Heat stress in mining MINE PORTAL TEAM www.MINEPORTAL.in CALL/WHATSAPP-8804777500 www.fb.com/mineportal.in

Heat source of underground mine Unusual high heat flow from earth. Need for development of new sources of minerals calls for an expansion of underground mining deeper therefore, hotter levels of the earth crust. Use of electricity and other mechanical processes adds to the heat load of underground mines. Estimated 90-95% of the energy released in blasting find its way into the underground environment as heat. By Autocompression

underground heat contributors Source--www.smenet.org/docs/meetings/2008/030.pdf

HUMAN BODY AND ENVIRONMENT Human body metabolism provides heat and energy for our physiological functions. When environment and our body has temperature difference ,part of difference become less through convection and radiation from body to surrounding environment. An active person loses part of his body heat through sweat evaporation . The body core can dissipate its heat only through the shell. Blood serves as a vehicle for heat transfer.

Assessing the heat risk Several factors can influence the heat load on the body. These include: air temperature (Wet Bulb and Dry Bulb); radiant heat; humidity; air movement; the level of physical work; and the amount and type of clothing being worn. It is not possible to estimate the strain placed on the body by examining any one of these factors in isolation. In the mining situation, where radiant heat is not a major factor, it has been found that the best index is the Effective Temperature (ET), because it takes air velocity into account.

Concern where,M=Metabolic heat generated The steady stage of thermal equilibrium is represented by the following heat balance equation M - E +/- K +/- C +/- R=0 where,M=Metabolic heat generated E=Evaporative heat loss K=Conductive heat exchange C=Convective heat exchange R=Radiative heat exchange For normal body function,heat exchange between the body and it’s environment need to be balanced and practically relies on convection,conduction and evaporation.

Continued… In hot environment,where ambient temperature reaches core body temperature ,conduction and convection as a mean of thermoregulation. Hyperthermia is caused by accumulation of heat . Humidity decreases sweat evaporation. Clothing impedes convective heat loss and interferes with the evaporation of sweat from the skin. Heat stress overall affects the worker efficiency and thereby affects the production.

Variation of mean skin temp. with ambient wet bulb temp Variation of mean skin temp. with ambient wet bulb temp. for clothed(light and heavy),unclothed Source--www.he.gov.uk/pubns/mines07.pdf

HOW HUMAN BODY COPES WITH HEAT STRESS Warm-blooded animals can function regularly in almost all types of weather and climate. At best, only some percent of the energy generated by the body's metabolism is converted into mechanical work. Too much heat will interfere with the metabolism and cause health problems.

Heat Illness Heat fainting- It may occur as a result of vasolidation,pooling of blood in dependent extremeties,reduced. Reduced blood volume (from dehydration ) result in reduced cardiac output. It is not associated with an elevated body temperature.

Heat exhaustion- There is a complex symptoms of fatigue,headache,nausea and giddiness. Heat exhaustion occurs as a result of either dehydration and/or electrolyte depletions.

Heat cramp- If the electrolytic balance of body fluids is sufficiently perturbed then painful muscular contraction occur in the arms,legs and abdomen. This may occur by salt deficiency or drinking lar amounts of water following dehydration.

Heat rash- Heat rash is caused by sweat duct obstruction and results in sweat retention within the gland. This may result in infection or more commonly rupture within the skin with an inflammatory respponse result. Sunburned skin and occulsive clothing interfering with free evaporation of sweat increse the risk of this condition.

Heat stroke- This is a life threatening medical condition.Symptoms include altered mental status and core body temperatures above 40 degree celcius. It occurs when the body’s thermoregulatory mechanism is overwhelmed by internal or external heat load and results in increasing core temperature. Multiple organ failure or distruption of function is common and shoul be expected.

Improving the environment The first step must be to reduce the impact of the environment, ie reducing effective temperature by engineering controls. Provision of good quality air Careful attention should be paid to the position and timing of ventilation connections, and the minimising of leakages between intake and return outbye, to maximise the quantity of air reaching the inbye workings.

Siting of equipment that generates heat Static equipment that generates heat should be kept sited either in the return airstream or in cross cuts. Such equipment includes conveyors, as detailed above, compressors, pumps, and electrical switchgear, particularly transformers.

Use of equipment A common source of excess heat is equipment that has been left running when not required. Equipment should also be selected for the duty to be performed . The selection of fire resistant hydraulic fluids can also have an effect on machine running temperature.

Control of water to minimise humidity This can be achieved by eliminating standing water and by minimising the amount of water that is introduced underground .

Artificial cooling Air coolers remove heat from the passing air, but then dump that heat elsewhere. The plant is an additional heat source, but its use must be considered as part of the control measures. Chilling the water supply underground is also worth considering.

CASE STUDY : The Granites Callie Mine - Australia INTRODUCTION- Mineral : Granite Production-2.1 Mtpa Depth- 1000 m Final Expected depth-1800 m Mining Method: Longhole open stoping

Severe heat condition in mine The mine heat load includes auto-compression, heat flow from rock and fissure water, heat released by the operation of electrical and diesel powered equipment. The mine geothermal gradient is approximately 2°C/100 m resulting in 50°C rock temperature at the base of the mine.

FUTURE INFRASTRUCTURE source-- www. deepmining2012 FUTURE INFRASTRUCTURE source-- www.deepmining2012.com/data/page/6998/5_howes.pdf

COOLING REQUIREMENT- Assuming an overall cooling requirement of 12500 kWR, for an average mine airflow of 675 m3/s, the amount of cooling required is 18.5 kWR/m3/s. The average mine cooling required is expected to average 10000 kW or 14.8 kWR/m3/s. .

WET AND DRY CONDENSING METHOD Firstly condensers of a refrigeration plant remove heat from the refrigerant. The refrigerant gas discharged from the compressor is superheated Condenser cools it initially to the condensing temperature and then to a fully condensed liquid refrigerant in the condenser.

CONCLUSION Heat Stress affects the mental condition of workers , hence affects the production. The best solution to control heat is to use available technologies. Better heat conditions in mine reduces mine accidents.

REFERENCES Dresosti A.O.,Problems arising out of temperature and humidity in deep mines of the Witwaterstand.Mine society of S.Africa ,vol.36:pp 102-129 retrieved from http://www.minetech.com/technology/miningheat/ visited on 29 august 2011 Polton,E.C.,Environment and human efficiency.vol 1:pp 204 McPherson M.J., Subsurface Ventilation and Environmental Engineering,chapter 17-18:pp 680-749 http://www.geoexpro.com/technology/miningheat/ Date:1 sep 2011 www.hse.gov.uk/pubns/mines07.pdf Date:30 aug 2011 http://www.sciencedirect.com/science/article/pii/037663497790013X Date:30 aug 2011 www.deepmining2012.com/__data/page/6998/5_howes.pdf Date:1 sep 2011