Development of a code of practice for work in hot and humid conditions in coal mines

It has long been recognised that, in a significant minority of British coalmines, hot and humid working conditions exist which could have an adverse effect on health and productive efficiency. Heat strain may develop in mines due to a combination of heavy physical work resulting in internally generated heat (metabolic heat) and the environmental conditions. It is recognised that humid conditions and low air velocities in particular can give rise to particular problems.Current environments in some mines have become more extreme than in the past, with deeper mines (and associated higher strata temperatures) and the coal face being considerable distances from the pit bottom (meaning that the air temperature at the face will be close to the strata temperature). The introduction of powerful machinery into mines also results in an additional heat source.These working environments create the potential for heat related health problems to develop in miners. It is known that some mild cases and at least one serious case of heat strain have occurred in British mines. This, and the advent of a legislative framework which increasingly requires employers to identify and reduce occupational risks to health, were reasons for providing guidance for employers in dealing with the problem of potential heat stress amongst miners. It was recognised that guidance is required not only on the important issue of duration of work and acceptable environmental temperatures for work, but also on the issue of management of the problem prior to any work limits being exceeded, and steps that can be taken to minimise the risks to health. The purpose of this research was to meet this need arid develop a code of practice for use in the mining industry.The work was undertaken in four main stages. Firstly, literature concerning the main sources of heat strain and the resultant health effects was collated and reviewed. Secondly, the current climatic conditions in mines were assessed, and discussions were held with mines managers to determine the extent of the problem and control measures which had been attempted. Thirdly, other international experts with experience of working with heat strain and miners were consulted for their opinion. Finally, different indices for assessing the thermal environment were considered, for their ability to predict the thermal strain in these environments. Based on the findings of these stages a code of practice was developed for working in hot and humid conditions in coal mines.The collation of the literature brought together findings of previous research which identified the physiological response to the heat and the health effects of working in hot and humid conditions. These health effects include minor effects (eg. burns, heat oedema, prickly heat), as well more serious effects such as heat exhaustion and heat stroke. Furthermore, it is recognised that an individual’s ability to cope with the heat is affected by a variety of factors, some of which will vary for that individual over time. These include age, medical conditions, physical fitness, obesity and diet, drug use and acclimatisation. Factors which contribute to heat load in the mines were identified in the literature, specifically the environmental conditions and the metabolic heat produced from mines activities. Previous data on metabolic costs were collated from the literature. Literature was also identified which outlined methods of controlling the heat stress problem. Various methods have been proposed for this in the past, and the advantages and disadvantages of these were considered. Engineering solutions have a limited success; increasing the air velocity in the mines can have a cooling effect where the environmental temperatures are less than approximately 37�C. Above this temperature the heat load on the body will increase as the air flow increases, meaning that above these temperatures there is no advantage in increasing air velocity. Air cooling is only effective over a limited range, and is largely inefficient. The refrigeration unit itself can contribute a heat load to the environment. Water cooling can be effective, but in conditions of high humidity, such as those experienced in the mines, it will be relatively ineffective. Other methods used include work reorganisation, so that for example, some of the work is carried out in cooler parts of the mine and this may be effective in reducing an individual’s exposure to hot conditions. More radical measures such as cool refuges have been used successfully in different mines internationally and provide a cooler environment in which workers can rest, thus allowing their core temperature to be reduced. Cooled garments also reduce an individual’s exposure to the heat, but they can be cumbersome to wear and restrict the worker to one position. Another method for controlling heat strain is to identify susceptible individuals prior to exposure to the heat (ie detecting those who may be heat intolerant), although most miners currently working in hot and humid conditions are unlikely to be heat intolerant as they would have changed their job sooner. In terms of managing the likelihood of heat strain, monitoring and surveillance of individuals can be effective, along with providing information and training.Three collieries were visited in order to determine the current climatic conditions. It was apparent that current climatic conditions are more extreme than those identified in previous studies. Air temperatures in excess of 37�C were often documented, with two collieries reporting dry bulb temperatures in excess of 40�C. At the coal face of one mine, basic effective temperatures (BET’s) of over 30�C were recorded for over 50% of the recorded temperatures. In a heading BET’s exceeded 30�C for over 75% of the recorded temperatures. The environmental conditions in the mines were being measured at the places where individuals were working, rather than at the statutory measuring points as was the practice in the past. Taking measurements at working locations gives a more realistic indication of the heat strain they are actually experiencing. Estimates of metabolic heat production were obtained from observation of the mining activities, taking account of how these have changed in recent years. The methods currently employed to reduce heat strain in miners were identified during these visits. In general it appeared that the issue of heat strain was seen to