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ORIGINAL ARTICLE
Int J Env Health Eng 2014,  3:37

Performance evaluation of two wet bulb globe temperature equipment for heat stress assessment in hot/dry and hot/wet conditions


Department of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran

Date of Web Publication31-Dec-2014

Correspondence Address:
Behnam Khodarahmi
Department of Occupational Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2277-9183.148282

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  Abstract 

Aims: The purpose of this study was to compare performance of two these WBGT measuring devices.
Materials and Methods: This study was performed in the climatic chamber located in Health School of Isfahan University of Medical Science. The WBGT Casella and the WBGT Model 686 were placed a wide range of hot/dry (28.5-38.5°C) and hot/wet conditions (25.9-37.7°C) in 3 air flow velocity (0.16, 0.27, 0.31 m/s) for 10 h in the climatic chamber. Wet bulb temperature (t nw ), the dry temperature (t a ), the globe temperature (t g ) and the WBGT were measured every 3 min for both instruments in the total period. The data obtained were analyzed by descriptive method, T-paired test and Regression analysis.
Results: The result of this study showed that there were statistically significant differences in the meteorological parameter (t nw , t a , t g , WBGT) obtained from the WBGT Casella and WBGT Model 686 (P < 0.001). A high correlation also was seen between the values obtained by the WBGT Casella and the WBGT Model 686 (r = 0.993). Furthermore, there were statistically significant differences in the air flow velocity parameter (0.157 m/s) and (0.27 m/s) and (0.314 m/s) in a hot/dry (r = 0.994) and (0.980) and (0.994) respectively. There were statistically significant differences in the air flow velocity parameter (0.157 m/s) and (0.27 m/s) and (0.314 m/s) in a hot/wet (r = 0.980) and (0.992) and (0.973) respectively.
Conclusion: Since there is a high correlation between the values recorded by two devices and a remarkable cost - efficacy of WBGT Model 686 , using WBGT Model 686 is an acceptable method for measuring the heat stress if the prediction equations are utilized. According to the different temperature conditions, was obtained dry temperature, wet temperature and globe temperature both devices measurement in different climatic conditions equation WBGT Casella = 2.04 + 1.03 (WBGT Model 686 ). About 2 units WBGT Model 686 lower than the WBGT Casella and recommend the measures to be considered in this case as well as the manufacturers also, recommend doing that the reform of sensor measurements and the calculation methods.

Keywords: Climatic chamber, heat stress, wet bulb globe temperature index, workplace


How to cite this article:
Dehghan H, Shakerian M, Khodarahmi B, Habibi P. Performance evaluation of two wet bulb globe temperature equipment for heat stress assessment in hot/dry and hot/wet conditions. Int J Env Health Eng 2014;3:37

How to cite this URL:
Dehghan H, Shakerian M, Khodarahmi B, Habibi P. Performance evaluation of two wet bulb globe temperature equipment for heat stress assessment in hot/dry and hot/wet conditions. Int J Env Health Eng [serial online] 2014 [cited 2019 Dec 14];3:37. Available from: http://www.ijehe.org/text.asp?2014/3/1/37/148282


  Introduction Top


Heat stress exposure considered as a permanent issue for workers in many industries. [1]

The workers' safety in the workplaces can be affected by several factors. The studies show that there is a significant relationship between high productivity level and learning capacity of workers and the appropriate climatic conditions in the workplace. [2] In extremely hot environments there is a significant decrease in productivity [3] and a high rate of accidents as well as the risk of workers suffering heat disorders. [4]

The continuous heat exchange between the body and the environment can result in physiological and psychological strain on the people that is also affecting the workers' health as well as their performance and effectiveness. [5]

Heat-related illnesses occur mostly during the summer at high environmental temperature. [6],[7],[8]

Heat-related illnesses also may happen in most of the hot workplaces especially at long-term exposures following by possible inappropriate heat adaptation. [9]

Some heat-related illnesses [10] are included heat syncope, heat cramps, heat exhaustion and classic heat stroke. [11],[12]

As some environmental factor such as the ambient temperature, [13] radiant temperature, [14] humidity [15] and air velocity as well as clothing and activity level are effective to induce heat strain on the workers, there has been always an attempt to concise all these factors to an index referred to as "heat index." [16]

Many indices have been developed to measure the intensity of heat stress on the workers [17],[18] these indices are classified into two groups as follow:

The analytical indices based on the heat exchange principles.

