Chapter 24

Heat Stress Management: An Australian Context

M.A. Tuck	B. Schwengler
Deputy Head of School, School of Engineering University of Ballarat Victoria, Australia	Student, BEng (Mining Engineering) School of Engineering University of Ballarat Victoria, Australia

ABSTRACT

The Australian mining industry is of primary importance to the economy of Australia. Current production in Australia is a moderate levels of depth, however despite this climatic conditions underground are a cause for concern at a number of mines across the whole continent. The main reasons for this are: a high geothermal gradient, high levels of mechanisation particularly with respect to diesel's, in some cases autocompression and surface climate.

The aim of this paper is to outline techniques employed within Australian mines to manage heat stress. Firstly the legal framework on a state by state basis are outlined. Secondly the methods available to manage heat stress are briefly discussed. Following this various heat stress management methods, also called heat stress protocols, as practiced at a number of sites around Australia are detailed. In conclusion the future likely heat stress management techniques that will be employed as the industry develops deeper orebodies is outlined.

KEYWORDS

Ventilation, heat, heat stress

INTRODUCTION

The Australian mining industry is of primary importance to the economy of Australia. Current production in Australia is a moderate levels of depth, however despite this climatic conditions underground are a cause for concern at a number of mines across the whole continent. Numerous sources of heat can exist in a mining context (Tuck 1997). In Australia the main sources are: a high geothermal gradient, high levels of mechanisation particularly with respect to diesel's, concentration of production operations, in some cases autocompression and surface climate. High temperatures and humidities are a concern to the mining industry for two primary reasons. Firstly they cause a loss in productivity and secondly they are an occupational health and safety hazard and can cause fatalities. It is recognised that a number of sites in Australia, for example Mount Isa Mine, have had a heat problem for a long time, however the problem is becoming of greater concern with the number of mines experiencing climatic difficulties expanding.

The aim of this paper is to outline techniques employed within Australian mines to manage heat stress. Firstly the legal framework on a state by state basis are outlined. Secondly the methods available to manage heat stress are briefly discussed. Following this various heat stress management methods, also called heat stress protocols, as practiced at a number of sites around Australia are detailed. In conclusion the future likely heat stress management techniques that will be employed as the industry develops deeper orebodies is outlined.

WHAT DEFINES A CLIMATE PROBLEM

This question is not a simple one to answer. In essence one is attempting to balance the metabolic heat generated by a human body against the ability of the external environment to accept this heat to be transferred to it. This obviously is dependent on a number of factors both environmental and physiological. Numerous attempts have been made over the years to provide an overall assessment of the cooling power of an environment (McPherson 1993, Tuck and Pickering 1997). The aim is to combine numerous factors into a single number in order to provide an index that enables the risk of heat related illnesses, productivity levels and the risk of fatality to be evaluated. Numerous heat stress indices have been developed over the last century, of these the most commonly applied include:

1. Wet bulb temperature

2. Effective temperature

3. Kata thermometer (wet and dry bulb)

4. Air Cooling power (ACP)

5. Modified Air cooling Power (MACP)

6. Predicted Four Hour Sweat Rate (P₄SR)

7. Heat Stress Index

These indices enable the risk of heat stress to be determined and can form the basis of a regulatory regime. Within Australia however this particular route has not been adopted, within all States the regulations with regard to hot conditions basically state that the ventilation system shall “render harmless any flammable gases or other atmospheric contaminants (in the case of other gaseous atmospheric contaminants, the ventilation to be supplied must be sufficient to render them harmless in accordance with the Exposure Standards for Atmospheric Contaminants in the Occupational Environment published by the National Occupational Health and Safety Commission), and” (NSW Regulations 1999). Thus one can adopt the position that no regulatory standards exist, however in common with regulatory systems elsewhere in the world this does not provide a “get out clause” and most companies choose to adopt a best practice methodology in accordance with the spirit of the regulatory bodies.

HEAT STRESS MANAGEMENT

The term heat problem can be defined in a number of ways but it basically refers to a limiting climatic condition for a specific ventilation flow rate above which the ability of the workforce to perform tasks at the required work rate is impaired in terms of safety. It is usual to define this limiting condition in terms of either a dry/wet bulb combination or more usually in terms of one or more of the heat stress indices. For example an ACP of 250 W/m² or an effective temperature of 28°C. Before attempting to solve a heat problem certain aspects of the problem need to be defined either by measurement in an existing mine or mine section or by the use of simulation techniques for planned areas of mine development. Those features requiring definition are:

1. The location and extent of the problem

2. The magnitude of the problem

3. Identification of the main contributing sources

4. Quantification of the problem.

Most heat problems in underground mines start in the working zones and gradually affect more of the mine the deeper one goes. The exception to this rule being in hot countries where the air entering the mine already is in a problem condition or in very deep mines where the heat from autocompression gives a heat problem from the shaft bottom. There can also be seasonal effects due to the surface. Thus when designing a mine ventilation system it is usual to assume summer conditions when taking heat and humidity into consideration.

