What is Vibration? Hand Arm and Whole Body Vibration

What is Vibration?

Vibration is a mechanical phenomenon whereby oscillations occur at an equilibrium point. The word comes from Latin vibrationem (“shaking, brandishing”). The oscillations may be periodic, such as the motion of a pendulum—or random, such as the movement of a tire on a gravel road. Vibration can be desirable: for example, the motion of a tuning fork, the reed in a wind instrument or harmonica, a mobile phone, or the cone of a speaker. Often, however, vibration is undesirable, wasting energy and creating unwanted sound.

For example, the vibrational motions of engines, electric motors, or mechanical devices are typically unwanted. Such vibrations could be caused by imbalances in the rotating parts, uneven friction, or the acoustic resonance of the air column in the case of musical instruments. Careful design of the components can reduce unwanted vibrations.

Vibration safety is important because it can help protect you from injuries caused by exposure to excessive vibration. Vibration-related injuries can occur when your body is exposed to too much vibration through work or leisure activities. Exposure to excessive vibration can cause a variety of health problems, including:

Carpal tunnel syndrome
Tendonitis
Raynaud’s phenomenon
Vibration white finger

If you are exposed to excessive vibration at work, you must talk to your employer about ways to reduce your exposure. There are a variety of ways to reduce exposure to vibration, including:

Using anti-vibration gloves
Taking breaks during exposure
Using vibrating tools for shorter periods

If you are experiencing any symptoms of a vibration-related injury, it is important to see a doctor as soon as possible. Early diagnosis and treatment can help reduce the severity of the symptoms and improve your overall prognosis.

Vibration Testing & Standards

Vibration testing is accomplished by introducing a forcing function into a structure, usually with a shaker. Alternately, a DUT (device under test) can be attached to the “table” of a shaker. Vibration testing is performed to determine if a device can withstand the rigours of its intended use. Generally, these include operational vibration (the vibration environment that a product will see in normal operation) and transport vibration (The vibration environment that a product will see when it is transported, usually in a truck or aeroplane).

There are many standards for vibration testing, including MIL-STD-810 and ISTA Procedure 1A. Transport simulations can include sine (smooth), random (rough), and shock (sudden) components. Operational vibration testing covers a wide range of frequencies, from very low (sub-audible) to extremely high (ultrasonic). Shock testing is generally in the medium frequency range. All these types of vibration can be present simultaneously, so a comprehensive test specification will list all of the desired waveforms and their frequencies.

Types Of Vibration

There are three main types of vibration:

1. Free or Natural Vibration

Free vibration occurs when a mechanical system is set in motion with an initial energy input but is not subject to externally generated forces. The subsequent motion of the system is due to its inertia and consists of one or more periodic vibrations of equal amplitude and constant frequency. Free vibration generally dies over time as the system loses energy to frictional forces.

2. Forced Vibration

On the other hand, forced vibration is when an external force is applied to a system at a frequency that matches one of the system’s natural frequencies. This can cause the amplitude of the vibrations, potentially leading to damage or failure of the system.

3. Damped vibration

Damped vibration is a type of mechanical vibration where the amplitude of the vibrations is reduced over time. This could be due to viscous friction or structural damping.

Damped vibration is an important phenomenon in many engineering applications, as it can help to reduce noise and vibrations. In some cases, damped vibration can also improve the performance of a system.

There are two main types of damped vibration: viscous damping and structural damping.

Viscous damping is caused by friction between the moving parts of a system. This type of damping is typically linear, meaning that the damping level increases in proportion to the speed of the vibrations.

Structural damping is caused by the flexibility of the structure itself. This type of damping is typically nonlinear, meaning that the damping level does not increase in proportion to the speed of the vibrations.

Damped vibration can be used to reduce noise and vibrations in several ways. For example, viscous damping can be used to reduce the amplitude of vibrations, while structural damping can be used to change the frequency of vibrations.

Hand Arm Vibration

Hand-arm vibration (HAV) is the vibration transmitted to the hand and arm from hand-held power tools, hand-guided machinery, or by holding materials being processed by these machines.

The harmful effects of HAV were first recognized in the 1950s, and since then, a large body of research has been carried out into the adverse health effects of vibration exposure. It is now known that HAV can cause a wide range of health problems, including:

Raynaud’s phenomenon
Vibration white finger (VWF)
Carpal tunnel syndrome (CTS)
Tendonitis
Muscular skeletal disorders

There are several factors that can contribute to the risk of developing these conditions, including:

The type of tool being used
The way the tool is being used
The level of vibration exposure
The length of time the person is exposed to vibration

Hand-Arm Vibration Syndrome

Hand-arm vibration syndrome (HAVS) describes a group of diseases caused by the exposure of the hand and arm to external vibration. Some of these have been described under WRULDs, such as carpal tunnel syndrome.

