What You’ll Learn 🎯

Define human vibration and its impact—understand whole‑body vs. hand–arm exposure, health effects (HAVS, white finger, lumbar issues) and relevant standards (ISO 2631‑1, 8041, 2631‑5, 5349)
Set up triaxial accelerometers using appropriate adapters (seat pad, hand‑held) and select suitable ICP sensors (50 g – 500 g range) connected via high-resolution Dewesoft DAQ (Sirius, DewE‑43)
Use the DewesoftX Human Vibration module to measure weighted RMS, peak, crest, VDV, MSDV, MTVV, SEAT transmissibility, lumbar response, and dose metrics per ISO standards

Configure whole‑body and hand–arm measurement modes, select appropriate frequency-weighted filters (Wb, Wk, Wh, custom), and adjust sampling rates and logging intervals
Monitor daily vibration exposure (A(8) value), apply Palmgren‑Miner accumulation logic, and compare results with EU Exposure Action/Limit Values
Test real-world use cases—e.g. motorcycle seat vibration, handhold tool exposure—with live monitoring and offline analysis

Course overview

This course comprehensively covers human vibration measurement using DewesoftX, following the ISO 2631, 8041, and 5349 standards. You’ll begin by learning vibration fundamentals and body-related health risks—from white finger and lumbar damage to motion-induced nausea—supported by exposure action and limit thresholds.

You’ll then configure the Human Vibration module: install seat‑pad or hand‑arm adapters, define triaxial accelerometer inputs, select measurement modes and filtering profiles (whole‑body vs hand‑arm), and use high-resolution Dewesoft DAQ for high-fidelity signal capture . Live displays will show weighted RMS, peak, crest factor, VDV, MSDV, MTVV, and frequency-weighted values per axis.

Advanced sessions explore practical applications: calculating SEAT transmissibility by comparing seat and floor acceleration, assessing lumbar spine responses, and deriving daily A(8) exposure values using interval logging . You’ll also monitor multi-day exposure with ISO-compliant dose computations.

By the end of the training, you’ll be able to design and deploy vibration tests, collect compliant measurements, analyze data in DewesoftX, and evaluate worker exposure against regulatory thresholds—empowering improved health, safety, and ergonomic outcomes.

Human vibration and why we need to measure it

Human vibration is defined as the effect of mechanical vibrations from the environment on the human body. In daily life, we are exposed to various sources of vibration, such as buses, trains, and cars. Many people are also exposed to additional vibrations during their workday, for example, vibrations produced by hand tools, machinery, or heavy vehicles.

Human vibration can be pleasant, unpleasant, or harmful. Gentle vibrations—such as those experienced when sitting in a rocking chair, dancing, or running—are generally pleasant. Stronger vibrations, for example, those experienced when traveling by car over a bumpy road or when operating a power tool, may be unpleasant or harmful. The harmfulness of vibration depends on its intensity, frequency content, and duration of exposure.

In workplaces with high vibration exposure, there is a significant risk of permanent damage to parts of the human body. One effect is known as Raynaud's disease, or the "white finger" effect, where fingers lose color and become painful. Another common effect of prolonged work with heavy machinery or vehicles (such as helicopters) is damage to the lumbar region.

The harmful effects of vibration on human health represent a serious problem. Mechanical vibrations transmitted from power tools and other vibrating devices to the human body may negatively affect tissues and blood vessels, stimulate vibrations in internal organs or body parts, and even impact cellular structures.

Hand-arm vibration is considered the most dangerous type, as it is transmitted to the upper parts of the body and can cause pathological changes in the nervous, vascular (cardiovascular), and osteoarticular systems. Changes in the human body caused by mechanical vibrations are recognized as an occupational disease, referred to as vibration syndrome. Three forms of this disease are identified: neurovascular, osteoarticular, and mixed.

According to 2008 data, the percentage of vibration syndrome among all occupational diseases was: 2.9% in forestry, 5.6% in mining, 4.3% in metal production, and as high as 8.7% in construction.

The Human Vibration Module provides measurements that help assess the risk of vibration-related damage. It is based on several ISO standards: ISO 2631-1 (1997), which defines basic procedures; ISO 8041 (2017), which specifies exact procedures for measurements; and ISO 2631-5 (2018), which defines the evaluation of human exposure to whole-body vibration.

There are two main types of measurements:

Whole-body measurements – performed using a so-called seat sensor, where a triaxial sensor is installed in a rubber adapter on which the subject sits.
Hand-arm measurements – performed by attaching sensors to special adapters designed for mounting them on tool handles or between fingers.

Both types of measurements are carried out using triaxial accelerometers (commonly 50 g sensors) with special adapters. For workplaces with high vibration levels (for example, impact hammers), high-g sensors (500 g or more) are required. These sensors must also withstand strong shocks.

For accurate measurement, several ICP channels with a 24-bit sigma-delta A/D card (e.g., Sirius or Dewe-43) are needed.

In theory, measurements should cover a full working day with all significant loads. In practice, shorter intervals are often used, but care must be taken to ensure that all significant vibration patterns are properly captured.

Several parameters must be calculated:

RMS (Root Mean Square) – a statistical measure of the magnitude of a weighted signal
Peak – the maximum deviation of the signal from the zero line
Crest Factor – the ratio between the peak and the RMS
VDV (Vibration Dose Value) – the fourth-power vibration dose value
MSDV (Motion Sickness Dose Value) – a measure of vibration effects leading to motion sickness
MTVV (Maximum Transient Vibration Value) – calculated over a one-second interval

Measuring human vibration

Vibrations can sometimes be desirable, perceived as pleasant, or provide useful feedback about ongoing processes. However, just as often, they are undesirable, irritating, cause stress, induce panic, and may lead to physical reactions such as sweating, nausea, and vomiting. While these can be extremely unpleasant experiences that strongly influence a person’s life and mental state, for most people the effects of vibrations are only temporary. Once exposure to vibration stops, the physical effects usually disappear over time.

