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Annals of Occupational Hygiene Advance Access originally published online on January 17, 2007
Annals of Occupational Hygiene 2007 51(3):305-310; doi:10.1093/annhyg/mel082
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© The Author 2007. Published by Oxford University Press on behalf of the British Occupational Hygiene Society

Rock Drills used in South African Mines: a Comparative Study of Noise and Vibration Levels

J. I. PHILLIPS1,*, P. S. HEYNS2 and G. NELSON3

1 National Institute for Occupational Health, National Health Laboratory Service PO Box 4788, Johannesburg, South Africa, 2000;
2 Dynamic Systems Group, Department of Mechanical and Aeronautical Engineering University of Pretoria, Pretoria, South Africa, 0002;
3 School of Public Health, University of the Witwatersrand 7 York Rd, Parktown, South Africa, 2000

*Author to whom correspondence and reprints should be addressed. Tel.: +27-11-712-6473; fax: +27-11-712-6450; e-mail: jim.phillips{at}nioh.nhls.ac.za


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Objectives: To compare the noise and vibration levels associated with three hand-held rock drills (pneumatic, hydraulic and electric) currently used in South African mines, and a prototype acoustically shielded self-propelled rock drill.

Methods: Equivalent A-weighted sound pressure levels were recorded on a geometrical grid, using Rion NL-11 and NL-14 sound level meters. Vibration measurements were conducted on the pneumatic, hydraulic and electric drills in accordance with the ISO5349-1 (2001) international standard on human exposure to hand-transmitted vibration, using a Brudigrel and Kjær UA0894 hand adaptor. PCB Piezo accelerometers were used to measure vibration in three orthogonal directions. No vibration measurements were conducted on the self-propelled drill.

Results: All four drills emitted noise exceeding 85 dB(A). The pneumatic drill reached levels of up to 114 dB(A), while the shielded self-propelled drill almost complied with the 85 dB(A) 8 h exposure limit. Vibration levels of up to 31 m s–2 were recorded. These levels greatly exceed recommended and legislated levels.

Conclusions: Significant engineering advances will need to be made in the manufacture of rock drills to impact on noise induced hearing loss and hand arm vibration syndrome. Isolating the operator from the drill, as for the self-propelled drill, addresses the problems of both vibration and noise exposure, and is a possible direction for future development.

Keywords: mining • noise • vibration • rock drills • South Africa


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
Noise induced hearing loss (NIHL) is not confined to the South African mining industry (Nelson et al., 2005). It remains a problem in other countries and is a neglected area for published research in the English language (McBride, 2004).

Almost two decades ago, NIHL in South African gold miners was reported in the medical literature (Hessel and Sluis-Cremer, 1987). Soon after, the South African Chamber of Mines published guidelines for the implementation and control of a hearing conservation programme (HCP) in the mining industry (COMRO, 1988). In 1996 the components of a HCP were included in the Mine Health and Safety Act (Department of Minerals and Energy, 1996).

Workers exposed to noise levels above 82 dB(A) are at risk for NIHL, and those exposed to levels above 90 dB(A) are at high risk (Franz and Phillips, 2001). In 1989 an amendment to the Minerals Act (1989) imposed a limit of 85 dB(A) for exposure to noise in mining operations over a nominal eight hour working day. With the use of personal protective equipment (PPE) and other measures recommended in the Mine Health and Safety Act (Department of Minerals and Energy, 1996), it may be possible to reduce noise exposure to permissible levels. However, it is well established that, despite training in the use of PPE and provision of equipment, many workers do not make proper use of PPE and continue to be exposed to high levels of noise (Phillips and Nelson, 2006). There is, however, no legislation in South Africa for the maximum emission of noise from machinery, and NIHL continues to plague the South African mining industry. In 2005, the Rand Mutual Assurance Company (the insurance company that underwrites the compensation and medical costs for mining industry employees injured because of their work) compensated 5 617 NIHL cases (Dr A. Begley, Rand Mutual Assurance Company); the total cost was 135.8 million South African Rands, at an average of 24 177 Rands per NIHL case.

There is no South African legislation pertaining to acceptable vibration levels or vibration exposure limits on mining equipment. The European Community Directive 2002/44/EC specifies a daily exposure limit of 5 m s–2 standardised to an 8 h reference period, and an action value of 2.5 m s–2. A South African study published in 1998 recorded vibration levels on rock drill handles of 24 m s–2 (van Niekerk et al., 1998). In 2002, hand arm vibration syndrome (HAVS) was described for the first time in South African miners (Nyantumbu et al., 2002, 2006). The prevalence of HAVS in 156 vibration-exposed gold miners was 15%; all cases occurred in miners who had operated rock drills. In addition, 8% of vibration-exposed miners had carpal tunnel syndrome (CTS) of which 5% occurred simultaneously with HAVS. CTS is also associated with exposure to vibration (Wieslander et al., 1989).

