFARE 

PUBLIC HEALTH SERVICE 

FOOO AND ORUG ADMINISTRATION 

ROCKVILLE. MARYLAND 20857 

To: All Manufacturers and hporters of Microwave Ovens 

SubJect : Open Door Operation of Microwaxe Ovens as a Result of 

Oven Miswiring 6 

c -L 

Recently there have been three incidents in consumer locations in which 

the microwave oven operated with the door open due to oven miswiring. 

These incidents have resulted in expensive oven retesting and recall 

programs. It has also been learned that several workers at one manufacturing location had accidently been exposed to microwave radiation in 

several instances during oven testing, due to oven misviring that resulted in the continued operation of the oven after the daor was opened. 

The Bureau is greatly concerned that future incidents such as these 

could occur and result in the exposure of individuals to high levels of 

microwave energy. To reduce the potential for such open door operation, 

due to miswiring of the oven circuitry, the Bureau strongly recommends 

that all manufacturers consider instituting design features that will, (1) 

preclude analagous accidental miswiring of microwave ovens, or (2) if 

miswiring occurred, prevent the unit from operating with the door open. 

It is recommended that all manufacturers consider: 

1. Locating one safety interlock on the neutral side of the line 

and another on the high side of the line. 

2. Locating the monitor circuit as the last circuit branch in 

parallel with the high voltage transformer, or msking the "hot" 

A.C. line connection to the monitor circuit the last connection prior 

to connection with the primary of tHe power transforaer. 

3. Performing s failure mode effects analysis on each unique 

design to identify critical connections and wires where the accidentd interchange would result in electrically by-passing all 

safety interlocks and the monitor. 

4. Designing critical wire terminal connect wints so as to 

mechanically preclude accidental interchange of these wires to 

any unsafe configuration. 

5. Covering the terminals of critical wires with insulation to 

prevent any loose wire from being able to contact another point 

that might result in by-passing the safety interlock or monitor 

circuit . 

6. Using wire ties to limit the degree of movement of any wire 

that could become disconnected. 
t 

Page 2 - All Manufacturers and Importers of Microwave Ovens 

7. Instituting other design features that would prevent the miswiring of units or prevent units that are miswired from operating 1 

with the door open. 

Manufacturers must be careful not to introduce design changes that could 

result in noncompliance with the Federal perforinance standard. It is 

requested that proposed changes be submitted to the Bureau for review 

prior to incorporating the changes on production models. It may also bek i 

appropriate to submit prototype units to the Bureau for evaluation. 

It is equally important that certain good quality control practices be 

observed to help prevent these undesirable conditions. The Bureau is 

hereby requesting that all manufacturers now institute, if not already 

a part of their quality control and testing program, a specific test of 

each unit to determine that the unit will cease operating when the door 

is opened, and that it cannot be restarted, when the door is open. Any 

test that provides positive indication of magnetron shutdown upon latch 

release or door opening will be acceptable. 

The test must also include an attempt to restart the unit while the door 

is unlatched. This should be attempted both with the unit programed and 

not programed (for operation)for digital units, and with and without time 

on the timer for nondigital units, if the status of these controls could . alter the possibility of starting with the door open. 

We recognize that these tests require caze in order to prevent the 

exposure of the operator to high levels of 'microwave energy. In each 

case the door should be unlatched slowly and the operator instructed to 

terminate the test Mediately if a problem is noted. Also a mechanical 

stop is recomecded that would allow the door to be unlatched and opened 

slightly but which would prevent the door from opening to a position 

that would allow hzzardous levels of microwave energy to leak from the 

oven. 

Regardless of the type of test performed the test must be conducted at a 

point on the production that is subsequent to any assenbly, adjustment 

or repair of the unit that could alter the oven wiring. All operators 

must be instructed to immediately report any findings of open door 

operation to the proper quality control person so thzt the defective 

unit can be analyzed to deternine the cause of the failure. Manufacturers should take corrective action to prevent future incidents. 

Since the failure could be the result of a defective wiring component 

that is assembled in-house or purchased from a vendor, it is recommended 

that the assemblers of such components receive additional training and 

assembly aids that will help prevent defective wiring corqonents. Units 

of the components should be inspected on a sampling or 100% basis prior 
.2 

., 

Page 3 - hll Pbnufacturers and Importers of Microwave Ovens 

to being sent to the production line. If a defective component is found 

in a lot, then that lot should be rejected or 100 per cent tested prior 

to allowing the compnents to be sent to the assembly line- Where 

sampling is used, lots received after a rejected lot should be tested 

under a tightened sampling schedule until the results allow for return 

to a normal sampling schedule. 

Please institute any design and testing program changes necessary to prevent 

open door operation. The Bureau would welcome other suggestions which , could help prevent such incidents. 

Y - Robert Go Britain 

Director 

Division of ~om&ianc e I 

Bureau of Radiological Health 
4 

DEPARTMENT OF HEALTH. EDUCATION. AND WELFARE 

PUDLlC HEALTH SERVlCE 

FOOD AND DRUG ADMINISTRATION 

FIOCKVILLE. MARYLAND 20852 

JAN 2 8 i975 

To: All Manufacturers and Importers of Microwave Ovens 

subject: Safety Interlock Monitor Requirement (21 CFR 1030.10 (c) (2) (vi) ) 

The Performance Standard for microwave ovens requires that "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 ptil repaired 

if the required safety interlock(s) should fail to perf oxm required functions 

as specified in this section." 

There have been some misunderstandings with regard to the meaning of the 

. phrase "monitoring one or both required safety hterlocl,~.~' This provision 

' requires that a micxowave oven be rendexed inoperable f oll.owing the f aiI.ure 

of-either the primary or secondary interlock or'the fai3.ure of both the 

primary and secondary interlocks. A microwave oven which is not xendered 

inoperable unless an additional interlock (other than the primary and/or 

secondary) also fails, does not comply with the performance standard. You 

are being notified of this to avoid such misunderstandings in the future. 