The physical effects of vibrations on the human body, however, may also be permanent. The risk of irreparable injuries is particularly high in occupational settings, where vibration magnitudes can be substantial, exposure times long, and exposure may occur regularly or even daily. Typical risk groups include drivers of lorries, trucks, agricultural and forestry machinery, construction machinery, pilots of certain helicopters, and workers operating hand-fed or hand-held power tools, or guiding machines and holding workpieces. During such work, the whole body—or specific regions, especially the hand-arm area—may be exposed to excessive vibrations.

Unfortunately, the relationship between vibration exposure and health damage is often not obvious. Injuries may develop over long periods of time, and other activities, such as lifting heavy loads, may also contribute to conditions such as lower back pain. A worker may feel numbness or fatigue after a day of exposure to intense vibrations, but initially, these effects are temporary and seem to disappear the next day. However, once they become permanent—such as cold fingers or chronic back pain—it is often too late. Many of these injuries are irreversible.

It is therefore of utmost importance to prevent excessive vibration exposure. In Europe, the Vibration Directive (Directive 2002/44/EC) was introduced to set minimum standards for controlling risks from both hand-arm and whole-body vibrations. The directive defines action values (above which employers must control vibration risks) and limit values (above which workers must not be exposed).

Hand-arm vibration values:

Daily exposure action value: 2.5 m/s²
Daily exposure limit value: 5 m/s²

Whole-body vibration values:

Daily exposure action value: 0.5 m/s² (or, at the discretion of the EU Member State, a vibration dose value of 9.1 m/s)
Daily exposure limit value: 1.15 m/s² (or, at the discretion of the EU Member State, a vibration dose value of 21 m/s)

Employers are obliged to determine and assess the risks resulting from both hand-arm and whole-body vibrations and ensure that exposure values are not exceeded. If analysis suggests that workers are at risk, employers must implement a management program to minimize vibration exposure and prevent injury development or progression.

At the first stage, analysis can be based on emission values—data describing vibration magnitudes when operating or working with a particular tool, vehicle, or machine. Such data are often provided by manufacturers or may be found in databases maintained by independent organizations and institutes. However, employers must be aware that these values are determined using harmonized codes and standards, intended primarily for comparing similar products. In practice, vibration levels under real working conditions may be significantly higher.

Reasons for this discrepancy include wear, rough road surfaces, operating vehicles or machinery on sloped terrain, and other real-world factors. Therefore, on-site measurements are strongly recommended to validate and verify that the actual vibration levels in context do not exceed manufacturer specifications.

Whether data are obtained from databases or from on-site measurements, it is essential to perform a detailed analysis of precise exposure times for each specific workplace. This is crucial not only for calculating actual daily vibration exposure but also for providing accurate data to guide strategies for reducing exposure and minimizing risk.

Measured parameters

To determine a person's vibration exposure, it is necessary to collect information about both the vibration magnitude and the duration of the various working processes—that is, how long and how often the person is exposed to vibrations of a certain type and magnitude.

Vibration magnitude

Vibration magnitude can be expressed in terms of acceleration, velocity, or displacement observed during a vibration process. All three are relevant, as the human body responds to each of them differently depending on the frequency of motion.

An example of acceleration, displacement and velocity signal in a frequency domain

However, in many standards related to the measurement of human vibration, acceleration is the agreed-upon quantity for expressing magnitudes. This is primarily a matter of convenience, since the classical vibration sensor—the accelerometer—delivers a signal proportional to acceleration.

In general, accelerometer signals are filtered and frequency-weighted before further processing. Filtering is applied because the analysis should only include those frequencies considered important for hand-arm or whole-body vibration. Furthermore, the included frequencies are weighted differently to reflect the likelihood of damage from vibrations at specific frequency ranges.

The choice of weighting depends on where the measurement is taken (e.g., feet, seat, backrest, palms) and in which direction it is applied (e.g., front-to-back vs. side-to-side). This distinction is necessary because the human body reacts differently depending on the point of entry and direction of vibration. For example, the fore-and-aft motion of a seated person differs significantly from side-to-side motion in the same person.

The purpose of subsequent analysis is to quantify the acceleration appropriately. Typically, the time-averaged weighted acceleration value—a frequency-weighted root mean square (RMS) of the vibration signal—is determined and reported. In the context of human vibration, this value represents the average amount of vibration energy that enters the human body.

RMS vibration magnitude is a good representation of processes where vibrations are continuous or intermittent rather than shock-like. Tools such as drilling machines, chainsaws, and vibrating plate tampers fall into this category. Even impact wrenches can be well described using RMS vibration magnitude, even though each individual operation cycle (e.g., tightening a single nut or a series of tightenings) may last only a few seconds. Whole-body vibrations, such as driving a bus or lorry on a well-maintained road or sitting in a train or other railway transport, are also effectively described with an RMS value.

However, care must be taken when analyzing shocks and processes with transients (i.e., sudden changes in acceleration), particularly for whole-body vibrations. For example, a vehicle driving over bumps in the road or construction machinery in operation (e.g., cutting and loading trees or crushing concrete) may cause shock-like vibrations. For such events, averaging over time periods much longer than the event’s duration (e.g., calculating RMS over the entire working day) would fail to capture the critical aspects of the problem. The intensity (magnitude) of a single shock, a few shocks, or sudden changes in acceleration may exceed what the human body can tolerate, but if averaged over a long period, their importance would be overlooked. Therefore, it is essential to examine the total energy of the event and the maximum vibration values reached during operation.

Better descriptors for these scenarios are the Vibration Dose Value (VDV)—a cumulative measure that sums the energy instead of calculating an average—and the Maximum Transient Vibration Value (MTVV), which is defined as the maximum of the so-called running RMS acceleration value, calculated with a 1-second integration time.