It is always better to effect engineering solutions to reduce a hazard at source, rather than relying on PPE to protect workers. Recently, the South African Mine Health and Safety Council (MHSC), a tripartite organisation, comprising representatives of state, labour and employer, signed an agreement with the mining industry to achieve milestones in the field of NIHL. These milestones include the goal of ensuring that, after December 2008, there will be no deterioration in hearing >10% amongst occupationally exposed individuals. After December 2013, in addition to the 85 dB(A) human exposure limit, the total sound pressure level associated with all equipment, or any individual piece of equipment, must not exceed 110 dB(A) (Mine Health and Safety Council, 2005). No similar action has been instituted for vibration.

The MHSC, together with rock drill manufacturers, has been working to produce a quieter, self-propelled rock drill that does not require the operator to guide it (Otterman et al., 2001). This drill comprises a standard pneumatic drill on guide rails enclosed within a sealed tube, and incorporating an automated thrusting mechanism. The acoustic shielding significantly reduces noise levels. At the same time, since the operator does not come into contact with the drill in operation, there is no transmission of vibration to the hands.

To investigate what is currently available to the mining industry, the MHSC commissioned a study into noise and vibration levels associated with rock drills. This study compared the noise and vibration levels recorded during the operation of three types of rock drills currently used in the mining industry, and the prototype self-propelled drill. This was the first time, as far as we are aware, that manufacturers allowed their products to be tested in a direct comparative way. This paper presents and evaluates the results from this study.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
The testing was carried out during the course of one day in an above-ground artificial stope (Fig. 1) that was developed to simplify and standardise various aspects of testing. The stope comprises a cast concrete floor and adjustable height concrete slab roof, to simulate various stope heights. The floor and roof are both profiled to correspond to typical rock conditions in South African stopes. The artificial stope was developed to reduce the logistical burden for some categories of routine ‘underground’ testing.


Figure 1
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  		Fig. 1 Self-propelled drill in the above-ground artificial stope.

 
Four rock drills in six configurations were tested, viz. the prototype self-propelled drill developed by the MHSC with standard and cladded drill steels, an electric drill, a hydraulic drill, and a pneumatic drill with standard and muffled configurations. The pneumatic, hydraulic and electric drills tested are in current use. The pneumatic drill that was tested has been the ‘industry standard’ since the late 1970s. The other two types are used to a lesser extent. The electric drill was adopted by the industry in the last few years.

The drills were all operated by representatives of the suppliers. The air pressure for the pneumatic drills was controlled at ~550 kPa, the water pressure for the hydraulic drill was between 12 and 18 MPa and the electrical supply for the electric drill was 220 V.

The rock penetration rate for each drill configuration was determined by recording the times required to penetrate 0.5 m into a block of norite rock.

A-weighted equivalent sound pressure levels (LAeq) were recorded for all six configurations on a geometrical grid, over a minimum period of 20 s, using two sound level meters, viz. a Rion NL-11 and Rion NL-14. These sound pressure levels were recorded at 28 pre-determined positions on a circular grid around the drill. During each of these measurements it was endeavoured to keep the drilling conditions as steady as possible in order to get consistent and comparable measurements at the maximum rate of penetration. To characterise the sound pressure field, the LAeq sound pressure level was used as representative metric. No attempt was made to factor in the effects of turn-around time between holes or the overall drilled distance during a shift on the 8-hour noise exposure level, because of the widely varying conditions underground, which affect these periods significantly. The results presented here should therefore be considered to provide an indication of the comparative sound pressure levels under steady drilling conditions, rather than as an indicator of the noise exposure.

No vibration measurements were conducted on the self-propelled drill as it is not designed to be hand-held. On the other drills, the vibration measurements were conducted in accordance with ISO5349-1 (2001), using a Brudigrel and Kjær UA0894 hand adaptor. This adaptor was employed as an alternative to mechanical filters and is indispensable for measuring under the highly impulsive conditions experienced on the rock drills. High levels of vibration may occur here at frequencies way beyond the ISO 5349-1 band of interest, and may cause saturation of the electronics or even failure of the transducers. PCB Piezo accelerometers were used to measure vibration in three orthogonal directions. The measured acceleration histories were subsequently recorded on a SigLab 20–42 analyser and post-processed to find the relevant weighted root mean squared (RMS) accelerations, using software developed for this purpose.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 
The hydraulic drill achieved the greatest penetration rate of 600 mm min–1 (Table 1). The shielded self-propelled drill and the pneumatic drill performed similarly; the electric drill had the lowest penetration rate of 130 mm min–1.


