Analysis of Spanish non-energetic mining accidents: age, experience and size of the work centers

Cátedra Iberpotash in sustainable mining / Universitat Politècnica de Catalunya / Avda. Bases de Manresa, 61-73 / 08242-Manresa (Barcelona), España+34 93 877 72 38 / sanmi@emrn.upc.edu

Vintró, Carla

Department of Business Management / Universitat Politècnica de Catalunya / Avda. Bases de Manresa, 61-73 / 08242-Manresa (Barcelona), España+33 93 877 72 81 / carla.vintro@upc.edu

Freijo, Modesto

Cátedra Iberpotash in sustainable mining / Universitat Politècnica de Catalunya / Avda. Bases de Manresa, 61-73 / 08242-Manresa (Barcelona), España+33 93 877 72 64 / freijo@ee.upc.edu

Joaquin, Edo

Cátedra Iberpotash in sustainable mining / Universitat Politècnica de Catalunya / Avda. Bases de Manresa, 61-73 / 08242-Manresa (Barcelona), España+33 93 877 72 44 / edo@emrn.upc.edu

Rossell, Josep M.

Department of Applied Mathematics III / Universitat Politècnica de Catalunya / Avda. Bases de Manresa, 61-73 / 08242-Manresa (Barcelona), España+33 93 877 72 48 / josep.maria.rossell@upc.edu

ABSTRACT

ABSTRACT

Aims: The aim of this paper is to analyze the correlation between different occupational accident indicators in the Spanish non-energetic mining, and the parameters age and experience of workers, and size of the work centers (expressed in number of employees), throughout period 1999-2008.

Methods: We analyzed the correlation between the accident indicators considered (risk, severity, and average duration indexes), and the parameters age and experience of workers and size of the mine, by means of non-parametric statistical Spearman’s rank correlation.

Results: The results reveal that when the age of the workers and the size of the mine increases, the incidence rate of accidents decreases; there is a weak negative correlation between these factors. On the other hand, the severity of accidents increases with the age and size of the work centers; the correlation is positive and stronger.

Keywords

Keywords

Non-energetic mining, Risk index, Average duration index, Severity index

In the total number of Spanish economic sectors, mining is one of those with the highest incidence in number of accidents per 100,000 workers. Thus, in 2006, Spanish mining had an incidence index that was 4.3 times higher than the total economic sectors.

The Spanish mining sector can be classified into two types, energetic and non- energetic mining. Energetic mining includes the activities related with the extraction and agglomeration of coal, the extraction of uranium and thorium, and the extraction and preparation of any solid fuel. Petrol and gas extraction are not included. Non- energetic mining includes the extraction and preparation of metallic and non-metallic minerals and quarry products such as limestone, marble, granite, sand and gravel or clay. According to mining statistics form year 2006 published by the Ministry of Industry, Tourism and Commerce, the number of people employed was 9,430 in energetic mining and 28,278 in non-energetic mining.

The high work related rate in the Spanish mining sector implies that research should be carried out in this field in order to show which aspects of the prevention systems have to be improved. That is the basic aim of this study. It pretends to analyze the relationship between work related accidents in non-energetic mining and the variables age of workers, labor experience, and size of the mine (expressed in number of employees).

The vast majority of accidents are due to human error [1], and a great number of them are suffered by a relatively small percentage of workers [2]. Some researchers have determined that the first event that immediately preceded the accident was mostly produced by environment events, while the second event, which is the event that took place just before the first event, was mainly attributed to behavior factors [3]. Different studies show that personal and environmental factors make some workers more accident prone than others [4,5,6,7,8,9]. The effect of age and mining experience on the occurrence of accidents has been analyzed by several authors and different conclusions have been obtained. Some studies have observed that younger injured workers suffer more serious injures than the older ones [10], while other studies have not found any relationship between the age and the seriousness of the injury. On the other hand, some researchers have observed a positive relationship between experience and injury severity and have concluded that less-experienced miners had a slightly higher possibility of having accidents than those with more experience [3]. Other authors have concluded just the contrary, thus older injured miners had a higher probability of having serious or fatal injuries than the younger ones [4].