Since MTVV is based on a short integration interval, it highlights the highest vibration magnitudes to which a worker is exposed. This parameter is especially useful when logged at short intervals (e.g., 1 s), as the logging profile quickly shows whether large vibration magnitudes were exceptions, occurred frequently, or were constant.

VDV, on the other hand, is well suited to reflect total exposure. It accumulates the vibration energy to which the worker is exposed, thereby giving more weight to peaks and sudden changes in acceleration.

Duration

For a correct assessment of human vibration exposure, a precise determination of duration is just as critical as an accurate determination of magnitude. The estimation should be based on detailed observation of the working process. A stopwatch or video recording may be used to capture the duration of operations that generate vibration exposure. Additionally, worker interviews should be conducted.

When determining exposure duration, it is important to consider the measurement approach used for vibration magnitude. Some operations can be consistent over periods of one or more hours (e.g., operating a vibrating plate tamper or driving a lorry). Other operations are intermittent or change rapidly (e.g., using chainsaws or operating forklifts). Finally, for some tools, a single operation cycle may last only a few seconds (e.g., impact wrenches).

In general, two approaches can be followed:

Measure only during exposure.
Each measurement reflects the vibration magnitude for a specific machine or vehicle operating in a particular mode (e.g., a chainsaw idling, trimming branches, or cutting through large stems; or a lorry driving on smooth roads, in stop-and-go city traffic, or on rough surfaces in a sandpit). In this case, the exposure duration used in the analysis should include only the periods when the worker is truly exposed to vibrations from the machine, workpiece, or vehicle.
Measure the entire working process, including breaks.
A single measurement covers different modes of operation as well as pauses, tool shifts, or breaks. This provides an average exposure over an entire working day or process. Here, the duration entered into the exposure analysis is the total time, including both vibration exposure and non-exposure periods.

Both approaches have advantages and disadvantages. The first method requires a detailed study of working processes and verification through observation, as workers often overestimate exposure time (reporting how long they operate or hold a machine rather than the actual period of vibration emission). The second method is easier but lacks detail—averaging conceals which operations or conditions are responsible for the exposure, making it harder to identify specific improvements. Additionally, irrelevant events, such as putting down a tool or a driver rising from a seat, may inflate recorded vibration magnitudes, even though they do not reflect actual exposure.

Whole-body vibration measurement

Human exposure to whole-body vibration should be evaluated according to the method defined in ISO 2631-1. Whole-body vibration refers to motions transmitted from workplace machines and vehicles to the human body through a supporting surface. For health and safety evaluations, this occurs through the buttocks and feet of a seated person or the feet of a standing person.

When performing whole-body measurements, it is preferable to measure over the entire exposure period. If that is not possible or necessary, measurements should cover at least 20 minutes. Where shorter measurements are required, they should last at least three minutes and be repeated until the total measurement time exceeds 20 minutes. Longer measurements of two hours or more are preferable, and in some cases, half- or full-day recordings are possible.

For whole-body vibration assessment, acceleration should be measured at the seat surface for a seated person or beneath the feet for a standing person. The accelerometer should be placed in a Seat Pad, preferably fixed to the floor or seat using tape or a strap. This ensures that the accelerometer remains in the correct position and can withstand any posture changes by the operator. To obtain correct results, the Seat Pad must be loaded during measurement by the worker, who should stand or sit on it.

The following parameters of the frequency-weighted acceleration should be measured simultaneously in all three directions: RMS vibration magnitude, Peak value, MTVV, and VDV. The Z-direction is always aligned with the main body axis (i.e., vertical to the seat and floor plane for measurements at the feet or seat). The X-direction corresponds to fore-and-aft motion, while the Y-direction corresponds to side-to-side motion.

Unlike hand-arm vibration assessment, the frequency weightings differ for the X, Y, and Z directions. For health risk evaluations, ISO 2631-1 specifies the use of Wk weighting for the Z-direction, and Wd weighting for the X- and Y-directions.

Whole-body vibrations are typically measured using a seat sensor, where a triaxial sensor is installed in a rubber adapter on which the person sits. It is essential that the Z-axis remains vertical, as it is weighted differently from the X- and Y-axes.

Vibration should always be evaluated by measuring the weighted vibration acceleration. The Crest factor determines the appropriate method for vibration evaluation. If the crest factor is high (greater than 9), the vibration should be evaluated using running RMS or VDV. For comfort and health risk assessment, using the vector sum (total vibration value) is recommended, especially when vibrations in two or three axes are comparable.

For assessing occasional shocks and short-term vibrations, the running RMS method is applied. In this case, the maximum value during the observation period is called MTVV, defined as the maximum instantaneous vibration magnitude. Vibration transmitted to the human body should always be measured at the interface point between the body and the vibrating surface. For a seated person, this would be the seat, seat back, or the floor beneath the feet.

Vibration should be measured according to the axis directions, which start at the point of human contact with the vibrating surface. The Z-axis should be aligned with the orientation of the body, meaning it does not necessarily have to be vertical. The direction of the measurement axes must always be clearly specified in the report.

The duration of the measurement must be sufficient to ensure statistical accuracy and should reflect typical vibration exposure. The measurement time itself should also be included in the report. The health of seated persons is most affected by vibrations in the frequency range of 0.5 Hz to 80 Hz. Measurements should be performed using the appropriate frequency weightings: Wk for the Z-axis and Wd for the X- and Y-axes. Because horizontal vibrations are generally more harmful, the weighting coefficients should be 1.4 for X and Y and 1.0 for Z. The weighted RMS should be assessed in all three directions at the seat surface. In special cases, other weightings, such as Wc, Wf, We, or Wj, may be required.

Whole-body vibration should be evaluated based on the daily vibration dose, A(8), expressed as the equivalent frequency-weighted acceleration over an eight-hour period. This value is calculated as the highest RMS or VDV measured across the three axes (X, Y, Z).

