AMSJ » Give vehicle operators a smooth ride
LATEST NEWS

Give vehicle operators a smooth ride

For zero harm to be achieved we must give vehicle operators a smooth ride, and where unacceptable exposures exist it is necessary to implement a suite of control measures, writes Phillip Byard.

Permanent injury or disease sustained by Australian workers comprises a huge burden. Fatality or permanent impairment is a significant issue for every industry including the mining industry. Whole body vibration (WBV) is considered a significant contributor to the permanent impairment problem which has been recognised for decades. WBV requires a suite of interventions to be appropriately managed in the work place. Current commercially available seats do not provide significant protection for operators of heavy mining vehicles. Regular vibration monitoring, with evaluation against standards for whole body vibration, is necessary to quantify the extent to which operating vehicles is damaging operators. Operation and maintenance managers must become sensitised to the phenomena of jolt / jar and vibration with priority given to road and vehicle maintenance above production pressures for WBV to be effectively managed into the future.

Personal Damage (injury or disease) can be usefully classified as Class I (permanent alteration of life), Class II (temporary alteration of life with full recovery), or Class III (minor irritation). Class I includes fatal and non-fatal (permanent impairment). There have been three snapshots of damage to people from work in Australia, published by the Industry Commission (1995)1, the National Occupational Health and Safety Commission (NOHSC 2004)2 and the Australian Safety and Compensation Council (ASCC March 2009)3. The three studies gave baseline estimates of economic costs for the years 1992-93, 2000-01 and 2005-06. The studies consistently demonstrated that Class I damage, while less than 10 per cent of the occurrences reported, contributed the majority of costs with Class I non-fatal occurrences contributing between 80-90 per cent of all costs. In 2005-2006 for example there were an estimated 2,603 fatalities and 60,000 permanent impairments. The fatalities contributed 3.3 per cent of all costs and the permanent impairments contributed 88 per cent of all costs. Class II contributed 8.7 per cent of all costs. Estimated costs associated with Class III damage is of the same order of magnitude as Class II damage. If one considers other than economic costs such as pain and suffering, social costs, family costs and sovereign risk the same conclusion could be drawn. The minority of incidents (Class I) contributes the majority of costs / burden. Occupational Health & Safety is essentially a Class I problem. Any organisation effectively managing OH&S will attempt to understand what produces Class I damage and adopt control strategies that effectively manage those exposures.

One valuable source of information to assist in understanding what produces Class I damage is to review industry injury statistics. The internal dataset of any organisation for fatality or permanent impairment is unlikely to be statistically significant and is of little use. Near miss reports will also be predictably focussed on potentially fatal outcomes and will not focus attention on permanent impairment exposures of the workforce. unfortunately most compensation-based datasets (including the national dataset) report occurrences not by the extent of impairment but by the number of days lost as a measure. Research into the pattern of personal damage by the author’s organisation has revealed that the pattern for long duration claims is very similar to the pattern for permanent impairment / disability. There are some differences. The pattern of short duration claims is very similar to the pattern for Class III minor damage. Any useful analysis of compensation or injury data where permanent impairment is not reported must, therefore, focus on long duration claims to give insight into the pattern of permanent impairment.

Further understanding can be gained by looking to subsequent levels of breakdown in the taxonomy. For specifically the Machine Energy cases 207 (81 per cent) involved mobile equipment, with 14 (7 per cent) involving fixed or portable machinery, and the balance (33 / 12 per cent) being motor vehicle road accidents.

Human Energy, Gravitational Energy and Vehicular Energy represented 80 per cent of all occurrences. Vehicular energy contributed 13 per cent of the total cases. The pattern of permanent damage has essentially not changed. So we shall say it again; any effective OH&S system within the mining industry must promote priority of focus on understanding and appropriately managing Human Energy, Gravitational Energy and Vehicle Energy for zero permanent impairments / disabilities to be achieved. understanding and effectively managing vibration / jarring is essential in our journey to zero as vibration / jarring contributes significantly to the problem.