An investigation on the US mining sector [11] concluded that the incidence rate of nonfatal accidents diminishes when the age of injured workers increases, whereas the incidence rate of fatal accidents increases with the age. The same conclusions have been reached when analyzing the Spanish economic sectors [12]. Other studies have obtained opposite results on the influence of the age and experience of injured workers on the occurrence and severity of accidents. In a study on transport injuries in small coal mines [13], the authors reported an increased risk of injury among less experienced workers, but did not observe any age effect. They also observed that small coal mines had the highest rates of transport-related injuries, as well as a greater share of fatal and permanently disabling injuries than larger mines.

Study population:

The study population was constituted by the accidents that took place in the Spanish non-energetic mining between 1999 and 2008. The accidents considered are those that took place in mining work centers, within regular work hours (the so-called “in itinere” accidents are not taken into account), and that caused the injured worker to miss at least one workday. Data have been obtained from the annual digital database on accidents of the Ministry of Work and Immigration, using the software ArcGis 9.2.

We should highlight that the annual accident database does not supply separated information about underground and surface mines for the period 1999-2002, hence it is not possible to analyze separately both types of non-energetic mining. However, this information is available since 2003, and two kinds of mining activities can be distinguished. In this paper, we analyze the overall accidents and the influence of age, experience and size of the mine, considering three different periods: 1999- 2008, 2003-2008 and 1999-2006.

Methodology:

We considered the age and experience of the workers, and the size of the work centre (expressed in number of employees) where the accident took place. For the variable age, six groups were established: 16-24, 25-29, 30-39, 40-49, 50-59 and 60 years. For the variable labor experience, five groups were defined: 13-60, 61-120, 121-180, 181-240 and 241 months. And for the variable size of the work centre, five groups were considered: 1-9, 10-19, 20-49, 50-99 and 100 workers.

In order to analyze the incidence of age, experience and size on the number of work-related accidents in non-energetic mining, a risk index was calculated. This index is indicative of the incidence of accidents among different groups or subpopulations [14], and it is defined as the ratio of percentage of injuries attributed to a given subpopulation (age group or size of work centre) to the percentage of the total workforce represented by this subpopulation.

Risk index = %Accidents

%Workers

A risk index=1.0 corresponds to an average incidence rate of work-related accidents, whereas a value greater than 1.0 indicates a higher risk for the group, and a value smaller than 1.0 means a lower incidence.

The percentage of accidents and lost workdays for the six age categories and the five size groups were obtained from the annual accidents digital database of the Ministry of Work and Immigration, using the software ArcGis 9.2. The percentage of workers per age category was obtained from the annual statistics on active population published by the Spanish National Institute of Statistics (INE) and from the labor statistics reports of the Ministry of Work and Immigration for the period 1999-2008. Finally, the percentage of workers per type of work centre (defined by its size) and the aggregated worked hours for each group were obtained from the annual mining statistics of the Ministry of Industry, Tourism and Commerce.

We also calculated the average duration index (as an indicator of the severity of the accidents) for each type of age group and size of the work centre, and the severity index for each group of work centre size.

Once the risk and the average duration indexes were calculated, we analyzed the degree of relationship between these rates and both the age of the workers and the size of the work centers. This was carried out by means of non-parametric statistical Spearman’s rank correlation with a signification level α=0.05.

When referring to experience of the workers, the risk index was not applied because it was not possible to obtain data of work related-accidents per categories of experience. Thus, only the average duration index was calculated. Nevertheless, in order to deepen the study, the analysis was conducted considering the seven most common types of occupational accidents in both underground and surface mines.

RESULTS

Age and experience of the injured workers:

The percentage of workers and accidents, and the risk index values, taking into account the year (throughout the period analyzed) and the age category, are represented in Table 1. The results show a weak relationship between the age of injured workers and the incidence rate. Only in 3 of 10 years of period 1996-2006, and in period 1999-2008, the Spearman’s rank correlation coefficients are higher than the critical value (0.829) with a signification level α=0.05. The correlation is negative and it indicates that when the age of the workers increases, the incidence of the accidents decreases. Therefore, younger workers have a higher incidence rate than the older ones. For the whole period analyzed, a risk index of 1.37 was obtained for 16-24 year- old workers, and 0.58 for workers just or over 60 years old.

