September 5, 1990
The Directorate of Technical Support issues Hazard Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65 to provide relevant information regarding unrecognized or misunderstood safety and health hazards, and/or inadequacies of materials, devices, techniques and engineering controls. HIBs are initiated based on information provided by the field staff, studies, reports and concerns expressed by safety and health professionals, employers and the public. Information is compiled based on a comprehensive evaluation of available facts, literature and in coordination with appropriate parties. HIBs do not necessarily reflect OSHA policy.
The San Francisco Regional Office has brought to our attention a potentially serious hazard involving burns on longshoremen caused by radiofrequency radiation. Two hazards were noted at this location. The burns were apparently caused by spark discharges from crane cables. Also present was an induced-current grasping hazard.
The longshoremen were working on a pier that is located in close proximity to several AM radio station transmitting towers. The radiofrequency radiation emanating from the transmitters induces electric currents in the longshoring operation cranes' cables due to the cables acting as antenna receptors to the radiation. The OSHA Health Response Team measured currents as high as 200 milliamps (mA). The American National Standards Institute C95 committee is considering a limit for this type of grasping current hazard of 100 mA. Measurements also indicated that electric field strengths in the general vicinity of the ship were on the order of 10 volts per meter. However, this is well within the ANSI C95.1 - 1982, Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 300 kHz to 100 GHz, limit of 632 volts per meter for AM radiofrequencies. Because of this induced current and an open circuit voltage from cable end to ground measured at approximately 300 volts by the Health Response Team, spark discharges occur just before and after grasping the cable. These discharges have resulted in burns.
Controls involve either isolating the crane hook from the crane cable and block assembly by an insulator or grounding the crane cable with a ground chain or wire. Either control has drawbacks. Insulators or insulated blocks are expensive and can affect the lift capability of a crane. Moreover, an isolated hook cannot prevent inadvertent employee contact with the crane cable itself. A grounding chain would have to be located manually with each individual lift thereby inviting inadvertent contact. Failing these controls, personal protective equipment in the manner of rubber-insert leather gloves, long sleeve shirts, safety helmets and safety glasses should be employed.
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