BAD VIBRATIONS

Briony Rowley, CMPA Administration Officer

Vibration refers to oscillatory motions of solid bodies. In this instance we are referring to whole-body (WBV) – where the vibration is transmitted to the body as a whole by its supporting surface (i.e. seat or floor).

Vibration energy can be passed on to operators from vehicles on rough roads, vibrating tools, vibrating machinery, or vibrating work platforms, and may give rise to adverse health effects. Whole body vibration is commonly experienced in mining by drivers, operators and passengers in a variety of vehicles.

The effects of exposure to vibration at best may be discomfort and interference with activities, at worst may be injury or disease. Vibration is believed to cause a range of problems including disorders of joints, muscles and the spine, as well as cardiovascular, respiratory, endocrine and metabolic changes. It can also lead to impaired vision and balance.

The most frequently reported problem is lower back pain. Muscular fatigue and stiffness have also been reported. Some studies have associated the degeneration of the lumber spine with intense long-term exposure to WBV.

Work-related back disorders are the commonest causes of workers’ compensation claims, sick leave and early retirement, and are believed to arise from damage to the spine and surrounding structures. Occupations such as mining have been associated with earlier, more frequent and more severe symptoms.

‘Rough rides’ refers to jolting and jarring which occurs while a vehicle is in motion, and are believed to be the main element of vibration responsible for the development of back and neck disorders in mining personnel. A study in NSW coal mines revealed that nearly 80% of workers had experienced back pain within the previous year.

The first step in controlling vibration hazards is to identify which activities and vehicles might need further investigation. This includes determining which vehicles and activities are associated with any problems which had occurred. Sources of information include consultation with employees, direct observation of the workers, statistics and injury records.

There are three main sources of harmful vibration in vehicles and machines including rough road and poor work surface condition, vehicle activity, and engine vibration. There are many other contributing factors including road construction and maintenance, vehicle type and condition, maintenance and design, vehicle or machine speed, driver skills and awareness.

The vehicle activity can have a major effect on vibration exposure for operators. Prolonged, intensive use of these machines may precipitate problems especially in older workers who have back or neck pain or other bone, muscle or joint disorders. Many older vehicles have little if any suspension and transmit most of the vibration from road surfaces through to the driver, operator or passenger. Seat complaints could be related to in correct installation and adjustment; inadequate maintenance; poor design; or lack of adjustability for particular individuals especially those with back or neck pain. These seat suspension systems deteriorate over time.

In some vehicles the orientation of the cab may mean that operators have o twist to look around. This accentuates discomfort arising from the lower back or neck. Increased speeds also accentuate ride roughness. The term ‘drive to conditions’ tends to be meaningless if it has not been defined. Drivers need to be alert to road conditions and obstacles such as potholes, soft spots, water and materials on the road. Long periods of sitting and unvaried work schedules can also contribute to back and neck pain.

Vibration measure procedure

A typical measurement system uses a sensor which detects vibration in three axes; forward to back, side to side, and up and down. A vibration sensor is placed on the seat to pick up the vibration being transmitted through to the driver’s body. The vibration signal is then amplified and recorded for later analysis.

After analysis, the results can be assessed against health, fatigue or comfort criteria in Standards for whole body vibration.

Standards for whole body vibration

The Australian Standard (AS 2670.1) was published in 1990 and was a complete adoption of the now superseded International Standard (ISO 2631
– 1, 1985).

The Australian Standard gives exposure limits for three criteria, comfort, fatigue and health. The exposure limit is set at approximately half the level considered to be the threshold of pain for healthy human subjects restrained to a vibrating seat. However, the assessment methods used in the Standard may underestimate the risks of damaging vibration particularly if they include jolts and jars.

The International Standard (ISO 2631.1) is quite different. It incorporates assessment methods for both steady state and shock type vibration. The International Standard is generally more stringent than the Australian Standard.

There are several points to note about the International Standard health guidance zones:

• The recommendations are intended as guidance rather than strict limits;
• Vibration exposure depends on the duration and level of vibration;
• It generally takes many years for the health effects to occur;
• The recommended exposure times do not predict possible immediate damage caused by a one-off jolt;
• Prolonged sitting may be more of a problem than vibration;
• Vibration is assessed in the worst axis, which is usually the z-axis (up and down). When vibration is high in all axes, the contribution from each axis is added to give the final exposure level.

Once the risks have been identified, the assessed resources can be directed towards solving the problems. Hazard elimination, process redesign, and engineered modifications are given preference over administrative controls that rely on people’s adherence to procedures.

Hard barriers are primarily design solutions such as modifying the process to eliminate the risk, redesigning the tasks, designing machines or vehicles that reduce the vibration transmitted through the operator, and improving road and surface conditions.

Soft barriers are usually less effective as they rely on human behaviour and are subject to error, these include rules such as speed limits, safe work procedures and standard operating procedures, etc.

Reducing exposure to harmful vibration cannot rely only on limiting exposure times as this is impractical. In the long term, the improved design of vehicles and machines and the development of reliable systems of road maintenance will significantly reduce WBV exposures.

Training in ways to avoid potentially harmful vibration could prove useful and cost effective. This training needs to include passenger comfort, and travelling at a speed that is comfortable for both the driver and passengers.

Instructions such as ‘drive to conditions’ need to be clearly defined. Training is important in many areas, some of which include raising awareness of health and safety, reinforcing safe procedures, and obtaining feedback.

Road construction needs to be done correctly and according to established procedures. Some of the important points include:

• Professional road construction methods
• Planned and systematic road maintenance programs
• Effective communication of information on road conditions
• More effective use of water pumps and drainage techniques

Vehicle suspension is extremely important in reducing the impact of harmful vibration on the driver or operator. It is important that operators are isolated from the frame of the machine, vehicle suspension is appropriate for operators and loads, appropriate tyres and tyre pressures are used, and good posture is also extremely important.

Resource: Bad Vibrations, a handbook on whole – body vibration exposure in mining, published July 2001

You must be logged in to post a comment Login