Hazards of Electromagnetic Radiation to Personnel (HERP)

Hazards of Electromagnetic Radiation to Fuels (HERF) Many studies have been done about fuel vapors being accidentally ignited by electromagnetic radiation. Tests aboard ships and in laboratories have shown that the chances of this happening are low because of other conditions that must exist at the same time to support combustion of the fuel. Although accidental ignition of fuel by RFR is unlikely, you still need to be aware of the potential hazards. The most likely time this might occur is during a ship’s refueling evolutions, commonly called UNREPs (Underway Replenishment). Many ships also carry at least one helicopter or have the ability to refuel a helicopter and, therefore, carry fuel to support helo operations. All of these operations are inherently dangerous by themselves and require the utmost attention and alertness. As a junior Fire Controlman you most likely will be personally involved in these refueling operations. You need to be aware of the potential hazards associated with Fire-Control radar and fuel. As a senior Fire Controlman, you need to know the hazards of electromagnetic radiation to fuel, so you can ensure that your division personnel are working in a safe environment. RADAR RESTRICTIONS.—Electromagnetic Radiation Hazards (U) (Hazards to Personnel, Fuel and Other Flammable Material) (U), NAVSEA OP 3565/NAVAIR16-1-529/NAVELEX 0967-LP-624- 6010/Volume I specifies the safe distances from radiating sources at which fueling operations may be conducted. Figure 3-1 indicates safe distances between fueling operations and a conical monopole antenna, based on transmitter power. Each type of antenna has its own chart. Refer to your ship’s Emissions Control (EMCON) bill for specific guidance concerning fueling operations. FUEL RESTRICTIONS.—As the RFR energy radiated from high-powered communications and radar equipment installed on ships increased in recent years, the Navy shifted to less volatile fuels. Under normal operating conditions, volatile mixtures are present only near aircraft fuel vents, open fuel inlets during over-the-wing fueling, and near fuel spills. Before fuel vapors can ignite, three conditions must exist simultaneously: 1. For a given ambient temperature, the mixture must contain a specific ratio of fuel vapor to air. 2. There must be enough energy in the arc or spark to produce the appropriate temperature for ignition. 3. The length of the arc must be sufficient to sustain the heat in the arc for the time required to initiate a flame. Each of these conditions is likely to vary for every situation, and two of the conditions may exist at any given time. Although all three conditions will probably not occur simultaneously, the consequences of an accidental explosion make it very important to be careful. Hazards of Electromagnetic Radiation to Personnel (HERP) The RFR hazard category of most immediate concern to you is HERP. The heat produced by RFR may adversely affect live tissue. If the affected tissue cannot dissipate this heat energy as fast as it is produced, the internal temperature of the body will rise. This may result in damage to the tissue and, if the temperature rise is sufficiently high, in death. The Bureau of Medicine and Surgery has established safe exposure limits for personnel who must work in an electromagnetic field based on the power density of the radiation beam and the time of exposure in the radiation field. Before we discuss these further, we must discuss some additional terms. Specific Absorption Rate (SAR)—This is the rate at which the body absorbs non-ionizing RFR. The threshold at which adverse biological effects begin is 4 watts per kilogram of body mass (W/kg). With a safety factor of 10 added, the accepted threshold is 0.4 W/kg for the whole body, averaged over any 6-minute (0.1 hour) period. A special limit for “hot spot” or limited body exposure has been set at 8.0 W/kg, averaged over any 1 gram of body tissue for any 6-minute period. Although this rate of absorption is very important in determining whether or not a safety hazard exists, it is very difficult to measure. Measuring this rate of absorption can also be dangerous since it requires actual exposure of body tissue. A related measure that gives an acceptable indication of SAR is “Permissible Exposure Limit”. Permissible Exposure Limit (PEL)—This is a limit to RFR exposure based on measurements of radiation’s electric field strength (E) or magnetic field strength (H) taken with instruments. You can use available charts to determine whether the 3-3