be a problem and that guidance was required for steps to reduce the risks. For example, although some collieries undertook pre-employment screening, there were no criteria with which to compare the findings.Other international experts working in mines were consulted to determine how these problems were tackled in other countries. The German mines in particular have similar, and in some cases more extreme, conditions to those experienced in the UK. They have determined limits for working time, with a reduced shift at conditions of over 28�C dry bulb temperature (or 25�C BET). They have an upper climatic limit for workers of BET 30�C, although in some conditions an upper BET of 32�C may be acceptable. It is not clear, however, how closely these limits are adhered to.For many years there has been debate concerning the assessment of the thermal environment, with the limitations of the BET scale being recognised by many authors. These limitations include the fact that all the lines on the nomogram converge at an approximate BET of 32�C, meaning that it is difficult to read, and the impact of different air temperatures in this temperature range is not clear. It has been reported that BET is not an effective predictor of the relative severity of severe climates (defined as BET 34.4 �C upwards); that it is not very accurate in conditions of either very low or very high air velocity; and it does not indicate the physiological strain that an individual may experience, as there is no physiological component in its calculation. Despite its limitations, it has been widely used in UK coal mines over the past 70 years.With the environmental conditions becoming more extreme in the mines (ie close to the conditions where BET is not an accurate predictor) and with the development of new thermal indices, particularly the Required Sweat Rate equation (SWreq) it was appropriate to examine the use of BET and other thermal indices to determine which is most suitable for use in the UK mines for predicting thermal strain. Earlier studies comparing BET with other indices had concluded that other indices offered little advantage over the BET and had therefore not recommended their use in the mines (eg. Morris and Graveling, 1986). Even with the higher conditions currently experienced, it was not thought that they offered any real advantage over BET. The thermal index which has developed the most in recent years is the SWreq which is now described in a British Standard (BS EN 12515). This index takes account not only of the environmental conditions, but also the metabolic rate of the worker, the clothing they are wearing and the proportion of the body which is covered by that clothing. It then predicts the amount of sweat which the body is required to evaporate in order to maintain thermal equilibrium in that environment. If the environmental conditions are such that the sweat cannot be evaporated, the index assumes a rise in core temperature. The index predicts where there may be an excessive rise in core temperature and therefore heat illness, and gives limits to work durations based on the acclimatisation of the worker. The accuracy of these predictions of sweat loss and time to limiting rise in core temperature were compared with the observed values determined in previous experimental work conducted by the IOM. From this it appeared that the observed data points do not relate well to the predictions. Further studies of the accuracy of predictions of SWreq were conducted using the environmental conditions, work rates and clothing levels observed in the mines. From this it appeared that below BET of approximately 31 ?C there was a wide range of times leading to limiting core temperatures. Above BETs of approximately 31�C the predictions of the index were closer, with all conditions observed giving rise to predict limiting times of less than 90 minutes. It was concluded that SWrcq was not a good predictor of strain (given the wide spread of predictions). Based on this finding and comments from the German mines experts (that the index could not be applied in conditions of high humidity and high velocity found in the mines) it was decided that the index did not offer any advantage over BET.Having decided and recommended that the mines should continue to use BET, it was necessary to provide guidance on how to control the heat stress problem, and what levels of BET should require actions to reduce the strain. Based on the findings of the literature review and the other expert guidance, it is recommended that action levels be set at BET of 25�C, below which heat illness is unlikely to occur. Between BETs of 25�C and 27�C, physical work should be reduced as far as possible through, for example, job rotation and mechanisation. Information and training should also be provided to all staff concerning the potential for heat related illness to occur, and what they should do to reduce the risk. Between BETs of 27�C and 30�C, health screening should be provided to identify those who may be at risk of heat illness, including those who may be temporarily at risk due to illness or hang-over. It would also be useful to monitor the extent of heat related illness through surveillance and monitoring of staff as they leave the mine at the end of a shift (eg, a simple questionnaire). This would allow identification of particular problem locations or activities and therefore allow remedial action to be taken. Above BETs of 30�C more stringent measures are required. The use of cool refuges or cooled jackets should be considered, and it may be necessary to limit the working shift at these conditions. Further work is required before firm guidelines on this can be provided.Clothing provided for an individual should be kept to a minimum, although concomitant with safety requirements; shorts and singlet should be provided. Individuals should be encouraged to take small amounts of fluid frequently, and snacks while working may also help prevent some heat illness. Further guidance on assessing and controlling the risk is provided in the Code of Practice which accompanies this report.This research has allowed knowledge on heat strain in hot and humid conditions to be brought together and to form the basis for guidance for the mining industry. Examination of current mining conditions and practices shows that this is required. The different actions recommended cover a range of severities of environmental conditions, from those which require simple education to those more complex engineering controls. “”