Based on the frequency-weighted acceleration signals, the daily vibration exposure is determined by calculating the exposure for each of the three axes separately and then selecting the highest of the three values. To achieve this, an additional factor, ki, must be applied to the measured vibration values. For the X- and Y-directions, the factor is 1.4, while for the Z-direction, the factor is 1.0.

A_x(8)=a_{wx} \cdot 1.4 \sqrt{\frac{T_{exp}}{T_0}}

A_y(8)=a_{wy} \cdot 1.4 \sqrt{\frac{T_{exp}}{T_0}}

A_z(8)=a_{wz} \cdot 1.0 \sqrt{\frac{T_{exp}}{T_0}}

The highest of these three values will represent the daily vibration exposure.

A(8) = max\{A_X(8),A_y(8),A_z(8)\}

This procedure differs significantly from the one used to determine hand-arm vibration exposure, where the three axes are combined into a single total vibration value. However, according to ISO 2631-1, Section 6.5, a total vibration value may be used if no dominant axis of vibration can be identified. The total vibration value for whole-body vibration is calculated using the following equation:

a_v=\sqrt{k^2_x a^2_{wx}+k^2_ya^2_{wy} +k^2_za^2_{wz}}

In some countries, different exposure limit values are specified for different axes. This can create a paradox: while the axis with the largest exposure value may not be considered critical, another axis with a smaller exposure value could still exceed its limit. Consequently, a report based solely on the axis with the highest value might indicate no risk, even though the limit has been violated for another axis.

If a worker is exposed to more than one source of vibration, the partial vibration exposure Aj,i(8) for each axis and operation i must first be calculated:

A_{x,i}(8)=a_{wx,i} \cdot 1.4 \sqrt {\frac {t_{exp}}{T_0}}

A_{y,i}(8)=a_{wy,i} \cdot 1.4 \sqrt {\frac {t_{exp}}{T_0}}

A_{z,i}(8)=a_{zy,i} \cdot 1.4 \sqrt {\frac {t_{exp}}{T_0}}

The partial vibration exposures are then summed separately for each of the three axes, and the total daily vibration exposure is determined as the maximum of these three sums:

\left. \begin{array}{cc} A_x(8)=\sqrt{A_{x,1}^2 (8)+A^2_{x,2}(8) + ...+A^2_{x,n}(8)} \\ A_y(8)=\sqrt{A_{y,1}^2 (8)+A^2_{y,2}(8) + ...+A^2_{y,n}(8)} \\ A_z(8)=\sqrt{A_{z,1}^2 (8)+A^2_{z,2}(8) + ...+A^2_{z,n}(8)} \end{array} \right\} A(8)=max \{A_x(8),A_y(8),A_z(8) \}

The total daily vibration dose, A(8), is appropriate when the vibration history is relatively smooth and free of shocks or sudden changes or peaks in acceleration. However, when driving a vehicle over rough surfaces, such as those found on construction sites or in sandpits, shock-like events may occur, and an assessment based on RMS values may no longer be adequate.

To account for such transients, the fourth-power vibration dose value (VDV) was developed. Unlike RMS vibration magnitude, the measured VDV is cumulative and increases with the measurement duration. Therefore, it is important for any VDV measurement to specify the period over which the value was obtained. Moreover, because of the fourth-power calculation, transients and peaks are given greater weight during integration. If the measurement duration is shorter than the estimated exposure time, the measured VDV must be extrapolated to represent the actual exposure period:

VDV_{exp,x}=VDV_x \cdot 1.4(\frac{T_{exp}}{T_{meas}})^{1/4}

VDV_{exp,y}=VDV_y \cdot 1.4(\frac{T_{exp}}{T_{meas}})^{1/4}

VDV_{exp,z}=VDV_z \cdot 1.0(\frac{T_{exp}}{T_{meas}})^{1/4}

Where Tmeas is the measurement period and Texp is the full expected exposure time. Note again the k-factors (1.4, 1.4, and 1.0). Furthermore, if a person is exposed to more than one vibration source, the total VDV should be calculated from the partial vibration dose values for each axis:

\left. \begin{array}{cc} VDV_x=(VDV^4_{x,1}+VDV_{x,2}^4+...+ VDV_{x,n}^4)^{1/4} \\ VDV_y=(VDV^4_{y,1}+VDV_{y,2}^4+...+ VDV_{y,n}^4)^{1/4} \\ VDV_z=(VDV^4_{z,1}+VDV_{z,2}^4+...+ VDV_{z,n}^4)^{1/4} \end{array} \right\} (dailyVDV)=max \{VDV_x. VDV_y, VDV_z\}

The highest of the three individual VDVs represents the daily VDV.

Another useful parameter when investigating human vibration with transients is the running RMS. It has a short integration time of 1 second and is therefore well suited to indicate the magnitude of short-duration events. The maximum transient vibration value (MTVV) represents the maximum running RMS value observed during a single measurement period.

ISO 2631-1 provides guidelines on when it is recommended to consider VDV, running RMS, and MTVV instead of the vibration magnitude (aw):

CF=\frac{Peak}{RMS}\gt 9

MTVV should be considered in addition to RMS.

\frac{MTVV}{RMS} \gt1.5

VDV should be considered in addition to RMS.

\frac{MTVV}{RMS \cdot T^{1/4}} \gt1.75

If one of these conditions is met, it indicates that the vibration history contained peaks significantly above the general average vibration level.

The ratio between the peak value and the RMS vibration magnitude—known as the crest factor (CF)—is considered an uncertain criterion, as the peak may have occurred at a different time, possibly minutes or even hours before or after the vibration event that determined the RMS.

Hand-arm vibration measurement

The second application is the measurement of hand-arm vibration, where the sensors are installed on special adapters that allow them to be mounted on a handle or positioned between the fingers. In this case, the orientation of the sensor is not important since all three axes have the same weighting.

Hand-arm vibration is experienced through the hands and arms. Daily exposure to hand-arm vibration over several years can cause permanent physical damage, often resulting in what is commonly known as white finger syndrome. It can also damage the joints and muscles of the wrist and/or elbow.

