Reprinted From http://www.lessemf.com/mw-stnds.html#AREC

Why do people worry about microwave radiation?

Microwave ovens are used daily in restaurants, cafeterias, lounges, kitchens, snack bars, and homes. Microwave oven users are often concerned about potential health hazards from the exposure to microwave radiation leakage. With the latest techno-logical advances in door seal design and with proper maintenance, microwave oven leakage has been greatly minimized or eliminated.

How do microwave ovens work?

In a microwave oven, food is cooked by exposing it to microwave radiation. Most household microwave ovens operate on a frequency of 2450 megahertz (MHz or million cycles per second) in a continuous wave (cw) mode. Larger ovens used for industrial applications sometimes operate at 915 MHz.

The source of the radiation in a microwave oven is the magnetron tube. The magnetron, basically, converts 60 Hz powerline electric current to electromagnetic radiation of 2450 MHz. The high voltage (typically 3,000 to 4,000 volts) which powers the magnetron tube is produced by a step-up transformer rectifier, and filter which converts the 120V AC (alternating current or 60 Hz line voltage) to 4 kV DC (direct current).

The microwave energy from the magnetron is transferred to the oven cavity through a waveguide section. A mode stirrer spreads the microwave energy more evenly throughout the oven.

The microwave radiation produces heat inside the food in the oven. Heat is produced when the water molecules in the food vibrate (at a rate of 2,450,000,000 times per second) when the food absorbs the microwave radiation. The movement of the molecules produce friction which causes heat. This heat cooks or warms up the food.

Can microwaves leak radiation?

Old or faulty door seals are the most common causes of microwave radiation leakage. Mechanical abuse, a build-up of dirt, or simple wear and tear of continued use can cause door seals to be less effective. Theoretically, there will be small amounts of leakage through the viewing glass but measurements have shown this to be insignificant.

How is the radiation measured outside the microwave?

Microwave radiation is measured as power density in units of milliwatts per square centimetre (mW/cm²) which is essentially the rate of energy flow per unit area. One needs special equipment for the detection and measurement of the leakage. Typical levels of radiation leakage from microwave ovens is about 0.2 mW/cm² which is far below the limit set by the national safety standard Safety Code 6: Limits of Exposure to Radiofrequency Fields at Frequencies from 10 kHz-300 Ghz (1994, 60 p., Health Canada pub. 91-EHD-160). This level of leakage cannot be sensed by the body.

The power density of the microwave radiation decreases rapidly with increasing distance from the oven. For instance, if you measure a power density of 5 mW/cm² at 5 centimetres (2 inches) from the oven, you can expect 1.5 mW/cm² at 30 centimetres (one foot) and less than 0.01 mW/cm² at 1 metre (three feet) from the oven. This means that the farther away from the microwave you stand, the less radiation you will be exposed to. At one metre, there is very little radiation left.

What are the health effects of microwave radiation?

A large amount of literature has been published on the biological effects of microwave radiation. Generally speaking, exposure to very high levels of microwave radiation can result in significant amounts of energy being absorbed by the body. Just as with food, this energy is transformed into heat in the body. Sensitive body parts, such as the eyes, testes and brain, are not able to get rid of the extra heat that may build up. However, the situations where effects of thermal (heat) damage has actually occurred to the eye or brain required long term exposure to very high power densities well in excess of those measured around microwave ovens.

Some biological effects cannot be explained by a temperature rise in the body or in any one part. Persons working in microwave fields have reported headaches, eyestrain, over-all fatigue and disturbance of sleep. These effects have been associated with the interaction of the microwave fields with the central nervous system of the body. Such effects have been labeled as "non-thermal" interactions. These may be responsible for some of the long-term effects from prolonged exposure to low levels of electromagnetic fields. There is no confirmed scientific evidence to prove a link between such effects and microwave radiation exposure. However, it must be emphasized that these effects usually occur with pulsed or pulse-modulated fields and not with the continuous wave fields associated with microwave ovens.

What happens to pacemakers when they are near microwave ovens?

In the past, there were some problems resulting from the microwave radiation interfering with the signal from the pacemaker. Because pacemakers are electronic devices, interference from other electrical sources can cause the pacemaker to malfunction and thus send incorrect information to the heart muscles. Although properly maintained and operated microwave ovens are unlikely to cause this interference, the electromagnetic shields have been put into the new pacemakers as an added precaution. Patients with pacemakers should consult their doctor if they believe that they may have a problem related to microwave or radiofrequency radiation.

What are some general safety precautions for microwave ovens?

Safety tips for operation of microwave ovens:

• Do not operate oven when empty.
• Exercise extreme caution if you have a pacemaker implant. Microwave radiation may cause pacemaker interference.
• Persons with pacemaker implants should not be near a microwave oven unless they are sure that it is in good operating condition and there is no leakage of microwave radiation.
• Check to see that door seal and inside surfaces of door and oven cavity are clean after each use.
• Keep out of the reach of children. Do not permit young children to operate the oven.
• Do not put face close to door window when oven is operating.

Safety tips for installation and maintenance of microwave ovens include:

• Take special care to ensure that no damage occurs to the part of the oven making contact with the door or door seals.
• Ensure that the microwave is unplugged or disconnected from electrical power before reaching into any accessible openings or attempting any repairs.
• Ensure that the adjustment of applied voltages, replacement of the microwave power generating component, dismantling of the oven components, and refitting of waveguides are undertaken only by persons who have been specially trained for such tasks. The services of a qualified repairman should be sought when any malfunction is suspected.
• Do not by pass the door interlocks.
• Do not test a microwave power generating component without an appropriate load connected to its output. The power generated must never be allowed to radiate freely into occupied areas.

Are there any standards that apply to microwave ovens?

Canada:

Exposure limits (Safety Code 6) -
Part III (Microwave Ovens) of the Radiation Emitting Devices Regulation (C.R.C., C. 1370) specifies the following limits for the leakage radiation at 5 cm from the surface of the microwave oven:

• 1.0 mW/cm² with test load
• 5.0 mW/cm² without test load
• X-ray exposure not exceeding 0.5 mR (milliroentgen) /hr spread over an area of 10 cm²

Information concerning measuring equipment for microwave oven leakage can be obtained from the suppliers and manufacturers of such instruments. The Radiation Emitting Devices Regulation requires that the measuring instrument must be capable of measuring a power density of 1.0 mW/cm² with an accuracy of ±2dB or better and have an indicator with response time not greater than 3 seconds.

This regulation also specifies standards of design construction, and functioning of microwave ovens. As well, it specifies what warning signs must be used. This regulation applies to sale, lease or import into Canada of any radiation emitting device.

U.S.A.:

ANSI/IEEE-C95.1-1991 - the power density should not exceed 1.6 mW/cm² at 2450 MHz (microwave oven frequency) for human exposure in uncontrolled environments.

International:

IRPA (International Radiation Protection Association) Guidelines: International Radiation Protection Association recommends exposure limit of 5 mW/cm² for RF workers and 1 mW/cm² for the general public. These exposure limits are averaged over 6 minutes (0.1 h) period. Now-a-days microwave ovens are designed to minimize leakage. Levels of leakage from normally functioning microwave ovens is far less than above limit

Source: Dr A Muc, Ontario Ministry of Labour, 1983
Copyright © 1997-1999 Canadian Centre for Occupational Health and Safety