In order to understand the phenomena of WBV it is useful to review literature. Research papers on exposure to WBV have been published from as early as the 1940s and 1950s with considerable work conducted internationally during the 1970s and 1980s. Much of this research work was completed in the mining industry. Standards have long been available within Australia which define exposures to vibration such as “reduced comfort”, “fatigue” and “exposure” limits. Australian Standard AS2670 – 19836 was the first such standard published in Australia. AS2670-19836 was superseded by Australian Standard AS2670.1-19907 and was identical to the International Standards Organisation ISO 2631/1:19858. Australian Standard AS2670. 1-20019 was later published and is identical to, and reproduced from, ISO 2631-1:199710. The 2001 standard specifi es methodologies for the measurement of whole body vibration and guidance as to the effects of vibration on health.

Clause 7.1 of AS 2670.1:2001 states; The relevant literature on the effects of long-term high-intensity whole-body vibration indicates an increased health risk to the lumbar spine and the connected nervous system of the segments affected. This may be due to the biodynamic behaviour of the spine: horizontal displacement and torsion of the segments of the vertebral column. Excessive mechanical stress and/or disturbances of nutrition of and diffusion to the disc tissue may contribute to degenerative processes in the lumbar segments (spondylosis deformans, osteochondrosis intervertebralis, arthrosis deformans). Whole-body vibration exposure may also worsen certain endogenous pathologic disturbances of the spine. Although a dose-effect relationship is generally assumed, there is at present no quantitative relationship available.

With a lower probability, the digestive system, the genital/urinary system, and the female reproductive organs are also assumed to be affected.

It generally takes several years for health changes caused by whole-body vibration to occur. It is therefore important that exposure measurements are representative of the whole exposure period.

Research suggests that the damaging frequency of vibration for the spine for example is 4-8Hz, which corresponds to the natural frequency of sections of the spine, however there is also a range of evidence that suggests that sudden shock loadings superimposed on vibration can also produce permanent damage to the lumbar spine. Troup et al11, for example, stated; Even where the driving posture, considered in isolation, may be satisfactory and unlikely to load the spine, the general level of vibration combined with the static and reactive levels of muscular activity in the trunk while driving may lower the threshold for resistance to impact and shock. There is no reason to doubt, therefore, that where the background level of vibration to which the spine is exposed is high, the risk of injury on exposure to jerk forces is increased.

They further stated that: Nevertheless, the increased muscular activity undoubtedly adds to the compressive load on the spine and reduces its resistance to trauma… Yet the evidence suggests that when spinal trauma is considered, it is the rate of increase in acceleration from a single compressive shock that matters.

Vibration and jolt / jar experienced by a vehicle operator is transmitted to the person essentially via the seat but also through the feet and hands. Movement is experienced in a combination of three directions; forward-aft (x direction), side to side (y direction) and up and down (z direction). Vibration is created through vehicle movement over rough surfaces, movement of vehicle components, such as buckets, and engine vibration. Jolt / jar exposures are essentially created when vehicles strike objects such as potholes, rough undulations in roadways, large rocks and tree stumps. Graders, scrapers, loaders, dozers and graders are particularly susceptible to jolt / jar. Striking objects while travelling produces movement in mainly the forward aft (x) direction. Loaders dropping large rocks into trucks or striking trucks can also produce the jolt / jar phenomena.

Early research measured the vibration produced by a range of equipment over a range of surfaces by placing accelerometers on the floor of the vehicle cab. Measurements were taken in situ on machinery under severe but typical operating conditions. It was readily identified that the dominant frequency of vibration for a range of mining and construction heavy equipment was in the 1 – 10Hz range. It is worth noting that the dominant frequency for vehicles on sealed roads is greater than 20Hz. The research concerning the off-road vehicle activity was formalised by ISO 7096:1994 which defined a method for testing seat suspensions by inputting vibration profiles representative of various classes of machines. The dominant frequencies of a range of profiles are shown in Table 1. This standard is now designated ISO 7096:2000 and is in its third edition.

SEAT (Seat Effective Amplitude Transmissibility) value is a metric used to characterise the vibration and shock isolation efficiency of a seat. SEAT value is a ratio of the vibration experienced on the top of the seat to the input vibration at the base of the seat. Ideally a seat needs to have a SEAT value of less than one for the range of critical frequencies in order to reduce the effect of the machine vibration on the operator.

