4-20. SPECIAL CONSIDERATIONS IN RECRUIT TRAINING
a. Basic trainees comprise a special group of unseasoned personnel who
require particular attention because of the unusual physical stress involved in basic
training in summer heat. Adjustment to this stress is difficult and must be taken into
account in planning training schedules. Curtailment of work and scheduling strenuous
training activities for the coolest parts of the day will yield greater efficiency and less
disruption of training than will ignoring the weather in the interest of completing a heavy
schedule. Heat casualties occur most frequently during the first 2 weeks of basic
training and during bivouac week. They are associated especially with firing on the rifle
range, road marches, and retreat parades. Particular attention should be paid to
decreasing the heat stress accompanying these activities.
b. Recruit heat casualties tend to occur in groups within particular units.
Responsible commanders and medical officers should therefore, promptly investigate
each case to determine the unsafe practice or condition responsible and institute
measures to prevent additional cases.
Three basic factors that determine the degree of heat stress exerted by the
environment are air temperature, relative humidity and air movement, and heat
a. The air temperature is read from the ordinary dry bulb thermometer. The
thermometer should be in the shade, so that the reading is affected only by the air
b. The relative humidity and air movement is determined by the wet bulb
temperature. The wet bulb temperature is the reading of a thermometer when the bulb
is covered with a wet wick and when a strong current of air is passed over the wick.
The amount of heat lost by the bulb under these conditions, and thus reading of the
thermometer, is affected by both temperatures and humidity. The wet bulb temperature
is always below the dry bulb temperature except when the relative humidity is 100
percent, at which point both temperatures are equal.
c. The radiant heat can be determined by a black "globe" thermometer or by a
radiometer. The globe thermometer, which is the simpler instrument, consist of a 6-inch
hollow copper sphere painted flat black, with an ordinary thermometer inserted so that
the temperature at the center of the sphere can be recorded.
d. Because of the difficulty in recording all three of these measurements and
combining the readings into a single index as a measure of overall heat stress for man,
usually only the dry and wet bulb temperatures have been used. The dry bulb
temperature is, in general, a poor indication of thermal stress because it is not affected
by humidity, air movement, or radiation. The wet bulb temperature is a better index