h. Special Consideration in Troop Transportation to Tropical Combat
(1) Transportation by ship. Troops being transported by ship to tropical
combat zones need two 50-minute periods of vigorous exercise daily to maintain
physical fitness and to begin acclimatization to heat. The type of exercise should stress
the cardiovascular system rather than development of muscle power. For example,
running in place is a better exercise in this situation than lifting (pushups).
(2) Transportation by air. Troops transported by air to tropical combat
zones may be injected into combat situations in hot environments without being able to
become acclimatized. In this case, all possible steps to induce heat acclimatization
prior to deployment should be attempted.
i. Special Consideration in Armed Forces Industrial-Type Settings Ashore.
In addition to preventing the adverse effects of heat in military situations and physical
activity in military training, there are WBGT threshold values for instituting proper
preventive measuring during hot weather in Armed Forces industrial-type settings
ashore. When WBGT values are reached for the hottest two-hour period of the
industrial work shift, the health practices described in paragraph 4-28 of this section
become particularly necessary.
Do not confuse the WBGT threshold values with the PHEL (physiological heat
exposure limits). The PHEL deals with maximum time-weighted-mean
limitations on an individual's work capacity in hot environments.
j. Special Consideration in Hot Environments Afloat.
(1) In certain environments afloat, heat frequently exceeds man's ability to
adapt. Therefore, exposure limits for high heat stress areas afloat have been
established through use of the PHEL (physiological heat exposure limits), described in
detail in Navy Medical Department publication NAVMED P-5010-3, Manual of Naval
(2) The PHEL's are maximum allowable conditions of work and WBGT
levels. The PHEL concept should be applied only in cases of short-term work
exposures of up to eight hours duration. The limits presume that no prior heat injury is
present and that no cumulative fatigue exists prior to reexposure.
(3) The physiologic impact of repetitive exposures to heat stress over the
span of several days is the subject of scientific investigations. The PHEL concept is
based upon a comprehensive set of physiologic criteria of heat tolerance that is
reversible without evidence of presistent injury.