Please address any inquiries ox questions concerning this matter to the 

attention of the consumer-Industrial Products Branch, Division of Compliance 

(301-443-6540) . 

Sincerely yours, 

Robert 6. Britain 

Director 

Division of Compliance 

Bureau of Radiological Health 
. . 

. * 

DEPARTMENT OF HEALTH. EDUCATION. AND WELFARE 

PUBLIC HEALTH SERVICE 

FOOD AND DRUG ADMINISTRATION 

ROCKVILLE. MARYLAND 20857 

MAR 2 2 1938 

TO: All Manufacturers of Microwave Ovens 

I 

SUBJECT: Potential Misad justment of Safety ~nterlock' Bnd .Monitor Switches 

The Federal Performance Standard for Microwave Ovens, 21 CFR 1030-10, 

requires that each microwave oven have a minimum of two operative safetyinterlocks which are intended to prevent generation of microwave energy 

when access to- the cavity is possible, -In addition, the performance 

standard requires that each oven be provided with a means of monitoring 

one or both: of the required safety- interlocks which shall cause the oven 

to- become inoperable if the monitored interlock(s) should fail in an 

unsafe condition. 

The -st <xrmmqn method of meeting these safety. interlock and nronitor requirements is through the use of snap action switches, On a-few models , 

tested at the FDA laboratory in Winchester, Massachusetts it has been 

possible to:mechanically adjust one or more of these safety switches to 

an unsafe failed condition, i.e., so that interlock contacts are always , 

( 

closed or monitor contacts are always opened. 

Service literature prwided by the manufacturers cautions serPice 

personnel to' make sure that these - switches are properly adjusted and 

provides adjustment procedures as required by the Standard, However, 

the Bureau is concerned that the procedures contained in service manuals. 

may not be adequate. to prevent these safety' switches from being inproperly 

installed or improperly adjusted during servicing so that one or more of 

these switches may be set to. an unsa£e failed condition, This concern 

is heightened by recent findings of noncompliance on individual ovens 

that were the result of impro&r servicing of ovens .for which proper 

service instructions had been published and made available in accordance 

with. the provisions of the Standard. 

- - 

To eliminate.the possibility of these safety-switches being improperly 

adjusted to an unsofe condition the Bureau requests each 'mufacturer of 

microwave ovens to.take the following actions; 

(1) Examine all model family designs in current production tr, 

determine if any of the interlock or monitor switches can be adjusted 

so that the interlocks are always closed or the monitors are always. - 

opened, 

(2) For those models or model families where such misadjusaaent is 

possible, manufacturers are requested to take whatever measures may 

be necessary to limit interlock or monitor switch adjustment range 

so that the switches cannot be adjusted to an unsafe failed condition, 
Page 2 - All Manufacturers of Microwave Ovens 

(3) Report any design or manufacturing changes made concerning 

these switches in a supplement to.& appropriate initial or 

model change report already submitted to the Bureau, 

(4) Examine all future model family designs to make sure that this 

problem does not exist in future models, 

The Bureau will closely monitor conforsnance with these-requests and 

believes that any necessary design or-manufacturing changes can be 

implemented within six months. If for any reason any specific models 

cannot be &f ied and the changes put .ininto- production in a six month 

period, please report to- the F&eau, the proposed changes, the reason 

for the delay and time needed to implement the change, 

Authokity: for this policy is found in 21 CPR, Subchapter J, 1030.10(c) (2) (iii), 

Your cooperation in investigating this matter and reporting on any 

changes made is appreciated. . I'f you have any questions &ncerning this 

matter please contact the Microwave/Acoustic Products Section at (301) 

443-6540, 

yours, 

- Robert G, Eritain 

Director 

Division of Compliance 

Bureau of Radiological Health. 
. . 

DEPARTMENT OF HEALTH & HUMAN SERVICES Publtc Health Service 

Food and Drug Administration 

8 7 5 7 Georgia Avenue 

Silver Spring MD 209 1 0 

TO: ALL MANUFACTURERS AND IMPORTERS OF MICROWAVE OVENS AND MICROWAVE 

BEATING EQUIPMENT 

SUBJECT: POTENTIAL CllEMICAL INTERACTION ON SAFETY INTERLOCK SWITCEES 

The Center for Devices and Radiological Health, Food and Drug 

Administration has documented a serious accidential radiation occurrence in 

which a laboratory worker was exposed to high levels of microwave radiation 

while using a household microwave oven to heat corrosive chemicals. Both 

the required safety interlock switches and the monitor system failed to 

prevent the oven from operating with the door open. The corrosive 

chemicals and vapors inside the oven cavity interacted with the contacts 

and springs of the safety interlock switches thereby rendering them 

inoperable. These chemicals, including reactive sulfides and chlorides, 

interacted vith the switches in one or two ways: (a) corrosion of critical 

metal parts such as springs and contacts occurred causing the springs to 

become brittle and the silver contacts to separate; and (b) the 

current-carrying switches became overheated due to high contact resistance 

caused by deposit of the chemicals on the metal parts. 

In this particular case the movable' spring inside the primary safety 

switch was fractured, one of the silver contacts inside the secondary 

safety switch was separated, and the movable spring inside the monitor 

switch was brittle. The oven was able to operate with the door open 

because there was permanent electrical continuity through the primary and 

secondary safety switches and permanent noncontinuity through the monitor 

switch. According to an analysis by an independent laboratory, it is 

believed that the corrosion and high contact resistance caused by the 

deposit of reactive chemicals were the primary initiators of severe 

overheating and spring failure of the switches. 