To analyze the possible relationship between the severity of the accidents throughout period 1999-2008 and the age of the injured workers, the average duration index was calculated for each age group (Table 2). The Spearman’s rank correlation coefficients obtained are higher than the critical value (0.829) with a signification level α=0.05, except in years 1999 and 2002. This result seems to indicate the existence of a positive correlation between the age of the workers and the severity of the accidents. It coincides with the results given by other authors [5].

Table 3 shows the distribution of the average duration index for the seven most frequent types of occupational accidents occurred in underground and surface energetic mining, according to the experience of the injured workers:

#31: Blows or hitting something as the result of a fall.

#32: Blows as the result of a fall, or crashing into an immovable object.

#41: Being hit by an object or projected fragments.

#42: Being hit by a falling object or one that is detached.

#44: Crash or blow against an object in movement, including vehicles#50: Contact with a cutting, piercing, hard or rough material agent.#63: To be trapped or flattened.#71: Physical over-exertion on the muscular-skeletal system.

We calculated the Spearman’s rank correlation coefficient for each type of accident in order to evaluate the relationship between the experience and the average duration index. The results obtained show a statistically significant relationship (Spearman’s correlation coefficient higher than the critical value 0.714 with a signification level α=0.05) between both parameters in accidents coded as #71, #31 and #32 and in the total number of non-fatal accidents (joined as one type of accident) in surface mining, as well as in accident #63 in underground mining. The correlation is positive and it indicates that when the experience of the worker increases, the severity of the injuries increases too.

Size of the mines (expressed in number of workers):

Table 4 shows the percentage of workers per year and group of work centre size, throughout period 1999-2006. Mines over 500 workers are nearly inexistent in the Spanish non-energetic sector, thus this category is not included in the analysis.

The results indicate that mine centers between 20-49 and 50-99 workers, and especially the ones just or over 100 workers, sustain a very high incidence rate due to a risk index value that significantly exceeds 1. The risk index values obtained for period 1999-2006 are 2.03 (mines of >=100 workers), 1.59 (mines between 50-99 workers) and 1.52 (mines between 20-49 workers). At the same time, a significantly lower risk for 10-19 and especially 1-9 workers category is observed, with an index of0.80 and 0.41 respectively.

Spearman’s coefficients calculated for distributions of risk index according to the size of the work centers, show a weak correlation (with a signification level α=0.05) between incidence rates and size of the mines or quarries. The critical value (0.900) is only exceeded in year 2005 and when considering the mean value of the 8-year period analyzed. For other years, Spearman’s rank correlation coefficients are equal to 0.900, except in 1999 and 2000. All coefficients are positive. This indicates that there is a certain degree of correlation between the incidence rate of occupational accidents and the size of the mines or quarries. Specifically, as the size of the mine or quarry increases (in number of employees), the incidence rate increases too.

To analyze the possible relationship between severity of non-fatal accidents and the size of the work centers, we calculated the annual average duration index in each group during the period 1999-2008 (Table 5). Spearman’s coefficients calculated for distributions of average duration index according to the size of the work centers are lower than the critical value (1.000) with a signification level α=0.05, except in 2001. Both coefficients have different signs. The results indicate no relationship between the size of the work centers where the accidents took place and the severity rates according to the average duration of disability per accident.

In order to analyze the seriousness of the accidents, we calculated the severity index for each group. The results in Table 6 seem to indicate a strong relationship between the severity rate (according to the total hours worked) and the size of the mine or quarry (in number of employees). Spearman’s coefficients calculated are lower than the critical value (0.900), with a signification level α=0.05, only for years 1999 and 2000. As the size of the work center increases, the severity rate increases too. The average severity rate for period 1999-2006 was 1.36 in mines with less than 10 workers, and 4.62 in mines just or over 100 workers. The average duration index values recorded were the same for the 5 groups of size of work centers while the severity rate values registered were very different.

