Tiêu Chuẩn Iso 05349-2-2001.Pdf

Microsoft Word C027511e doc Reference number ISO 5349 2 2001(E) © ISO 2001 INTERNATIONAL STANDARD ISO 5349 2 First edition 2001 08 01 Mechanical vibration — Measurement and evaluation of human exposur[.]

Terms and definitions

For the purposes of this part of ISO 5349, the terms and definitions given in ISO 2041 and ISO 5805 and the following apply

3.1.1 hand-fed machine machine where the operator feeds workpieces to the working part of the machine, such that the vibration exposure is obtained through the hand-held workpiece

EXAMPLE band-saw, pedestal grinder

3.1.2 hand-guided machine machine which is guided by the operator with his hands, such that the vibration exposure is obtained through the handles, steering wheel or tiller

EXAMPLE ride-on lawn mower, powered pallet truck, swing grinder

Hand-held workpieces are those that are held directly in the hand, allowing vibration exposure to be transmitted through the workpiece itself, in addition to or instead of the power tool handle This method of handling significant in assessing vibration risks and ensuring safety during manual tool operation.

EXAMPLE casting held against a pedestal grinder, wood fed into a band-saw

Copyright International Organization for Standardization

3.1.4 hand-held power tool powered tool which is held in the hand

EXAMPLE electric drill, pneumatic chisel, chain saw

3.1.5 inserted tool interchangeable or replaceable attachment which fits into or onto a power tool or machine

EXAMPLE drill bit, chisel, chain saw chain, saw-blade, abrasive wheel

Operation identifiable task refers to a specific activity for which a representative vibration magnitude measurement is conducted This measurement may be performed on a single power tool, a hand-held workpiece, or a particular phase of a task Accurate vibration assessment ensures safety compliance and helps in minimizing health risks associated with hand-arm vibration exposure.

3.1.7 operator person using a hand-fed, hand-guided or hand-held machine or power tool

3.1.8 tool operation any period during which a power tool is operating and the operator is being exposed to hand-transmitted vibration

3.1.9 workpiece item being operated upon by a power tool

Symbols

In this part of ISO 5349, the following symbols are used: a hwi single-axis root-mean-square (r.m.s.) value of the frequency-weighted hand-transmitted vibration for operation i, in m/s² An additional suffix x, y or z is used to indicate the direction of the measurement, i.e. a hwix, a hwiyand a hwiz a hvi vibration total value (formerly denoted vector sum or frequency-weighted acceleration sum) for operation i

(root-sum-of-squares of the a hwivalues for the three axes of vibration), in m/s²

A i (8) contribution of operation i to the daily vibration exposure, in m/s² (for convenience, this is referred to as the

T i total duration (per day) of vibration exposure to operation i

There are two principal quantities to be evaluated for each operation i during exposure to vibration:

– the vibration total value a hvi, expressed in metres per second squared (m/s²); this value is calculated from the three single-axis root-mean-square values of the frequency-weighted hand-transmitted vibration a hwix, a hwiyand a hwiz;

– the duration (per day) T iof vibration exposure to operation i

The principal parameter to be reported is the daily vibration exposure A(8) This is calculated from the values of a hviand T ifor all operations i (see clause 8)

5 Preparation of the measurement procedure

General

Operator tasks at the workplace typically involve a series of operations, some of which may be repetitive Vibration exposure can vary significantly between different tasks, influenced by the use of various power tools or machines and their modes of operation Understanding these variations is crucial for assessing occupational vibration risks and implementing effective safety measures.

To effectively evaluate daily vibration exposure, it is essential to identify operations that significantly contribute to overall vibration levels Selecting appropriate measurement procedures for each of these operations depends on factors such as the work environment, work patterns, and vibration sources These considerations ensure accurate assessment and management of vibration exposure risks.

Selection of operations to be measured

Accurate measurement of all power tools and workpieces contributing to daily vibration exposure is essential for assessing overall risk To ensure a comprehensive understanding of average daily vibration levels, it is crucial to identify all sources of vibration, including machines and tools in use Additionally, understanding the modes of operation of these power tools, such as their specific working patterns, helps in evaluating their impact on vibration exposure and implementing effective control measures.