Measurement of hand-arm vibration applies to three main situations:

When the operator's hands are in direct contact with the surface of a vibrating machine (e.g., steering wheel or handle).
When the operator feeds material into a machine, through which vibrations are transmitted to the hand (e.g., woodcutting).
When the operator holds a vibrating device directly (e.g., drills, pneumatic hammers).

Typical vibration exposure consists of short periods during which the operator is in contact with the tool. Therefore, it is recommended to perform several short measurements rather than one long measurement. For each task, measurements should be taken at least three times, and the results averaged. The total measurement time should be at least one minute. Measurement blocks shorter than 8 seconds should be avoided, as they do not accurately capture low-frequency content.

The fundamental quantity used in evaluating hand-arm vibration is the vector sum, known as AEQ, which forms the basis for calculating daily exposure.

To determine daily exposure, it is necessary to identify all sources of vibration. This includes recognizing all working modes of tools (e.g., drilling with and without a hammer) and variations in operating conditions. Such information is crucial for proper measurement planning, ensuring that as many common operator tasks as possible are included. Daily exposure should be calculated for each identified source of vibration.

Vibration sources for hand-arm vibrations

The next step is to choose how to mount the accelerometer. Hand-arm vibration should be measured in place, at the exact point of contact with the hand tool. The best location is the center of the handle, as it provides the most representative measurement—provided that the position does not interfere with task performance.

The accelerometer should be rigidly attached to the vibrating surface. Measurements directly at the hand are performed using special adapters. For some power tools, it is also recommended to take measurements on both sides of the hand.

The mounting location should always be documented in the measurement report. The measurement time should reflect a representative tool operation period. Measurement should begin the moment the operator touches the vibrating device and end when contact is broken or when the vibration stops.

If the actual contact time is very short, the measurement period may be artificially extended to better estimate vibration exposure during tool use.

Measuring hand-arm vibrations with an accelerometer attached to the device

In the event that the device generates a sudden shock, the measurement should include the shock itself as well as the appropriate length of time before and after the occurrence. It is also important to determine the number of shocks per shift. The minimum measurement period depends on the vibration signal, tools, and activities. However, the total measurement time should not be less than one minute. Measurements shorter than eight seconds are considered unreliable, particularly for assessing low-frequency content, and should therefore be avoided.

If it is not possible to measure for longer than one minute in a single run, multiple measurements should be taken and combined to achieve a total duration of at least one minute. Typical exposure time is calculated based on the relevant exposure during the complete task, or over a representative 30-minute period of typical work, along with information about the work cycle (number of cycles per shift). Exposure time can be determined using a timer, the analyzer, or by analyzing video recordings.

A three-axis measurement is recommended. If this is not possible, measurement along one dominant axis is acceptable.

ISO 5349-1:2001 recommends determining the frequency-weighted RMS acceleration in three directions: along the axis of the arm and in two perpendicular directions within the plane between the hand and grip. The most accurate method is to use a miniature triaxial accelerometer, which measures vibration in all three directions at the same point while adding only a few grams of transducer mass.

When reporting root mean square values of acceleration in human vibration, ISO standards use lowercase a. The frequency range analyzed is 8–1000 Hz. Frequency weighting Wh is applied for all three axes, even though the anatomy—and thus the sensitivity—of the hand-arm system differs along the arm and in the transverse direction.

The three frequency-weighted acceleration components are denoted as ahwx, ahwy, and ahwz. These are then combined into the so-called vibration total value, ahv, which is calculated as the root-sum-of-squares of the three components:

a_{hv}=\sqrt{(k_xa_{hwx})^2+(k_ya_{hwy})^2+(k_za_{hwz})^2}

In contrast to whole-body vibrations, when calculating the root-sum-of-squares for hand-arm vibrations, all axes are theoretically multiplied by the same weighting factor, k = 1.0. Typically, to simplify the equations, these factors are omitted.

The daily vibration exposure, A(8), is then calculated from this vibration total value:

A(8)=a_{hv}\sqrt{\frac{T_{exp}}{T_0}}

Where T₀ is the reference duration of 8 hours, and Texp is an estimate of the time that the tool operators are exposed to vibration, or the duration of the entire operation including breaks. If a person is exposed to more than one source of vibration, a partial vibration exposure, Ai(8), for each operation i must be calculated:

A_i(8)=a_{hv,i}\sqrt{\frac{T_{exp,i}}{T_0}}

The partial vibration exposure values are then combined to determine the overall daily exposure value, A(8), for that person:

A(8)=\sqrt{A^2_1(8)+A^2_2(8)+...+A^2_n(8)}

Exposure point system

The measurement engineer, or any other professional regularly dealing with vibration measurements, will easily develop a good understanding of quantities such as the daily vibration exposure value (A(8)) and VDV. However, for a layperson, exposures expressed in units such as m/s² are usually difficult to grasp. If this person must make decisions based on such quantities, those decisions may become unnecessarily difficult.

To simplify decision-making, a more intuitive way to express daily vibration exposure A(8) has been introduced: exposure points. For the user or decision-maker, expressing exposure with the point system offers two main advantages:

The point system avoids units. The critical vibration magnitudes for hand-arm and whole-body vibrations differ (the hand-arm system can cope with larger magnitudes). In contrast, the exposure point system is defined so that, in both cases (hand-arm and whole-body vibrations), the exposure action value is reached at 100 points.
Exposure points are easy to combine. Once exposure is expressed in points, there is no need for complicated power laws. Exposure points are simply added together. If a worker is exposed to several vibration sources, the total number of exposure points is the sum of the points for each source. This also means that exposure points change proportionally with time: twice the exposure time equals twice the number of points.

For hand-arm vibrations, exposure points are calculated for the combined three axes as follows:

P_E= \biggl(\frac{a_{hv}}{2.5 m/s^2}\biggl)^2 \frac{T_{exp}}{T_0}100

Where ahv is the vibration total value (RMS VTV), Texp is the exposure time in hours, and T0 is the reference duration of 8 hours. Note that a vibration magnitude of 2.5 m/s² corresponds to the action value for hand-arm vibrations.

