Microwave Devices – Why can’t I use a microwave oven that I can buy from an appliance store? Part 1

I still get asked this question, particularly by people whose lab is becoming CAP accredited for the first time and they are suddenly confronted with a non-compliance citation by the CAP. Laboratory microwave oven specification standards are strictly regulated by federal agencies governing laboratory safety. CLSI addresses the standards in publication GP-281 “Microwave Use in the Histology Laboratory”, which summarily states that kitchen microwave ovens are forbidden in the laboratory setting. OSHA regulation 29CFR1910.303(b)(2) addresses the laboratory microwave oven standards by stating that lab equipment is to be used in accordance with the manufacturer’s instructions. Underwriters Laboratories safety instruction UL 923 for the common kitchen microwave oven states “Use this appliance only for its intended use as described in the manual. Do not use corrosive chemicals or vapors in this appliance. This type of oven is specifically designed to heat, cook, or dry food. It is not designed for industrial or laboratory use.

So why did all these agencies decide that kitchen microwave ovens cannot be used in the histology laboratory? Two main reasons: they are designed with inadequate Safety features and they cannot produce Consistency and Quality to the degree required in laboratory procedures for reliable results.

SAFETY FEATURES:

1. Seal: The seal around the door of a kitchen microwave device was designed for food vapors, not chemical vapors. The laboratory microwave device was designed for chemical exposure, though the quality of the seal should still be checked every year, to see if there is breakdown of the seal, or leaking of microwaves.

2. Ventilation: Kitchen microwaves vent the fumes out into the atmosphere. This is no problem when food is being heated. In a laboratory however, fumes from silver nitrate or alcohol should never be released into the laboratory, exposing lab techs. Laboratory grade  microwave ovens are constructed to vent the fumes through the laboratories ventilation system.

3. Electrical: The electrical system  of a kitchen microwave oven is not insulated from flammable vapors. Laboratory chemicals inside the chamber, especially being heated, release flammable vapors that would likely cause a fire or explosion. The electrical system of a laboratory microwave is designed so there is no exposure to flammable vapors.

The next blog will cover the Consistency/Quality issues related to microwave devices (Part 2).

REFERENCES:

– Bancroft JD and Gamble M: Theory and Practice of Histological Techniques, 5th edition, 2002, Chapter 19 “Application of Microwave Technology to Histology” by Steven Slap

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