– chain saws may be idling, operating under load while cutting through a tree trunk, or operating under low load while cutting side branches,

A power drill offers versatile functionality with both impactive and non-impactive modes, along with multiple speed settings to suit various tasks It's important to consider changes in operating conditions, as these can influence vibration exposure levels, ensuring safe and efficient use of the tool.

– a road breaker being used initially on a hard concrete surface followed by use on the softer soil underneath,

– a grinder being used initially for bulk metal removal followed by more intricate operations of cleaning and shaping; d) inserted tools which might affect vibration exposure, e.g.:

– a sander may be used with a series of different grades of abrasive paper, ranging from coarse to fine, – a stonemason may use a pneumatic chisel with a range of different chisel bits

Gathering information from workers and supervisors about situations that produce the highest vibration levels can help identify critical risk scenarios Additionally, estimating potential vibration hazards for each operation is essential, which can be achieved by using manufacturer-provided vibration emission data (refer to annex A) or by reviewing published measurements from similar power tools This comprehensive approach supports effective vibration risk assessment and promotes workplace safety.

Organization of the measurements

The organization of measurements can be approached in four basic ways: a) Long-term measurement of continuous tool operation

Prolonged and continuous operation of power tools involves sustained contact between the operator and the vibrating surface, allowing for long-term vibration measurements during normal use This approach captures typical vibration exposure throughout regular work activities Additionally, variations in vibration levels may occur naturally within the scope of normal operation, ensuring accurate assessment of vibration exposure during different phases of the work process.

In addition to vibration magnitude information, the evaluation of daily vibration exposure requires an evaluation of the duration of exposure to vibration per day

Long operation times with short breaks without vibration exposure occur, but during both work and breaks, the operator maintains contact with the vibrating surface Vibration measurements can be conducted over extended periods during normal tool use, as long as breaks are part of routine work, and the operator remains in contact with the tool or workpiece without losing grip or changing hand positions significantly.

Effective evaluation of daily vibration exposure must consider not only vibration magnitude but also the duration of operation each day This includes accounting for short breaks in vibration exposure, which can extend the overall exposure period beyond the actual time the tool is actively vibrating Short-term measurements of intermittent tool operation are essential for accurately assessing the cumulative vibration risks and ensuring compliance with health and safety standards.

During various work scenarios, the operator often removes their hand from the power tool or workpiece, such as setting the tool down, repositioning their hand, or handling a different workpiece Additionally, adjustments to the power tools, like changing abrasive belts, drill bits, or switching to alternative tools, are common These tasks typically require short-term measurements that are only feasible during specific phases of each work operation.

When reliable measurements cannot be obtained during standard work processes due to short exposure durations, simulated work operations are used to replicate real conditions These controlled simulations artificially create longer, uninterrupted exposures, allowing for accurate measurement while maintaining work environment authenticity.

Effective assessment of daily vibration exposure involves not only measuring the magnitude of vibrations but also evaluating the duration of exposure during each work phase This includes fixed-duration measurements of tool operation bursts or individual and multiple shocks, ensuring a comprehensive understanding of vibration impact in the workplace.

Certain operations involve short bursts of vibration, such as riveting hammers, nail guns, or powered impact wrenches, making it challenging to accurately assess total exposure time While estimating the number of vibration bursts per day is possible, precise evaluation of actual exposure duration can be difficult Measurements should be conducted over a fixed period that encompasses one or more complete tool operations, ensuring minimal time before, between, and after the vibration bursts to accurately capture exposure levels.

Effective evaluation of daily vibration exposure involves not only measuring the vibration magnitude and estimating the number of vibration bursts per day but also accounting for the measurement duration and the total number of vibration bursts during that period.

When workers are exposed to multiple single shocks or transient vibrations, such as those from fastening tools, the ISO 5349-1 method may not accurately assess the severity of shock exposure and could underestimate the risks In the absence of a more precise method, ISO 5349-1 can be used cautiously, but this limitation should be clearly noted in the reported information to ensure safety assessments remain transparent.

When comparing vibration magnitudes between different power tools or tool options, it is essential to measure vibrations during continuous operation without any breaks Accurate comparison requires consistent testing under continuous use conditions to ensure reliable and meaningful results.

Duration of vibration measurements

To ensure accurate assessment, measurements should be averaged over a representative period that reflects typical power tool, machine, or process use Ideally, the measurement period begins when the worker's hands first contact the vibrating surface and ends when contact is broken This duration may encompass fluctuations in vibration intensity and can include intervals of no exposure, providing a comprehensive view of vibration exposure levels.