Manufacturers of household/commercial microwave ovens are encouraged to 

warn their users in the user instruction manuals to avoid using corrosive 

chemicals and vapors in the ovens, This type of oven is specifically 

designed to heat, cook or dry food and for use in homes, restaurants, food 

vending, or service establishments, on interstate carriers, and in similar 

facilities. They are not designed for industrial or laboratory use, 

Manufacturers of industrial microwave heating equi'pment such as those 

designed for laboratory use, should be aware of all potential environmental 

contamination of electronics and critical safety interlock switches, If a 

microwave oven or an industrial microwave heating unit is to be used or 

modified for hea'ting substances containing or producing corrosive 

chemicals, then it is essential that the equipment be designed to prevent 

harmful effects to the safety systems, i.e., adequate shielding of the 

electronics and venting of the corrosive fumes away from the oven as well 

as the user. Periodic checks of the continuity of the safety interlock 

switches is also recommended if the equipment is subjected to a severely 

corrosive chemical environment. 
If you have any further questions or concerns please contact the Microwave/ 

Acoustics Products Section at (301) 427-7187. 

Edwin A. Miller . Director, Division of 

Radiological Products 

Office of Compliance 

Center for Devices 

and Radiological Health 
DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service 

Food and Drug Administration 

OCi 3 1 19% 8757 Georgia Avenue 

Silver Spring MD 2091 0 

TO: ALL MANUFACTURERS AND IMPORTERS OF MICROWAVE OWNS 

.SUBJECT: INFORMATIONAL REQUIREMENTS FOR COOKBOOKS AND USER 

AND SERVICE MANUALS 

This notice is issued by the Center for Devices and Radiological Health (CDRB) 

to serve as guidance to manufacturers, importers, and assemblers of microwave 

oven products in the preparation of cookbooks and user and service manuals for 

their products. The outline below summarizes the specific requirements 

developed by CDRH for use in reviewing submissions. All microwave oven 

cookbooks and user and service manuals must meet these requirements to be 

considered acceptable. 

USER MANUALS AND COOKBOOKS 

The user manual must contain the required wording of the user 

precaution statements specified in 21 CFR 1030.10(~)(4)(iii). The 

required wording is specified by the regulations and cannot be changed. 

The Director of CDRH may also decide, if additional radiation safety 

precautions or instructions are necessary. 

The PRECAUTIONS title must be emphasized to elicit the attention of the 

reader. This can be accomplished by the use of bold print, contrasting 

color, or a heavy-lined border. The print size of the title should be 

at least as large as that of any other title that appears on the same 

page as the user instructions. The print size of the precaution 

statements should be at least as large as that of any other statements 

(excluding titles) that appear on the same page. 

The user precaution statements must be printed near the front of the 

user manual and before the operating instructions. 

Additional precaution statements are permitted so long as they do not 

detract from the required warnings. 

If the user precaution statements do not appear on the inside front 

cover of the manual or on a page prior to the table of contents, then 

the precaution statements should be referenced by page number in the 

table of contents. The table of contents should contain the wording 

"PRECAUTIONS TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE 

ENERGY" and the page number on which the user precaution statements 

appear. 

Supplements'to the user manual or cookbook, such as recipe booklets or 

quick reference cards or guides, may or may not require user precaution 

statements. In general, any supplements which include operational 

information for the oven should include the precaution statements or 

reference the location of the caution statements in the user manual or 

cookbook. 
SERVICE MANUALS 

REOUIRED STATEMENTS 

The service manual must contain the required wording of the service 

precaution statements as specified in 21 CFR 1030.10(~)(5). The 

required wording is specified by the regulations and cannot be changed. 

The Director of CDRH may decide that additional radiation safety 

precautions or instructions are necessary for particular oven designs. 

The PRECAUTIONS title must be emphasized to elicit the attention of the 

reader. This can be accomplished by the use of bold print, contrasting 

color, or a heavy-lined border. The print size of the title should be 

at least as large as that of any other title that appears on the same 

page as the user instructions. The print size of the precaution 

statements should be at least as large as that of any other statements 

(excluding titles) that appear on the same page. 

The service precaution statements must be printed near the front of the 

service manual and before the servicing instructions. 

Additional precaution statements are permitted so long as they do not 

detract from the required warnings. 

If the service precaution statements do not appear on the inside front 

cover of the manual or on a page prior to the table of contents then 

these statements should be referenced by page number in the table of 

contents. The table of contents should contain the wording: 

"PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID 

POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY," and the page number 

on which the service precaution statements appear. 

SCHEMATICS 

21 CFR 1030.10(~)(2)(~) states that the two required safety interlocks 

shall be designated as "PRIMARY" or "SECONDARY" in the manual for the 

oven. This designation should be shown on the schematic or wiring 

diagram or it may appear in the body of the service manual. 

Although not required by the regulations, we recommend that the monitor 

be identified on the schematic or in the manual as "MONITOR" or 

"SHORT SWITCH" or other similar wording. 

There should be no discrepancies between oven wiring diagrams and the 

schematic diagrams. 

The monitor circuit (system) may contain a maximum of two safety 

interlocks. One interlock system may be made up of a switch and a 

relay. 
5. Additional timers, fuses, and thermal protectors in the monitor circuit 

(system) are acceptable. Other components such as relays, triac, etc. 

may not be acceptable. 

6. If a relay or other unusual component is present in the monitor circuit 

(system), it must not be able to disrupt the monitoring function if 

any electrical or mechanical failure occurred. If it is able to, then 

the circuit is noncompliant and cannot be used. We recommend active 

testing of the monitor circuit (system) by simulating a failure and 

then checking to see that the oven will not operate with the door open. 

SERVICING PROCEDURES 

21 CFR 1030.10(c)(2)(iii) states that: 

"Service adjustments or service procedures on the microwave oven shall not 

cause the safety interlocks to become inoperative or the microwave 

radiation emission to exceed the power density limits of this section as a 

result of such service adjustments or procedures." 

Manufacturers, importers, and assemblers should incorporate review procedures 

for the following requirements in their quality control and testing programs to 

ensure that user and service instructions will not violate this standard. 

A. General: 

1. Adherence to the servicing instructions listed in the service manual, 

including adjustment and replacement procedures, should result in 

proper operation of the oven. 

2. The service manual should advise the reader that if the oven is 

operative prior to servicing, a microwave emission check should be 

performed prior to servicing the oven. 

