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Standard Interpretations - Table of Contents
• Standard Number: 1910.1450; 1910.1450(e)(3)(vii); 1910.97; 1910.303(b)(2); 1910.399; 1910.106; 1910.1000

August 8, 2002

Gary Login, D.M.D., D.M.Sc.
Assistant Professor of Oral Pathology
Harvard School of Dental Medicine
209 Harvard Street, Suite 402
Brookline, MA 02446

Dear Dr. Login:

Thank you for your March 2 letter to the Occupational Safety and Health Administration's (OSHA's) [Directorate of Science, Technology and Medicine]. Your letter was forwarded to the [Directorate of Enforcement Programs] to answer your request for safety information related to microwave devices in medical laboratories. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any question or concern not delineated within your original correspondence. Some of your questions were clarified by telephone. Your questions are summarized below, followed by our responses.

Background: You represent two committees that are collecting safety and usage guidelines for microwave devices in medical laboratories. The sponsoring agencies for these committees are the National Society for Histotechnology and the National Committee for Clinical Laboratory Standards.

Microwave devices are used in hospital laboratories to facilitate preparation of human and animal tissues for microscopic examination of disease. Tissue preparation techniques include heating tissue fragments in aldehyde fixatives, dehydrating solutions, and dyes to accelerate the chemical reactions.

Question 1: What are the OSHA regulations that apply to laboratories when microwave devices are used as part of the laboratory process control?

Response: We clarified that you wanted information about additional OSHA regulations that may apply because of the microwave devices, not regulations such as Occupational Exposure to Hazardous Chemicals in Laboratories (29 CFR 1910.1450) and many others that apply to laboratories in general. The Non-Ionizing Radiation standard (29 CFR 1910.97) and the Electrical standards in 29 CFR 1910 Subpart S apply to occupational exposure to microwave radiation devices. In addition, the Flammable and Combustible Liquids standard (29 CFR 1910.106), the permissible limits in the Air Contaminants (29 CFR 1910.1000), and specific chemical standards in 29 CFR Subpart Z may apply.

Question 2: What are the OSHA safety issues that we should consider for any microwave device used in a hospital laboratory?

Response: We list some possible hazards here. However, these are not comprehensive.
  • Microwave radiation may leak from damaged door seals, hinges, or latch, or because someone defeats the interlock system.
  • When flammable or combustible materials are heated and the temperature nears the flash point, fire or explosion is more likely.
  • When flammable liquids are heated in a closed area, the vapor concentration increases and may exceed the lower flammable limit.
  • The electrical wiring can provide an ignition source.
  • The electrical wiring could be damaged or not installed correctly.
  • When hazardous chemicals are heated in a closed device, employees will be exposed to higher than usual vapor concentrations when the device is opened.
  • The microwave radiation or the heating process may act on chemicals to produce more hazardous chemical by-products.
Question 3: If the laboratory does not use caustic materials or vapors (per the 1988 FDA bulletin) can a household microwave oven be used?

Response: If a household microwave oven was accepted, certified, listed, labeled in accordance with UL 923, Microwave Cooking Appliances, and it was placed into use in a laboratory such as you described, this would not meet the OSHA requirement in 29 CFR 1910.303(b)(2) that the equipment be used in accordance with any instructions included in the listing or labeling. The safety instructions in UL 923 state, "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." However, if a household microwave oven is accepted, certified, listed, labeled, or otherwise determined to be safe by a nationally recognized testing laboratory (NRTL) for a standard that includes laboratory use, then OSHA would consider it acceptable.

Question 4: Does OSHA require a specific UL approval code?

Response: No, OSHA does not require a specific UL code. The definition of "acceptable" in 29 CFR 1910.399 states that an installation or equipment is acceptable [to OSHA] and approved within the meaning of Subpart S, if it is accepted, certified, listed, labeled, or otherwise determined to be safe by a NRTL. However, even if a device or equipment is "approved," 29 CFR 1910.303(b)(2) requires that the "listed or labeled equipment shall be used or installed in accordance with any instructions included in the listing or labeling."

Question 5: What agency (internal or external to the hospital) should provide the oversight of the safety standards for microwave devices?

Response: The Food and Drug Administration's (FDA's) requirement to obtain market clearance for medical devices is unrelated to OSHA's requirements. FDA's jurisdiction is limited to testing the safety and efficacy of medical devices with regard to the manner in which these devices are used (i.e., medical safety of patients). OSHA's jurisdiction concerns protecting the employees (i.e., physicians, nurses, medical technicians) who use the devices. The FDA evaluates the extent to which the devices meet the purported treatment objectives in a manner that does not endanger the patient, while OSHA is responsible through NRTL testing for ensuring that electrical conductors and equipment are electrically safe for use by employees in the workplace. For safety concerns within the hospital, laboratories that must comply with 29 CFR 1910.1450 must designate "personnel responsible for implementation of the Chemical Hygiene Plan including the assignment of a Chemical Hygiene Officer, and, if appropriate, establishment of a Chemical Hygiene Committee."

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult the OSHA website at
http://www.osha.gov. If you have any further questions, please feel free to contact the [Office of Health Enforcement] at (202) 693-2190.


Richard E. Fairfax, Director
[Directorate of Enforcement Programs]

Standard Interpretations - Table of Contents

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