Where possible, a series of sample measurements should be taken at different times of the day, and averaged, so that variations in vibration through the day are accounted for

NOTE The average vibration magnitude of a series of N vibration magnitude samples is given by

= 1 ∑ where a hwj is the measured vibration magnitude for sample j t j is the measurement duration of sample j

Vibration exposures typically occur over short durations but are frequently repeated throughout the workday While measurements can be averaged across entire operational cycles—including times when the vibration source is inactive—generally, they are limited to averaging during the brief periods when the hand contacts the vibrating surface This approach helps accurately assess the worker’s exposure to hand-arm vibration and supports effective risk management.

The minimum measurement duration should be at least 1 minute, depending on the signal, instrumentation, and operational characteristics It is preferable to collect multiple shorter samples rather than a single prolonged measurement to ensure accuracy For each operation, a minimum of three samples should be taken to ensure reliable results, optimizing measurement quality and consistency.

Short-duration measurements under 8 seconds are generally unreliable, especially for assessing low-frequency components, and should be avoided whenever feasible When such brief measurements are unavoidable, such as in pedestal grinding with very short contact times, it is recommended to collect significantly more than three samples to achieve a total measurement duration exceeding one minute, ensuring more accurate and representative results.

Where measurements are not possible, or difficult, during normal tool operation then simulated work procedures can be used to simplify the vibration measurement process

Simulated work procedures are primarily used to enable measurements over extended periods that are impractical during standard production For instance, pedestal grinding of small castings typically lasts only a few seconds per piece; instead of measuring short durations on numerous castings, simulations can be performed on a few scrap castings, allowing each to be reused multiple times This approach enhances measurement efficiency and provides accurate data for process analysis.

To ensure accurate measurements, avoid disturbing the workpiece by picking up, putting down, or replacing the power tool or handheld workpiece To further prevent measurement disruptions, conduct measurements during simulated work procedures designed to eliminate interruptions between operations.

Estimation of daily vibration duration

The daily exposure duration for each vibration source shall be obtained Often a typical daily vibration exposure time will be based on

– a measurement of the actual exposure time during a period of normal use (e.g as evaluated over a complete work cycle, or during a typical 30 min period) and

– information on work rate (e.g the number of work cycles per shift or the shift length)

To assess operator vibration exposure, the initial step involves measuring the duration and sources of vibration during a specified period Various techniques, such as precise measurement devices and analysis methods, can be employed to accurately determine vibration levels and identify their sources, ensuring compliance with safety standards.

– use of a dedicated data logger linked to power tool usage;

Work records are the most reliable source of information on typical work rates, but it is crucial to ensure they align with the data needed for evaluating daily vibration exposure While work records provide accurate counts of completed work items daily, they may not be directly applicable for vibration assessments when multiple operators are involved or when work items remain unfinished at the end of a shift.

To accurately assess vibration exposure, it is essential to determine the total exposure time per day When vibration levels are averaged over an entire work cycle, the daily exposure duration is calculated by multiplying the work cycle length by the number of cycles performed daily If measurements are taken during periods when the hand contacts the vibrating surface, it is important to evaluate and include the total contact time each day Properly accounting for these factors ensures precise vibration exposure assessment for health and safety considerations.

Operators often overestimate their daily power tool usage by including breaks and pauses, such as downtime between nuts when operating a nut runner or preparation time for new workpieces This tendency can lead to inflated estimates of actual tool operation time, impacting accurate resource planning and safety assessments Understanding these overestimations is essential for optimizing tool efficiency and ensuring precise data collection.

ISO 5349-1 provides a system for evaluating daily vibration exposure within a single working day but does not support extrapolation for averaging exposures over multiple days In certain industries, such as construction and shipbuilding, daily vibration exposure can vary significantly, making it challenging to assess typical exposure based on single-day data When evaluating multi-day vibration exposure, alternative methods outlined in Annex B can be employed, especially when work duration and vibration levels fluctuate considerably.

Measurement equipment

Vibration measurement systems primarily utilize accelerometers to detect the motion of vibrating surfaces, providing accurate data on vibrational activity The signals captured by these accelerometers can be processed through various methods to accurately determine frequency-weighted acceleration, ensuring effective monitoring and analysis of vibrations for machinery health and structural integrity Proper signal processing techniques are essential for obtaining meaningful vibration measurements, which are crucial for predictive maintenance and operational efficiency.