3. The service manual should direct the reader to inform the manufacturer, 

importer, or assembler of any certified oven ynit found to have a 

microwave emission level in excess of 5 mW/cm . The manufacturer, 

importer, or assembler should instruct the service person to repair any 

unit found to have excessive emission levels at no cost to the owner 

(see 21 CFR 1004.2) and should attempt to ascertain the cause of the 

excessive leakage. The owner of the unit should be instructed not to 

use the unit until the oven has been brought into compliance. 

4. If the oven operates with the door open, the manual should instruct the 

service person to: 1) tell the user not to operate tile oven and 2) 

contact the manufacturer and CDRH immediately. 

B. Electrical Continuity Test: 

1. Review the continuity test procedures for accuracy and completeness. 

Check that the test should correlate with the wiring diagram and 

schematic in the manual. 

2. All page references in trouble-shooting sections should refer to the 

correct test procedures. 
C. Safety ~nterlocks/~onitor Replacement and Adjustment: 

The procedures listed in the service manual should be adequate to 

ensure that replacement and adjustment of the safety interlocks, 

monitor, mounting bracket, and/or latch mechanism will not result in 

excessive microwave emission. 

If the oven has been rendered inoperative due to the failure of the 

monitored safety interlock(s) then the manual should instruct the 

service person to replace all of the monitored safety interlock 

switches and the monitor switch. 

The procedures listed for changing the safety interlocks and monitor 

should correlate with the wiring diagram. 

The procedures listed should remind the serviceman to connect the 

monitor switch after replacement and to check interlock/monitor 

continuity. 

For non-zero motion door model designs, the procedures listed should 

include a check to ensure that the safety interlocks and monitor 

switches will actuate within a specified distance recommended by the 

manufacturer. 

D. Magnetron, Door and Hinge Replacement and Microwave Emissions Test: 

1. There should be adequate instructions provided in the service manual to 

allow the correct replacement of the magnetron, including a check for 

the presence of the wire mesh gasket. 

2. There should be adequate instructions provided to allow the correct 

replacement of the door, including a check for correct alignment with 

the hinge and cavity front face. 

3. Microwave emission testing procedures provided in the manual should be 

adequate. Instructions for testing should include: the correct wa er 5 load (275 ml.), the correct emission limit (no greater than 4 mW/cm to 

allow for measurement uncertainty), the correct scan speed (no faster 

than one inch per second), instructions to check all surface and vent 

openings, etc. 

Questions regarding this guidance should be directed to the Microwave/Acoustics 

Products Section of CDRH at (301) 427-7187. 

Ann B. Holt, DVM 

Acting Director 

Office of Compliance 

Center for Devices and 

Radiological Health 
DEPARTMENT OF HEALTH, ED'JCATION. AND WELFARE 

PUBLIC HEALTH SERVICE 

FOOD AND DRUG AD'?INlSTRATION 

ROCKVILLE. MARWS3 +OBV 

TO: All ~icr&wave Oven Manufacturers 

SUBJECT: Microwave Emission in Excess of the Standard as a Result of 

Improper Repair Procedure 

Two recent instances of excessive leakage from microwave ovens have been 

traced to.inadequate servicing procedures in which a magnetron was 

replaced +nd the metal mesh gasket used to provide an RF shield was 

2 omitted. In both instances emission levels in excess of 70 mW/a were 

found. 

As a result of these occurrences, the Burwu of Radiological Health wishes 

to remind all microwave oven manufacturers that 21 CFR 1030.10(c) (4) (i) 

requires that adequate instructions for service adjustments and procedures 

be provided. This includes adequate instructions (including precautions) 

for installation of RF seals and other devices to prevent microwave leakage. 

The Bureau requests that all manufacturers zeview their service instructions 

and replacement parts handling procedures to assure that they have provided 

adequate safeguards to prevent similar occme?ces. 

Specifically we'suggest that the following areas be checked: 

1- Packaging of magnetrons and fit of - gaskets to the magnetron 

to prevent accidental loss. 

2. Insertion of warning sheet wieth replacenmt magnetrons 

emphasizing importance of correct inscallation irlclbding 

any shielding device and of making &I esission check after 

instqllation whenever possiSle3. Review cf service instructions for aZequacy of warnings in 

this regard. 
Page 2 - All Microwave Oven Kanufactarers 

4. Training programs for repair persorinel for adequate emphasis 

on the need for proper installation of all R.F. shielding devices 

and of the importance of emission checks whenever repair work is 

carried out on components or asseiblies bhich must contain the 

microwave energy. 

5, Quality control procedures to assure proper packaging of 

magnetrons and inclusion of all necessary shielding devices 

and instructions, 

Sincerely yours, 

Robert G. Britain 

Director , 

Division of Compli~~ce 

Bureau of Radiological Health 
PUBtlC HEALTH SERVlCE 

FOOD AND DRUG ADMlNlSTRATlON 

SEP 2 9 195 REF :DOC: 3556-MA 

TO: Microwave Oven Manufacturers, Zndustry Association, State 

Radiation Control Agencies and Other Infz?rested Parties 

4 .* :L . 

SUBJECT: FDA Interpretation Pursuant to 21 CFR 1030-10(c) (6) (ii) , Location of Warning Labels to wce Personnel 

It is apparent f- the analysis of reports submitted by manufacturers 

that certain types of residential cooking ranges and built-in wen 

combinations which include a microwave ~~ -are egned to have service 

performed without moving the range or bailt-in unit. Location of the 

warning label for s&ice perscknel, reqrrired by 21 CFR lO3Q.10 (c) (6) (ii) , on the back of such a unit is inappropriate, but the regulation as now 

.worded requires that the label be on the extend. surface of the ovenLocation of such a label on the front or side of such a product may be ' . 

undesirable to both the user and 'the m;rrmfacturerIt is essential that the label "be legible and readily viewable during 

servicing," and "be so located as t& elicit the attention of service 

personnel" as required by the regulation, These requirements are of 

overriding. consideration in determining an acceptable location for the 

label- In the case of ranges or other mia-owave ovens not intended for 

portable or countertop nse and in which the rear surface is not normally . . 

accessible for servicing, the intent of the regulation would be met if - 

the label is located on any surface of the oven which meets the follow+g 

conditions: . . 