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  		Table 1 Drill penetration rates for the six configurations of rock drills

 
Measured LAeq sound pressure level contours for four of the configurations are depicted in Fig. 2. In these diagrams the contour lines are spaced at 1 dB(A), and a consistent grey scale is used; the darker areas represent higher sound pressure levels. The contours for the self-propelled drill with the standard and cladded drill steels were very similar, while the contours for the pneumatic drill standard and muffled configurations were similar in nature, albeit typically some 3–4 dB(A) lower for the muffled configuration. These contours for the muffled system are therefore not reproduced here. For a quantitative indication of the sound pressure levels, the actual measurements at three positions: about half a meter behind, close to the operator's right ear, and at 45° ~3 m to the right and rear of the operator, are reported in Table 2.


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  		Table 2 Sound pressure levels at the three grid positions

 


Figure 2
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  		Fig. 2 Measured sound pressure levels around the drills.

 
The self-propelled drill produced by far the lowest sound pressure levels. These levels were well within reach of the 85 dB(A) limit even if the drill was to operate continuously for an 8-h period.

The standard conventional pneumatic drill generated the highest noise levels—as high as 114 dB(A) at some positions. As indicated above, muffling reduced the sound pressure levels marginally, by ~3–4 dB(A).

The evaluation of human exposure to hand-transmitted vibration entails determination of a frequency-weighted RMS acceleration, and combines the weighted acceleration along three orthogonal axes ahwx, ahwy and ahwz in an overall ahv value (ISO 5349-1, 2001) which is defined as the root-sum-of-squares of the three component values. These values are expressed in metres per second square (m s–2). A basicentric coordinate system is used with z corresponding to drill feed direction, x perpendicular to z and essentially in the down direction, and y perpendicular to z in the lateral direction.

The vibration levels recorded for the standard configurations of three drill types (excluding the self-propelled drill) are recorded in Table 3. Vibration from the hydraulic drill was particularly high at 31.0 m s–2. The vibration from the pneumatic drill was lower at 21.9 m s–2. As one would expect, muffling made no difference to the vibration measured. The lowest level of vibration was recorded for the electric drill, at 9.2 m s–2.


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  		Table 3 Vibration levels of three rock drills (standard configurations): weighted RMS

 
Table 4 summarises the penetration rates, and noise and vibration levels for all the drill configurations. In summary, while the hydraulic drill had the highest penetration rate (600 mm min–1), it produced medium to high sound pressure levels [103.4 dB(A)], and the highest vibration levels (31.0 m s–2). The electric drill caused the lowest vibration levels (9.2 m s–2) and medium sound pressure levels [94.7 dB(A)] but the penetration rates were low (130 mm min–1). The pneumatic drill had medium penetration rates (350 mm min–1), and medium noise [~105 dB(A)]; vibration levels were high (21.9 m s–2). The self-propelled drill was the quietest drill with the two configurations at 84.9 and 86.1 dB(A), respectively, with medium penetration rates of 300–400 mm min–1.


   DISCUSSION AND CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION AND CONCLUSIONS
ACKNOWLEDGEMENTS
 REFERENCES
 
The present noise exposure limit specified in South African mining regulations is 85 dB(A) over an 8-h working day but this applies to the levels to which workers are exposed (with PPE, if necessary) rather than the levels emitted by the machines. The noise levels emitted by individual drills in this study were, in most cases, below 110 dB(A) during periods of steady drilling. Thus, the MHSC's milestone to reduce the total noise emitted by all equipment installed in any workplace to below 110 dB(A) should be possible to meet using technology that is currently available. Assuming that the drill typically operates for 2 h per shift (van Niekerk et al., 1998) and, bearing in mind that every 3 dB(A) increase in noise level requires a 50% reduction in exposure time, a 2 h shift equates to maximum unprotected levels of around 91 dB(A). It is therefore clear from Fig. 2 and Table 2 that typical noise levels on conventional equipment are still too high. This emphasizes the need for further development on alternatives such as electrical drilling and the self-propelled acoustically shielded drill.


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  		Table 4 Summary of penetration, noise and vibration measurements for each rock drill configuration

 
Vibration levels as high as 31 m s–2 (measured on the hydraulic drill handle) were measured in this study. The lowest vibration levels were recorded from the electric drill. However, even these ‘lower’ levels far exceeded the European Community Directive recommended action limit of 2.5 m s–2 for hand-held vibrating tools. Although the actual time that the operator is in physical contact with the drill can be assumed to be <2 h per day (van Niekerk et al., 1998), it is clear that the vibrations levels are excessive.

