Hand-arm vibration

Background

The EC – Directive 2002/44/EC lays down minimum requirements for the protection of workers from risk to their health and safety arising or likely to arise from exposure to mechanical vibration.

The assessment of the vibration exposure is calculated in relation to a standardised 8h daily exposure value A(8). After establishing the A(8) value, this should be compared with the exposure action- and limit-values. As the Directive lays down minimum requirements, it is also vital to check legislation in each individual Member State of interest to find out if this legislation has stricter exposure values.

Depending on the daily Exposure Action Value (EAV) and the daily Exposure Limit Value (ELV), the employer has an obligation to take appropriate action in order to control the vibration exposure.

Exposure Action Value (EAV)

Whenever an operator is subjected to vibration exposure A(8) exceeding the EAV at 2.5 m/s², the employer must carry out a risk assessment of the operation and introduce control measures. For more details, see Directive 2002/44/EC and Member State legislation.

Exposure Limit Value (ELV)

In any event, workers shall not be exposed above the ELV (5.0 m/s²).

Recommended action to bring down the vibration exposure

Use only low vibrating power tools. This recommendation could be regarded as the most important one. Vibration data can often be found in the manufacturer’s technical information.

Shorten the usage time of the tool. As the A(8) value is a function of both vibration value and exposure time, one alternative is always to cut down on the working time.

Service and maintenance of the machine. Follow the manufacturer’s recommendations. It is especially important to maintain the cutting equipment and the rotating elements that can become unbalanced due to wear.

Hand-Arm vibration exposure calculator

This calculator was developed as an aid to perform calculation of vibration exposure and was carried out under the following conditions:

Equivalent vibration value, ahv,eq. Measured according to ISO 5349-1 or according to relevant measuring standard based on ISO 5349-1 for the specific power tool.

Typical daily exposure time, Texp. The exposure time is always less than the daily working time. For most power tools, the estimation of Texp comes from an international study (CEN Technical Report - “Guideline for the assessment of exposure to hand-transmitted vibration based on information provided by manufacturers of machinery”). For machine types not included in this report, the Texp has been estimated from time studies. See table 1.

The assessment of A(8) is thereby only valid for these conditions. If a machine is used in a non-standard working application or if the exposure time is not relevant, the assessment of A(8) should be made taking these factors into consideration.

Instructions for use

The calculator is divided into two sections of which the left section immediately produces each power tool’s individual A(8) exposure value, based on 8 hours usage time.

The right section is the actual calculator, which calculates each tool’s partial exposure to any usage time if other than 8 hours. If the worker chooses to use multiple tools over the working day, the calculator produces their total A(8) exposure values as well.

Choose model of power tool. The chosen model's A(8) value and the model's equivalent vibration value ahv,eq will show next to the left section’s model field. The model field adds one row for each model.

To calculate a new A(8) exposure value when using multiple power tools or for various user times, simply enter the specified tools’ estimated daily working times into the white fields. Read the result for each tool from the column partial daily exposure. If you use multiple tools, the calculator will produce the tools’ accumulated A(8) exposure value during the full working day in the cell below the partial daily exposure column.

The lights at the bottom will change with the A(8) value.
Green - The daily vibration exposure is below 2.5 m/s².
Yellow - The daily vibration exposure is above the exposure action value at 2.5 m/s².
Red - The daily vibration exposure is above the exposure limit value at 5 m/s².

To clear all cells and start again, click the "Reset form" button.

Calculation for non-listed power tools

The A(8) exposure value is known

The calculator has two options to include other hand-arm vibrating power tools as well. The simplest option is when the tools’ rated A(8) exposure values are known.

Choose “other” from the model list. By selecting “other” the calculator automatically uses the typical vibration exposure time for that specified tool group. See table 1.

Edit the name in the model field (not necessary).

Enter the A(8) exposure value into the third column in the left section. Then use the calculator as described in section “Instructions for use”.

The A(8) exposure value is unknown

If the A(8) exposure value is unknown, the equivalent vibration value ahv,eq for each handle must be determined. In order to determine ahv,eq the vibration acceleration values ahv for each handle and working mode are needed. The ahv is the square root of the arithmetic sum of the squares of vibration values ahw measured in three axes at the handle and should be supplied by the manufacturer.

equation 1: ahw = square root of the sum of a²hwx + a²hwy + a²hwz

(1)

The equivalent vibration value ahv,eq is the sum of vibration within the various working modes. Here the calculator uses ahv in conjunction with each operating mode’s time sequences ti in order to calculate ahv,eq. The ahv,eq must be calculated for each handle separately. However, since only the worst handle’s value is used, it will be the value to enter into the calculator. Now the calculator determines the daily exposure value A(8), which will show in the left section of the calculator. The calculator uses third equation (3) to determine the daily exposure normalised to 8 hours A(8) by using the equivalent vibration value ahv,eq. and the typical daily exposure time Texp for the specific tool. See table 1.

Equation 2: ahveq = square root of the sum of 1 divided by T deriva of n by i=1 multipied by a²hvi multiplied by ti

(2)

Equation 3: A(8) = ahveq multiplied by square root of Texp divided by 8

(3)

Choose “other” from the model list. By selecting other the calculator will automatically use the typical vibration exposure time for the specified tool group. See table 1.

Edit the name in the model field (not necessary).

Enter the worst (maximum) handle’s ahv,eq value into the second column in the left section of the calculator. Now the calculator determines the daily exposure value A(8), which is shown in the third column in the left section of the calculator.

Table 1 - Typical daily exposure times

Typical daily exposure times for the use of single power tools during an 8-h working day. From CEN-Technical report “Guideline for the assessment of exposure to hand-transmitted vibration based on information from manufacturers of machinery”.

Machine type

Application

Typical exposure time

Top handle chain saws

Tree service

2.4 hours

Prof. chain saws < 80 cm³

Logging farming, Landscaping

3.7 hours

Prof. chain saws > 80 cm³

Heavy logging

3.7 hours

Grass trimmers

Landscaping

4.0 hours

Brushcutters

Road maintenance, Landscaping

3.5 hours

Hedge trimmers

Landscaping

3.5 hours

Leaf blowers

Municipalities

3.0 hours

Edgers

Landscaping

3.0 hours

Cutting-off machines (handheld)

Construction

1.0 hours

Cutting-off machines (carriage)

Construction

2.5 hours

Note! The given typical daily exposure times were evaluated in field tests under representative conditions. In 90% of all investigated applications the daily exposure time was shorter than the values in the table. It is estimated that 10% of the investigated applications have longer exposure times. Therefore, it is important that the specific work task is carefully analysed to establish whether the exposure time is longer.

Table 2 - Time sequences

Time sequences of the operating modes for chain saws and other power tools as described in CEN-Technical report “Guideline for the assessment of exposure to hand-transmitted vibration based on information from manufacturers of machinery”.

Machine type

Idling

Rated Speed

Max Speed

Top handle chain saw

1/3 T

1/3 T

1/3 T

Prof. chain saws < 80 cm³

1/3 T

1/3 T

1/3 T

Prof. chain saws > 80 cm³

1/2 T

1/2 T

Grass trimmers

1/2 T

1/2 T

Brushcutters

1/2 T

1/2 T

Hedge trimmers

1/5 T

4/5 T

Leaf blowers

1/7 T

6/7 T

Edgers

1/2 T

1/2 T

Cutting-off machines (handheld)

1/7 T

6/7 T

Cutting-off machines (carriage)

1/7 T

6/7 T