The analysis performed to test the possible relationship between incidence and severity rates, and size of the work centers, yielded contradictory results to the findings of an investigation on the Spanish energetic mining [14] and to the findings of other studies, which concluded that higher incidence and severity indexes were recorded in small than in bigger mines. A possible explanation for the discrepancies in the findings can be found in the Spanish mining statistics year 2006: 66% of energetic mining workers performed their professional activity in a coal underground mine, while 96% of non-energetic mining workers did it in a surface mine. The aforementioned study [14] covered coal mining centers, therefore, it seems logical the coincidence with the results of the Spanish energetic mining (mainly formed by coal mines) and the contradiction with the study of the Spanish non-energetic mining performed in this paper (mainly formed by surface exploitations of industrial stones). The resultsobtained in the analysis of the Spanish non-energetic mining also differ from the conclusions of different studies covering all economic sectors, that indicate a lower occupational severity in bigger work centers [15,16].

DISCUSSION

The occupational incidence rates registered in the Spanish non-energetic mining slow down as long as the age of injured workers increases. The correlation is weak. Just the contrary, the severity of occupational injuries increases with the age of workers. The correlation is statistically significant. Using these results, the competent administrations and prevention services of the Spanish non-energetic mining sector should program specific safety training and information for the youngest workers (especially those who are younger than 29).

The causes of the most serious accidents suffered by the oldest workers should also be analyzed (especially those older than 59). A possible explanation could be that the older workers take longer to recover from the same injuries than the younger ones.

In the open non-energetic mining, the results indicate that when the experience of the workers increases, the severity of the injuries increases too. The increase experimented is especially statistical significant for accident code #71 (physical over exertion on the muscular-skeletal system), #31 (blows or hitting something as the result of a fall) and #32 (blows as the result of a fall, or crashing into an immovable object) and for the total number of non-fatal accidents (joined as one type of accident). However, a significant correlation between severity of accidents and experience of workers has not been possible to establish in the underground non- energetic mining.

Both the risk index (as an indicator of the incidence of accidents in a population) and the average duration index (as an indicator of the severity of the accidents) in the Spanish non-energetic mining, increase with the size of work centers (expressed in number of workers). This fact is surprising as occupational health and safety management is generally better in big than smaller companies. A possible explanation lies in the fact that bigger mines also have bigger treatment plants, workshops and storages; whereas many small mines of industrial stone do not have these work areas or if they have them, they are considerably of smaller dimensions. These work areas accounted for 47.6% of the total number of accidents (18,207) registered in the Spanish non-energetic mining throughout period 2003-2006, according to data from the Spanish Ministry of Work and Immigration. Therefore, the higher incidence and severity rate recorded in big mines would be influenced by the existence of an important number of dangerous workplaces. Whatever the reason, future investigations could focus on analyzing the exact phenomena that have an influence on the occupational security of the Spanish non-energetic mining.

ACKNOWLEDGEMENTS

We would like to thank the Directorate of Statistics of the Spanish Ministry of Work and Immigration, for giving us access to the annual databases on accidents in the mining sector from 1999-2008.

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Table 1: Percentage of workers and accidents, and risk index values in the Spanish non-energetic mining, per age groups (period 1999-2008)

Table 2: Lost workdays, non-fatal accidents and average duration index values in the Spanish non- energetic mining, per age groups (period 1999-2008)

Table 3: Average duration index of the seven most common types of accidents in the Spanish surface and underground non-energetic mining, depending on the worker’s experience (period 2003-2008).

Table 4: Percentage of workers and accidents, and risk index values in the Spanish non-energetic mining, per size of the w (period 1999-2008).

Table 5: Lost workdays, non-fatal accidents and average duration index values in the Spanish non-energetic mining, per size of the work centers (period 1999-2008).

Table 6: Lost workdays, worked hours and severity index values in the Spanish non-energetic mining, per size of the work centers (period 1999-2006)