The empirical indices developed based on the human responses to different environmental factors. Out of the empirical indices, [19] the wet bulb globe temperature (WBGT) index has the most applicability to measure the heat stress in the hot environments, inside buildings and outside buildings without solar load. [16],[20]

The WBGT index is the most applicable index in Iran. This index, however, has several restrictions. One of the important applied limitations is that the WBGT measuring devices was built in foreign countries and it is expensive therefore commercially unavailable.

A new WBGT measuring device WBGT Model 686 that is nearly 0.1 cheaper than foreign-made WBGT device (WBGT Casella ), has been recently built by Iranian experts.

The present study, therefore, aimed to compare and validate the result obtained from the WBGT Model 686 with those of the WBGT Casella .


  Materials and methods Top


This study was conducted under controlled experimental conditions [Table 1] in a Climatic Chamber located in the Health School in Medical University of Isfahan.
Table 1: Wide variety of environmental factor for hot/ dry and hot/wet climatic conditions

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Two WBGT measuring devices performance were under study including the WBGT instrument made in Iran (WBGT Model 686 ) and the foreign - made WBGT instrument (WBGT Casella ).

Both devices were firstly placed into the climatic chamber for 5 h under a wide range of hot/dry temperature (28.5-38.5°C) and for another 5 h under a wide range of hot/wet temperature (25.9-37.7°C). Furthermore, air flow velocity, both climatic conditions hot/dry and hot/wet temperature, were 0.16, 0.27 and 0.31 m/s.

The environmental factor including wet bulb temperature (t w ), the dry bulb temperature (t a ), the globe temperature (t g ) and the WBGT index measured and recorded [17],[21] every 3 min for both WBGT instruments.

The variation range of the meteorological parameters during the experiment under both hot/dry and hot/wet conditions is represented in [Table 1].

The WBGT instruments under study were both placed into the Climatic Chamber and mounted on a tripod with equal heights of 1/5 m from the floor.

The WBGT Casella had been bought nearly 6 months before the experiment. The WBGT Casella , therefore, was considered as an initial standard in this study.

When the experiment ended, data were recorded for each meteorological experiment including t w , t a , t g , WBGT under both hot/dry and hot/wet climatic condition.

The data were finally statistically analyzed by the descriptive method, T-paired test and regression analysis.


  Results Top


The study result indicated that the mean values of t nw , t a , t g and WBGT recorded by the WBGT Casella and the WBGT Model 686 are significantly different under hot/dry condition (P < 0.001).

[Table 2] represents mean, standard deviation and correlation co-efficient of t nw , t a , t g and WBGT under hot/dry conditions, recorded in hot/dry climatic condition by the WBGT Casella and the WBGT Model 686 .
Table 2: Mean (SD) and correlation coeffi cient of WBGT measured by both WBGTModel 686 and WBGTCasella in hot/dry climatic conditions

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[Table 3] shows mean, standard deviation and correlation co-efficient of t nw , t a , t g and WBGT under hot/wet conditions, recorded in hot/dry climatic condition by the WBGT Casella and the WBGT Model 686 .
Table 3: Mean, standard deviation and correlation coeffi cient of tnw, ta, tg and WBGT under hot/wet conditions, recorded in hot/dry climatic condition by the WBGTCasella and the WBGTModel 686

Click here to view


[Figure 1] also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/dry conditions.
Figure 1: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/dry climatic conditions

