Reducing exposure to industrial noise primarily concerns two communities, separated by a property boundary:
- workers, with regard to their health. In this matter, European Directive 2003/10/EC (which can be considered a reference document beyond the geographical scope of the Member States) sets the limits of sound levels for the prevention of deterioration of hearing abilities (this is also beneficial with regard to the prevention of accidents at work which could be caused - in the case of excessive noise - by the lack of auditory perception of the traffic of vehicles and machinery, and/or warning signals e.g. sirens):
- limit exposure values for workers to noise: exposure level L EX,8h = 87 dB (A) and peak sound pressure pcrête = 200 Pa or 140 dB (C) ref. 20 μPa
- lower exposure values for workers to noise triggering action: exposure level L EX,8h = 80 dB (A) and peak sound pressure pcrête = 112 Pa or 135 dB (C) ref. 20 μPa
- higher exposure values for workers to noise triggering action: exposure level L EX,8h = 85 dB (A) and peak sound pressure pcrête = 140 Pa or 137 dB (C) ref. 20 μPa
- local residents, with regard to their quietness and even their health, as the observation of psychosomatic disorders is not rare in the event of excessive noise levels, which are likely to degrade the quality of life in general - that of sleep in particular - and to generate highly undesirable stress during waking periods. The French regulations, if applied, distinguish between the daytime period (7 a.m. to 10 p.m. except Sundays and public holidays) and the nighttime period (10 p.m. to 7 a.m. as well as Sundays and public holidays):
- in some cases, a prefectural decree (when it is not ministerial) sets the noise levels not to be exceeded at the property boundary: this is particularly the case for Facilities Classified for the Protection of the Environment (FCPE) e.g. 70 dB(A) during the day and 60 dB(A) at night
- emergence i.e. the difference between the equivalent continuous A-weighted pressure levels of ambient noise (industrial noise sources in operation) and residual noise (in the absence of industrial noise sources, but measured over the period of operation of the industrial noise sources) is limited in the Regulated Emergence Zones (REZ), which generally include, near the technical facility: homes, building zones and areas occupied by third parties e.g. Public Access Buildings (PAB), other industrial establishments. If the ambient noise level in the REZ (including the industrial noise sources) is between 35 dB(A) and 45 dB(A) then the admissible emergence is 6 dB(A) during the day and 4 dB(A) at night. If the ambient noise level in the REZ (including industrial noise sources) is greater than 45 dB(A) then the admissible emergence is 5 dB(A) during the day and 3 dB(A) during the night.
- in the case of a Facility Classified for the Protection of the Environment (FCPE), the marked tone, the presence of which is linked to the difference between the sound pressure level in a given 1/3 octave frequency band and the adjacent frequency bands, is considered undesirable if it exceeds 10 dB in the frequency range 50 Hz-315 Hz or 5 dB in the frequency range 400 Hz-8000 Hz
ITS helped reduce exposure to industrial noise for workers and local residents at a site in the Middle East.
As it came to a gas-fired power plant, the main sources of noise covered by the soundproofing work to which this article relates were (not to mention other noisy equipment covered by other phases of the site's noise control project, e.g. generators and steam turbines):
- the (2) combustion turbines themselves
- plenums for air intake ducts and exhaust ducts
Design study and construction of equipment for the reduction of exposure to industrial noise
The design study and construction of equipment to reduce exposure to industrial noise are at the heart of ITS's business, which markets:
- silencers of all types
- noise barriers
- soundproofing canopies
- high-performance (industrial) buildings
Given the nature of the noise sources concerned, their size and their unusual sound emissions (the sound power level of some of the sub-assemblies listed above is around 140 dB(A) in a wide frequency range, which is considerable - it is the last soundproofing principle listed above which has been retained, both for the turbines and for the plenums. In such cases, the structures considered include a metal framework and:
- for fixed or easily removable parts, by elements: industrial soundproofing panels with an absorbing face (modular)
- for acces: (rotating) acoustic doorsets with, for translucent parts (with glazing guaranteeing residual safety in the event of accidental breakage): acoustic window sets
In addition, the ventilation air inlets and outlets (the latter: with fans which must - also - be soundproofed -) have been equipped with ventilation silencers (to ensure the necessary continuity of sound insulation).
For such buildings, the studies are, of course, multidisciplinary:
- structural calculations: taking into account site conditions (rain, snow, wind, and seismic risks) and enabling the dismantling of very large wall surfaces (sometimes including roof parts) to provide the required stability during repair/replacement of very large enclosed hardware
- acoustic calculations: sound transmission through the building's structural elements and noise propagation towards various locations of interest, near the walls for the protection of personnel - a sound pressure level below 80 dB(A) at 1 meter is often required - such as at the boundary of industrial property or even beyond for the protection of neighbors (simulations using predictive acoustics software [1] are essential)
- aeraulic calculations: for the sizing of a ventilation system that must maintain the temperature rise due to the heat output of the enclosed sources within specified limits to achieve acceptable working conditions for personnel assigned to supervision and maintenance and to prevent overheating of sensitive equipment
- electrical study: for the installation of fans and sensors
The construction meets the highest standards, both for the sourcing of raw materials and components, and for the manufacturing and assembly involved, for structures that must withstand the test of time and the various stresses resulting from their installation location.
ITS and its commercial partners have experience with numerous similar projects, providing a basis for a long-term performance commitment for such equipment aiming at reducing industrial noise exposure.
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Buildings for the reduction of exposure to industrial noise in a power plant similar to those covered by this article |
In addition to sound enclosures and noise-barrier walls, ITS markets, for reduction of exposure to industrial noise (visible in the photo opposite but not delivered as part of the project subject of this article) soundproofed air intake systems for combustion turbines / gas turbines, exhaust silencers for combustion turbines / gas turbines, and also Vent silencers for pressurized gas | |