GREEN MINING METHODS
THEME
1. Atmosphere
MINE LIFE
PHASE 
Exploration
LEVEL OF REALISATION
TOPIC
1.3 Heat and humidity
FORM
1.3.0 Generalities
Design
Development
Exploitation
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Concept
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Laboratory
Prototype
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Reclamation
Realisation
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Context / Description
Thermal conditions in underground mines are the result of thermal
conditions on the surface, sources of heat and humidity underground,
and ventilation/refrigeration.
The human body has several mechanisms for rejecting heat and
remaining cool. However, once the air temperature exceeds about
34°C, the only effective mechanisms is by evaporation of sweat for
skin (AUS050). The body has to remain well hydrated because
dehydratation causes significant decreases in the ability to work in
heat. Below 100 m depth, temperature almost always increases with
depth. Typically, the geothermal gradient is between about 15°C/km
and 40°C/km.
Auto compression and other sources of heat: temperature will
increase due to auto compression by up to 10°C per kilometre of
vertical depth. Since the effect of auto compression combines with the
surface air temperature to contribute to underground air temperature,
it is clear that this is a very significant source of mine heat, particularly
in hot areas of the world. Groundwater (through increased humidity),
service water and oxidation also contribute to the heat load.
Explosives and mechanical processes also contribute. For example,
the diesel engines contribution is generally estimated at 33%.As
mines become deeper and more complex, the air resistance
increases.
As mining depth increases towards 1000m and beyond, the ability to
remove heat and cool the underground work force is reduced most
rapidly. At these depths, engineers may consider the advantages and
disadvantages of adding refrigeration and cooling potential to the
ventilation system. Suttil (AUS052) presents that uncooled surface air
begins to form a heat load at about 2000 m due to adiabatic
compression. If air is cooled to 8°C, a heat load does not begin to
build up. Adiabatic compression of surface air results in a
temperature rise of approximately 4°C/1000m so refrigeration is
essential for workings below 2000 m.
Awaited impacts
Thermal conditions in underground mines are the result of thermal
conditions on the surface, sources of heat and humidity underground
FORM 1.3.0 – Page 1 / 2
GREEN MINING METHODS
and ventilation/refrigeration.
The presence of one or more symptoms of heat exhaustion
commencing after starting work (headache, dizziness, fatigue,
nausea, vomiting, transient loss of consciousness) and the reasonable
clinical exclusion of alternative diagnoses (AUS051).Relative risk of
heat exhaustion on days when the 24 h mean wet bulb globe
temperature was in the range 26-28°C.
Surface temperature data could be used at this mine to warm miners
about the risk of heat exhaustion. This is consistent with the
observation that incidence of heat exhaustion increases in summer.
Where depth and rock temperature are such that air temperature are
excessive mechanical refrigeration systems may be used to
supplement effects of ventilation.
Principles of treatment or
remediation
There are two ways in which heat load can be reduced: through use of
refrigeration/vent/cooling to reduce thermal stress on workers or to
reduce the contribution that heat sources have to underground heat
load.
The best solution to avoiding or reducing heat problems is likely to be
a mixture of available technologies.
Illustrated examples
Mt Isa, a metalliferous mine (AUS050), which has been a focus for
heat related study in Australia, has successfully implemented
protocols for working in heat. Through combining these with the
installation of a surface bulk air cooling plant, Mt Isa has decreased
the incidence of heat illness. This is likely to be the most cost effective
method of reducing heat load for deep mines in Australia.
FORM 1.3.0 – Page 2 / 2