ENVIRONMENTAL IMPACT ON PHYSIOLOGICAL RESPONSES OF ...

J. Hum. Ergol., 43: 69-77, 2014

ENVIRONMENTAL IMPACT ON PHYSIOLOGICAL RESPONSES OF UNDERGROUND COAL MINERS IN THE EASTERN PART OF INDIA NETAI CHANDRA DEY1*, SUVA NATH1, GOURAB DHARA SHARMA1 AND AVIJIT MALLIK2 Department of Mining Engineering, Indian Institute of Engineering Science and Technology, West Bengal, India *e-mail: [email protected] 2 General Manager, Coal India Limited, India 1

Abstract Coal in India is extracted generally by semi-mechanized and mechanized underground mining methods. The Bord and Pillar (B & P) mining method still continues to be popular where deployment of manual miners is more than that of other mining methods. The study is conducted at haulage based mine of Eastern Coalfields of West Bengal. Underground miners confront with a lot of hazards like extreme hostile environment, awkward working posture, dust, noise as well as low luminosity. It is difficult to delay the onset of fatigue. In order to study the physiological responses of trammers, various parameters like working heart rates, net cardiac cost and relative cardiac cost including recovery heart rate patterns are recorded during their work at site. Workload classification of trammers has been done following various scales of heaviness. The effect of environment on the physiological responses has been observed and suitable recommendations are made. The work tasks are bound to induce musculoskeletal problems and those problems could be better managed through rationalizing the work-rest scheduling. Key words: workload; trammer; fatigue; work-rest scheduling; physiological indices INTRODUCTION

Coal is the greatest national treasure of India. Almost 70% of the power is generated from the coal now-a-days. Coal mining is an ancient occupation in which many citizens are intimately involved. Coal is extracted in India by two main systems of operation; open-cast mining and underground mining. Research especially in the field of work physiology is still in progress in India. Underground miners perform tremendous hard work which is associated with a lot of hazards like extreme hostile environment, awkward working posture and low luminosity. Underground miner’s health constitutes a very important domain towards ergonomics-based research work in India (Dey et al., 2007). Underground miners are facing different types of health problems due to varied designed operations. Occupational stress is seen to be the most in mining disciplines compared with any other professions belonging to the mineral sector globally. Strain is the response of the body cropped out of the stress. Cardiovascular strain plays an important role to the ergonomists. Cardiac workload is very high with respect to job severity. The adverse environmental condition may be another relative cause of the higher cardiac strain (Kampmann and Piekarski, 2005). The sluggish air velocity with a high effective temperature may cause slow recovery of fatigue of workers (Dey and Pal, 2012). Basically fatigue is experienced when the cardiovascular system cannot furnish sufficient oxygen to the muscles involved in coping with the imposed workload (National Institute for Occupational Safety and Health, 1986). Increased barometric pressures in deep mines increase air temperatures, increase convective heat exchange and reduce sweat evaporation rates (Gagge and Gonzalez, 1996). Although mining has become increasingly mechanized, there is still a substantial amount of manual Received 26 July 2013; accepted 16 September 2014

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NETAI CHANDRA DEY et al.

handling. Cumulative trauma disorders continue to constitute the largest category of occupational disease in mining and often result in prolonged disability (National Institute for Occupational Safety and Health, 2000). The total physiological response of the body during work is almost vividly expressed by the cardiovascular status. Working heart rate (WHR) is the main indicator of the said response of the human body during work. Working with high heart rate becomes further risky to the miners and it may cause early mortality (Donoghue et al., 2000; Donoghue, 2004). The heart can not pump too much blood to the working muscles of the body because it has to pump out a sufficient amount of blood to the brain accordingly. Due to high blood circulatory demand to the working muscles the heart cannot send the average amount of blood that is needful to the brain. Sudden heart attack and cerebral stroke can occur due to heavy working conditions. Description of the mine The study is conducted in an underground coal mine of the Eastern Coalfields of West Bengal, India. The mine is having degree II of gassiness (the seam produces more than 1 m3 of gas per ton of coal raised). The inclination of coal seam is 1 in 15. The distance of face of the district is about 1.5 km and the depth of mine is around 200 m. The mine does not have the man riding facility so the workers are to go down the working site by walk only. The working is done in the Bord and Pillar (B&P) system which is the main method of underground working in India (Figure 1). In this method, coal transportation is done by side discharge loaders (SDL) following the dotted lines in the layout where one SDL is supposed to cater two consecutive faces. ⑴