Suspension seats are predominately selected for mining equipment. Traditional suspension seats are reactive, or passive, suspension seats in that the cab floor moves and the mechanical / air system moves the seat in response to the movement of the floor. Traditional suspension seats for offroad heavy equipment have been essentially the same as for on-road vehicles. The dominant frequency of on-road vehicles is not the same as off-road applications. Tests on a range of reactive suspension seats for mining applications have yielded SEAT values of greater than 1 for frequencies in the 1 – 4 Hz range. Reactive suspension seats have resonate frequencies in the 1 – 4 Hz range and so amplify the vibration in this frequency range. Recognition by seat manufacturers of this problem has resulted in the prototype development of active or semi-active suspension systems for seats. These seats are actuated to move the seat pan in response to detected vibration at the floor level. SEAT values of less than 1 are being reported which is encouraging but the reliability of the technology is proving problematic. It is also worth noting that current seat suspension systems predominantly focus on managing vibration / jolt / jar in the up-down (z) direction. Further research and development is required to identify suitable seat designs that will effectively manage movement in the forward-aft (x) and side to side (y) directions. A mining operation must understand the current limitation of seat design in managing the WBV problem.

In order to effectively manage WBV in mining operations it is necessary to identify whether the mine has a problem with WBV. McPhee et al12 identified that measured values of whole body vibration correlate very well with operator’s subjective opinion of ride quality. Simple word descriptions such as “Good”, “Fair”, “Rough” and “Very Rough” can give an indication of the degree to which an operator is exposed to vibration and jarring which may exceed desirable limits. Encouraging reporting of “Rough” or “Very Rough” ride conditions can identify particular roads or particular vehicles or particular road / vehicle combinations where intervention must be prioritised. Armed with this information it is then essential to quantify the exposure. This can be readily achieved by monitoring the vibration at the seat for a sample of time. A range of service providers can provide the monitoring equipment. The vibration monitoring data can then be assessed against AS2670.1:2001 to provide guidance on the daily vibration exposure and also the level of jolt / jar being experienced as vibration dose value (VDV). Interpretation of the vibration data requires a person familiar with AS2670. Mining equipment has been measured to reach exposure limits within two to five hours on average, depending on the machine and activity. Under ideal conditions this time can be doubled. Non-suspended vehicles can reach exposure limits within 30 minutes. If it becomes apparent that operators are being exposed to WBV beyond recommended levels then it is necessary to manage either the duration of exposure or the exposure levels.

Modifying exposure durations can be achieved by task rotation which is easy to suggest but significantly more difficult to enact. Modifying exposure levels can be achieved by a range of interventions. Vehicle suspension maintenance and vehicle seat maintenance will lower exposures. These interventions must be seen as priority by production and maintenance personnel. Returning a non-functioning seat into service must be seen by all as unacceptable. Reducing speed of vehicle movement will lower exposures. However with production pressures this administrative control is not likely to provide long-term protection unless the appropriate reduced speed can be quantified, signposted and reinforced by speed detection or speed limiting. Newer vehicles have a lower exposure than older versions of the same vehicle. Seat design also presents a significant contribution to the exposure particularly for jolt / jar. Many seats have a suspension range where it is preferred that the seat is set midrange to cater for the seat “bottoming out” or “topping out”. Ranges of 150mm are not uncommon. Many seats however do not have an independent height adjustment so operators chase comfortable ride height through the suspension mechanism. This can result in taller operators setting seats near the top of ride height so topping out becomes more likely and shorter operators setting seats near the bottom of ride height so bottoming out becomes more likely. Seats with auto-adjusting suspension to mid-range and an independent seat height mechanism need to be selected for heavy vehicles. Providing smoother road and work surfaces will lower exposures. Road maintenance must be prioritised with accompanying standards for acceptable and non-acceptable road conditions. Size and frequency of potholes and ruts can form part of the standard for permitting continuing road usage. Dedicated road maintenance teams with appropriate resources such as graders, loaders, trucks, personnel and road base can ensure roads continue to remain useable and not hold up production. In every case, however, each intervention must be quantified by measurement to identify the success or otherwise of the intervention and the extent to which it is actually reducing the critical frequencies of vibration experienced by the operator. Operators’ ride perception must be considered as the first warning of unacceptable ride conditions and appropriate controls must be prioritised by maintenance and production managers alike for intervention.