.I. me lael- .must be legible and readily vieuatfle before the 

microwave oven is accessible for any servicing which could 

expose servicing personnel to microwave radiation levels which 

exceed the &its of the standard or which could affect compliande 

of the product with the standard2. The location and design of the l&l must elicit the attention 

of service personnel. I - 

Examples of such locations include interior surfaces of control panels 

which must be opened to perform maintenance service, or surfaces exposed -' - - 

by removal of trim which must be removed for servicing- 
Page 2 

Samples of labels and details of their location must be submitted in a 

report supplement for all affected models, An appropriate amendment to 

the regulations to reflect the interpretation set forth above will be 

promulgated in the near future. 
DEPARTMENT OF HJL4L'I'I-I & HUMAN SERVICES Public Health Service 

Food and Drug Administration 

Center for ~eices and 

Radiological Health 

2098 Gaither Road 

Rockville MD 20850 

To: All Importers and Manufacturers of Microwave Ovens 

Subject: Excessive Rusting Inside Microwave Ovens 

In the last several years, the Center for Devices and Radiological 

Health (Center) has received several reports of radiation leakage 

incidents as the result of excessive rusting in microwave ovens. 

The reports were on ovens built more than 7 years ago. This is not 

surprising because many microwave ovens purchased in the late 1970s 

and early 1980s are still operating in consumers' homes and 

commercial establishments. This issue is of serious concern to the 

Center because of the potential health hazard to consumers and food 

service employees. 

In several incidents, the Center has found excessive rusting which 

resulted in penetration of the cavity wall or deterioration of the 

door, thereby allowing harmful microwave radiation to escape. In 

some cases the user could not see the rust because it was hidden 

under the glass tray, along the rim or above the stirrer fan cover 

in the ceiling of the cavity. Contributing factors for the 

excessive rusting include design problems such as poor ventilation 

of moisture, entrapment of moisture in confined spaces, poor sealing 

of shelves, doors, etc., inadequate painting of the cavity at the 

factory, and of course, use of a steel that will rust. 

Any manufacturer or importer who becomes aware of any excessive 

rusting or deterioration should pay special attention to this 

problem and determine the cause and extent of the rust. An attempt 

should be made to ascertain whether the rust is surface rust or if 

there is excessive rusting that will likely result in penetration 

through the cavity wall in the future under continued operation. 

If the rusting is advanced beyond what is considered a slight 

cosmetic problem, or there is penetration through the cavity wall, 

the oven should be examined by qualified service personnel, usually 

connected with the oven manufacturer. The service person should 

examine the rust area for size and depth and determine if the rust 

patches are near the rim of the glass tray, site of welds or near 

corners or cavity seams where sides are joined together. 
Page 2 

Sometimes poor ventilation of moisture is the cause of rusting, 

especially if the oven fan is not working properly or the oven is 

installed so that condensed water vapor cannot be properly vented. 

Significant rust problems, of course, should be reported to the oven 

manufacturers for tracking, analysis and possible field testing of 

similarly designed ovens. If an oven manufacturer determines that 

particular oven models are prone to rusting, then further action, 

such as field testing and possible recall, may be necessary. 

Records concerning microwave oven rust problems should be kept by 

manufacturers in the same manner as files on consumer.inquiries on 

radiation safety of microwave ovens. If an oven violates the 

Federal performance standard radiation limit of 5 mw/cm2, the 

manufacturer must notify the Center immediately as requi;ed by 

21 CFR 1003. 

The Center hereby requests all microwave oven manufacturers and 

importers to search their service record and customer complaint 

files for occurrences of similar rust problems. If such occurrences 

are found that may result in excessive leakage of microwave 

radiation, this should be reported to the Center immediately. 

Of course, minor rust affecting only cosmetics is not a concern. 

Service personnel should not be allowed to take advantage of worried 

consumers or food service employees. 

The Center and FDA offices throughout the United States will monitor 

microwave oven rust problems through -reports and communications from 

manufacturers, service personnel, consumers, field surveys and 

inspection of manufacturers' records. 

Reports of rust problems should be sent to attention of the 

Non-Medical ~adiological Devices Branch (NMRDB) at the Office of 

Compliance (HFZ-312), Center for Devices and Radiological Health, 

2098 Gaither Road Rockville, Maryland 20850. If there are any 

questions you may contact the NMRDB by telephone at 301 - 594 - 4654 or 

by facsimile at 301 - 594 - 4672. 

Sincerely yours, 

Ronald M. ~ohnsonL 

Director 

Office of Compliance 

Center for Devices and 

Radiological Health 
DEPARTMENT OF HEA,L,TH. EDUCATION. AND WELFARE 

PUBLIC HWLTH SERVICE 

FOOD AND ORUG ADMINISTRATION 

ROCKVILLE. MARYLANO 20857 

To: All Manufacturers and Importers of Microwave Ovens 

Subject: Field Nodifications of Microwave Ovens 

The Bureau has learned of a field modification program that involved 

replacement of the main Kire harness aad which was performed by service 

organizations at the direction of an oven mmfacturer. In order to. 

camplete the modification it was necessary to essentislly rewire the - 

oven. The modification instructions required that, at the completion of 

the modification, the servfce organization check only for proper operation of the oven in the cooking mode. 

Since the replacement of the wfre harness involved reconnecting the 

safety interlock and monitor wiring it is possible that an~improperly 

performed modification could have resulted in the failure of the safety 

interlocks or monitor to perform their intended function. There is also 

concern that other miswirings could have been introduced that would have 

resulted in hazsrdous situations or additional noncam~liances. 