SOLID COAL PILLAR

SOLID COAL PILLAR

SOLID COAL PILLAR

SOLID COAL PILLAR

SOLID COAL PILLAR

SOLID COAL PILLAR

⑵

SDL 1

⑶

⑷ HEADING

Fig. 1. Bord and Pilar (B&P) layout of underground mining. SDL 2

METHODS

Subjects The mine production comes from different unit operations comprising face drilling, blasting, tramming, supporting, updating the ventilation, shoveling and coal loading (either manual or by face loading machines). Tramming is the vital operation which helps hauling up of the coal loaded tubs on the surface. This operation finally decides on the total tonnage of production from the underground district. It is done by a group of team comprising of skilled workers named trammers. They are stationed in different places and supposed to send the empty tubs and draw out the loaded ones from the section. The study has been

IMPACT ON MIINER'S UNDER HOSTILE ENVIRONMENT

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designed in such a way that trammers from important areas have been chosen namely from face and pitbottom (the place where diamond crossings of tracks are available to dispatch loaded tubs on the surface via cage through shaft). Before the study, extensive interviews are carried out with the trammers, during which they are motivated to co-operate as required by the design of the study. Thirty such underground trammers (15 each from face and pit-bottom section) who opted for participating in the study were chosen from this particular mine. The informed consent for conducting the study in particular collieries was taken from the respective authorities. The exclusion criteria of the subjects included any symptoms or clinical signs of cardiovascular, musculoskeletal or neurological disorders that could interfere with the interpretation of the experiment. While selecting the subjects, special care was taken to establish homogenous groups. Their ability to getting used to the B & P method of working is also taken into account to avoid unexplained variations in the test results.

Task description The major share of underground coal production in India comes from such mines where haulage is placed as transport system. In this system of mineral transportation, trammers play a key role. The turnaround of coal tubs (one and half tonne capacity container) during the productive hours depends on the trammer’s skill. Pre-determined number of tubs is sent to the underground site where side discharge loaders (SDL) are deputed to load the tubs. They couple and decouple empty and loaded coal tubs for onward transmission to the surface as per the requirement. The shift work (coupling, de-coupling, pushing of empty and loaded tubs) of the trammer is distributed in spells. They do on an average five such spells where tubs remain in operation and the time percentage of various work is shown in Figure 2. 1%

1%

Decoupling empty tubs (7 no.)

38% 60%

Pushing empty tubs to the face (7 no.) Pushing loaded tubs from the face (7 no.) Coupling loaded tubs (7 no.)

Fig. 2. Time stretch of underground trammers.

