Health hazard evaluation report: HETA-2001-0153-2994, Naval Computer and Telecommunications Station, Cutler, Maine.
On February 2, 2001, the American Federation of Government Employees (AFGE) Local 2635 submitted a health hazard evaluation (HHE) request on behalf of civilian employees at the Naval Computer and Telecommunications Station (NCTS), Cutler, Maine. The request indicated that electronics workers, technicians, antenna workers, and administrative staff were exposed to radiofrequency (RF) electromagnetic fields (EMF) in the antenna fields and on the transmitter decks. The request noted that employees suspected that they were incurring eye injuries as a result of exposure to RF fields. In response to the HHE request, a NIOSH team of two industrial hygienists, two research physicists, and a physician conducted a site visit on May 14-16, 2002. During the site visit, the industrial hygienists and physicists conducted environmental monitoring to characterize exposures to electromagnetic radiation at various locations throughout the facility. The NIOSH physician reviewed employee medical records and Occupational Safety and Health Administration (OSHA) Illness and Injury Logs, and conducted the confidential employee interviews on May 15-16, 2002. On October 15, 2002, the NIOSH industrial hygienists returned to the site to characterize very low frequency (VLF) electric fields beneath antenna downleads. In May 2002, worker exposures to RF fields in the high frequency (HF) transmitter building (Building 400) and antenna field were well below the Institute of Electrical and Electronics Engineers (IEEE) recommendations for occupational (controlled) environments. Field strength measurements were below occupational exposure limits in locations accessible to employees (most were below the limit of detection). Induced and contact currents (wrist and ankle) were nondetectable in the HF transmitter building, and well below IEEE limits at fence lines around HF antennas. Data from the May 2002 site visit indicate that workers in the VLF transmitter Control Room (T-Deck, Building 100) were not overexposed to electric fields (E-fields) while performing their duties. All spatial average E-field measurements in the VLF Control Room were well below the IEEE exposure limits. During the October 2002 visit, spatial average E-field strength beneath VLF downleads in the north array exceeded the IEEE maximum permissible exposure (MPE) of 614 volts per meter (V/m) in four locations approximately 60 feet from the helix house. Wrist and ankle currents at these four locations were well below IEEE limits, as were magnetic flux field measurements. The 24 kHz fields at NCTS Cutler can cause potentially hazardous RF shocks in workers who touch conductive objects such as vehicles, fencing, metal roofing, supporting guy wire metallic cables, and metallic rigging cables used during painting and maintenance. Effective measures should be taken to reduce potential shock hazards when workers could touch conductive objects in VLF fields. Worker interviews, medical records, and the OSHA Log did not reveal any findings that could be related to workplace exposures. Health problems reported during confidential employee interviews were not consistent with health problems associated with EMF exposure and presented no consistent pattern. NIOSH investigators conducted an extensive review of the IEEE "exclusion rule" as it pertains to VLF exposures at NCTS Cutler. (The exclusion rule specifies conditions under which workers may be exposed to electromagnetic field strengths exceeding the MPE.) NIOSH concluded that the exclusion rule (IEEE C95.1 1999, Section 4.2.1) should not be applied at NCTS Cutler where VLF electric field strength exceeds the MPE, i.e., MPEs for field strengths and body currents (contact and induced) must be met. Although no exposure-related health problems were identified, NIOSH investigators concluded that the potential exists for exposure to E-field strengths beneath VLF arrays which exceed the IEEE MPE, and that VLF E-fields can cause potentially hazardous RF shocks in workers who touch metallic objects. Recommendations are provided in this report for training employees, restricting access to areas where RF fields exceeding MPEs may be present, posting warning signs, conducting monitoring, and reporting burns and shocks.