“THERE IS NO GENERAL METHOD FOR SOLVING A MINE HEAT PROBLEM, EACH SITUATION REQUIRES INDIVIDUAL ATTENTION”, however good design practises can be adopted. In designing a means for solving a mine heat problem the following should always be borne in mind:

1. The method should fit with the remainder of the mining operation

2. The method should be flexible

3. The method should be economic

4. The method must cope with the need to expand to follow current and future mining activities.

A number of means exist which can be used in isolation or in combination to solve a heat problem:

1. Good ventilation control

2. Ventilation methods

3. Reduction or elimination of heat flow at source

4. Refrigeration

5. Acclimatisation

6. Education

7. Heat money.

“The main parameters influencing the ability of a human to work in hot and humid conditions are”:

1. The air dry bulb temperature

2. The air wet bulb temperature

3. The air velocity

4. The work rate

5. The ability of the body to cope with hot humid conditions.

Thus in order to ameliorate the working climate it is necessary to affect an improvement in one or more of the above; the most important parameters to improve are the wet bulb temperature of the air and the air velocity. A heat stress protocol aims to enhance the last of the above list in addition to or rather than providing an engineering solution to the problem, the justification for this can be summarised as in Table 1 or illustrated as in Figures 1 and 2.

HEAT STRESS PROTOCOLS

A heat stress protocol involves a number of different facets but as a general rule avoids the full scale engineering alternatives which can be applied to improve climatic conditions in mines. Stage one of developing such a profile is to decide which heat stress index or combination of indices is to be applied to determine the risk of heat stress in a mining environment. Stage two is the determination of which level of the index or indices selected constitutes a safe environment, an exposure-limiting environment or a stop work situation. Incorporated into these decisions are other methods of minimisation of heat stress ranging from improved physiological response, education and the application of personal cooling systems. Numerous methods and tools are available to improve a human's response to a hot and humid environment these include:

Table 1: Methods of solving heat problems, cost and usage comparison

Item	Cost Factor	Cooling Power	Used	Response
Refrigeration Plant	Very High	High	Mount Isa Telfer Mine	Very Good Very Good
Spot Coolers	Medium - High	Medium but localised		Sceptical
Air Movers	Low	Medium increases sweating efficiency	Osborne Mine	Good
Ventilation Upgrade	Low to Medium to High	Good if fresh air is being increased. More airflow can cool workings	Telfer Osborne Stawell	Good but did not stop heat problem Moderate Air still hot. Good but did not stop heat problem in long term
Clothing Issue Alterations	Low	Increase body- cooling efficiency by allowing sweat to stay near body.	All Mines	A pant and shirt combination better than overalls.
Ice Jackets	Low	High for wearer	Eloise	Poor
Cool Scarves	Extremely Low	Low	Osborne	Still Under Trial
Cool Hat	Extremely Low	Low	Not Safe

Figure 1. Comparison of cooling alternatives

Figure 2. Heat stress protocol comparisons

Hydration

Hydration is the level of water in a person's body. For the body to efficiently cool itself in hot condition a good consistent hydration level is required. If a person becomes thirsty, that person has already become dehydrated. It is essential to get workers into a routine where a high water intake is maintained and take regular breaks while working in hot environments.

It is important to start the shift with a good hydration level as well. If an employee starts the shift dehydrated they will be in a high risk category for heat stress. If they do not hydrate themselves throughout the day that employee will feel more tired and physically drained at the end of shift compared to a well-hydrated person of similar physical disposition at the end of shift. It is for this reason that many mines around Australia will not allow workers who are very dehydrated to start work until they re-hydrate themselves. This principle is very good and should be employed more often through the mining industry. These mines are removing their workers from a high-risk category into a more acceptable level.

A tool which can be used to measure hydration, is a refractometer. It will display a value for the specific gravity of the urine sample. The instrument will give a reading between 1.000 and 1.050. These values are generally interpreted into four major categories. These categories are depicted in Figure 3.

Ideally people should try to stay inside the well hydrated area but the hydrated section is also acceptable. Depending on the type of work being carried the pink section should be deemed as an unacceptable reading, it is however, acceptable for a worker who has worked hard in hot conditions for the shift to record a reading of 1.022 to 1.025. They would only be moderately dehydrated but are still within a reasonable limit. It must be stated however, that it would be beneficial to those workers if their readings were below 1.022 and more so below 1.015.