Physiological parameters Age (years), height (cm), weights (kg), body surface area (BSA in m2) and body mass index (BMI in Kg m-2) were the principal physical characteristics considered. BSA was measured using the formulae proposed by (DuBois and DuBois, 1916). Resting heart rate (RHR) was measured with the polar heart rate monitor (HRM) by allowing the subjects to take rest in a comfortable area for at least 30 minutes at the surface before they entered into the mine. The minimum of the heart rates obtained during this period was considered as the resting heart rate. Working heart rate (WHR) was measured by using the portable heart rate monitor (Polar-RS400sd, USA) at a regular interval of 30 sec during work. Recovery heart rate was measured in sitting posture at the end of work shift. This was obtained by counting the pulse during the last 30 seconds of each minute in the first, second and third minute of the recovery period, i.e. from 30 sec to 1 minute after work stops, from 1½ −2 minute and again from 2½ −3 minute. These three recovery heart rates were designated as P1 (1st recovery heart rate), P2 (2nd recovery heart rate) and P3 (3rd recovery heart rate). Net cardiac cost (NCC) was obtained from the difference between WHR and resting heart rate and expressed in beats min-1. HR max was calculated using the formula [220 − Age, (yrs)] proposed by American Heart Association (AHA, 1972). Heart rate reserve (HRR) was evaluated by the difference between HRmax and WHR. Relative cardiac cost (RCC) was found by expressing the NCC as the percentage of the HRR of the subjects by using the following formula RCC = NCC/ HRR × 100. The recommended limit of RCC was considered as 30% HRR as proposed by Lablanche-Combier and Lay (1984) and the maximum heart rates of the subjects were estimated by using the formula of AHA (1972). Energy expenditure (EE) was also calculated using equation (0.045 × Peak heart rate) – 1.42 as proposed by Datta and

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Ramanathan (1969) and expressed in Kcal/min.

Physical characteristics of the subjects Physical and physiological characteristics of the subjects exhibit that the mean age of pit-bottom and face trammers (Table 1) was nearly 49 ± 5.29 and 45.33 ± 7.03 years with a body weight ranging from 40 to 72 kg and 69 to 75 kg respectively. The BMI of both group of workers (23.32 ± 3.01) and (24.28 ± 2) showed that the subjects were typical of the average populations from eastern India (Naidu and Rao, 1994) and remains in normal range. The body surface area (BSA) of the subjects was also in an acceptable range according to the classification of the World Health Organization (Table 2). Table 1. Physical characteristics of the pit bottom trammers and surface trammers. Pit bottom trammers Mean ± SD (range)

Surface trammers (n=15) Mean ± SD (range)

49±5.29 (40-57)

45.33±7.03 (33-58)

25±4.23 (19-33)

22.87±6.72 (13-38)

Height(cm) (cm) Height

165.2±5.00 (155-171)

164.93±3.75 (158-170)

Weight Weight(kg) (kg)

63.8±9.38 (40-72)

66.07±5.93 (69-75)

BMI (Kg m-2)

23.32±3.01 (16.65-26.77)

24.28±2.00 (21.05-28.13)

1.70±0.14 (1.33-1.84)

1.73±0.08 (1.58-1.84)

Age(years) (years) Age Experience (years) Experience (years)

2 )2) BSA BSA(m(m

Table 2. The BMI values for adults (both men and women) based on the World Health Organization’s (WHO, 1969) body weight categories.

Category Severely underweight Underweight Normal

BMI range (kg/m2) < 16.5 16.5-18.5 18.5-25

Over weight

25-30

Obese classes

>30

Environmental parameters Dry bulb temperature (DB), wet bulb temperature (WB), natural wet bulb temperature (NWB) and air velocity were recorded; subsequently effective temperature (ET) and wet bulb globe temperature (WBGT) values were worked out as an index to get a picture of the average ambient conditions in which the miners are deputed for working. WBGT measurements were made based on the accepted formula (Yaglogou and Minard, 1957) while effective temperature (ET) was calculated by taking into consideration the temperature values of DB and WB with respect to corresponding air velocities of different working places. All environmental parameters were recorded in coalfaces of the underground district and pit-bottom section for a period of 3 weeks.