Simple, single-unit vibration meters with built-in frequency weightings and integrating capabilities are commonly used for measuring workplace vibration exposure These systems are generally sufficient for most scenarios outlined in ISO 5349, providing effective assessment of vibration levels However, basic instrumentation may not detect measurement errors, highlighting the importance of using appropriate, accurate tools for reliable vibration analysis.

Advanced measurement systems typically utilize frequency analysis methods such as one-third octave or narrow band analysis to enhance accuracy These systems often incorporate digital or analogue data recorders for precise time data storage and leverage computer-based data acquisition and analysis techniques While offering higher precision and detailed insights, these sophisticated systems tend to be more costly and complex to operate compared to simpler, single-unit measurement solutions.

When there is uncertainty about the quality of the acceleration signal, such as DC-shift (see 6.2.4), conducting frequency analysis is highly recommended Frequency analysis helps identify dominant frequencies and harmonics, providing valuable insights that can aid in selecting effective vibration control measures.

At the limits of application of ISO 5349-1 (e.g repeated single shocks, dominant frequency components exceeding

1250 Hz) any additional information available e.g from more sophisticated measurement systems may be useful

Minimum performance requirements (e.g frequency weighting characteristics, tolerances, dynamic range, sensitivity, linearity and overload capacity) for appropriate measuring and analysing equipment are given in ISO 8041

Selecting the right accelerometer depends on several factors, including the expected vibration magnitude, the necessary frequency range, and the physical characteristics of the surface being measured Additionally, the environmental conditions in which the accelerometer will be used play a crucial role in the decision-making process.

Hand-held machines, such as pneumatic hammers, can generate very high vibration magnitudes, with maximum accelerations reaching 20,000 to 50,000 m/s² However, much of this energy exists outside the relevant frequency range specified in ISO 5349, which focuses on 6.3 Hz to 1250 Hz (one-third-octave band mid-frequencies) Therefore, selecting an accelerometer capable of measuring both very high vibration magnitudes and responding accurately within this specific frequency range is essential Mechanical filters can be employed to suppress vibrations at extremely high frequencies, as detailed in Annex C.

When selecting an accelerometer, it is essential to consider its fundamental resonance frequency, also known as the mounted resonance or natural frequency Manufacturers provide this critical specification, which influences the device’s accuracy and responsiveness According to ISO 5348, the fundamental resonance frequency should be at least five times higher than the maximum frequency of interest to ensure reliable vibration measurements, especially in applications involving hand-transmitted vibration.

6250 Hz) For piezoelectric accelerometers, the fundamental resonance frequency should normally be much higher, ideally greater than 30 kHz, to minimize the likelihood of DC-shift distortion (see 6.2.4)

The fundamental resonance frequency of an accelerometer should not be confused with the resonance frequency of the mounted system when attached to a hand-held workpiece or power tool The resonance frequency associated with the mounted setup depends on the entire system, not just the accelerometer itself In practice, the resonance frequency when mounted on a hand-held workpiece or power tool is significantly lower than the accelerometer’s fundamental resonance frequency, affecting measurement accuracy and system performance.

When accelerometers are attached to a vibrating surface the vibration characteristics of that surface are altered The lighter the accelerometer(s) the smaller the error introduced (see 6.1.5)

When selecting accelerometers, particularly for use in harsh environments, it will be necessary to consider the accelerometer’s sensitivity to temperature, humidity or other environmental factors (see ISO 8041)

Vibration measurements should be conducted at or near the hand surface where vibrations enter the body, in accordance with ISO 5349-1 standards Ideally, the accelerometer is positioned at the midpoint of the gripping zone, such as halfway along the width of the hand gripping a power tool handle, to ensure the most accurate assessment of vibration exposure However, due to practical constraints, it is often not feasible to place transducers at this ideal location, as they may interfere with the operator's normal grip and handling of the tool.

Measurements directly beneath the hand require specialized mounting adaptors, which can be placed under the hand or between the fingers For practical purposes, accelerometers are typically installed on either side of the hand or on the underside of the tool handle near the middle to ensure accurate vibration measurement When using adaptors placed between the fingers, it is important to mount the transducers as close as possible to the surface of the tool handle to minimize the amplification of rotational vibrations Additionally, the adaptors should be free of structural resonances that could affect the accuracy of the vibration measurements.

