- For a given ambient temperature, the mixture must contain a specific ratio of fuel vapor to air.
- There must be enough energy in the arc or spark to produce the appropriate temperature for ignition.
- The length of the arc must be sufficient to sustain the heat in the arc for the time required to initiate a flame.
Sunday, 20 February 2011
Hazards of Electromagnetic Radiationto Fuels (HERF)
Many studies have been done about fuel vaporsbeing accidentally ignited by electromagneticradiation. Tests aboard ships and in laboratories haveshown that the chances of this happening are lowbecause of other conditions that must exist at the sametime to support combustion of the fuel. Althoughaccidental ignition of fuel by RFR is unlikely, you stillneed to be aware of the potential hazards. The mostlikely time this might occur is during a ship’s refuelingevolutions, commonly called UNREPs (UnderwayReplenishment). Many ships also carry at least onehelicopter or have the ability to refuel a helicopter and,therefore, carry fuel to support helo operations. All ofthese operations are inherently dangerous bythemselves and require the utmost attention andalertness. As a junior Fire Controlman you most likelywill be personally involved in these refuelingoperations. You need to be aware of the potentialhazards associated with Fire-Control radar and fuel.As a senior Fire Controlman, you need to know thehazards of electromagnetic radiation to fuel, so youcan ensure that your division personnel are working ina safe environment.
RADAR RESTRICTIONS.—ElectromagneticRadiation Hazards (U) (Hazards to Personnel, Fueland Other Flammable Material) (U), NAVSEA OP3565/NAVAIR16-1-529/NAVELEX 0967-LP-624-6010/Volume I specifies the safe distances fromradiating sources at which fueling operations may beconducted. Figure 3-1 indicates safe distances betweenfueling operations and a conical monopole antenna,based on transmitter power. Each type of antenna hasits own chart. Refer to your ship’s Emissions Control(EMCON) bill for specific guidance concerningfueling operations.
FUEL RESTRICTIONS.—As the RFR energyradiated from high-powered communications andradar equipment installed on ships increased in recentyears, the Navy shifted to less volatile fuels. Undernormal operating conditions, volatile mixtures arepresent only near aircraft fuel vents, open fuel inletsduring over-the-wing fueling, and near fuel spills.Before fuel vapors can ignite, three conditionsmust exist simultaneously:
Each of these conditions is likely to vary for every situation, and two of the conditions may exist at anygiven time. Although all three conditions will probablynot occur simultaneously, the consequences of anaccidental explosion make it very important to becareful.