However, the best-known disease is the vibration white finger (VWF), in which the circulation of the blood, particularly in the hands, is adversely affected by the vibration. The early symptoms are tingling and numbness in the fingers, usually sometime after the end of the working shift. As exposure continues, the tips of the fingers go white, and the whole hand may become affected. This results in a loss of grip strength and manual dexterity. Attacks can be triggered by damp and/or cold conditions and, on warming, ‘pins and needles are experienced.

If the condition is allowed to persist, more serious symptoms become apparent, including discoloration and enlargement of the fingers. In very advanced cases, gangrene can develop, leading to the amputation of the affected hand or finger. VWF was first detailed as an industrial disease in 1911. The risk of developing HAVS depends on the frequency of vibration, the length of exposure, and the tightness of the grip on the machine or tool.

Assessment Of Hand-Arm Vibration

When assessing the risk of HAVS developing among employees, the source of the vibration, such as reciprocating, rotating, and vibrating tools and equipment, needs to be considered first, together with the age of the equipment, its maintenance record, its suitability for the job and any information or guidance available from the manufacturer. The number of employees using the tooling or equipment, the duration and frequency of their use, and any relevant personal factors, such as a pre-existing circulatory problem, all form part of the assessment.

Environmental factors, particularly exposure to cold and/or wet weather and the nature of the job, are also important factors to consider during such a risk assessment. Finally, an examination of the existing controls and their effectiveness and the frequency, magnitude, and direction of the vibration are important elements of the evaluation. Other issues could include the effectiveness of any personal protective equipment (PPE) and any instruction or training.

Control Measures Of Hand-Arm Vibration (HAV)

Many machines and processes used in industry produce HAV. Typical high-risk processes include:

Grinding, sanding, and polishing wood and stone;
Cutting stone, metal, and wood;
Riveting, caulking, and hammering;
Compacting sand, concrete, and aggregate;
Drilling and breaking rock, concrete, and road surfaces; and
Surface preparation, including de-scaling and paint removal.

There are several ways to ascertain the size of the vibration generated by equipment and machines. Manufacturers must declare vibration emission values for portable hand-held and hand-guided machines and provide information on risks. Other sources of vibration information include scientific and technical journals, trade associations, and online databases. HSE experience has shown that the vibration level is higher in practice than that quoted by many manufacturers. The reasons for this discrepancy may be that:

The equipment is not well maintained;
The equipment is not suitable for the material being worked;
The tool has not been purchased from a reputable supplier;
The accessories are not appropriate or are badly fitted;
The operative is not using the tool properly.

Given these problems, it is recommended that the declared value should be doubled when comparisons are made with exposure limits. As the exposure limit or action value is averaged over 8 hours, it is possible to work with higher values for a reduced exposure time.

The Guidance (L140) gives very useful advice on measuring vibration, undertaking a suitable and sufficient risk assessment, control measures, health surveillance, and training of employees. The following points summarise the important measures which should be taken to reduce the risks associated with HAV:

Avoid, whenever possible, the need for vibration equipment;
Undertake a risk assessment that includes a soundly based estimate of the employees’ exposure to vibration;
Develop a good maintenance regime for tools and machinery. This may involve ensuring that tools are regularly sharpened, worn components are replaced or engines are regularly tuned and adjusted;
Introduce a work pattern that reduces the time exposure to vibration;
Issue employees with gloves and warm clothing. There is a debate as to whether anti-vibration gloves are effective, but it is agreed that warm clothing helps with blood circulation, reducing the risk of VWF. Care must be taken so that the tool does not cool the hand of the operator;
Introduce a reporting system for employees to use so that concerns and any symptoms can be recorded and investigated; and
Encourage employees to check regularly for any symptoms of vibration-related ill-health and to participate in any health surveillance measures provided.

It is important that drill bits and tools are kept sharp and used intact – an angle grinder with a chipped cutting disc will lead to a large increase in vibration as well as be dangerous.

Whole Body Vibration (WBV)

Whole-body vibration (WBV) is caused by vibration from machinery passing into the body either through the feet of standing workers or the buttocks of sitting workers. It is the shaking or jolting of the human body through a supporting surface (usually a seat or the floor), for example, when driving or riding on a vehicle along an unmade road, operating earth-moving machines, or standing on a structure attached to a large, powerful, fixed machine, which is impacting or vibrating. The most common ill-health effect is severe back pain which, in severe cases, may result in permanent injury. Reasons for back pain in drivers can include:

Poor design of controls, making it difficult for the driver to operate the machine or vehicle easily or to see properly without twisting or stretching;
Incorrect adjustment by the driver of the seat position and hand and foot controls so that it is necessary to continually twist, bend, lean, and stretch to operate the machine;
Sitting for long periods without being able to change position;
Poor driver posture;
Repeated manual handling and lifting of loads by the driver;
Excessive exposure to whole-body vibration, particularly to shocks and jolts;
Repeatedly climbing into or jumping down from a high cab is difficult to get in and out.