Vibration measurement can vary across the width of the hand, especially when using hand-held power tools with side handles like angle grinders This variation is more pronounced with flexible-mounted handles To ensure accurate assessment of vibration exposure, it is recommended to use two accelerometers placed on opposite sides of the hand and calculate their average measurement.

Many hand-held power tools have designated measurement locations and axes for vibration emission assessment, as specified by ISO 8662 and other international standards These measurement points, outlined in annex A, serve as examples but are often tailored for specific types of measurements, typically focusing on a single axis While ISO 8662 standardizes these locations, they may not always be suitable for evaluating overall vibration exposure In certain situations, selecting appropriate measurement locations is essential to accurately assess vibration risks and ensure compliance with safety standards.

For accurate vibration measurement, accelerometers must be securely attached to the vibrating surface using appropriate mounting methods detailed in Annex D It is essential to select a mounting method that provides a stable fix without interfering with the power tool's operation or altering the surface's vibration characteristics The choice of mounting method depends on the specific measurement scenario, as each approach offers distinct advantages and disadvantages, ensuring reliable and accurate vibration data collection.

A reliable mounting system should provide a flat frequency response across the entire measurement range, ensuring no attenuation, amplification, or resonances within the targeted frequencies It must be securely attached to the vibrating surface, with all fixings thoroughly checked before and after measurements to ensure stability and accuracy.

Mounting accelerometers on power tools or hand-held workpieces is inherently invasive and may influence the operator's technique To ensure accurate measurements while minimizing disruption, transducers should be positioned to allow as natural a workflow as possible Before taking measurements, it is essential to observe how the tool or workpiece is held to determine the optimal location and orientation of the accelerometers The specific placement and orientation of the sensors should be clearly documented to ensure data consistency and reliability.

Sources of uncertainty in vibration measurement

Ensuring a reliable connection between the accelerometer and the signal cable is the most common challenge in measuring hand-transmitted vibration To achieve accurate readings, it is essential to secure all cable connections and inspect cables for potential damage Special attention should be given to the connection at the accelerometer, ensuring that the cable and connector are not subjected to excessive stresses during the operation of power tools or hand-held workpieces Proper securement and careful handling of cables are crucial for accurate vibration measurement.

Faulty signal connections often manifest as a complete loss of signal, giving the impression that there is no vibration detected Additionally, intermittent signal disconnections can cause DC-offsets, where the signal appears normal during normal operation but reveals underlying connection issues Ensuring reliable signal connections is essential for accurate vibration measurement and diagnostics.

Faulty cable screening connections can lead to electrical pickup, resulting in high levels of mains frequency interference For electrical tools, where vibration frequencies are often related to the mains power frequency, detecting these faults can be challenging In the case of piezoelectric accelerometers, which utilize high-impedance signal conditioning amplifiers, a loss of cable earth screening connection can cause significant electrical mains frequency interference, affecting measurement accuracy.

To ensure accurate vibration measurements, it is essential to prevent interference from electrical, magnetic, or electromagnetic fields Capacitively and inductively coupled interference signals can impact measurement quality, but their effects can be minimized by implementing effective mitigation strategies Employing proper shielding, grounding techniques, and filtering methods helps reduce electromagnetic field influence, ensuring reliable and precise vibration data.

– earthing the signal cable's screening at one end only, normally at the amplifier end;

– provision of a connection to the transducer balanced to earth (e.g by using a differential amplifier);

– avoiding signal cables running parallel to power cables;

– provision of electrical insulation between the accelerometer and the vibrating surface

Instrument cables should be protected from high-amplitude vibrational stress, as such conditions can generate electrical signals in systems with high internal resistance, like piezoelectric accelerometers To ensure accurate signal transmission, cables should be securely attached to the vibrating surface near the accelerometer, for example, using adhesive tape For pneumatically powered hand tools, fixing cables at regular intervals along the air supply line is an effective method to prevent damage and signal interference.

Exposing piezoelectric transducers to high accelerations at high frequencies, such as on unmitigated percussive tools, can lead to DC-shift distortion by generating false low-frequency components in the vibration signal This distortion occurs when the transducer is mechanically overloaded by transient vibrations that exceed its capacity, resulting in signal distortion Implementing mechanical filters is an effective method to prevent DC-shift, ensuring accurate vibration measurements.

