A review of local and international heat stress indices ...

1 313 The Journal of The South African Institute of mining and MetallurgyJUNE 2003 IntroductionIn order to plan effectively for ultra-deepmining (UDM) projects, a number of issuesmust be addressed, not the least of which isthe provision of workplace environmentalconditions that are conducive to safe andproductive mining operations. Although manyaspects of an ultra-deep mining environmentwould be much the same as those alreadyprevailing in deep-level gold mines, thevariations in barometric pressure to whichworkers are exposed would increase by virtueof increased depth. Of even greater concern arethe anticipated engineering requirements tocontend with a tendency towards higherworkplace temperatures, which will result fromthe auto-compression of air and higher virginrock temperatures at greater depth and will becomplicated by longer delivery routes forcooling media and ventilation costs of providing acceptable thermalconditions will be crucial for assessing theviability of ultra-deep mining , and willultimately prove to be a major determinant inthe decision on whether or not to proceed withsuch projects.

2 It is, therefore, essential todetermine what conditions can be regarded asacceptable, as well as the criteria and limitsthat should be adopted in assessing them. Theimportant issues are clearly worker health,safety and productivity and, accordingly, anevaluation of local and international thermalstandards is essential. This will satisfy theneed for soundly based standards, criteria andlimits for ultra-deep mining that are alignedwith established norms, in order to ensure thatUDM projects yield the required results withoutundue risk to workers, or the perception ofsuch risks among workers, regulatoryauthorities or potential detailed review of the literature andother sources of information relating tostandards and regulations and certain environ-mental limits, and of various heat stressindices and their use (both locally and in othercountries) were investigated.

3 This investi-gation was done to establish what heat stressindices do exist locally and internationally andwhich would be most applicable to the UDMenvironment. In establishing this, acomparison was done to find out whatstandards and limits relating to theseidentified heat stress indices were used inA review of local and international heatstress indices , standards and limitswith reference to ultra-deep miningby Webber*, Franz , Marx , Schutte SynopsisMining up to depths of 5 000 m would be a world first and,accordingly, no previous experience in the determination ofacceptable heat stress limits, criteria or indices is wholly , some South African gold mines are already operating atdepths beyond 3000 m and much of the knowledge gained inreaching and working at such depths will be helpful in makingadequate provision for acceptable environmental control at thegreater depths being contemplated.

4 Accordingly, it is necessary totake cognisance of the industry s experience in deep-level miningand of standards and regulations already established in SouthAfrica and elsewhere in order to ensure acceptable workingconditions and control standards, that compare favourably anddefensibly with those in other mining local and international use of heat stress limits, criteriaand indices were investigated as it was necessary to determine towhat extent any other indices , limits or criteria would be applicableto South African deep mine conditions. In addition, it wasnecessary to establish whether there was a single heat stress indexthat could be used for South African ultra deep mining was found that an appropriate combination of heat stressindices would be required in planning for and ultimately controllingthermal conditions in ultra-deep mining .

5 The depths being contem-plated and the concomitant potential heat hazard present too greata risk for reliance on a single environmental component of heatstress, such as wet-bulb temperature at present in common uselocally. The study recommends that a heat stress index, preferablyAir Cooling Power (ACP), be used to design an ultra deep mine sventilation system and that wet-bulb temperature be used tomonitor and control the system once it is implemented.*Department of mining Engineering, University ofPretoria. CSIR Miningtek. The South African Institute of mining andMetallurgy, 2003. SA ISSN 0038 223 + Paper received Feb. 2001; revised paperreceived Nov. review of local and international heat stress indicesother countries.

6 The paper therefore offers some guidelinesfor the use of heat stress indices , standards and limits aswould be applicable for to the investigationThermal conditions and the heat stress imposed on workerswill be the most significant environmental consequences ofmining at ultra-deep levels, indicating a need to quantify theeffects of heat on workers health and their workperformance. This represents a difference in purpose from thetraditional concern with heat stress . The principal motivationin efforts to evaluate and control heat in the workplace hasbeen to minimize its detrimental health effects on has resulted in the development of standards; heatstress indices and exposure limits based more on physio-logical tolerance and health considerations than on workperformance criteria.

7 Given the critical impact thatperformance and resultant productivity will have on thesuccess or failure of ultra-deep mining , worker performancecriteria should form part of the fundamental basis fordetermining the thermal standards and exposure limits to , given the crucial balance between the costsand potential returns of ultra-deep mining , ensuring itsviability would appear to require the inclusion of workerperformance criteria in assessments of hot workplaces, ratherthan basing such assessments solely on physiologicaltolerance, as is presently the case. It is equally important tocreate investor confidence in ultra-deep mining projects, notonly in terms of viability, but also in terms of minimizingfuture compensation claims and litigation.

8 Accordingly, it isimportant to ensure, as far as is practicable andadvantageous, that environmental standards for ultra-deepmining are aligned with international norms and the past, a number of heat stress indices have beendevised in attempts to combine various thermal-relatedcharacteristics of the environment into a single numberindicative of the heat stress imposed on workers. Althoughsuch a number can provide some measure of environmentalheat stress , there are many and varied criteria for evaluatingthe acceptability of thermal conditions for safe work (Schutteet ).Aim of heat stress indicesHeat stress is the aggregate of environmental and physicalwork factors that constitute the total heat load imposed onthe human body.

9 A heat stress index is a composite measureused for the quantitative assessment of heat stress . It isaimed at integrating into a single number the components ofthe thermal environment and/or the physical and personalfactors that influence heat transfer between the person andthe environment. Unfortunately, an index that integrates allthese parameters and hence correlates them precisely to oneor more physiological responses had not yet been developed(Ramsey and Beshir22). However, there are several indicesfor measuring heat stress , each with special advantages thatmake it more suitable for use in a particular common aim of all heat stress indices is therefore torelate man's physiological and other responses to environ-mentally imposed thermal stress , in order to enable it to beassessed, predicted or controlled.

10 As a result of differences intheir treatment of various environmental parameters,commonly used indices tend to vary somewhat in theirassessments of a given environment. In addition, continuouspersonal monitoring to assess workers responses to heatexposure in the workplace is unpractical. It is neverthelessessential to accommodate personal factors and physicalcharacteristics that could potential affect an individual sability to work in heat. Emphasis should, therefore, be placedon comprehensive screening mechanisms, such as risk-basedmedical examinations and heat tolerance screening, todetermine overall fitness for work in heat. The heat stressmanagement procedures used in the South African miningindustry is a prime example of such an approach.