The risk increases when the driver or operator is exposed to two or more factors. Other acute effects include reduced visual and manual control and increased heart rate and blood pressure. Chronic or long-term effects include permanent spinal damage, damage to the central nervous system, hearing loss, and circulatory and digestive problems.

The most common occupations which generate WBV are driving forklift trucks, construction vehicles, and agricultural or horticultural machinery and vehicles. There is a growing concern throughout the European Union about this problem. Control measures include properly using the equipment, including correct adjustments of air or hydraulic pressures, seating, and, in the case of vehicles, correct suspension, tyre pressures, and appropriate speeds to suit the terrain. Other control measures include selecting suitable equipment with low vibration characteristics, work rotation, good maintenance, and fault reporting procedures.

The HSE commissioned measurements of WBV on several machines; some of the results are shown in the table below.

How To Prevent Workers From Vibration Hazards

Control Measures For Whole Body Vibration

The common measures used to control ergonomic ill-health effects are to:

Implement results of task analysis and identification of repetitive actions;
Eliminate vibration-related or hazardous tasks by performing the job in a different way;
Ensure that the correct equipment (properly adjusted) is always used;
Introduce job rotation so that workers have a reduced time exposure to the hazard;
During the design of the job, ensure that poor posture is avoided;
Undertake a risk assessment;
Keep reports from employees and safety representatives;
Keep ill-health reports and absence records;
Introduce a program of health surveillance;
Ensure that employees are given adequate information on the hazards and develop a suitable training program;
Ensure that a program of preventative maintenance is introduced and includes the regular inspection of items such as vibration isolation mountings;
Keep up to date with advice from equipment manufacturers, trade associations, and health and safety sources (more and more low vibration equipment is becoming available).

The Regulations require the control of the risks from whole-body vibration. This should be based on an assessment of the risk and exposure. In most cases, it is simpler to make a broad assessment of the risk rather than try to assess exposure in detail, concentrating the main effort on introducing controls. The requirements of the Regulations are to:

Assess the vibration risk to employees;
Decide if they are likely to be exposed above the daily exposure action value (EAV) and if they are: introduce a program of controls to eliminate or reduce their daily exposure so far as is reasonably practicable; decide if they are likely to be exposed above the daily exposure limit value (ELV) and if they are: take immediate action to reduce their exposure below the limit value.
Provide information and training on health risks and controls to employees at risk;
Consult the trade union safety representative or employee representative about the risks and the plans to address these risks;
Keep a record of the risk assessment and control actions;
Review and update the risk assessment regularly.

If a broad risk assessment has been made and the appropriate and reasonable control actions are taken, there is no need to measure the exposure to vibration of the employee. Most machine and vehicle activities in normal use produce daily exposures below the limit value. But some off-road machinery operated for long periods in conditions that generate high vibration levels or jolting may exceed the exposure limit value.

Measurement Of Whole Body Vibration (WBV)

The measurement of WBV is very difficult and can only be done accurately by a competent specialist. If the risk assessment has been made and the recommended control actions are in place, there is no need to measure employees’ exposure to vibration. However, the HSE has suggested that employers can use the following checklist to estimate whether exposure to WBV is high:

There is a warning in the machine manufacturer’s handbook that there is a risk of WBV;
The task is not suitable for the machine or vehicle being used;
Operators or drivers are using excessive speeds or operating the machine too aggressively;
Operators or drivers are working too many hours on machines or vehicles that are prone to WBV;
Road surfaces are too rough and potholed or floors uneven;
Drivers are being continually jolted or when going over bumps rising from their seats;
Vehicles designed to operate on normal roads are used on rough or poorly repaired roads; 8. operators or drivers have reported back problems.

If one or more of the above applies, exposure to WBV may be high. If checks on exposure levels are required, information in the vehicle manufacturer’s handbook or data published by the HSE may be used. An exposure calculator is available on the HSE website for various machines and vehicles in different working conditions. However, it is more effective for most employers to direct their efforts toward controlling the risks rather than trying to assess vibration exposures precisely. WBV in industry arises from driving vehicles, such as tractors or forklift trucks, over rough terrain or uneven floors. It is highly unlikely that driving vehicles on smooth roads will produce WBV problems. The HSE Guidance document, L141, gives detailed advice to help with the risk assessment and estimating daily exposure levels. WBV risks are low for exposures around the action value; only simple control measures are usually necessary.