DC-shift primarily manifests in the low-frequency region below the percussive frequency, making frequency analysis a useful tool for its detection Unrealistically high low-frequency vibration values during spectral analysis often indicate the presence of DC-shift Converting unweighted RMS acceleration to displacement using the formula d = a / (40 f²), where f is the center frequency of the analysis band, helps identify DC-shift If the calculated displacement significantly exceeds the observed transducer motion—particularly if it is more than twice the actual movement—this suggests that DC-shift has likely occurred, affecting accurate vibration measurements.

Detecting DC-shift involves analyzing the low-frequency components of the vibration signal, as it primarily affects this spectrum However, DC-shift distortion impacts the entire vibration spectrum, so measurements indicating DC-shift should be discarded It is important not to calculate frequency-weighted vibration values from spectra that exhibit DC-shift by removing or modifying low-frequency bands, ensuring accurate and reliable monitoring.

Check and verification of the measurement chain

The whole measurement chain shall be checked, both before and after a sequence of measurements, by using a vibration calibrator (a reference vibration source) which produces known sinusoidal acceleration at a known frequency

In practical applications, accelerometers typically maintain stable sensitivity during measurements, though mechanical failures can occur and impact their performance It is essential to monitor any changes in apparent sensitivity throughout data collection, as such deviations may indicate sensor issues If significant sensitivity drift is detected, measurements should be discarded to ensure data accuracy and reliability.

6.3.2 Routine verification of the measurement system

Regular verification of the measurement system's characteristics is essential, ideally every two years, to ensure optimal performance These checks confirm that the instrumentation operates within the specified tolerances outlined in ISO 8041 and DIN 45671-3 standards, maintaining accuracy and reliability.

Regular verification of the measurement system is essential, especially after any rough handling of critical components, to ensure ongoing accuracy All verification results must be properly recorded to maintain traceability and compliance with quality standards.

7 Uncertainty of evaluation of daily vibration exposure

Acceleration measurement uncertainty

When measuring vibration transmitted to workers the uncertainty will be affected by factors related to individual measurements, such as

– changes from the normal operation of the power tool and changes to hand posture and applied forces brought about by the measurement process (i.e mounting of accelerometers and associated cables);

– changes in the operator’s method of working, as a response to being the subject of the measurement

In addition uncertainty of the overall evaluation of vibration exposure will be affected by changes which occur in the course of any working day, such as

– changes in the condition of power tool and inserted tool (e.g changing the wheel of a grinder may change the vibration transmitted to the operator dramatically);

– changes in posture and applied forces;

– changes in the characteristics of the materials being processed

While uncertainties from instrumentation, calibration, electrical interference, and accelerometer mounting and mass are typically minimal, the primary sources of measurement variability stem from the chosen measurement location and the inherent variations in work operations.

When examining an individual's exposure history, it is important to measure the vibration levels of machines and attached tools across various generations and maintenance conditions to ensure accurate assessment.

When measuring vibration exposure related to a specific task, it is important to consider that differences among operators—such as variations in expertise and stature—may introduce additional uncertainty into the results (see 7.3).

Exposure time measurement uncertainty

The uncertainty of the estimation of exposure time is affected by the uncertainty of

– measurements of the durations of exposure;

– estimates of the number of work cycles per day;

Operators often provide exposure time estimates that may be inaccurate due to misinterpretation of questions, particularly confusing the use of power tools with actual vibration exposure Additionally, these estimates can be unreliable because of poor assessments of the durations during which individuals are exposed to vibration, potentially leading to inadequate risk evaluations.

Evaluation of uncertainties

Sources of uncertainty vary depending on the specific operation being measured; it is essential for the experimenter to identify key factors such as wheel unbalance in grinders To accurately assess measurement variability, multiple measurements should be taken, enabling calculation of the standard deviation associated with the predominant sources of uncertainty For example, evaluating a grinding machine with wheels of different unbalance can provide valuable insights into the extent of measurement variation and enhance the accuracy of uncertainty analysis.

When assessing vibration exposure for a specific task rather than individual workers, it is recommended to base measurements on at least three different workers to ensure representative results The reported vibration exposure should be the arithmetic mean of these measurements, with the standard deviation documented to provide insights into variability This approach enhances the accuracy and reliability of vibration risk assessments, aligning with best practices in occupational health and safety.

