Ergonomic design of a cooling vest in deep and ultra-deep mining environments

1.1Background

In deep and ultra-deep mining, heat and humidity may reach levels in excess of 35∘C and 100% relative humidity [6]. These extreme thermal constraints will continue to rise as extraction continues at greater depths [4], which presents a real challenge as well as a threat to the health and safety of miners [7].

While air conditioning can and has been used to control temperature and humidity, it becomes a costly solution at great depths not only in terms of energy consumption, but also as to investment and maintenance costs [7, 8]. In the literature reviewed, annual costs for ventilation and cooling systems start from 20% of the annual energy usage [9], 23% of the operating costs [10], and 25% of the mine’s electricity costs [11]. It is thus a significant expense for any mine operation. Ventilation on demand has been looked at as a possible solution, since not every sector of a mine has either machinery or workers in it at all times [12]. However, this can only postpone the need for mechanical refrigeration.

In the near future, full automation of mining vehicles in Canada might not yet be deployed extensively and humans should and will continue to be at the forefront of operations [1]. Moreover, some mining equipment such as shuttle-cars are not always equipped with air conditioned cabins.

It is thought that a personal cooling vest might be a solution that could protect the workers as well as reduce the costs of the cooling of the mine. Several types of cooling vests exist on the market [13, 14, 15, 16], such as, air cooling garments, liquid cooling garments, cooling garments based on gas expansion, phase changing garments and thermoelectric cooling. In their work, Al Sayed et al. [17] list the many issues that may arise when using an ordinary cooling vest in deep underground mines, such as reduced cooling efficiency, risk of condensation on the interior of the vest, bulkiness of the apparel and low autonomy [17]. They conclude that no cooling technology is perfectly compatible with deep mining environments. A matrix of ergonomic criteria is thus a welcomed aid that could help in the design of such an equipment.

1.2Research problem

Developing a PPE to help cool down the body of miners in extreme environmental conditions might be a less costly solution than the ones currently in use. While ventilation will always remain an essential part of a mine, a vest would bring the cooling directly to the miners who most need it.

Two key problems must be addressed: the working environment and conditions that it will be used in, as well as the workers wants and needs towards a new protective garment. The answers to these two problems will help create a matrix of ergonomic criteria, which will be used to develop an appropriate cooling vest.

3.1Miners’ receptivity towards a new PPE

In the semi-directed interviews, participants were asked three questions: whether they thought a cooling vest would be a good PPE to be implemented, the reason why they thought so and if they would be willing to try out a future prototype.

All participants agreed that the environment was hot and humid and that a cooling vest would be beneficial to their work. Two miners spoke openly of their awareness of the consequences of heat exposure. They thought a cooling vest would help alleviate the risk of a heat stroke, as well as improve the worker’s well-being during work. All 20 miners were in favor of trying out a prototype if it was made available to them. Three miners expressed some concerns regarding the weight and fit of the equipment.

3.2Population

As mentioned, most Canadian mining workers are male. In the first half of the 20th century, Polish immigrants came to settle in the region of northern Quebec [21]. They integrated the local communities to form the population that exists to this day. The data concerning the participants’ weight, height and shirt size was collected during the field study. Due to time constraints, it was not possible to precisely measure each participant. Since the exactness of the data was unnecessary at this stage, their verbal descriptions were sufficient.

Table 1 summarizes the results, while Figs 1 and 2 compare weight and height with the Human Scale (1, 50 and 99 percentiles which are yellow, orange and red respectively) for each participant.

Figure 1.

Weight distribution of the participants. Weight of all the participants compared to “The measure of man and woman” [20] where the green line represent the 1st percentile of the population, the yellow line the 50th percentile and the red line the 99th percentile.

3.3Occupation

The word miner refers to all classes and laborers who work in a mine. However, the tasks are different depending on the miners, for example the work of a manual drill operator will involve the whole body, compared to shuttle-car operators who are sitting while driving which requires less use of the upper or lower body. During the field study, a variety of miners were interviewed to ensure a larger scope of answers. Their class distribution is detailed below.

3.4Shift and break times

The participants mostly worked on a 10-hour set shift; two of these worked 11 and 12 hours, respectively. Fourteen workers mentioned never taking a break except for lunch, or not at all. Observations showed that the workers do take “micro-breaks” when having a drink for example, or resting against a wall. They also stop working at times when they speak with their colleagues or supervisor. Having many short breaks is more beneficial, because of the steepness of recovery at the beginning of a work break [22]. Although the work objective is determined at the beginning of the day, 18 of the workers mentioned they self-pace while ensuring they complete the work in the allotted time. Seven mentioned taking a break because of the heat or based on their perception of their physical capacity.

Figure 2.

Height distribution of the participants. Height of all the participants compared to “The measure of man and woman” [20] where the green line represent the 1st percentile of the population, the yellow line the 50th percentile and the red line the 99th percentile.

3.5General work environment

Temperature and humidity levels were recorded on four levels of the mine using a portable wind, humidity and temperature meter (Kestrel 3000 Wind Meter, uncertainty 1.4∘C and 3% RH). The findings are shown in Table 2, where we can observe that high amounts of heat and humidity can be found at all levels, regardless of the depth.

All shelters in the mine were equipped with an air conditioning unit, which would ordinarily help the miners during their cooldown period (such as a lunch break). However, to meet and possibly exceed their quota on time, some miners do not return to the cooling shelter at all during their work hours.

3.6Personal protective equipment

Any additional PPE will have an impact on the existing PPE worn by miners or may even interfere or be incompatible with it. Thus, the type of PPE currently worn by miners needed to be determined. Table 3 establishes the mandatory and optional equipment used in the mine. The data was obtained both by questioning miners during semi-directed interviews and by obtaining the list of equipment from the health and safety team of the mine. When designing a cooling vest, this equipment will need to be considered.