As explained earlier, back pain is the most common health problem associated with WBV. Other activities may have caused this pain, but WBV will aggravate it.

The actions for controlling the risks from WBV need to ensure that:

The driver’s seat is correctly adjusted so that all controls can be reached easily, and the driver’s weight setting on their suspension seat, if available, is correctly adjusted. The seat should have a backrest with lumbar support;
Anti-fatigue mats are used if the operator has to stand for long periods;
The speed of the vehicle is such that excessive jolting is avoided. Speeding is one of the main causes of excessive WBV;
All vehicle controls and attached equipment are operated smoothly;
Only established site roadways are used;
Only suitable vehicles and equipment are selected to undertake the work and cope with the ground conditions;
The site roadway system is regularly maintained;
All vehicles are regularly maintained, with particular attention being paid to tire condition and pressures, vehicle suspension systems, and the driver’s seat;
Work schedules are regularly reviewed so that long periods of exposure on a given day are avoided, and drivers have regular breaks away from the vehicle;
Prolonged exposure to WBV is avoided for at-risk groups (older people, young people, people with a history of back problems, and pregnant women);
Employees are aware of the health risks from WBV, the risk assessment results, and the ill-health reporting system. They should also be trained to drive so that excessive vibration is reduced.

A simple health monitoring system that includes a questionnaire checklist should be agreed upon with employees or their representatives (available on the HSE website) to be completed by employees at risk once a year. Employees with back problems should be referred to an occupational health specialist.

Personal information about the health of individual employees must be treated confidentially.

Different Types Of Vibration Hazards

There are four main types of vibration hazards: whole-body, hand-arm, knee-leg, and foot. Whole-body vibration is when the entire body is exposed to vibrations from a stationary source or while in motion. Hand-arm vibration is when only the hands and arms are exposed to vibrations. Knee-leg vibration is when only the knees and legs are exposed to vibrations. Foot vibration is when only the feet are exposed to vibrations.

Whole-body vibration can cause various health problems, including back pain, neck pain, headaches, dizziness, fatigue, and even hearing loss. Hand-arm vibration can cause carpal tunnel syndrome, hand-arm vibration syndrome, and other health problems. Knee-leg vibration can cause knee-leg vibration syndrome and other health problems. Foot vibration can cause foot vibration syndrome and other health problems.

How To Prevent Workers From Vibration Hazards

There are a few things employers can do to prevent workers from being exposed to vibration hazards:

1. Use engineering controls: One of the most effective ways to control exposure to whole-body vibration is to use engineering controls. This could involve installing cushioned flooring or using vibration-isolating mounts for equipment.

2. Limit exposure time: Another way to reduce workers’ exposure to vibration is to limit the amount of time they are exposed to it. This can be done by scheduling work so that employees are not working with vibrating equipment for more than a few hours.

3. Encourage workers to take breaks: Breaks give workers a chance to rest and can help reduce their exposure to vibration. Employers should encourage workers to take breaks often, especially if uncomfortable.

4. Provide training: Employees should be trained on the dangers of exposure to vibration and how to minimize their risk. This training should include information on the equipment that emits a vibration, the potential health effects of exposure, and how to use engineering controls and work practices to reduce exposure.

5. Use personal protective equipment: In some cases, personal protective equipment (PPE) may be necessary to protect workers from vibration hazards. PPE such as gloves, earplugs, or respirators can help reduce workers’ exposure to vibration.

By following these guidelines, employers can help protect their workers from the dangers of exposure to whole-body vibration.

Role of Health Surveillance

The Control of Vibration at Work Regulations require the employer to ensure that employees should be given suitable health surveillance if:

The risk assessment indicates that there is a risk to the health of any employees who are, or are liable to be, exposed to vibration; or
Employees are exposed to vibration at or above an exposure action value.

Health surveillance records must be kept, employees given access to their own records, and the enforcing authorities provided with copies, as required by them. If problems are found with the health surveillance results, a range of specified actions must be taken.

Conclusion

The best way of dealing with the risks from WBV is to design out the need for workers to be exposed in the first place. However, this is not always possible, and other controls will be needed to reduce exposure to as low a level as reasonably practicable. Work should be designed or organized wherever possible so that employees are not exposed to high vibration levels for long periods. This might include, for example, using a task rotation system.

Employers should consider all vibration sources when designing out or controlling the risks from WBV. They should also ensure that employees are included in the process and aware of the risks and how they are controlled.

Thank you for reading. Please note that this is only a guide and that you should consult your health and safety representative for more specific information.

What is Vibration? Hand Arm and Whole Body Vibration

What is Vibration?

Vibration Testing & Standards