Evaluation of heat strain experienced by furnace workers at an iron smelter

Abstract

Background: Any working environment where industrial processes create heat, the worker is potentially exposed to heat-related illnesses because of the increase in thermal load from the environment. For these workers to work a full 12 hour shift, without developing any heat illnesses, their body temperatures must be kept within a narrow range of 1 to 2°C (Joubert and Bates, 2008). Body temperatures substantially higher than optimal temperatures (36.5-37.5°C) may cause a decrease in the mental and physical performance of workers. Objectives: To evaluate the heat strain experienced by furnace workers at an iron smelter. The evaluation will include an anarysis of data for the full period of the shift (8 hours or 12 hours), as well as the high risk periods (window periods). These window periods consist of the tapping and cleaning time periods. Methods: Intra abdominal core temperature was measured by means of a miniature data logging transponder for the duration of the shift. This sensor transmits a wireless signal to a recorder worn on the worker's waist. This method provides continuous measurement of core temperature with limited work interference and no physical annoyance. Heart rate was measured with Polar heart rate transmission straps and hydration by means of Urinary Specific Gravity (USG). The Physiological Strain Index (PSI) was calculated using heart rates and core temperatures. Environmental temperatures on the tap floor were measured with a Heat stress instrument and 150 mm Globe for measuring radiant heat. Results: Results indicated that cleaners and tappers of the 8h and 12h shift experience moderate strain. Subjects were adequately hydrated and mean core temperatures did not exceed the limit of 38.5°C for acclimatized individuals. Mean WBGT○ values did not exceed the limit as given in ISO 7243, namely 26 for cleaners and 28 for tappers. An analysis off each individual's data indicated inter-individual differences. The group showing the highest amount of strain also had the highest mean BMI. Conclusions: When evaluating heat strain it is important to evaluate each individual's physiological indicators and not just general environmental conditions. A subject's strain can be limited by applying adequate hydration, acclimatization, work-rest ratios and engineering control measures. Recommendations: Depending on the severity and intensity of heat strain there are certain general- and job specific controls that should be applied to limit heat

strain. Always consider and include short term exposure in the investigation and not just mean values for the day.