- Standard Number:
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. Note that 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 OSHA's website at http://www.osha.gov.
April 14, 1993
Mr. Thomas P. Stanley
Federal Communications Commission
Washington, DC, 20554
Dear Mr. Stanley,
This is in response to your letter of November 23, 1992, to Ms. Dorothy L. Strunk, former Acting Assistant Secretary for Occupational Safety and Health Administration (OSHA), requesting an opinion regarding the effectiveness of "NAPTEX" Radiofrequency (RF) Electromagnetic Protective Clothing. Your letter has been forwarded to the Directorate of Technical Support for response. As you are aware, our response was delayed until additional test results were provided by the manufacturer of this product.
As you know, OSHA does not approve nor endorse products. The variable working conditions at jobsites and possible alterations or misapplication of an otherwise safe product could easily create a hazardous condition beyond the control of the manufacturer. However, we have reviewed the product data provided by the manufacturer and offer the following comments.
Due to problems experienced with the use of previous RF protective clothing, we feel it is necessary that manufacturers address the following characteristics of RFR Protective clothing prior to marketing:
- Material Breakdown Threshold
- Surface Temperature Stability
- "Specific Absorption Rate" Reduction
- Maintainability and Worker Acceptance
The Material Breakdown Threshold must be well in excess of the RF induced heating experienced during the intended use of the protective clothing. For this reason, limitations on the use of the clothing must be specified, such as in terms of maximum field strength for a given range of frequencies. This limitation diminishes the possibility of using the product in fields which could cause adverse reactions upon the fabric.
Surface Temperature Stability data must ensure that the fabric dissipates RF induced heating sufficiently so that its surface temperature does not become excessive to the wearer within the field intensities of intended use.
Current ANSI standards for RF exposures include limits expressed in terms of Specific Absorption Rate (SAR). The capability of RF protective clothing to provide SAR Reduction will vary significantly with certain RF field characteristics, particularly frequency. Therefore, the actual reduction in SAR must be determined for the specific field conditions of intended use. It is the responsibility of the user to ensure the protective clothing will provide adequate SAR reduction, e.g., to achieve compliance with ANSI C95.1-1992 SAR limits. This determination should be based on both product performance data and an assessment of intended worst-case field exposures.
Regarding the Maintainability and Worker Acceptance of the clothing, the material should be able to withstand treatment comparable to standard-issue industry work-clothes. Construction of the clothing should minimize restriction of the wearer's movements and vision.
As with all personal protective equipment, the worker must visibly inspect the protective clothing to ensure it is in good condition. In the event of a rip or tear in the fabric, the performance of the suit could be compromised. Depending on the severity of the tear, the item may require subsequent testing for shielding integrity after repair.
To provide full-body protection, components of the RFR Protective gear must include a full integrated hood, overshoes, and gloves. It is recognized that worker acceptance of fully encapsulating protective clothing will require training and diligent supervision. However, omission of these accessories should only be permitted with substantiating data that ensures compliance with recognized limits for both SAR and Partial Body exposures.
Summarily, assuming the above criteria are met, it is our position that RFR Protective clothing can be a valuable addition to existing safety measures for a variety of practical applications, such as FM radio, Television, and microwave tower maintenance, when used within prescribed field parameters.
Regarding your specific inquiry about NAPTEX, we have reviewed the data provided by the manufacturer, Maxwell Safety Products, and it appears this product successfully addresses the criteria described above. The actual breakdown threshold for NAPTEX has not been determined as yet, but test data shows the threshold to be in excess of 200mW/cm2. Surface temperature stability data shows that, at a sustained exposure level of 124 mW/cm2, the increase in surface temperature of the material is limited to 6.5 degrees C.
The manufacturer currently restricts use of NAPTEX products to field intensities of 20 mW/cm2 for frequencies up to 60 MHz, and 125 mW/cm2 for frequencies from 65 MHz to 10 GHz. Test data demonstrate that compliance with ANSI is easily achieved when using the products within these limits. It is expected that additional testing currently being conducted by Maxwell will allow for even higher field intensities.
if we can be of further assistance, please do not hesitate to contact [the Office of General Industry Enforcement at (202) 693-1850].
Patricia K. Clark
Director, Directorate Technical Support