In order to prwent field modifications Prom resulting in mncompliance 

of the modified wens it is requested that all manufacturers follow the 

procedures below prior to starting a field modification program: 

1. Perfom an analysis of the proyosed modification to determine 

if the modification could affect the flrnction of the safety interlock or monitor circuits, the RF leakage cbacteristics of the 

oven, or if improperly performed, could result in a hazardous 

situation or any other noncampliance with the microwave oven 

st zo-d . 

2. If the progosed modifications can in any way affect ra&Lation 

safety of the oven, or campliance with the standard, su.bmit to the 

Bureau, a cow of the proposed zodlficatian instructions, the 

reason for performing the modification and the affected nodel 

numbers. This informetion shculd include, as applicable: a) a scyy 

of the rev5sed wen schematic diagram, b) a list of c~acezta f 3 

be replaced, e) a complete description of the electrical or ~echmical modifications that will be perfamed, md d) can@- ate instructions to be prcvided to personnel performixg the scdificatLoc 

incluunq instructions for ?erfomiag aq checks, or tests to assure that the mdificat ions were groperly nerf orzed. 
Page 2 - All Manufacturers and Importers of Microwave Ovens 

3. Include as a part of the program instructi~ns that the service 

organizations perform an RF leakage check and a complete check of 

the mctioning of the interlock and monitor circuits prior to 

releasing the oven to the owner. 

The Bureau will review the proposed in~t~uctions and may suggest other 

specific tests, preczutions, or steps that should be included in the 

instructions. Manufacturers may be requested to submit a unit to the 

Bureau along with the modification kit and final instructions for our 

evdluat ion. 

Director 

Division of Compliance 

Bureau of Radiological Health- 
Food and Drug Administration 

87 57 Georgia Avenue 

Silver Spring MD 209 10 

TO: ALL PERSONS WHO MODIFY MICROWAVE OVENS OR MICROWAVE HEATING EQUIPMENT 

SUBJECT: FDA REGULATIONS CONCERNING MODIFICATION OF HOUSEHOLD OR 

COMMERCIAL MICROWAVE OVENS AND/OR MICROWAVE HEATING EQUIPMENT 

The Center for Devices and Radiological Health (CDRH), of the Food and Drug 

Administration (FDA), is issuing this guidance to assist persons or 

manufacturers who modify household (consumer) and commercial microwave 

ovens or microwave heating equipment in understanding the Federal 

regulations which cover such products. The products of concern are 

commercially available but then modified for special industrial, laboratory 

and/or medical uses, such as laboratory heating equipment, blood-plasma 

warmers, pathological and biological analyzers, etc. 

The CDRH is concerned that any modification of original radiation safety 

components, such as the door sealing systems, door latching mechanism, 

safety interlocks and monitor actuation system, etc., could increase the 

level of microwave energy emitted by the modified product. This could be 

hazardous to the user. CDRH is mandated by Federal law, the Radiation 

Control for Health and Safety Act of 1968, to protect the public or user 

from unneccessary exposure to electronic product radiation. Therefore, it 

is essential that CDRH review any changes to these products to ensure that 

they will not be hazardous. 

Any individual or manufacturer who is engaged in the business of modifying 

and offering any of these products for sale to purchasers is subject to the 

regulations set forth in the Act. The regulations also affect those 

individuals or manufacturers who offer a conversion kit with all of the 

components necessary to assemble a complete modified product for special 

uses. The regulations do not apply to those individuals who are modifying 

products solely for their own laboratory or research uses and are not 

offering the product for sale or transfer to another individual. In 

addition, this guidance is not to be confused with the present Federal 

Performance Standard for Microwave Ovens which applies to those products 

used in homes, restaurants, food vending or service establishments, on 

interstate carriers and in similar locations (21 CFR 1030.10). 

Manufacturers or individuals who are offering modified microwave ovens or 

microwave heating equipment for sale are required to submit an initial 

report on radiation safety and design modifications prior to introducing 

any products into commerce. The initial report requirements are detailed 

in 21 CFR 1002.10 of the regulations. Reports of model changes are also 

required as specified in Section 1002.12 of the regulations. In addition, 

Sections 1003 and 1004 of the regulations concerning product defects, and 

Section 1002.20 concerning reporting of accidental radiation occurrences 

must be met. 
Page 2 - FDA Regulations Concerning Modification of Household or Commercial 

Microwave Ovens and/or Microwave Heating Equipment 

It is unlawful for manufacturers or importers to fail to submit reports 

required by 21 CFR 1002. IF a company fails to comply with the reporting 

requirements, it may be restrained by a U.S. District Court from further 

violation and be subject to a penalty of up to $1,000 per violation and a 

maximum penalty of $300,000. 

If a microwave oven or microwave heating equipment is modified for medical 

or clinical uses, manufacturers or individuals should be aware of the 

medical device requirements of the Food, Drug and Cosmetic Act 

(FD&C Act). Assistance in understanding these medical device regulations 

can be obtained from the Division of Small Manufacturers Assistance, Office 

of Training and Assistance, CDRH (HFZ-220), Rockville, Maryland 20857, 

telephone 800-638-2041 or 301-443-6597. . Briefly, the main requirements of 

the FD&C Act include: 

1. filing of a 510(k) notice (Premarket Notification, 

21 CFR Sections 807.81 - 807.97), 

2. registering as a medical device manufacturer and listing the 

device to be manufactured (21 CFR Sections 807.20 - 807.401, 

3. complying with the labeling provisions of the FD&C Act 

(21 CFR Section 801), and 

4. complying with Good Manufacturing Practices for medical devices 

(21 CFR Section 820). 

