delta
 

Evaluation of the results

To correctly evaluate the vibration exposure risk, you need to:
1. identify the work phases implying an exposure to vibrations and evaluate the actual exposure times associated to each phase;
2. identify the machines and tools used in each phase.

The evaluation of the results for the worker exposure to vibrations is performed through the calculation of the frequency weighted equivalent acceleration referred to the 8 hours of work, conventionally indicated by the symbol A(8).

As a worker usually performs several operations with different tools, it is useful to calculate the i-th partial exposure to vibrations Ai(8), using this formula:

(1)

 

where = total acceleration level measured (summation vector)
 

Ti

 = exposure time to the i-th source of vibrations
  To = 8 hours

The total daily exposure A(8) due to the n partial exposures Ai(8) is given by this formula:

(2)

 

If the daily exposures are different each day, you can calculate the average value with this expression:

(3)

 

where

Ad(8)

 = daily exposure during day d
 

N

 = number of days considered

If the value of the vibrations is the same each day (for example, because you use the same tool every day), but the exposure time varies, you can use this expression:

(4)

 

where

= daily exposure average duration

 

The A(8) level calculated according to n measurements should be compared with the risk levels set by current regulations. For each type of vibrations (hand-arm, whole body) the following levels have been defined:

The threshold level represents the level A(8) under which a permanent and/or repetitive exposure does not have negative consequences for the health of the exposed person.

The action level represents the exposure value A(8) from which you should take specific measures to protect the exposed person. These measures include: training of the worker on the specific risk, implementation of special interventions to reduce the risk, medical check of the exposed person.

The limit value represents the exposure level A(8) that cannot be exceeded or should be avoided. This level implies an unacceptable risk for the person exposed without protection devices.

The remarkable risk level represents the frequency weighted acceleration equivalent level (r.m.s.). Over this level any operation is forbidden, even for very short times (it is not an A(8) value). Machines that can produce vibrations that could exceed the “remarkable risk level” should be properly signalled.

For example, the levels of vibrations transmitted to the hand-arm system in the "UE Directive Proposal on Physical Agents 94/C230/03" are:

and the levels of vibrations transmitted to the whole body are: