Industrial Hygiene Qualitative Exposure Risk Assessment
- Evaluation of potential personal exposure to workplace Hazards
- A walk-around survey of the area/facility for vibration assessment
Vibration is defined as oscillatory motions of particles (molecules) around their equilibrium in a solid body, liquid, or gas in the areas of infrasound (i.e.< 20 Hz) and partially in the audible sound frequency ranges (upto 1500 Hz), Since in industrial situation vibration usually occurs in air and in the audible range it is normally experienced as sound. Understanding the source and mode of transmission of vibration and so it’s appropriate control measures can be complex.
There are two forms of exposure that can be distinguished:
- Whole-body vibration (WBV), which is transmitted by mobile or fixed machines where the operator is standing or seated. The whole body vibrations was followed based on ISO 2631-1 Standard,
- Hand-Arm vibration (HAV), which is transmitted by hand-held or guided tools, which is caused by regular exposure to vibrating and percussive tools or working with material in contact with plant operations. followed by interpretation of results and thus providing implementable solutions.
The directive defines the terms as follows:
- Whole-body vibration: the mechanical vibration that, when transmitted to the whole-body,
- Entails risks to the health and safety of workers, in particular, lower-back morbidity and trauma of the spine;
- Hand-arm vibration: the mechanical vibration that, when transmitted to the human hand‑arm system,
- Entails risks to the health and safety of workers, in particular, vascular, bone or joint, neurological or muscular disorders.
In simple terms, vibration is defined by its magnitude (traditionally described using acceleration, expressed in m/s2)
|ACGIH TLVs (Threshold Limit Value)
|Whole body vibration
|Four hours and less than eight hours
|Two hours and less than four hours
|One hour and less than two hours
|Less than one hour
The ISO Vibration Occupational Guidelines establishes exposure action values above which employers must control vibration hazards to their employees, as well as exposure limit values below which workers must not be exposed:
- A daily exposure action value (EAV) of 0.5 m/s2 (WBV) or 2.5 m/s2 (HAV);
- An employee’s exposure limit value (ELV) is the maximum amount of vibration above which employers are required to take action to control exposure.The higher the degree of exposure, the higher the danger & more actions to be taken by employers to mitigate it.
- A daily exposure limit value of 1.15 m/s² (WBV) or 5 m/s² (HAV).
- The exposure limit value (ELV) is the maximum amount of vibration to which an employee can be subjected on any single day. A daily exposure of 5 m/s2 is the ELV for hand-arm vibration. It is a high-risk situation to which no employee should be exposed.
Vibration Modelling Methodology
A typical vibration measuring system consists of a device that detects vibration (accelerometer) & vibration level along with a frequency-weighting network, & a display such as a metre, printer, or recorder, are included in this equipment.
An electrical signal is generated by the accelerometer, this signal’s magnitude is proportional to the amount of acceleration applied to it. The frequency-weighting network simulates human sensitivity to various frequencies of vibration.The application of weighting networks results in a single number that is represented as the frequency-weighted vibration exposure in metres per second squared (m/s2) units of acceleration.
The International Organization for Standardization (ISO) standard ISO 5349 specifies the frequency-weighting network for hand-arm vibration. The human hand is not equally responsive to all frequencies of vibration energy. The sensitivity is at its peak around 8-16 Hz, (Hertz or cycles per second). A weighting network is used in measuring equipment to account for this phenomenon. The gain is set to 1 for vibration frequencies to which the hand-arm system has the highest sensitivity.
|Class IV large equipment
|0 to 2.8
|2.8 to 7.1
|7.1 to 18
|18 to 45