If you have any questions concerning this guidance or need additional 

assistance in filing the required reports, please contact the Microwave/ 

Acoustic Products Section at (301) 427-7187. Our address is: Office of 

Compliance, Center for Devices and Radiological Health, HFZ-312, 

8757 Georgia Avenue, Silver Spring, Maryland 20910. 

Edwin A. Miller, Director 

Division of Radiological Products 

Office of Compliance 

Center for Devices 

and Radiological Health 
DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service 

8 

Food and Drug Administration 

2098 Gaither Road 

Rockville MO 20850 

TO: Manufacturers and Importers of Consumer Electronic .Products 

SUBJJ?CT : Importation of Radiation-Emitting Electronic Products for 

Investigation and Evaluation During Design Development 

ISSUE 

The Consumer Electronics Manufacturers Association has requested that the 

Food and Drug Administration (FDA), Center for Devices and Radiological 

Health (CDRH), expand the exemption for conkumer products imported for the 

purpose of test and evaluation during design and production development. 

BACKGROUND 

- Section 536(a) of the Electronic Product Radiation Control ~rovisions of the 

the standards and shall bea; certification of such compliance. ~;f&e the 

products can be permitted to enter the U.S., importers are required to 

submit with each shipment certain import entry papers through the District 

Director, U.S. Customs Service, to the appropriate FDA district office. 

Exemption from certification of electronic products for the purpose of 

research, investigations, studies, demonstrations, or training is permitted 

by Section 538(b) of the Act. Current policy permits FDA district offices 

to grant such exemptions for individual entries, usually for 180 days, while 

the products remain in import detention status. Importers must make a 

written declaration to FDA (Form FDA 2877, "Affixmation Cn) and execute a 

bond with the U.S. Customs Service. Liquidation of the Customs bond is 

attained only through exportation or destruction of the products. 

By letters dated May 17, 1982; August 25, 1983; and May 22, 1987, CDRH 

exempted up to 10 units of the following products from the applicable 

performance standard when they are intended for investigations: television 

products, microwave ovens, and laser products that do.not exceed the limits 

of Class I during any conditions of operation, maintenance, or service 

(hereafter referred to as inherent Class I laser products). The products 

are not subject to certification requirements or the Customs bqnging process 

under certain conditions. These products are generally used for acceptance 

testing (FCC, UL, etc.), establishment of production line procedures, and 

applications evaluation. While they may be fully operational, they may not 

be the final design and have not received final acceptance testing. 

On March 7, 1996, the Consumer Electronics Manufacturers Association (CEMA) , a sector of the Electronic Industries Association, requested a change to the 

industry-wide investigations and evaluation exemption. CEMA asks that the 

number of units to which thehemption applies be increased to 50 units for 

TV products and Class I laser products ana to 200 units for CD-ROM and new 

DVD (digital versatile disc) laser products, to reduce unnecessary costs to 

manufacturers in both time and money. Increase to 50 units will accommodate 

the industry need for establishing production processes. Increase to 200 

units for CD-ROMs and DMs will accommodate the need for software evaluation 

and development. Because there will be no commercial distribution of the 

products. the change is expected to reduce the tracking and paperwork burden 

on industry, FDA, and U.S. Customs, without impact on public health. 

Federal Food, Drug, and Cosmetic Act (the Radiation control- for Health and 

Safety Act of 19689 requires that all imported electronic products, for 

which applicable radiation performance standards exist, shall comlv with 
Page 2 - Manufacturers of Consumer Electronic Products 

EXEMPTION 

Under the authority of Section 538(b) of the Act, exemption from- certification to the applicable radiation performance standards and the 

execution of a customs bond is granted for consumer electronic products 

imported into the U.S. for investigations and evaluation during the design 

and production development phase with the following conditions: 

1. The quantity of products in any single import entry of 

television products, microwave ovens, and inherent Class I laser 

products can not exceed 50 units; except other laser products 

requiring software to operate, such as CD-ROMs and DVDs, are 

limited to 200 units. 

2. Each product and its shipping carton must bear a label stating: 

"TEsTING/EVALUATION ELECTRONIC PRODUCT - NOT TO BE SOLD IN THE 

UNITED STATES. THIS PRODUCT HAS NOT BEEN TESTED FOR COMPLIANCE 

WITH THE APPLICABLE U.S. RADIATION PERFORMANCE STANDARD." 

3. The importer or consignee must establish written procedures for 

maintaining control and final disposition of the products, 

4. Form FDA 2877 (Declaration For Electronic Products Subject to 

Radiation Performance Standards), or the equivalent electronic 

filing, must be submitted to the FDA district office before the 

shipment arrives. Until the Form 2877 is revised to provide an 

affirmation for this exemption, mark Affirmation A and write: "These products meet the CDRH Exemption For Product Development 

and will not be commercially distributed at any time." 

5. Shipments in excess of the quantities specified in item 1, or 

otherwise not meeting the conditions above, shall be placed in 

import detention status. 

Movement of uncertified products in U.S. commerce is a violation of 

Section 538(a) (1) of the Act. Violations will result in voiding this 

exemption for the responsible parties and are subject to civil penalties not 

to exceed $1000 per violation and $300,000 maximum. Providing false 

information to the U.S. government is a violation of the U.S. Code, 

Title 18, and subject to criminal prosecution. - - 

This exemption supersedes the previous exemptions dated May 17, 1982; 

August 25, 1983; and May 22, 1987. 

Any questions regarding this exemption or any imports procedure should be 

directed to the imports officer at the FDA district office nearest the port 

of entry. 

. -. 

. Sincerely yours, &+ Lillian J. Gill 

Director .- 

Office of Compliance 

Center for Devices and 

Radiological Health 
DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service 

Food and Drug Administration . 

JUN 2 8 19% 87 57 Georgia Avenue 

Silver Spring MD 209 10 

TO: All Manufacturers and Importers of Microwave Ovens 

'SUBJECT: Importation of Noncompliant Microwave Ovens Which Are 

Intended for Use in Countries Other Than the United States 

Importers have been allowed to import certain noncertified television 

receivers for exportation purposes provided that certain specific criteria 

for exemption from the television performance standard were met. These 

products were sold to United States (U.S.) distributors who, in turn, sold 

them to consumers who were either traveling or relocating overseas. The 

receivers were not designed to operate in the U.S. from 60Hz, 110-120 VAC 

power sources or U.S. television signals. Those distributors now would 

like to sell noncertified microwave ovens the same way. If properly 

labeled for export only as explained below such importation and sale of 

noncertified microwave ovens will be permitted. 

