Evaluation of physiological strain of shovellers in underground coal mines in India

Abstract

The functional capabilities of 37 male shovellers (25 - 58 years) during working spells in a shift were studied. They were selected following a random sampling technique stratified on the basis of their age. Prior to work anthropometric and cardiorespiratory variables were measured at the surface and VO_2max was estimated by an indirect method following a standard step test protocol of Martiz et al. (1961). Heart rates and oxygen consumption during work were measured using Heart Rate Monitor and Oxylog II. Recovery heart rates were also taken after each spell of work by counting the pulse for the last 30 secs of each minute for three successive minutes to determine the Pulse Deceleration Index (Brouha 1960). Effective temperatures and WBGT were taken at regular intervals throughout the shift. The task was performed in two spells where shoveling and hand filling of coal contributed the maximum time in a spell followed by a longer non-volitional pause inbetween. In the present study, miners, irrespective of age maintained an intermediate shovelling rate of 12-14 scoops/min with an average scoop load of 5.5 - 6.5 kg. Heart rates of miners varied between 132 and 136 beats / min with a corresponding mean RCC of 56.6% – 67%.The latter showed significant difference (6.18; p<<0.001) along with net cardiac cost (65-70 beats/min) between two age groups (2.23; p<0.05). Deceleration of pulse between the shovellers was significant too (2.32; <0.05).The average working VO₂ was 1.0-1.1 l/min corresponding to an energy expenditure of 5.2-5.6 Kcal/min. The relative aerobic strain (55.9-57.1%) did not vary significantly. Acceptable levels of physiological strain were surpassed frequently, and older workers experienced the greatest strain. The task appears to be ‘heavy to very heavy’ in nature according to the classification as suggested by Astrand (1986) and the prevailing environmental conditions have an impact on miner’s work efficiency.

Keywords: Coal mine, Energy cost, Heart rate, Shoveller.