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[Figure 2] represents the scatter plot and regression line related to the values obtained from the WBGT Casella based on the values obtained from WBGT Model 686 under the hot/wet climatic condition.
Figure 2: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/wet climatic condition

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[Figure 3] also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/dry conditions in the air velocity (0.157 m/s).
Figure 3: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/dry climatic condition in the air velocity (0.157 m/s)

Click here to view


[Figure 4] also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/dry conditions in the air velocity (0.27 m/s).
Figure 4: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/dry climatic condition in the air velocity (0.27 m/s)

Click here to view


[Figure 5]a also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/dry conditions in the air velocity (0.314 m/s).
Figure 5:

Click here to view


[Figure 5]b also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/wet conditions in the air velocity (0.157 m/s).

[Figure 6] also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/wet conditions in the air velocity (0.27 m/s).
Figure 6: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/wet climatic condition in the air velocity (0.27 m/s)

Click here to view


[Figure 7] also shows the scatter plot and regression line of the values measured by the WBGT Casella based on the values measured by WBGT Model 686 under hot/wet conditions in the air velocity (0.314 m/s).
Figure 7: Scatter plot and regression line of the wet bulb globe temperature (WBGTCasella) values based on the WBGTModel 686 values under the hot/wet climatic condition in the air velocity (0.314 m/s)

Click here to view


[Table 4] prediction equations below accounts for the values obtained from the WBGT Casella based on the WBGT Model 686 under the hot/dry and hot/wet climatic conditions and the values obtained from the WBGT Casella based on the WBGT Model 686 under the hot/dry and hot/wet climatic conditions in 3 air velocity.
Table 4: Prediction equations in hot/dry and hot/wet conditions

Click here to view



  Discussion Top


T -test showed that under the both hot/dry and hot/wet conditions, there was a significant difference between t nw , t a , t g and WBGT measured by WBGT Casella and WBGT Model 686 .

The values recorded by WBGT Model 686 , however, were lower than those of the WBGT Casella .

Also, t-test showed that under the both hot/dry and hot/wet conditions in the air velocity (0.16, 0.27, 0.31 m/s), there was a significant difference between t nw , t a , t g and WBGT measured by WBGT Casella and WBGT Model 686 (P < 0.001).

The values recorded by WBGT Model 686 , however, were lower than those of the WBGT Casella .

Nevertheless, as it can be inferred from [Table 1] and [Table 2]. As well as [Figure 1] and [Figure 2] show the correlation coefficient of the values measured by the WBGT devices under study was higher than 0.98.

The WBGT Model 686 , therefore, can be easily afforded in terms of its lower price and shorter time to be provided than the WBGT Casella .

Moreover, regarding the study results, the WBGT Model 686 is possible to be replaced with the WBGT Casella , if obtained values by WBGT Model 686 , are put in the WBGT prediction equation based on the values measured by WBGT Casella .

This study was performed only under hot/dry and hot/wet condition, so to achieve more precise results as well as more practical predator equations a variety of climatic parameters and environmental conditions such as different wind velocities and different intensity level of thermal radiant are required to be investigated by WBGT Casella and WBGT Model 686 .


  Conclusion Top


This study showed a high correlation between the values obtained by the WBGT Casella and those by the WBGT Model 686 in a similar environmental condition. Furthermore, the WBGT Model 686 is easier and cheaper to be applied than the WBGT Casella provided that the WBGT predictor equation is used for the values measured by the WBGT Model 686 based on the WBGT Casella measurement results.

According to the different temperature conditions, was obtained dry temperature, wet temperature and globe temperature both devices measurement in different climatic conditions equation WBGT Casella = 2.04 + 1.03 (WBGT Model 686 ).

About 2 units WBGT Model 686 lower than the WBGT Casella and recommend the measures to be considered in this case as well as the manufacturers also, recommend doing that the reform of sensor measurements and the calculation methods.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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