Statistical Analysis Statistical analysis in the form of ‘t’ test for independent variables is done to determine whether there are any significant differences between the test variables within the selected working groups. The computed

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t is compared with critical t values to find the level of significance (p < 0.05 and 0.01). RESULTS AND OBSERVATIONS

Cardiovascular responses of the subjects The average resting heart rate (RHR) of the pit-bottom trammers and face trammers were found to be 65.87 ± 8.19 and 77.07 ± 8.08 beats min-1 respectively (Table 3). The mean heart rate reaching the sites (HRS) values of pit-bottom trammers and face trammers depicts a range from 67 to 98 beats min-1 and 82 to 94 beats min-1, respectively. Statistically significant difference was observed between the values of RHR and HRS on the two groups of workers. The average working heart rate (WHR) of pit-bottom trammers (111.05±14.93 beats min-1) statistically differed from that of face trammers (127.58±9.34 beats min-1). HR max and NCC did not show significant difference between the means values of two groups while RCC, HRR and EE values of both groups showed significant difference. The peak heart rate (135.53±10.18 beats min-1) of face trammers (Table 3) during work was also significantly higher than that of the pit bottom trammers (119.27±15.23 beats min-1). Characterization of the Workload Workload classification of trammers with respect to various physiological indices (WHR, EE and NCC) is shown in Table 4. From the observed mean values, it is clearly seen that WHR and NCC of both Table 3. Direct and derived physiological variables in the subjects, mean ± SD, and their statistical analysis. Subjects Pit bottom trammers (n=15 ) Face trammers (n=15) ) Mean ± SD (range Mean ± SD (range)

Variables

p - value (t test unpaired, one tail, homoscedastic)

RHR (beats min-1)

65.87±8.19 (52-86)

77.07±8.08 (68-86)

< 0.01

HRS (beats min-1)

79.21±7.96 (67-98)

88.59±6.00 (82-94)

< 0.01

111.05±14.93 (89-135)

127.58±9.34 (117-137)

< 0.01

171±5.29 (163-180)

174.67±7.03 (182-166)

Not significant

119.27±15.23 (98-141)

135.53±10.18 (113-150)

< 0.01

97.6 ± 9.37 (87-120)

105.13 ± 8.68 (89-118)

< 0.05

43.32±12.43 (26.57-63.03)

52.16±8.91 (43.25-61.07)

< 0.01

3.95±0.69 (4.93-2.99)

4.68±0.46 (4.22-5.14)

< 0.01

-1

WHR (beats min ) -1

HR max (beats min ) -1

Peak HR (beats min ) -1

HRR (beats min ) RCC (%) EE (Kcal/min)

SD: Standard deviation; RHR: Resting heart rate; HRS: Heart rate during reaching the site; HR max: Maximum heart rate; WHR: Working heart rate; Peak HR: Peak heart rate; NCC: Net cardiac cost; RCC: Relative cardiac cost; EE: Energy expenditure

Table 4. Physiological work load classification comparison with observed values. Classification of workload Ligh t

Moderat e

Heav y

Very heavy

Extremely heavy

Pit-bottom trammers (n=15)

Face trammers (n=15)

Working heart rate Astrand and Rodhal(1986) (beats min-1)

8

*3.95

*4.68

Pit bottom trammersmoderate in nature face trammers-heavy in nature

20

20-30

31-40

41-50

51-60

*45.18

*50.52

Both are heavy in nature

Parameter

Net cardiac cost (beats min-1 )

Reference

Chamoux et al.(1985)

Remarks

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groups are heavy in nature while the EE value of pit-bottom trammers falls in the moderate category as exception to the value of face trammers. The physiological gradations of different activities proposed by different researchers are either based on the principal parameters like HR during work (Åstrand and Rodhal, 1986), EE or on some derived parameters like NCC (Chamoux et al., 1985). On the basis of such scales of heaviness, the underground tramming operation is considered as heavy-intensity job (WHR and NCC values) although, due to availability of much better environmental status at pit bottom, the mean EE value of pit-bottom trammers falls in the moderate category (Ramanathan et al., 1967). It is also found that the group with lower cardiovascular (face trammers) has much a greater amount of energy expenditure, peak working heart rate and also the NCC. This occurs mostly due to adverse environmental conditions which may have posed additional cardio-respiratory strain which limits physical capacity as also found in this study (Table 4).

