Physiological Evaluation of Industrial Heat Stress

Heart rate (HR) and body temperature (t b) were studied in men on jobs in the open hearth department of a Pittsburgh steel mill. In 19 subjects on various jobs, mean HR for the shift was compared with mean HR off work and during sleep. Results showed these men expend 31 to 36% of maximum cardiocirculatory capacity on the job. In 12 tests on five second helpers, continuous ECG records on magnetic tape revealed individual mean HR's for the shift ranged from 99 to 136/min in summer and 97 to 111/min in winter. HR on the job varied inversely with individual work capacity estimated from pre-shift performance on an ergometer. Performance decrement was observed post-shift in two subjects with the lowest work capacity. HR responses, counted each 0.5 minute of the shift, were analyzed by computer with task effort and heat exposure as independent variables. HR gradients to heat levels are nearly as great as to task levels in summer. In winter, HR gradient to heat is only 33% of that in summer, but HR responses to task are unchanged.