Guidelines

Microwave Oven Safety - Guidelines

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1. Purpose and Objectives

This guideline provides assistance to researchers who are planning to use or are using domestic microwave ovens in laboratories.

2. Definitions, Terms, Acronyms

RF - Radiofrequency radiation

EME - Electromagnetic Energy

GHz - Giga Hertz

Microwave - Radiofrequency radiation nominated as microwaves are in the range 0.3-300 GHz.  Microwave ovens use a specific frequency being 2.45 GHz.

3. Guidelines Scope/Coverage

This guideline covers the use of domestic microwave ovens for general laboratory use and their effects on human health.  It does not cover specialised or unconventional microwave usage.

4. Guidelines Statement

Where domestic microwave ovens are being used in laboratory or research settings, persons must be aware that they may be changing the intended use as stipulated by the manufacturer. It is therefore important to risk assess the work involving the use of domestic microwave ovens in a laboratory or research setting, and where appropriate instigate safety and control measures. Regular maintenance of the microwave ovens should be considered. Domestic microwaves should not be modified for research purposes.

5. Hazards

All microwave ovens have at least two safety interlock switches which stop the generation of microwaves immediately if the door is opened. The design of modern microwave ovens are such that the microwaves should be contained within the oven, but it is still possible for some leakage to occur around the doors of certain microwave ovens. Generally, the required design of oven doors should restrict this leakage to a level well below that recommended by the Australian/NewZealand Standard AS/NZS 60335.2.25:2002 Household and similar electrical appliances ‑ Safety Part 2.25: Particular requirements Microwave ovens. The Standard specifies a test to assess the level of microwave leakage and states that 'The microwave leakage at any point 50 millimetres or more from the external surface of the appliance shall not exceed 50 watts per square metre. This Standard applies to ovens designed for domestic applications, even if used in a workplace. The recommended limit is conservative and includes significant safety factors, so that even leakage levels appreciably above the limit will have no known effect on human health.

6. Controlling the Risks

To minimize the risks associate with microwave ovens, users must adopt the following rules:

  • Never attempt to heat flammable liquids or solids, hazardous substances or radioactive materials in any type of microwave oven, whether domestic or laboratory-grade.
  • Never attempt to defeat the interlock switches that prevent a microwave oven from operating with the door open.
  • Users should always ensure that the oven cavity is adequately ventilated. To help ensure this, the unit should be operated only on a clear open bench and not in a location where the vents could be obstructed by books or equipment.
  • Do not place any wires, cables, tubing etc. between the door and the seal.
  • While there is no requirement for recurrent testing for microwave leakage, regular visual inspections are recommended to check for the following:
    • The sealing surfaces are clean and do not show any sign of damage;
    • The door closes cleanly and there is no distortion of the frame;
    • The window panel is not damaged;
    • The door is not damaged in any way.

If there is any evidence of this type of damage the unit should be taken out of service and referred to the authorised service agent.

  • Do not attempt unauthorised repairs or modifications to the mechanical or electrical systems of a microwave oven. Where a unit is suspected to be faulty it should be disconnected from the power supply, removed from service and labelled with an appropriate tag while awaiting repair or disposal.
  • Any irreparable or redundant microwave oven should be unplugged from the GPO, and rendered inoperable by removing the power cord or cutting off the plug before disposal.
  • Never use a microwave oven in a laboratory for food preparation (or vice versa).
  • Do not heat sealed containers in a microwave oven. Even a loosened cap or lid poses a significant risk since microwave ovens can heat material so quickly that the lid can seat upward against the threads and containers can explode either in the oven or shortly after removal.
  • No metal objects of any kind should be placed in a microwave oven. This includes aluminium foil and plastic coated magnetic stirrer bars.
  • Users need to take care to avoid overheating liquids (super-heat) in a microwave oven. It is possible to raise water to a temperature greater than the normal boiling point; when this occurs, any disturbance to the liquid can trigger violent boiling that could result in severe burns.
  • Microwave ovens must be electrically grounded and connected using a properly rated three pin cord and plug. Microwave ovens should be inspected by a competent person to ensure compliance with this requirement before going into service and if not connected to a safety switch protected circuit, they need to be tested and tagged at appropriate intervals.
  • Defects in equipment or difficulties in operation with a microwave oven should be reported promptly to the laboratory manager or supervisor.
  • Laboratory users who have cardiac pacemaker implants are not likely to be susceptible to interference where leakage levels are within the recommended limits. Persons with pacemakers should obtain and rely on their own medical advice in this respect.
  • Proper heat resistant gloves should be worn when handling items that come out of a microwave oven. Laboratory gloves such as latex or nitrile gloves do not offer protection if heated liquid is spilled on you.

7. Specialised Microwave Usage

The use of microwave heating as a reaction accelerator in the chemical research field is to be treated with caution.  While techniques have been developed, these involve the use of specialised laboratory-grade equipment rather than domestic ovens.  Should a need be identified for this application of microwave heating, the researcher(s) should consider purchase or gain access to such specialised microwave ovens.

Application of microwave heating to industrial processes in, for example, the chemical engineering field, will require detailed risk assessment in the design phase.

8. Contact for Additional Information

Contact your local Radiation Safety Officer, or 

OHS Division Radiation Protection Advisor OHS@uq.edu.au

Custodians
Director, Occupational Health and Safety
Mr Jim Carmichael
Custodians
Director, Occupational Health and Safety
Mr Jim Carmichael