Some manufacturers already test and certify their microwave ovens in 

accordance with the U.S. standard. These products may be imported into the 

U.S. claiming Affirmation B on Form PD 2877. They should - not be labeled 

for export only. Other manufacturers have chosen not to certify these 

products for U.S. use. These manufacturers should notify their customers 

that these products may not be imported into the U.S., and they should not 

ship such products to U.S. addressees unless they meet the exemption 

criteria below. 

Food and Drug Administration (FDA) District personnel and the U.S. Customs 

Service have been notified that all microwave ovens which are capable of 

operation in the U.S. may not be imported and are to be detained unless 

they are certified by the manufacturer to comply with the Performance 

Standard for Microwave Ovens. 

Exemption Criteria 

Importers are permitted to import for exportation purposes only 

noncertified microwave ovens which are designed to operate on 50Hz 220 VAC 

and which are sold without U.S. power plugs or adaptors and when specific 

criteria for exemption from the appropriate performance standard have been 

met. Such products are excluded from the performance standard as prescribed 

in Section 358(a)(3) of the Radiation Control for Health and Safety Act if: 

- The foreign manufacturer affixes a label or tag to each shipping 

container which states 

"WARNING - MICROWAVE OVEN FOR EXPORT ONLY/NOT INTENDED FOR USE IN THE 

UNITED STATES. THIS PRODUCT HAS NOT BEEN TESTED FOR COMPLIANCE WITH 

THE U.S. FEDERAL PERFORMANCE STANDARD FOR MICROWAVE OVENS." 
Page 2 - Microwaves 

- The warning statement shall be in all boldface capitals, no smaller than 

5 mm, on a contrasting background. 

- The microwave oven also has one label permanently affixed to the product's 

exterior (excluding the bottom) and another "stick on" temporary label 

affixed to the center of the oven door. These labels shall contain the 

wording shown above. 

- The importer (on or prior to date of entry) provides FDA with a statement 

that all imported products bear the required labeling for exemption. 

/A Edwin A. Miller oh&J 

Director, Division of 

Radiological Products 

Office of Compliance 

Center for Devices 

and Radiological Health 
DEPARTMENT OF HEALTH & HUMAN SERVICES Public Health Service 

6 

Food and Drug Administration 

2098 Gaiier Road 

Rockville MD 20850 

w 141997 

TO : ~anufacturers and Importers of Consumer 

Electronic Products 

SUBJECT: Date of Manufacture Label for Electronic 

Products Subject to Radiation Standards 

ISSUE 

The Consumer Electronics Manufacturers Association has 

requested that the Food and Drug Administration (FDA), 

Center for Devices and Radiological Health (CDRH), exempt 

manufacturers of electronic products from the required label 

providing the date of manufacture or to permit date coding. 

BACKGROUND 

Manufacturers of electronic products are required to comply 

with radiation performance standards promulgated under 

Section 534 (a) (1) of the Electronic Product Radiation 

Control provisions of the Federal Food, Drug, and Cosmetic 

Act (the Radiation Control for Health and Safety Act of 

1968). The regulations, 21 CFR 1010.3, specify that an 

identification label or tag must be affixed to each product 

with the date of manufacture. 

On March 7, 1996, the Consumer Electronics Manufacturers 

Association (CEMA), a sector of the Electronic Industries 

Association, requested a change in the date format specified 

in the regulations and then subsequently questioned the need 

for providing a date on the label at all. ,The original 

intent of the label was to identify which products are 

subject to a standard (as opposed to ones manufactured prior 

to the effective date) and to identify products subject to 

differing requirements when the performance standards-are 

amended. Since the television and microwave oven standards 

have not been amended since 1983 and the laser standard is 

seldom amended in any manner that affects the consumer 

product industries, CEMA asks that the requirement for the 

label be exempted until any future amendments to these 

standards are promulgated. The change is expected to reduce 

the tracking resources aGd paperwork burden on industry, 

with negligible impact on FDA or public health. 

GUIDANCE 

The CDRK concurs that there is little need for the.d& of 

manufacture on the identification label at this time and 

failing to provide the information does not impact public 

health. As permitted by Section 539(d) of the Act, the CDRH 
Page 2 - Manufacturers of Consumer Electronic Products 

will not object to manufacturers omitting the date of 

manufacture from the identification label required by 21 CFR 

1010.3 from consumer (non-medical) electronic products under 

the following conditions: 

1. Each product is marked with a serial number or 

other identification by which the manufacturer may 

identify the date of manufacture in case of any 

regulatory action or investigation. 

2. The date of manufacture is included on the label 

within 30 days after a final rule to amend an 

applicable standard is published in the Federal 

Register, if the amendment adds or amends (not 

reduces or eliminates) any aspect of performance 

to which that electronic product must comply. 

Failure to comply with an applicable standard is a violation 

of Section 538 (a) (1) of the Act. Violations will result in 

disallowing this guidance by the responsible parties and are 

subject to civil penalties not to exceed $1000 per violation 

and $300,000 maximum. Providing false information to the 

U.S. government is a violation of the U.S. Code, Title 18, 

and subject to criminal prosecution. 

In accordance with FDA's Good Guidance Practices, comments 

are invited. This guidance document represents the agency's 

current thinking on date of manufacture labeling on consumer 

electronic products. It does not create or confer any right 

for or on any person and does not operate to bind FDA or the 

public. An alternative approach may be used if such 

approach satisfies the requirements of the applicable 

statute and/or regulations. - 

Any comments or questions should be directed to the 

Electronic Products Branch at the address above, by ' - 

telephone at 301-594-4654 or by facsimile at 301-594-4672. 

Sincerely yours, 

~il'lian "J. Gill 

Director 

Office of Compliance 

Center for Devices and, 

Radiological Health