As a result, the conversion between A(8) and PE is defined so that exposures equal to the action value (2.5 m/s² A(8)) correspond to 100 points, while exposures equal to the limit value (5 m/s² A(8)) correspond to 400 points.

It is also possible to directly convert between A(8) and PE:

P_E=A(8)^2 \frac{100}{(2.5 m/s^2)^2}

For whole-body vibrations, exposure points are calculated separately for each of the three axes, as follows:

P_{E,j}= \biggl(\frac{k_ja_{wj}}{0.5 m/s^2} \biggl)^2 \frac{T_{exp}}{T_0}100

Where kj is the weighting factor for the X, Y, or Z-axis respectively; awj is the vibration magnitude (RMS value) of the X, Y, or Z-axis; Texp is the exposure time in hours; and T0 is the reference duration of 8 hours. Note that a vibration magnitude of 0.5 m/s² corresponds to the action value for whole-body vibrations. In the case of whole-body vibrations, the conversion between A(8) and PE is defined such that an exposure action value of 0.5 m/s² equals 100 points, while the exposure limit value of 1.15 m/s² equals 529 points.

To directly convert between A(8) and PE:

P_{E}= A(8)^2 \frac{100}{(0.5 m/s^2)^2}

Measurement of seat effective amplitude transmissibility - SEAT

The determination of Seat Effective Amplitude Transmissibility (SEAT) does not directly provide information about human exposure to vibration. Instead, the goal of this measurement is to assess the capability of a seat design to attenuate the vibrations present in a vehicle, thereby protecting the driver from excessive vibration.

The measurement involves determining the vibration magnitude at two positions:

On the seat pan
Directly on the floor of the vehicle, beneath the seat

Measurements at these two points are taken simultaneously, and SEAT is then computed as the ratio between these two magnitudes. To express SEAT, one may use the frequency-weighted RMS vibration magnitudes (aw) or the VDVs. Furthermore, instead of presenting only the ratio (the SEAT factor), the result can be multiplied by 100 to express the seat’s effective vibration amplitude as a percentage.

Whether to use RMS or VDV depends on the type of vibrations encountered during the measurement. If the vibration history is relatively smooth, the RMS vibration magnitude is preferable. However, if the vibrations include transients and shocks, it is recommended to compute SEAT using VDVs.

SEAT_{RMS}=\frac{a_{w,seat}}{a_{w,floor}}

SEAT_{VDV}=\frac{VDV_{seat}}{VDV_{floor}}

SEAT \% =SEAT \times 100

A seat improves ride comfort when the SEAT value is smaller than 1, or, expressed as a percentage, when SEAT% is less than 100%. If the value exceeds these limits, the seat actually amplifies vibrations and thereby worsens ride comfort.

For health risk assessment, the frequency weighting used for SEAT measurements is the same as that used for whole-body vibration measurements.

When assessing a seat’s ability to attenuate vibrations, it is important to consider the seat and driver as a single system. The driver adds mass to the seat, which preloads the seat springs and changes the resonance behavior. Furthermore, depending on posture, the seat–driver combination can result in a stiffer or less stiff system (e.g., vibrations differ when the driver sits in a relaxed position compared to when the feet are pressed firmly against the floor).

Thus, depending on the driver’s body and posture, seat performance can vary significantly. As a result, multiple measurements with different drivers and postures should be performed to obtain a complete picture.

Standards for laboratory SEAT measurements specify exact test masses, seat adjustments, and detailed procedures, including steps such as warming up the seat. However, the main focus in practice should be the assessment of SEAT factors under real working conditions, with actual workers and without warm-up times. SEAT assessment standards may and should be consulted, as they provide valuable guidance.

Lumbar spine measurement

The adverse health effects of prolonged exposure to vibration, including multiple shocks, are related to dose measures.

The method described in ISO 2631 is generally applicable in cases concerning adverse health effects in the lumbar spine.

The calculation of the lumbar spine response in ISO 2631 assumes that the person subjected to vibration is seated in an upright position and does not voluntarily rise from the seat during exposure. Different postures can result in different spinal responses.

Predictive models are used to estimate lumbar spine accelerations (aIx,aIy,aIza_{Ix}, a_{Iy}, a_{Iz}aIx,aIy,aIz) in the x, y, and z directions, based on accelerations measured at the seat pad (aSx,aSy,aSza_{Sx}, a_{Sy}, a_{Sz}aSx,aSy,aSz) along the same bicentric axes.

The determination of the spinal response acceleration dose involves the following steps:

Calculation of the human response
Counting the number and magnitudes of peaks
Calculation of an acceleration dose by applying a dose model related to the Palmgren-Miner fatigue theory

In the x- and y-axes, the spinal response is approximately linear and can be represented by a single-degree-of-freedom (SDOF) lumped-parameter model, with the following characteristics:

Natural frequency, fn=2.125f_n = 2.125fn=2.125 Hz (ωn=13.35\omega_n = 13.35ωn=13.35 rad/s)
Critical damping ratio, ζ=0.22\zeta = 0.22ζ=0.22

The lumbar spine response, aIka_{Ik}aIk in [m/s²], is calculated using the equation of motion of an SDOF system.

a_{Ik}=2\zeta \omega(v_{Sk}-v_{Ik})+\omega^2_n (s_{Sk}-s_{Ik})

- k is either x or y.
- sSks_{Sk}sSk and sIks_{Ik}sIk are the displacement time histories in the seat and in the spine.
- vSkv_{Sk}vSk and vIkv_{Ik}vIk are the velocity time histories in the seat and in the spine.
The values for the SDOF resonance frequency and damping ratio given above result in the following multipliers: 2ζwn=5,87s−12=5,87−1 and w2n=178s−22=178−2.