8 Calculation of the daily vibration exposure

Workers’ daily vibration exposure often results from multiple operations, each contributing to overall risk For each operation, it is essential to measure the vibration total value (a_hvi) and the duration of exposure (T_i) Accurate assessment of daily vibration exposure helps ensure compliance with safety standards and reduces the risk of vibration-related health issues.

A(8), in m/s², shall be obtained from

T 0is the reference duration of 8 h (28800 s) n isthe number of operations

To effectively compare various operations and assess each operation's specific contribution to daily vibration exposure A(8), it is essential to calculate the partial vibration exposure for individual operations, denoted as A_i(8) This approach enables precise evaluation of the impact of each operation on overall vibration exposure, supporting better health and safety assessments Calculating A_i(8) helps identify high-risk activities and optimize ergonomic practices, ensuring compliance with occupational safety standards.

The daily vibration exposure is then given by

A(8) should be evaluated separately for both hands of the operator

The uncertainties associated with the evaluation of A(8) are often high (e.g 20 % to 40 %) Therefore, values of

A(8) should not normally be presented with more than two significant figures

Practical applications of the calculation of the daily vibration exposure are given in annex E

The evaluation report shall refer to this part of ISO 5349 and provide, dependent on the situation investigated, the following information: a) General information:

– purpose of the measurements (e.g evaluation of vibration exposure of individual workers, worker groups, evaluation of control measures, epidemiological study);

– subject or subjects of the individual exposure evaluation;

– person carrying out the measurements and evaluation b) Environmental conditions at the workplace:

– location of measurements (e.g indoor, outdoor, factory area);

– noise c) Information used to select the operations measured (see 5.2) d) Daily work patterns for each operation evaluated:

– machines and inserted tools used;

– patterns of exposure (e.g working hours, break periods);

To assess daily exposure times accurately, it is essential to consider factors such as work rate, the number of work cycles or components processed per day, and the duration of exposure for each cycle or hand-held workpiece Additionally, identifying and detailing vibration sources are crucial for a comprehensive evaluation of vibration exposure in the workplace.

– technical description of the power tool or machine;

– age and maintenance condition of the power tool or machine;

– weight of the hand-held power tool or hand-held workpiece;

– vibration control measures on the machine or power tool, if any;

– type of hand grip used;

– automatic control systems of the machine (e.g torque control on nut runners);

– rotational frequency or percussive speed;

– models and types of inserted tools;

– any additional information (e.g unbalance of inserted tools) f) Instrumentation:

– date of most recent verification test;

– results of any interference tests g) Acceleration measurement conditions:

– accelerometer locations and orientations (including a sketch and dimensions);

– mass of the transducers and mount;

– arm posture and hand positions (including whether the operator is left- or right-handed);

– any additional information (e.g data on feed and grip forces) h) Measurement results:

– x-, y- and z-axis frequency-weighted hand-transmitted vibration values ( a hwix , a hwiyand a hwiz), possibly for each operation;

– if frequency analysis is available, the unweighted frequency spectra;

When evaluating daily vibration exposure, the use of single- or two-axis measurements is justified based on the specific vibration sources and measurement objectives Applying appropriate multiplying factors to the measured values ensures accurate estimation of the total vibration exposure, accounting for the contribution of all axes involved These correction factors are essential for aligning measurement results with occupational safety standards, providing a reliable assessment of potential health risks associated with vibration exposure in the workplace.

– vibration total values, a hvi, for each operation;

– duration of vibration exposure for each operation, T i;

– partial vibration exposures for each operation, A i (8), if available;

– evaluation of the uncertainty of daily vibration exposure results

Measuring hand-transmitted vibration directly at the point of contact, particularly in the middle of gripping zones, is often impractical due to the design of power tools such as those with closed or open bow grips or pistol grips, where trigger placement can obstruct measurement In practice, accelerometers are typically positioned to one side of the hand to facilitate accurate readings The location of power controls and hand guards further influences where measurements can be effectively taken Figure A.1 provides visual examples of suitable measurement locations on common power tools for reliable vibration assessment.

A.2 Measurement locations used in vibration type test standards

Table A.1 provides key measurement locations based on ISO standards such as ISO 8662-2 to ISO 8662-14, ISO 7505, and ISO 7916, which establish laboratory methods for assessing handle vibration in hand-held power tools These standards are essential for accurately determining vibration emission values to ensure worker safety and compliance with international safety guidelines.