It should be noted though that a person who starts and finishes their shift in the yellow well-hydrated section would be more alert, more productive, safer, and feel better at the end of their shift.

WORK WEAR FOR HOT ENVIRONMENTS

A large degree of the body's ability to handle heat is reliant on clothing that a worker is wearing. Ideally a worker in a hot environment would wear next to nothing with an average to high air velocity passing over the body. This is not a feasible code of practice so we must look at what is being worn now and try to improve on current uniforms.

Work Clothes

In the Australian mining industry strict regulations apply to employees wearing the correct safety equipment. It is essential in Australia that a worker be protected from potential dangers. One form of protection is the clothing, which is worn on the job site. Although, for some mines, the full body coverage policy cannot be changed better alternatives to help the body cool itself more efficiently can be developed.

Safety Overalls

Many underground mines around the world use safety overalls which retail for about $A 80. These overalls are equipped with reflective tape and provide excellent protection for the wearer from the inherent dangers associated with underground mining. The problem posed by these overalls is that the material they are made of is hot and fairly heavy with the entire weight of the overalls resting on the wearer's shoulders. They are strong and durable which makes them an attractive option for a mine from an economic point of view. The most effective way for the body to reject heat is by sweating. Overalls are very inefficient when it comes to assisting the body cool itself. Most overalls are loose and when they absorb the sweat falling off of the wearer's body the moisture is held away from the body. This will essentially negate the efficiency of the sweat. Workers will find themselves losing more sweat than is necessary and hence could also see decrease in their hydration levels.

Figure 3. Hydration

Cotton undershirts

Cotton undershirt or singlets are widely worn right throughout Australia. These shirts have a significant affect on the overall cooling efficiency of sweating. The cotton material readily absorbs the sweat and holds it against the body. The shirt will prevent most sweat from dripping off of the wearer. The sweat then evaporates off of the singlet and provides the intended cooling affect of the sweat. These singlets should be tight fitting.

Work Shirt and Pants

An alternative to wearing overalls would be to wear long pants and a cotton work shirt. This would provide greater comfort for the workers' as a pants shirt combination would have greater flexibility for different body shapes. There is only a minimal difference in price between overalls and a pant/shirt combination. The pant/shirt combo would cost approximately A$ 83

Work Shirt

The work shirt should be made of a material, which will breathe. The most obvious choice for this would be cotton. The shirt should be loose fitting to allow airflow the torso of the wearer. This airflow is essential for the evaporation of sweat and therefore the cooling of the wearer. It would be beneficial for the wearer to also wear a cotton singlet. A cotton work shirt fitted with the necessary reflective tape (As per underground requirements) would retail for approximately A$ 37.

Work Pants

Many people would find a pair of pants much more comfortable than overalls. This is largely due to greater flexibility in sizes. By separating the top and bottom halves of a worker's uniform the individual clothing sizes can be made more appropriately. The work pants would have no real influence on making a worker feel cooler but they would make the wearer feel more comfortable. A pair of work pants fitted with the necessary reflective stripping would retail for approximately A$ 46.

COOLING GARMENTS

There are many different types of cooling garments available on the market. They vary in accordance to the extremity of the conditions and the type of work being carried out. The final decision will be made on a product, which is durable, not restricting, comfortable, and cost effective.

The product will have to be able to withstand the rigours of the every day working environment. A reasonable life span needs to be expected. It is no good having an excellent cooling device, which needs to be recharged on a half-hour basis. In the mining industry workers are required to do a variety of tasks which may or may not require a lot of movement or climbing in and out of confined spaces. A product must be chosen which will not restrict the workers in any way when they perform their daily activities. The product must not weigh the worker down throughout the shift. If the employee is weighed down the benefits gained by being cooled will be outweighed by the extra effort needed to carry the device throughout the day.

If the product is not comfortable chances are that the employee will not wear the device in its intended manner or not wear it at all. The product must not become uncomfortable throughout the course of the shift.

There are a number of different types of cooling equipment available on the market. These include:

1. Cool Scarf;

2. Cool Vest;

3. Cool Hat.

The Cool Scarf

The cool scarf is a very simple design which has lead to a higher degree of comfort experienced by employees throughout the open cut mining industry. The cool scarf provides a cooling affect through water crystals, which are stitched into the scarf. When the scarf is placed into cold water the crystals begin to swell and absorb the coolness of the ice water. The cold part of the pack is at the back of the neck with the tie up around the front. The knot cannot be made tight so that the wearer is restricted or made to feel uncomfortable in any way. The coolness of the pack is concentrated to the back of the neck and the bottom of the brain. The cool scarf retails for about A$ 6 and may just be good enough to take the edge of the heat and bring the workers body temperature down to a more acceptable level.