Spinal response in a vertical direction

In the z-direction, the spinal response is nonlinear and is represented by a recurrent neural network model.

The lumbar spine z-axis acceleration, aIza_{Iz}aIz (in [m/s2][m/s^2][m/s2]), is predicted using the following equations:

a_{Iz}(t)= \sum^7_{j=1}W_ju_j(t)+W_8

u_j(t)=tanh \bigg[\sum^4_{i=1}w_{ji}a_{Iz}(t-i)+ \sum^{12}_{i=5}w_{ji}a_{Sz}(t-i+4)+w_{j13}

The model coefficients are specific to a sampling rate of 160 samples per second. Therefore, data collected at a different sampling rate must be resampled to 160 samples per second.

The z-axis model coefficients for the equation of aIza_{Iz}aIz are as follows:

Calculation of acceleration dose

The acceleration dose, DkD_kDk [m/s²], in the kkk-direction is defined as:

D_k = \bigg[\sum_{i}A_{ik}^6 \bigg]^{1/6}

Aik is the i-th peak of the response acceleration aik(t)a_{ik}(t)aik(t).
k=x,y,k = x, y,k=x,y, or zzz.
A peak is defined here as the maximum absolute value of the response acceleration between two consecutive zero crossings. For the x and y directions, peaks in both positive and negative directions shall be counted. For the z direction, only positive peaks shall be counted, as compression of the spine is of primary interest in assessing exposure severity.
When calculating the dose, peaks with magnitudes considerably lower (by a factor of three or more) than the highest peak will not significantly contribute to the value associated with the 6th power term and may therefore be neglected.
For the assessment of health effects, it is useful to determine the average daily dose, DkdD_{kd}Dkd, in metres per second squared (m/s2m/s^2m/s2), to which a person is exposed. This is calculated using the following equation:

D_{kd}=D_k \bigg[\frac{t_d}{t_m}\bigg]^{1/6}

td is the duration of the daily exposure.
tmt_mtm is the period over which DkD_kDk has been measured.
The equation for DkdD_{kd}Dkd may be used when the total daily exposure can be represented by a single measurement period. However, when the daily vibration exposure consists of two or more periods of different magnitudes, the acceleration dose, expressed in metres per second squared (m/s2m/s^2m/s2), for the total daily exposure shall be calculated as follows:

D_{kd}=\bigg[ \sum^n_{j=1}D^6_{kj} \frac{t_{dj}}{t_{mj}}\bigg]^{1/6}

tdj is the duration of the daily exposure to condition jjj.
tmjt_{mj}tmj is the period over which DkjD_{kj}Dkj has been measured.

Flowchart for calculation of the acceleration dose

Flowchart for calculation of acceleration dose

Relationship between acceleration dose and health effects

This guidance applies to people in normal health who are regularly exposed to vibrations containing multiple shocks. Individuals with pre-existing spinal disorders, including latent osteoporosis or other spinal conditions, may be more susceptible to injury. The guidance in this part of ISO 2631 applies to the rectilinear x, y, and z basicentric axes of the human body. It does not apply to high-magnitude single-event shocks, such as those resulting from a traffic accident that causes trauma.

It is assumed that multiple shocks cause transient pressure changes at the lumbar vertebral endplates, which, over time, may result in adverse health effects arising from material fatigue processes. Essential exposure-related factors include the number and magnitude of peak compressions in the spine. These peak compressions are influenced by anthropometric data (body mass, endplate size) and posture.

Adverse health effects of long-term whole-body multiple-shock exposure include an increased risk of damage to the lower lumbar spine and the associated nervous system segments. Excessive mechanical stress and/or impaired nutrition and diffusion to the disc tissue may contribute to degenerative processes in the lumbar segments. Multiple shocks and vibration exposure may also exacerbate certain endogenous pathological disturbances of the spine.

For evaluating the effects of internal pressure changes, the Palmgren-Miner approach is applied. Experimental data show that the Palmgren-Miner exponent varies with biological tissue type and test methodology: from 5 to 14 for cortical and trabecular bone, and up to 20 for cartilage. For estimating adverse health effects, a conservative exponent of 6 has been selected here.

The relationship between predicted pressure changes and the predicted total tolerance of the exposed individual can be used to assess the potential risk of adverse health effects. The predicted response refers to the bony vertebral endplate (hard tissue). This assessment is based on an upright posture. A forward-bending or twisting posture is likely to increase the severity of adverse health effects.

Assessment of health effects

Using a biomechanical model based on experimental data, it has been shown that there is a linear relationship between the portion of compressive stress caused by input shocks and the peak acceleration response in the spine. The equivalent static compressive stress, Se, in megapascals, is calculated as follows:

S_{e}=\bigg[ \sum_{k=x,y,z}(m_kD_k)^6\bigg]^{1/6}

Recommended values of mk are:

mx = 0,015 MPa/(m/s2)
my = 0,035 MPa/(m/s2)
mz = 0,032 MPa/(m/s2)

The daily equivalent static compression dose, Sed, is obtained by normalizing Dk to the acceleration dose Dkd for the average daily exposure time.

S_{ed}=\bigg[ \sum_{k=x,y,z}(m_kD_kd)^6\bigg]^{1/6}

In general, a factor R can be defined for use in the assessment of adverse health effects related to the human response acceleration dose. R should be calculated sequentially, taking into account increased age (and reduced strength) as the exposure time increases. It is defined as follows:

R=\bigg[ \sum^n_{i=1}\bigg(\frac{S_{ed} \cdot N^{1/6}}{S_{ui}-c} \bigg)^6\bigg]^{1/6}

- N is the number of exposure days per year
- i is the year counter
- n is the number of years of exposure
- c is a constant representing the static stress due to gravitational force
- Sui is the strength of the lumbar spine for a person of age (b+i) years
- b is the age at which the exposure starts
A value of c = 0.25 MPa can normally be used for driving posture.
The value of Sui varies with the bone density of the vertebrae, which typically decreases with age. From in vitro studies, the following relationship between Sui (in megapascals) and b+i (in years) has been derived:

S_{ui}=6,75-0,066(b+i)

There is significant human variability, and R < 0.8 indicates a low probability of an adverse health effect, while R > 1.2 indicates a high probability of an adverse health effect.

