Efficacy of a water-cooled garment for auxiliary body cooling in heat.

The efficacy of a water-cooled jacket for auxiliary body cooling was examined under a simulated hot environment. The personal garment comprised of a water re-circulating three-layered vest of cotton fabric lined with 2 mm diameter latex tubing and inter-spaced coating of rubberized solution. Four subjects wearing the water-cooled jacket were tested in the environment chamber (30, 35 and 40 degrees C DB, 50-60% RH, air velocity 0.3, 0.6 and 0.9 m/s, with corresponding average effective temperature of 26 +/- 2.3, 33 +/- 1.1 and 36 +/- 1.5 degrees C). The inlet water temperature was maintained at 10-12 degrees C, with flow rates of 2.6 +/- 0.3, 4.3 +/- 0.3 and 5.1 +/- 0.3 l/h). At 30 degrees C DB, variation in water flow had marginal effect on microclimate, while at higher temperatures (35 and 40 degrees C DB), the re-circulating cooled water had noticeable effects in lowering microclimate, trunk and other skin temperatures, and maintaining the body core within 36.7 +/- 0.2 to 37.5 +/- 0.2 degrees C, over 2 h exposure at 35 and 40 degrees C DB. The observation indicates that the water-cooled jacket provided auxiliary cooling to maintain comfortable microclimate, skin and body core temperatures. This enabled subjects to sustain comfortable heat balance over 2 h heat exposure without any noticeable heat strain.

Influence of air flow on skin temperature.

The skin temperature is fundamental to heat exchange between the human body and the environment. The convective and evaporative heat exchanges depend on the temperature gradient and the extent of air flow over the skin surface. An attempt was made to study the topographical differences in skin temperature (Tsk) under varied levels of air flow and to examine the possible body temperature regulatory mechanism. Five volunteers were examined in a climatic chamber at 30 and 36 degrees C DB at 55-60% RH (ambient vapour pressure of 2.58 and 3.53 kPa and air flow of 0.6, 1.4, 1.9, 2.1 m/s). The deep body temperature (Tc) and local Tsk were recorded at 5-min intervals during 10 min pre-exposure, 30 min exposure to heat and 15 min recovery period after air flow was withdrawn. The time taken to attain at the lowest Tsk in different air speeds varied from 30 to 45 min. The highest drop in Tsk (2.4 degrees C) was recorded for forehead at 30 degrees C DB and significant skin cooling was achieved at an air flow of 0.6 m/s for most body regions. The overall drop in local Tsk was more greater at a higher ambient temperature (36 degrees C) and the changes were significantly different (p < 0.05) to those recorded at the preexposure level. There was a consistent drop in Tsk with time, while no definite pattern of drop was noted with the magnitude of air flow. The Tc increased significantly with the continued air flow and following withdrawal of air flow the Tc tended to drop, suggesting heat gain by the body with a consequent increase in Tc.

Human performance capability in psychomotor tasks at variable difficulty levels and physiological reactions under noise and heat conditions.

The effects of noise and heat on the efficiency of human performance of psychomotor tasks at variable difficulty levels were investigated. Twenty four young, healthy volunteers with normal hearing, randomly divided into 4 equal sized groups, were tested in a climatic chamber under 4 combinations of two environmental conditions made up of noise and heat, each at two levels: 70 dB (A) (quiet), 100 dB (A) (noise): 28 degrees C (comfortable), 35 degrees C (heat). A statistically balanced procedure was followed. Three physiological variables were also recorded: Heart rate, blood pressure and body temperature. A 2 x 2 analysis of variance showed rise in the physiological variables by noise and heat respectively as well as by their interactions. Performances of the psychomotor tasks were affected differently by noise and heat depending on the difficulty levels of the tasks. The interaction of noise and heat entailed superior performance of the tasks of memory and search, two hand coordination and reaction time, at moderate difficulty levels, but no distinct interaction effect was observed on the performance of tweezer dexterity.

Acute effects of heat on neuropsychological changes and physiological responses under noise condition.

To examine the effects of heat and noise individually and jointly on certain physiological responses and cognitive and neuromotor based functions, 12 male participants were tested under 6 experimental conditions which resulted by combining 3 levels of heat (25 degrees, 30 degrees and 35 degrees C) and 2 levels of white noise (70 and 100 dB). The experiment was carried out in a controlled climatic chamber following two 6 x 6 latin square designs. The results indicated elevations in heart rate, oxygen uptake and body temperature due to the independent effect of heat or the combined effects of heat and noise. The independent action of noise was found to be depressive on the first two responses. On the neuropsychological effects, the heat adversely affected the speed in card sorting (by design configuration) and digit symbol tests, and also the accuracy and error rate in the reasoning ability test. The noise caused performance improvements in critical flicker frequency (simultaneous) and in error rates in card sorting (by design configuration). The combined effects of heat and noise indicated higher error rates in card sorting (by face value), decreased accuracy in reasoning ability and improvements in performance in accuracy scores and error rates in digit symbol test.

Ergonomics in sickle operation.

Sickle operation in harvesting has been analysed with reference to design features of nine different types of sickles, and field and laboratory based investigations on biomechanical stresses and physiological valuation on six farmers. It has been indicated that the blade geometry contributes significantly to human performance and there is ample scope for further design optimisation. The suggested modifications are: (i) sickle weight - 200 g; (ii) total length of sickle - 33 cm; (iii) handle length - 11 cm; (iv) handle diameter - 3 c cm; (v) radius of blade curvature - 15 cm; (vi) blade concavity - 5 cm; (vii) serrated sickle: tooth pitch - 0.20 cm and tooth angle - 60 degrees; (viii) ratio of the length of cutting surface to chord length - 1.20.

Performance evaluation of lower extremity disabled people with reference to hand-cranked tricycle propulsion.

A study was designed to evaluate physiological cost and work performance of lower extremity disabled people with reference to hand-cranked tricycle propulsion. Eleven volunteers took part in this study. For an average body weight of 39.7 kg, VO2 max (arm cranking) was only 0.777 l/min at STPD. The pulmonary demand and oxygen uptake of the disabled subjects during tricycle propulsion at 8.45 +/- 0.6 km/h corresponded to about 70% of their maximal response; hence, work stress was categorised as heavy. Mechanical efficiency of cranking was best when a hand-rim propulsion system was arranged for two-arm cranking at the heart level of the disabled person and at a cranking pace of 60 rev/min.