Permanent injury or disease sustained by Australian workers comprises a huge burden. Fatality or permanent impairment is a significant issue for every industry including and especially the mining industry. Whole body vibration (WBV) is a significant contributor to the permanent impairment problem which has been recognised for decades. Effective management of WBV begins with quantifying the exposure of operators to levels which exceed standards. Vibration monitoring can initially target those vehicles / roads / activities that operators describe as “rough” or “very rough”. Where unacceptable exposures exist it is necessary to implement a suite of controls ranging from vehicle suspension maintenance, selecting seats with auto suspension and independentheight adjustment, and seat suspension maintenance to road maintenance and provision of a dedicated road maintenance team. Reactive / passive suspension seats will not effectively protect operators. For WBV to be effectively managed production and maintenance personnel must consider poor ride conditions as unacceptable in the mining environment. For zero harm to be achieved we must give vehicle operators a smooth ride.

Phillip Byard is a Senior Consultant and Training Manager for InterSafe. InterSafe investigates 300 to 400 incidents per year which have resulted in fatality or permanent impairment across all industries including the mining, construction, manufacturing and transport industries. With the learnings from more than 13,000 incident investigations InterSafe is committed to partnering with stakeholders to produce workplaces free from the potential for permanent personal damage. InterSafe is dedicated to applying scientific principles of modeling, taxonomy and hypothesis forming and testing to the safety arena. This has resulted in challenging conventional wisdom in order to produce value free information based paradigms of thinking that produce long term effective change. InterSafe provides a range of services including incident investigation, high-risk audits, risk assessments, design reviews, implementation of OH&S systems, behaviour-based safety, and training. InterSafe offers vibration monitoring and data interpretation services. For more information of InterSafe’s services please phone Justin, Roger or Phillip on (07) 3895 8111 or visit www.intersafe.com.au

References

1 Industry Commission, Work Health & Safety, An Inquiry into Occupational Health & Safety, Vol 1: Report, Report No. 47. Industry Commission, Australia, September 1995.

2 National Occupational Health & Safety Commission, The Cost of Work-Related Injury and Illness for Australian Employers, Workers and the Community, August 2004, Canberra.

3 Compendium of Workers’ Compensation Statistics Australia 2006-2007, March 2009, Australian Safety and Compensation Council.

4 Geoff McDonald & Associates Pty Ltd, Taxonomy: Incidents in the Coal Mining Industry 1990- 1995, Reproduced with permission from “Taxonomy of Incidents in the Coal Mining Industry New South Wales and Queensland: Open Cut Mines”.

5 InterSafe, Taxonomy: Incidents in the West Australian Mining Industry July 2003 – June 2007, (datasource: WorkCover WA) 2008 InterSafe, Brisbane.

6 Standards Australia, Vibration and shock – Guide to the evaluation of human exposure to whole body vibration, Australian Standard 2670-1983.

7 Standards Association of Australia, Evaluation Of Human Exposure To Whole Body Vibration, Part 1: General Requirements, Australian Standard AS 2670.1-1990 (ISO 2631/1-1985).

8 International Standards Association, International Standard ISO 2631-1:1985, Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole-Body Vibration – Part 1: General Requirements, 1985.

9 Standards Australia International, Evaluation Of Human Exposure To Whole Body Vibration, Part 1: General Requirements, Australian Standard AS 2670.1 – 2001.

10 International Standards Association, International Standard ISO 2631-1:1997, Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole-Body Vibration – Part 1: General Requirements, 1997.

11 Tapio Videman, Markku Nurminen and Troup, J.D.G., J. Spine, Vol. 15, No. 8, 1990.

12 McPhee, B., Foster, G., & Long, A. Bad Vibrations – A Handbook on Whole-Body Vibration Exposure in Mining, Coal Board Health & Safety Trust, Sydney, 2001.

Add Comment

Click here to post a comment