Employers have a legal duty to protect the hearing of their employees. You may have a noise problem in your workplace if people have to shout or having difficulty being heard clearly by someone about 2 metres away. In addition to causing noise-induced hearing loss and tinnitus, noise can create stress and be a safety hazard at work interfering with communication.
Previously accepted action levels by noise at the workplace have been reduced by the new EU-Directive 2002/44/EF. These noise exposure levels require employers to take certain steps to reduce the harmful effects of noise on hearing.
The first step is to carry out noise assessments on a regular basis. Norsonic provides a variety of measurement solutions and reporting software for this application.
An important field of sound measurements is the field of occupational noise measurements. The primary concern here is measurements of the total noise and the noise exposure of human beings for health reasons.
In these cases, emphasis is moved towards assessing the total noise level, irrespective of the number of sources and reflections involved.
In addition the noise must be measured where the employee works. If she works in the near-field, measurements should be made in that near-field, regardless of the techniques used in other fields of acoustics.
The presence of other machines and reflecting surfaces becomes important when we decide to take measures to bring down the noise level, but also to determine whether one ear receives more energy than the other.
If that is the case, measure at the one with the highest level or measure at both, but don’t make an average of the two measurements – in general, your task is to assess the hearing damage, which you’ll fail to do if you reduce the maximum level by mixing it with lower levels to create an average level.
The harmful effects of vibrations imposed on man have been well known for years. People exposed to too high vibration levels may experience vision and balance disturbances and in the most severe cases your body may be injured. The white finger syndrome is a typical example.
There are several national and international standards describing human exposure to vibrations. ISO has a range of standards. It is recommended to visit the ISO site for further information and latest updates. The most important standards are:
- ISO 8041 – Human response to vibration – Measuring instrumentation. This standard sets requirements to the measuring system and also defines the vibration weighting networks.
- ISO 5348 – Mechanical vibration and shock – mechanical mounting of accelerometers.
- ISO 2631 Evaluation of human exposure to whole-body vibration- general requirements.
- Part 1 General requirements.
- Part 2 Vibration in buildings.
- Part 4 Guidelines for the evaluation of vibration and rotational motion on passenger and crew comfor in fixed guide way transport system.
- ISO 5349-1 Measurement and evaluation of human exposure to hand-transmitted vibration – general requirements.
- ISO 5349-2 Measurement and evaluation of human exposure to hand-transmitted vibration – practical guidance for measurement at the workspace.
The human body’s sensitivity to vibrations is at its most sensitive within 4-8Hz in the longitudinal direction and 1-2Hz in the transverse direction. Longitudinal direction will be the vertical direction for a standing person.
ISO 2631 requires the whole body to be measured in the frequency range 0,5 – 160 Hz. Maximum allowed limit is 1.15m/s2. Single action level is set to 0.5m/s2.
The measurements should be measured simultaneously in all three axes using a triaxial accelerometer mounted into a seat cushion for a sitting person or on a plate or the basement for a standing person.
Besides the whole body vibration there is also hand-arm vibration standards. The ISO 5349 defines measurements to be taken in the frequency range from 1 to 1000 Hz. Maximum allowed limit is 5m/s2. Single action level is set to 2.5m/s2.
The measurements should be measured simultaneously in all three axes using a triaxial accelerometer mounted onto the vibrating device while the person is operating the device under test.