A sequential calculation for a person who begins exposure at the age of 20 years (b = 20) will reach R = 0.8 at the age of 65 (n = 45) if the daily dose Sed is equal to 0.5 MPa. The same person will reach R = 1.2 at the age of 65 if the daily dose Sed is equal to 0.8 MPa.

This calculation is based on 240 days of equal exposure (N) per year. For application to a different number of exposure days per year, the appropriate Sed limits are obtained by multiplying 0.5 MPa and 0.8 MPa by (240/N)^(1/6).

The procedure for assessing adverse health effects from the acceleration dose is as follows:

Procedure for assessment of adverse health effects from the acceleration dose

Human vibration module in Dewesoft

A new Human Vibration module can be added by clicking on the Human Vibration icon.


Required hardware	SIRIUS ACC, MULTI, DEWE-43+DSI adapter
Required software	DewesoftX, SE or higher + HBV option, DSA or EE
Setup sample rate	At least 5 kHz

To use the Human Vibration module, first select at least three vibration analog channels in the Analog In tab.

An example of a triaxial accelerometer, each axis has its own channel

Then, add a new Human Vibration module. Multiple modules can be used within a setup, with three channels required for each module.

Setup screen of Human vibration module in Dewesoft

The next step is to assign them in the Input section of the Human Vibration module. At this point, the live values should already be visible in the calibration area of the screen.

Measurement modes

The next step is to define the measurement parameters. There are two basic modes of operation: Whole-Body Mode and Hand-Arm Mode.

Each mode uses different basic filters designed to simulate the human response to vibrations. These filters are derived from numerous measurements of the natural frequencies of specific parts of the human body.

Different calculation types in Dewesoft HBV module

Linear – Individual filter and K-factor settings cannot be selected, as they are predefined. The Linear filter can also be used to check the measurement chain.

Whole-Body – Individual filter and K-factor settings cannot be selected, as they are predefined. Whole-body mode is typically used for evaluating motion sickness (e.g., on ships).

Hand-Arm – Individual filter and K-factor settings cannot be selected, as they are predefined.

Custom – The filter and K-factor must be defined manually.

Custom filter

Filter selection for each axis individually

- Lin – unweighted linear
- Wb – vertical whole body, z-axis (older ISO 2631-4)
- Wc – horizontal whole body, x-axis
- Wd – horizontal whole body, x or y-axis
- We – rotational whole body, all directions
- Wf – motion sickness, z-axis
- Wh – hand-arm, all directions
- Wj – vertical head vibration, x-axis
- Wk – vertical whole body, z-axis
- Wm – building vibration, all directions
With a custom filter, we also need to define the weighting K-factor. This is a multiplication factor applied to each axis when calculating the vibration sum.
It is important to consider the high-pass frequency limit of both the sensor and the amplifier used. For hand-arm mode, the high-pass frequency is 6.4 Hz, which is manageable for almost any sensor. For whole-body mode, the frequency limit is 0.4 Hz, which requires careful selection of both the sensor and amplifier. (There is also the option of integrating a custom high-pass filter into the accelerometer, different from the standard 1 kHz filter, which is too high.) Higher filters (such as 3 Hz) may also be used if there is no frequency content below that limit. This helps achieve faster measurements with fewer errors, since lower frequency filters result in longer settling times.
The recommended sampling rate of the measurement also depends on the application. For hand-arm measurements, the minimum sampling rate is 5 kHz, while for all other applications, 1 kHz is sufficient.
Special attention must be paid to the whole-body filter for motion sickness (e.g., on ships), where the frequency limit is as low as 0.08 Hz. A very specialized sensor is required for this purpose. One suitable option is a DC accelerometer with micro-g resolution and a range from 2 g to 200 g.

DC accelerometer for motion sickness measurement

Calculated parameters IN HBV module

Next, we need to select the calculated parameters in the Calculate Type section. These parameters can be either Overall values, which provide a single value at the end of the measurement, and/or Interval logged values.

If interval logged values are selected, the time interval for logging is defined in seconds in the corresponding field. For example, if we choose interval logging for RMS with 5-second intervals, a new RMS value will be generated after each 5-second interval. Afterward, the value is reset, and the calculation begins again.

We have several parameters to calculate.

The root mean square (RMS) value is a statistical measure of the magnitude of a weighted signal.
Peak is the maximum deviation of the signal from the zero line.
Crest factor is the ratio between the peak value and the RMS value.
VDV refers to the fourth power vibration dose value.
MSDV is the motion sickness dose value.
MTVV is the maximum transient vibration value, calculated at one-second intervals.
Weighted raw channel refers to the full-speed time signal weighted with a chosen filter. These channels can be used for calculating the FFT or CPB spectrum.
al and D are values based on ISO 2631-5, which describe the calculations and limits for lumbar spine response to vibrations. This standard is based on the fact that professional drivers of buses or trucks are exposed to vibrations when driving on rough roads or over bumps. Multiple shocks can cause transient pressure changes at the lumbar vertebral endplates, which may result in damage after years of driving.
The al value represents the lumbar spine response from excitation measured in all three directions, while the D value represents the acceleration dose, measured from the lumbar spine response. Together, these values are sufficient to evaluate human vibration exposure in accordance with ISO 2631-5.

Output channels with description, unit, type and rate

The output unit can be selected from:

g
m/s²
mm/s²

Each value is calculated separately for each axis, while the RMS, MSDV, VDV, and MTVV are also calculated as the combined sum of all three axes. These values are sufficient to evaluate human vibration exposure in accordance with ISO 2631 and ISO 8041.