3.7Impact on the worker’s body

The miners were asked if their garment snagged on wires or other mine hazards in the mine or if they used any vibrating tool or if they had been struck during their work. They were asked to use an outline of a human to annotate where various events happened on their body, and this diagram helped us generate a heat map. The heat map was used to visualise, using colors, the areas where the workers considered themselves more at risk of getting hit or snagged on wires or other mine hazards (Fig. 3). Heat maps can also be used to show a thermal environment similar to what an infrared camera would show [23].

Figure 3.

Areas at risk of getting hit or snagged. Areas of the body, perceived by the interviewed miners, as being at risk of getting hit or snagged by elements of the miner’s environment.

Figure 3 illustrates the areas which are considered more or less at risk of impact, vibration or snagging on wires or other mine hazards. The numbers on the figure indicate the frequency at which it was mentioned by a participant and the colour value is as follows: 1–3 Yellow, 4–6 Orange, 7–10 Red. The choice of colors was intended to make it easy to distinguish them on a scale of importance and facilitate visual interpretation when printing in grayscale, by respecting that a darker color means a higher value [24, 25]. The area that was mentioned the most was the arms, because the sleeves tend to get caught on the protective wiring on the mining shaft walls. The head was mentioned, because of the type of light used in the participating mine, which requires a wire that connects to a battery at the waist. Some mining hats are now equipped with an integrated battery in the hardhat which eliminates that risk. The feet were mentioned because of the absorption of vibrations during the use of manual drills when the worker supports the equipment with his body. The objective of this map is to prevent damage to the future PPE during the time it is worn and minimizing any potential risks to the user.

3.8Concerns about a new PPE

An open question was asked to the participants as to their concerns regarding a cooling vest. The data was compiled and is shown in Fig. 4. We can observe that comfort and ease of movement are primary concerns, while efficiency and fitting did not cross their minds or seem to matter as much. With directed questions, it is possible that the results would have differed.

Figure 4.

Concerns raised by the participants. Concerns the miners had about potential new personal protective equipment.

3.9Additional criteria established by Normal PPE development literature

3.10Final matrix setup

The final matrix setup is show in Table 4. The criteria are separated into two categories: one is centered on the user, while the other is centered on the general design of the equipment. The definition of each criteria is based on existing literature. The columns weight of criteria and selected method of evaluation should be completed in further studies using expert elicitation.

4.1Limited number of participants and time constraints

In a mine, the environment and situation is constantly changing. Miners are always on the move. Each day, even multiple times in a single day, changes in work schedule and assignment can occur. For these reasons, we could not effectively plan where and when we would meet the miners and if they would have time to answer our questions. This is the main reason why this study was limited to 20 participants, a convenience sample, even though a larger sampling would have been preferable.

The time constraints on our side and that of the miners and the mining company, meant the numbers related to weight, height and t-shirt size were obtained from the miner and were not directly measured. While it might have added a level of error, we considered that it would be negligible in terms of the answer to the question: what size should a vest be for a miner? Obviously, in the case of a fitted vest, more measures should be considered such as the ones for the coverall, harness and other items fitted on the body depending on whether the vest is inside or outside the coverall.

4.2Population

During our search on miner’s anthropometry, we were unable to find any specific database pertinent to our mining population in Quebec, and even in Canada. In his thesis, Boudreau-Trudel [32], states that our mining population in Abitibi-Témiscamingue comprises both French Canadians, English Canadians and two waves of Polish, Ukrainian and Italian immigrants. This is also confirmed by Lambert-Racine and St-Pierre [21].

Due to the previously mentioned absence of a specific database on Canadian miners, the data that was used for comparisons came from The Measure of Man and Woman [20], also known as the Human Scale. It is based on civilian anthropometric data from the 90s (Pheasant 1996, Roebuck 1995) and The Military Handbook: Anthropometry of U.S. Military Personnel (DoD, 1991), which means the data is already two decades old.

According to Figs 1 and 2, miners are within the normal range defined by 98% of the U.S. population from 2002. This is shown clearly by the boundary lines for the 1, 50 and 99 percentiles which are yellow, orange and red respectively.

4.3Variability of working environment conditions

We needed to meet the miners in four different levels of the mine, since their working environment (heat, humidity, type of work) and availability differed depending on the mine level and also, we wanted to have the largest possible representation of the population. This also influenced the rate at which they were seen to take “micro-breaks” and we can make the general hypothesis that self-pacing is also affected in the same way.

We believe the heat and humidity measures that were taken during the four days of field study represent what a miner endures in general. However, we can hypothesize that the temperature might rise even more during the summer season. Also, even though we could have consulted the records on the mines’ temperatures as recorded by static thermometers throughout the year, these readings are not always relevant since they might not be from an area of the mine where the workers will be exposed to those conditions.

The main reason miners were found to be receptive to the idea of a cooling vest was because their working environment was already hot and humid as seen in Table 2. Miners in a working environment where cooling systems are in use might not be as receptive to the idea since their work conditions differ.

4.4Price of equipment

In Québec, Canada, legislation states that the employer must supply the necessary protective equipment to their workers at no cost. Thus, workers who already are experiencing heat in their current working conditions, but are still able to deliver and meet their objectives, might not be willing to invest in PPE if the employer does not provide it.

4.5Impacts on the worker’s body

Any new cooling vest should be resistant to impacts and vibrations in the critical areas of the heat map shown in Fig. 3. Critical components should not cover the sections in red, and should be evaluated for the sections in orange and yellow, unless proper precautions are taken.