The Cool Vest

The cool vest houses the similar principle to the cool scarf but like the name suggests it comes in the form of a vest which, is worn by the workers. It can also be commonly referred to as an Ice Jacket. In past experiences it has been determined that the vest had a reasonable life span due the fact that it is covered by the workers standard PPE. The vest is however restricting and heavy. The vest will add to the overall mass of the worker and therefore, will also increase the effort requirements of the wearer. This effectively will make the worker feel uncomfortable by the end of the working shift. A basic model for a cool vest or jacket can be made to suit a variety of body types and sizes but will only provide cooling for 2 hours. After this time the vest needs to soak in ice water for 20 minutes to `recharge'. The approximate retail price for a cool jacket with cooling inserts is approximately A$550.

Cool Hat

A large percentage of the bodies convectional heat loss comes from the head. This poses a problem due to fact that miners are required to wear hard hats as part of the Personal Protective Equipment. Many workers find large amounts of sweat dripping of their face or down the back of their neck. The cool hat is based on this principle. By cooling the head, the amount of sweat running down peoples faces or necks can be minimised. This would lead to increased hydration due to decreased sweat loss. The cool hat also has a water crystal inner and is charged by soaking in water. There would not be a long life expectancy for the coolness of the pack and it would require the wearer to remove their hat fairly often. This posses a safety risk as well as an annoyance in an underground environment. The cool hat would also add to the overall weight of the wearer's hat. This could have long-term side affects such as neck problems. The cool hat retails for about A$12.

PROPOSED IMPLEMENTATIONS TO ASSIST HEAT PROTOCOLS

As a result of investigations undertaken at Osborne Mine in Queensland the following have been suggested as means to assist heat protocols:

1. Diet cordial has been introduced but there has been a negative feedback from workers about the flavour. The primary requirement is to lower the sugar and caffeine contents of mine supplied drinks. This will help with the hydration levels of the crews.

2. Convert all coffee into decaffeinated coffee. This will lower the caffeine intake from 67 to 172 mg per cup. This again will assist in lower hydration values for the crews.

3. Provide fresh lemons and limes near the tap, which the workers use to fill their water bottles. A slightly easier and more convenient way of supplying lemons and limes would be to put lemon and lime concentrate above the ice machines with the cordial. This would provide a low sugar, low caffeine alternative to cordial and a cleaner substitute for fresh lemons or limes.

4. The cordial drinks in the dining area are to be replaced by diet cordial.

5. There is still a small percentage of employees which have a BMI (Body Mass Index) higher than 35. It would be worthwhile to employ a dietician on a monthly basis to discuss what foods are good and which are bad for working in hot environments. The dietician could also liase with the chiefs to produce some more low fat, healthier foods. An alternative to this would be to provide information about healthier eating on site.

6. A possible solution to the lack of water while working at the face can be removed by introducing a water bottle attachment to the utility belt. The attachment would work similarly to a bicycle water bottle holder. This would give workers the opportunity to drink in small regular dosages without needed to stop work.

7. A final but most important issue is the continuity of the education program about heat stress. A booklet for distribution, which informs people about heat stress and states the company's position, is useful. This booklet should be easy to read and explain what is good and bad rather than right and wrong.

CONCLUSIONS

Heat problems have been a problem at some Australian mine sites for an extended period, however as a ventilation pollutant heat is becoming a more widespread pollutant within mine ventilation systems. In order to be able to adequately protect miners against the detrimental effects of heat and humidity whilst also maintaining the production requirements of mining companies a number of tools can be applied by a ventilation engineer. These include the more traditional engineering approaches. However as a first stage and as an add on where engineering solutions are required additional steps can be applied. These are termed heat stress protocols and can be used to satisfy a number of goals depending on their depth and complexity. As the Australian industry develops the need to ensure appropriate heat stress protocols are instituted in addition to well designed engineering solutions to heat problems will need to be developed. Given the site specific nature of heat problems this will require a considerable research as well as educational input from both academics, practising engineers and health and safety specialists.

REFERENCES

Tuck M.A and Pickering A.J. `Heat: Sources, evaluation, determination of heat stress and heat stress treatment', Mining Technology, June 1997, 79, pp 147-156

Tuck M.A `Control of Mine Climate', Mining Technology, August 1997, 79, pp 215-220

McPherson M. J. “Subsurface Ventilation and Environmental Engineering”, London: Chapman and Hall, 1993

Anon New South Wales Coal Mines (Underground) Regulations 1999, Part 4, Division 1, 73 (2) part b (ii)

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Heat Stress Management: An Australian Context

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