Despite legislated noise limits and the requirement for HCPs, the prevalence of NIHL in the South African mining industry remains at an unacceptable level. Muffling reduces sound pressure levels by up to 4 dB(A) and further developments along these lines are likely to lead to only marginal improvements. A solution to both the noise and vibration problems would appear to be the isolation of the operator from the drill as in the case of the shielded self-propelled rock drill. However, the drilling machine is large and cumbersome and cannot be easily manoeuvred, especially in the confined spaces underground in which much drilling takes place. It is thus not currently in use in South African mines. The reduced noise exposure and total absence of transmission of vibration through the hands suggest that this fundamentally different, hands-off approach to drilling should, however, be further explored as a direction for future development.


   ACKNOWLEDGEMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
REFERENCES
 
The authors would like to acknowledge the Safety in Mines Research Advisory Committee (SIMRAC) of the MHSC for funding this research. Particular thanks go to Alec Gumbie and Paul van der Heever for their invaluable input. Thanks also go to the rock drill manufacturers and suppliers whose willingness to participate in these tests showed a desire to improve the safety of their products.

Received June 23, 2006; in final form December 15, 2006


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION AND CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES
 

COMRO. User guide No. 11: guidelines for the implementation and control of a hearing conservation programme in the South African mining industry. (1988) Johannesburg: Chamber of Mines Research Organization.

Directive 2002/44/EC of the European Parliament and of the Council on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration) (sixteenth individual Directive within the meaning of Article 16(1) of Directive 89/391/EEC), 2002.

Department of Minerals and Energy. Mine Health and Safety Act 29 of 1996. (1996) Pretoria: Government Printer.

Department of Minerals and Energy. Mines and Works Act. Regulations 4.17.1-4, Government Gazette, 2 June. (1989).

Franz RM, Phillips JI. Handbook of Health and Safety for the Mining Industry. Guild H, Ehrlich R, Johnston J, Ross M, eds. (2001) Johannesburg: Mine Health and Safety Council. 193–230. Chapter 7. Vibration.

Hessel PA, Sluis-Cremer GK. Hearing loss in white South African goldminers. S Afr Med J (1987) 71:364–7.[Web of Science][Medline]

McBride DI. Noise-induced hearing loss and hearing conservation in mining. Occup Med (Lond) (2004) 54:290–6.[CrossRef][Medline]

Mine Health and Safety Council. Mine Health and Safety Council Annual Report April 2004–March 2005. (2005) Johannesburg: Mine Health and Safety Council, ISBN 1-919853-18-9.

Nelson DI, Nelson RY, Concha-Barrientos M, et al. The global burden of occupational noise-induced hearing loss. Am J Ind Med (2005) 48:446–58.[CrossRef][Web of Science][Medline]

Nyantumbu B, Phillips JI, Dias B, Kgalamono S, Curran A, Barber C, Fishwick D, Allan L. Health 703: the occurrence of hand-arm vibration syndrome in South African gold mines and identification of the potential effects of whole body vibration. (2002) Johannesburg: Mine Health and Safety Council.

Nyantumbu B, Barber CM, Ross M, et al. Hand-arm vibration syndrome in South African gold miners. In: Occup Med (Lond) (2007) 57:25–29. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=16928782. (Accessed on 15 December 2006).[Medline]

Otterman RW, von Wieligh AJ, Burger NDL, de Wet PR. GAP 642: design and development of a quiet, self-thrusting blast hole drilling system. (2001) Johannesburg: Mine Health and Safety Council.

Phillips JI, Nelson G. Health 806: best practices in preventing adverse effects of noise and vibration: an integrated technology transfer programme of project outcomes and deliverables pertaining to noise and vibration. (2006) Johannesburg: Mine Health and Safety Council.

van Niekerk JL, Heyns PS, Heyns M, Hassall JR. GEN 503: the measurement of vibration characteristics of mining equipment and impact percussive machines and tools. (1998) Johannesburg: Mine Health and Safety Council.

Wieslander G, Norback D, Gothe CJ, et al. Carpal tunnel syndrome (CTS), exposure to vibration, repetitive wrist movements, and heavy manual work: a case-referent study. Br J Ind Med (1989) 46:43–7.[Web of Science][Medline]


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This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
51/3/305    most recent
mel082v1
Right arrow Alert me when this article is cited
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