While the locations listed in Table A.1 can be suitable solutions, they may not be appropriate for measuring actual exposure The primary goal of exposure measurement differs significantly from that of type testing Specifically, for vibration exposure assessment, accelerometers should be placed where the hand actually grips the power tool, not necessarily where the tool is held during standardized tests Vibration test standards emphasize measuring at the main gripping zone, where operators typically hold and apply feed force to the tool Generally, these standards specify a single measurement location and axis to ensure consistency.

The examples listed in Table A.1 apply to tools having rigid handles or grip zones (see 6.1.4 for elastically mounted handles)

Figure A.1 – Examples of practical measurement locations for some common power tool types

Table A.1 details the placement of accelerometers on power tools such as chipping hammers, riveting hammers, and needle scalers, as specified in international standards According to ISO standards 8662-2 and 8662-14, the mounting locations are critical for accurate vibration type testing, with specific requirements outlined to ensure consistent measurement and compliance during type testing procedures Proper accelerometer positioning enhances the reliability of vibration assessments for stone working tools and other power equipment.

Open or closed bow grip Pistol grip Straight power tool 8662-3 Rock drills Rotary hammers Rock drill Heavy rotary hammer Light rotary hammer 8662-5 Pavement breakers Pick hammers 8662-6 Impact drills

Pick hammer Pavement breakerImpact drill

The transducer should be mounted halfway along the main handle where the feed force is applied, ensuring accurate measurement For power tools with closed, open bow, or pistol grips, if trigger placement prevents this, position the transducer as close as possible to the hand—between the thumb and index finger—or near the midpoint In power tools with two symmetric handles, the transducer must be mounted on the handle without a trigger For tools lacking damping systems, emission measurements can be conducted in a direction parallel to the percussive motion or drill bit axis to ensure precise assessment.

ISO standardType of power tool Mounting location Details of requirements for type testing 8662-9Rammer 8662-4 Grinders Small angle grinderLarge angle grinder Vertical grinderStraight grinder

Measurements should be performed on both handles using two transducers per handle, with placement preferably on the underside for optimal results Transducers must be symmetrically mounted relative to the area where the operator typically grips the handle, approximately 60 mm from the end Ensure that transducers are mounted perpendicularly to the surface of the handle for accurate measurement, adhering to ISO 2001 standards.

The ISO 8662-7 standard specifies testing requirements for various power tools, including straight and angled models such as wrenches, screwdrivers, and nut runners with pistol or bow handles Measurements should be taken at the handle locations where operators typically grip the tool, with the transducer positioned halfway along the handle whenever possible If trigger placement prevents this, the transducer should be placed as close as possible to the ideal position For straight control-handle power tools, the transducer must measure tangential acceleration on the tool surface near the motor shaft, positioned as close as possible to ensure accurate testing of vibration levels.

According to ISO standards, measurements for power tools such as orbital sanders, polishers, and angle sanders must be conducted on both the housing and the handles where the operator typically holds and applies force If the tool is designed to be held by a knob-handle rather than the main housing, measurements should be taken on the knob-handle For tools with two handles, measurements are required on both handles, whereas in the case of small rotary angle sanders and polishers where the motor housing is intended to be held, the housing itself is treated as a handle The transducers used for measurement should be positioned halfway along the handles, preferably on the underside, to ensure accurate assessment of the tool’s ergonomics and safety compliance.

The article outlines ISO standards and testing requirements for various power tools, including nibblers, shears, and saws For nibblers (ISO 8662-10), measurements should be taken on the main handle where the operator holds the tool and applies force, with the transducer positioned on the underside of the handle or near the fingers if the trigger placement prevents direct placement Shears designed for circular cutting are also covered under these standards For saws such as circular saws and reciprocating saws (including jig saws), specific mounting locations and testing procedures are detailed to ensure safety and performance compliance.

Tiêu đề	Mechanical Vibration — Measurement And Evaluation Of Human Exposure To Handtransmitted Vibration
Trường học	International Organization for Standardization
Chuyên ngành	Mechanical vibration
Thể loại	tiêu chuẩn
Năm xuất bản	2001
Thành phố	Geneva

Định dạng
Số trang	46
Dung lượng	1,15 MB