Assessment of fatigue from recovery heart rate pattern The recovery heart rate pattern of both groups of workers was accomplished with the help of Brouha’s fatigue assessment technique. The first recovery heart rate of pit-bottom trammers and face trammers were 113.2±16.07 and 108.87±15.96 beats min-1, respectively. The second and third recovery heart rates of pit bottom trammers were 110.87±15.96 and 108.73±15.36 beats min-1, respectively (Table 5). The P2 and P3 values of face trammers were 123.93±9.65 and 20.67±9.48 beats min-1, respectively. The rate of recovery for both the group of workers is found to be very poor and this is well supported by the result since the Table 5. Recovery heart rate patterns of trammers.

P1

Recovery heart rate (beats min-1 ) P it b ot t om t r a m m er s F a ce t r a m m er s P2 P3 P1 P2

P3

mean±sd

113.20±16.07

110.87±15.96

108.73±15.36

127.60±9.66

123.93±9.65

120.67±9.48

(range)

(90-137)

(89-135)

(88-134)

(108-143)

(106-140)

(104-135)

No recovery

remarks

No recovery

Table 6. Comparison of recovery heart rate patterns. Subjects Variables

Recovery heart rate (beats min -1 )

p - value (Students t test unpaired, one tail, homoscedastic)

Pit bottom trammers (n=15)

Face trammers (n=15)

P1

113.20±16.07 (90-137)

127.60±9.66 (108-143)

< 0.01

P2

110.87±15.96 (89-135)

123.93±9.65 (106-140)

< 0.01

P3

108.73±15.36 (88-134)

120.67±9.48 (104-135)

< 0.01

Brouha’s index (Brouha, 1960) fails to show any significance (Tables 5 and 6). The three consecutive recovery heart rates (P1, P2 and P3) of both groups are significantly different from each other (Table 6). Environmental interpretation The dry bulb temperatures 26.23±0.19 ºC (Table 7) and 30.76±0.18ºC at the pit-bottom and face respectively showed significant differences from each other. The wet bulb temperature at the pit-bottom (24.23±0.19ºC) significantly varied the face (28.99±0.30ºC) (Table 7). Natural wet bulb temperature and globe temperature were in the range (24.67-25ºC) and (25.5-26.33ºC) and (29.5-30ºC) and (30.25-30.5ºC), respectively. These two parameters show significant difference between the two working site as stated earlier. Relative humidity was quite high in both areas and also differs significantly from the values of each site. Air velocity was significantly different at the pit bottom (1.60±0.10ºC) than that of the face (0.08±0.05ºC). Effective temperature (ET) at the pit bottom ranged between 23-25ºC and 29-30ºC at the

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face and the mean of the values of two working sites significantly varied from the each other. The WBGT values also showed significant difference between the mean value of pit-bottom and face (25.2±0.16ºC and 29.93±0.20ºC), respectively. According to classification of environmental zone based on ET (Mookherjee and Sharma, 1953), the pit-bottom trammers belongs to the comfortable zone while the face trammers are in the hot zone (Table 8). It is observed that mean ET value of that pit-bottom (Table 9) is within the permissible heat exposure limits for acclimatized personnel but in case of face trammers, the value is above the accepted limits. Table 7. Environmental heat load in the working sites. p – value (Students t test unpaired, one tail , homoscedastic )

Environmental parameters

Pit botto m (Day 1 to Day 19 )

Face (Day 1 to Day 19)

Dry bulb temperature (°C)

26.23±0.19 (26-26.67)

30.76±0.18 (30.50-31)

< 0.01

Wet bulb temperature(°C)

24.23±0.19 (24-24.67)

28.99±0.30 (28.63-29.5)

< 0.01

Natural wet bulb temperature (°C)

24.9±0.16 (24.67-25)

29.70±0.23 (29.5-30)

< 0.01

Globe temperature (°C)

25.74±0.21 (25.5-26.33)

30.33±0.11 (30.25-30.5)

