The role of global radiation measured by a light sensor on heat stress assessment
Introduction
The wet bulb globe temperature (WBGT), developed by Yaglou and Minard (1957) is considered to be the most common heat stress index for describing environmental heat stress for outdoor and indoor use. It has been adapted by the World Health Organization (WHO) and it is in use by the US army for setting limits at US military training exercises in hot weather (Montain et al., 1999; Moran and Pandolf, 1999; Burr, 1991). This index has also been recognized by other organizations for setting limits in industrial plants (National Institute for Occupational Safety and Health, 1986), adopted by sport associations as guidance to prevent heat injury (American College of Sports Medicine, 1996; McCann and Adams, 1997), and as a safety index for workers in different occupations (Chaurel et al., 1993; Froom et al., 1992; Gun and Budd, 1995; Singh et al., 1995). The WBGT is calculated from ambient temperature (Ta), wet bulb temperature (Tw), and black globe temperature (Tg). The Tg is usually measured by a thermometer surrounded by a 6″ blackened sphere, and quantifies the global radiation component of the thermal load. However, measuring Tg is cumbersome in many circumstances for two main reasons. First, Tg measurement requires about 30 min for the instrument to reach equilibrium. Second, the commonly used blackened sphere is of a relatively big size (6″), even though smaller sized spheres are available. Therefore, measuring Tg becomes inconvenient and simply not practical, especially in transient situations. The purpose of this study was to evaluate a new relatively small (5 mm) light sensor to measure global radiation for use in heat stress assessment.
Section snippets
Materials and methods
This database was obtained from a study conducted near Tel Aviv, Israel, during the autumn season (September–October) for 25 days. Global radiation (GR) measurements were collected daily every 15 min from 09 : 00 until 17 : 00. These data were collected from three instruments placed under the open sky at 1 m height: black globe temperature (Tg) using the Vernon-black globe thermometer, EPLAB pyranometer (P), PSP model with sensitivity of 285–2800 nm, and infra-red light (L) sensor (Centro Vision,
Results
The collected data in this study were carried out over a wide range of weather measurements as depicted in Table 1.
Analysis of the daily collected data from these three instruments revealed, that in spite of the different units, the same pattern for P and L occurred during each day, where Tg was slower in its response and lagged behind P and L in its values (Fig. 1). During morning days Tg did not reflect solar radiation (Fig. 1, top panel), whereas in other days Tg accounted for the change
Discussion
In the present study, the newly developed PGR model from light sensor measurements seemed to evaluate global radiation as the correlation coefficient between PGR and global radiation measured by pyranometer is R2=0.933. Although the database for this study was collected only at one location, the range of the measurements for each day was wide as seen in Table 1. Furthermore, since the study was conducted during the autumn, we had many days where the sky was not clear, partly cloudy or
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