Mathematical modeling of thermal responses allows testing of wide performance limitations in individuals exposed to environmental extremes. One important application is in the determination of hazard materials (HAZMAT) workers’ endurance times to execute a task. The simulation approach is especially important when operational settings with such individuals are restricted to finite thermal limits necessary to protect the individual. In essence, the ideal mathematical model of thermal strain (both heat and cold stress) should incorporate all essential variables active in thermoregulation. Although almost an insolvable task, a great many worthwhile models do a reliable job describing the heat balance equation. Models are quite useful in a first approach prediction of physiological effector response (sweating rate, skin blood flow, etc.), particularly when a given metabolic activity stays constant over the time of the given exposure. Early forerunners of rational thermal models employed elements of heat exchange that predict physiologic response and incorporate extensive descriptions of the passive system in terms of a steady-state bio-heat equation. In our Institute, a significant database has been collected from human experimental studies and wide clothing systems by which predictive modeling equations can be developed for individuals working in various environments. One model developed takes into consideration different clothing ensembles, varied levels of aerobic fitness in a population, and effects of progressive dehydration to heat stress/exercise. This review encompasses approaches conventionally used in both rational and operational models and presents a comparison between measured and predicted core temperature responses during exercise and environmental exposure often encountered during HAZMAT operations.
During prolonged exercise or work in the heat, human thermal homeostasis is first challenged, and eventually lost, as one moves from a compensable state through to uncompensable heat stress. During the first week of such exposure, work and athletic performance is most affected, and the threat of heat illness is greatest. However, given adequate time, the body will undergo a three-phase adaptation to better tolerate the heat. In this review, the principles and practices of the six primary methods by which such heat adaptation may be achieved are evaluated. One technique involves repeated exposure to both heat and exercise, and is designed to elevate and maintain a target body temperature, by varying the intensity of the work rate during the acclimation period: the controlled-hyperthermia (isothermal) technique. It is recommended that this method provides the most dependable, and least hazardous, means of adapting workers and athletes for heat stress.
Variables affecting the ‘wet’ thermal resistance of infant bedding materials arranged to simulate use are identified. Thermal resistance was determined when the materials were flat, and also when spaced to simulate use, using a guarded-hotplate similar to that specified in ISO11092:1993(E). The relationship between ‘wet’ thermal resistance and thickness is explored, and the effects of increasing thickness of the air space under and among the various layers of bedding were determined.
Circadian variations of the dynamic properties in sweating activity were investigated by power spectral analysis. Subjects were exposed to a fixed level of thermal radiation at 3 different times of day. Variability in the rate of sweating was measured using a ventilated-capsule method, and the results were analyzed by the fast Fourier transform. In the spectra obtained, the frequency component around 0.04 Hz, at which a peak was observed on the logarithmic plot, showed a higher power value in the early and late afternoon than in the morning. This component was correlated to a similar frequency component of skin blood flow, and both components showed similar circadian variation. These findings suggest the presence of a circadian oscillatory system that influences both the sweating rate and skin blood flow during thermoregulation.
The color temperature of general lighting in an interior space is an important lighting factor that contributes to making lighting environment more comfortable or pleasant. It is desirable for making atmosphere more comfortable or pleasant to clarify how air temperature affects psychological preferences for the color temperature of general lighting. Two kinds of psychological evaluation experiments were conducted by using a laboratory whose air temperature was kept at a constant value. As a result of the experiment-1, it was cleared that the air temperature to which the subjects were exposed was low, as in winter, a low color temperature was preferred. On the other hand, the air temperature was high, as in summer, a high color temperature was preferred. Accordingly, it was cleared that the color temperature preference for general lighting varies depending on the air temperature in a room. In the next stage, the experiment-2 was made to study whether a sudden change like step in air temperature as experienced during ordinary activities in human life affects color temperature preference. As a result, it was cleared that the color temperature preference for general lighting in Room A immediately after entering Room A from Room B varies depending on air temperature in B.
A longitudinal study of thermal sensations of occupants of an air conditioned commercial office building was conducted at approximately monthly intervals over a period of two years. In the morning and again in the afternoon of each visit day, participants recorded their thermal sensations together with details of current clothing ensembles and activities while concurrent measurements of physical variables were made nearby. A total of 1627 responses were collected. Operative temperatures were recorded in the range from 20°C to 27.5°C depending on location, time of day and season. Temperatures were concentrated toward the upper end of the range in summer and the lower end in winter. Seventy one participants contributed ten or more reports. A large majority indicated acceptability within a personal range of 5°C to 6°C at some time during the study. However a number of them indicated one or more occasions when a condition was unacceptable both within and outside the range of personal acceptability. Large between-subject variation was observed in estimated values for clothing insulation and metabolic rate. Mean clothing insulation values varied during the year from lower in summer to higher in winter. It was also observed that a significant proportion of subjects added or removed an item of clothing during the day with consequent change to the value of insulation provided by it. Overall 80 percent of responses indicated acceptability. It is concluded that the respondents were engaged in an adaptive dialogue with the thermal control system, intended to achieve a balance between available thermal conditions and their individual requirements at the time. This dialogue appears successful most of the time but breaks down occasionally, possibly when an unexpected event during the day produces a set of conditions that cannot be accommodated by the available options for change.
The purpose of this study was to compare the preferred water temperatures of showers and to investigate the post-shower physiological and subjective responses. The experiments were carried out in summer and winter. Two different groups of sixteen healthy females participated as subjects for each season. They each took a shower, and then rested for 30 minutes in a resting room. Skin temperatures, heart rate and blood pressure of the subjects were measured before and after the shower. Two kinds of subjective responses for thermal sensation were measured at three times after showering: immediately, then 15 minutes later, and finally 30 minutes after the showering. Water temperature and flow rates were measured during showering. The main results were as follows: 1) The preferred temperature was significantly higher by 2.1°C in winter than in summer, but there was no difference shown in water consumption between the two seasons. 2) Mean skin temperature increased abruptly after showering in winter, while it showed smaller increment after showering in summer. The temperature was kept at a significantly high level after showering compared to before showering in winter. 3) Heart rate increased slightly immediately after showering, but it fell towards the pre-showering level in the subsequent 15 minutes in both seasons. 4) Blood pressure descended after showering in both seasons, except in one case where it rose by about 5 mmHg immediately after showering in summer. Significant differences were confirmed between the initial level and 15 minutes level or 30 minutes level after showering in winter. 5) Subjects felt warm immediately after showering in the resting room which was heated at 24°C in winter and cooled at 26°C in summer. The proportion of subjects feeling warm was higher in winter compared to that in summer with no significance and this dissipated by the 30 minutes level in both seasons. In winter facial discomfort due to heat was observed in 30% of subjects immediately after