< 0.01

Wet bulb globe temperature (°C)

25.2±0.16 (24.97-25.43)

29.93±0.20 (29.75-30.2)

< 0.01

23.89±0.66 (23-25)

29.37±0.50 (29-30)

< 0.01

84.79±0.16

87.47±0.94 (86.75-89.25)

< 0.01

0.08±0.05 (0.075-0.085)

< 0.01

Effective temperature (°C) Relative humidity (%)

(84.67-85) 1.60±0.10

Air velocity (m/sec)

(1.50-1.70)

Table 8. Classification of environmental zones at various levels of ET (Mookherjee and Sharma, 1953). Classification

Mean ET value (°C)

ET (°C)

Very hot zone

Pit bottom

Face

23.89*

29.37*

These trammers are in the comfortable zone

These trammers are in the hot zone

>30

Hot zone

28.33-29.94

Warm zone

26.67-28.28

Comfortable zone

21.11-26.61

Remarks

Table 9. Permissible heat exposure limits. Recommended by WHO Type of job

ET ( °C) for the non-acclimatized

ET ( °C) for the acclimatized

Light

30

32

Moderate

28

30

26.5

28.5

Heavy Remarks

Mean ET ( °C) value Pit Bottom

23.89*

Within the limit

Face

29.37*

Above the limit

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DISCUSSIONS

Physical and physiological strain of the trammers HR is the key parameter used not only for determining circulatory strain imposed by the workload of different intensity with negligible interference of the subject’s performance but also provides response to energy requirement including thermal and postural demands (Nielson and Meyer, 1987). As HR response to the equivalent workload is responsive to many inter- and intra-individual influences, the resultant indices are selected to take into account inter-individual variations (Barbant et al., 1989). Furthermore, NCC being related to RHR is used to determine workload strictly associated with the job; whereas RCC, related to the subjects’ resting and maximal HR, expresses the individual circulatory strain better (Costa et al., 1989). The variation of environmental status directly imposes the physiological response of the trammers as shown in the different cardiovascular parameters through the work shift. Mostly, high relative humidity and very sluggish air movement make the job much harder at the face than at the pit-bottom. Environmental influence on the health status of the workers is clearly seen from the variation of NCC, peak HR and WHR values between the two groups of workforce. RCC and HR max values predominately depend on the age and resting heart rate of workers and because of that, these values do not illustrate considerable variation between the two groups. Due to a greater amount of physical exertion, energy expenditure is also significantly greater for face trammers than pit-bottom trammers. The physical strain of the present underground tramming job in terms of HR could be compared with underground coalface miners of poorly mechanized mines in Austria (Montoliu et al., 1995) and metalliferous miners in Australia (Brake and Bates, 2001). The heart rate recovery is also slow because of the higher cardiac strain of the tramming activities.

Rationalization of the task in perspective of environmental status The knowledge of acceptable workload is of vast importance in the perspective of rationalizing a job; the workload of a particular task is often so heavy that it imposes excessive physiological strain resulting in fatigue and gradual decrement of the work capacity. It is obviously seen that, the environmental status in respect to effective temperature (ET) value at the face and pit-bottom are falling in the hot zone and the warm zone correspondingly. The ET value at the face is above the permissible heat exposure limits recommended by the World Health Organization (1969). CONCLUSION

It can be concluded that the environmental conditions at the coalfaces are almost intolerable to the trammers and have clear impact on their daily performance. Although, for the higher cardiovascular demand of the job, the physical exertion of pit-bottom trammers is also high in spite of being better environmental status at the pit-bottom. An ergonomic intervention program could be implemented to diminish the static component of the trammers’ tasks. Additionally, strategies towards the improvement of the existing environment are one of the important contributions to making the tramming operations more comfortable for the workers irrespective of the nature of their job. Furthermore, work tasks are bound to inducing musculoskeletal problems. Those problems could be better managed through rationalizing the work-rest scheduling. REFERENCES

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