Apparent  Temperature  105°F  to  130°F— Category II, DANGER—Heat exhaustion or heatstroke likely with prolonged exposure and physical  activity Apparent Temperature 90° to 105°F—Category III, EXTREME CAUTION—Heat exhaustion or heatstroke possible with prolonged exposure and physical activity Apparent Temperature 80°F to 90°F—Category IV,   CAUTION—Fatigue   possible   with prolonged exposure and physical activity Since   this   index   is   based   on   the   dry-bulb temperature, which by definition and practice is a shielded  (in  the  shade)  temperature,  the  presence  of direct sunlight increases the danger. Wet-bulb Globe Temperature Index The Wet-bulb Globe Temperature Index is a heat stress  indicator  that  considers  the  effects  of temperature,  humidity,  and  radiant  energy.  The required inputs for the index are measured by a wet-bulb globe temperature meter. The standard wet-bulb globe temperature meter in use by the Navy, called the "Navy Heat Stress Meter," gives a digital readout of dry- and wet-bulb temperatures and globe temperature, and computes a wet-bulb globe temperature (WBGT) index. Although similar to an electric psychrometer in that it has shielded, fan-ventilated dry- and wet-bulb thermometers, this device also has a globe temperature meter (a flat-black metal sphere that measures radiant energy). Aboard ship, medical Corpsmen usually monitor WBGT  readings.  Chapter  B2  of  the Navy Occupational Safety and Health (NAVOSH) Program Manual for Forces  Afloat,  OPNAVINST  5100.19,  provides additional information on the shipboard heat stress control program. Since about 1980, the WBGT index has been gaining in usage as a regulatory guide for outdoor  work  situations;  operational  activities;  and general training, such as field exercises, marching, and physical  training. The  WBGT  index  is  used  in conjunction  with  a  Physiological  Heat  Exposure  Limits (PHEL)  chart  to  determine  maximum  exposure  time  for personnel working in high-heat interior environments. When applied to outdoor functions in hot climates, the PHEL charts are used to set activity limits, but a simplified guideline based strictly on the WBGT index is available for certain applications. When used in an outdoor environment, the WBGT index is the only index that compensates for the heating caused by direct or reflected sunshine. A variation of the computation, although not routinely used, also compensates for the cooling effect of the wind. Various color codes are used outdoors to indicate the  varying  danger  levels  of  heat  stress.  Some commands  fly  appropriate  color-coded  flags  to  indicate the heat-stress danger level. WBGT index readings less than 82°F generally mean little threat of heat stress, while readings between 82°F and 89.9°F indicate increasing   danger   levels.   OPNAVMST   6110.1, Physical Readiness Program, recommends no physical readiness testing or training be done if the WBGT index is 85°F. WBGT index readings 90°F indicate a great heat-stress danger, and all strenuous outdoor activity should be avoided. The "danger" level is decreased to 80°F when heavy clothing, NBC gear, or body armor is worn. The WBGT index is calculated by the formula W= 0.7WB + 0.2GT + 0.1DB, where W  = the WBGT index, in degrees Fahrenheit; WB = the wet-bulb temperature (°F); GT = the globe temperature (°F); and DB  =  the  dry-bulb  temperature  (°F). Additional information on WBGT index readings, PHEL charts, heat-stress dangers, and danger-level color codes may be found in in NAVMED P-5010-3, Manual of Preventative Medicine. EFFECTS  OF  COLD Just as the temperature alone is not a reliable indicator for how hot a person feels, the temperature of the air is not always a reliable indicator of how cold a person feels. Increased wind speeds may increase the rate of evaporation of moisture from exposed skin areas. This not only will make a person "feel" cooler, but will actually lower the skin temperature, and consequently, body temperature. While the type of clothing a person wears can provide protection from the chilling effects of the wind, the person’s state of health and metabolism may affect his or her ability to produce heat. These factors all affect how cold a person will feel. Generally, coldness is related to the actual lowering of internal body temperature by the loss of heat from exposed flesh. The two primary dangers to people exposed to the cold are frostbite and hypothermia. Frostbite is the freezing of the skin, which damages the skin and underlying flesh. Hypothermia is the lowering of the 1-57