ITS will contribute to the reduction of the exposure to noise emitted by a high-capacity industrial compressor located at a chemical plant in Northwestern Europe. Such a mechanism for increasing fluid pressure (in this case, hydrogen) invariably generates significant noise emissions - spanning a wide frequency range - from various components such as motors, drive assemblies, and compression elements, even though strict noise exposure limits must be observed.
- for site employees who need protection against the risk of long-term hearing damage and against risks associated with the potential masking of alarm signals such as those indicating process malfunctions or warnings related to the movement of vehicles or machinery. European Directive 2003/10/EC concerning the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (noise) is a reference document, fixing:
- 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
- for local residents who need to be protected from noise nuisance. French regulations, if applied, distinguish between the daytime period (7:00 a.m. to 10:00 p.m. except Sundays and public holidays) and the nighttime period (10:00 p.m. to 7:00 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 (considered industrial site in operation) and residual noise (in the absence of the considered industrial site, but measured over the period of operation of the considered industrial site) is limited in the Regulated Emergence Zones (REZ), which generally include, near the considered industrial site: 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 considered industrial site noise) 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 considered industrial site) 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
Besides air intake soundprrofing (using a silencer with sound-absorbing baffles, often integrated into a filtration stage), reducing noise exposure from such a large-capacity outdoor compressor requires the construction of a fairly large building (in this case, a footprint of around 100 m² and a height of approximately 6 m). To allow for the dismantling required for maintenance operations (during which structural stability must be guaranteed, even - and especially - in high winds when elements contributing to the building's overall rigidity are absent) the structure is often, as in this instance, a metal building featuring a steel 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
To meet the project's ambitious goals for noise mitigation regarding the high-capacity compressor - which necessitates construction systems achieving a weighted sound reduction index (Rw) of 55 dB for facades and 49 dB for the roof (with significantly higher acoustic insulation performance at high frequencies) - special construction designs will be considered. These designs will combine two essential functions:
- reducing the sound power transmitted through the partitions
- limiting sound transmission at interfaces; on the one hand between structural elements themselves and on the other hand between those elements and their boundaries (such as the ground or obstacles)
Controlling reverberation within the building (exacerbated by its large volume) will be a key factor in the project's success. The aim is to use sound-absorbing materials to eliminate the amplification of internal noise levels - caused by sound waves reflecting off the building's boundaries - as this phenomenon would otherwise lead to increased external noise levels, which is highly undesirable in a soundproofing context. Regarding the building's acoustically reinforced partitions, only acoustic door assemblies and glazing units will lack such materials, which are characterized by an absorption coefficient close to 1 (i.e. 100%) based on the weighted sound absorption coefficient alpha-w (αw).
Limiting noise propagation at the openings will also be a key requirement of the project to reduce noise exposure from this industrial compressor. For this reason, the air intakes and outlets will be equipped with ventilation silencers; the resulting total pressure loss will have to be compensated for by the use of fans—which are inherently noisy—that will also need to be soundproofed.
When entrusting such a project to ITS and its business partners, the Client (a major international engineering firm) notably relies on:
- the full consideration of all technical constraints
- the development of a high-performance solution to reduce compressor noise exposure - using an extensive experience in the field - based on in-depth analysis across diverse areas such as acoustic insulation, metal construction, and electrical systems (including the ventilation system and its control sensors)
- the manufacture of robust noise-control equipment that undergoes rigorous quality checks and integrates seamlessly into the specific industrial site environment
- a smooth project management and a constructive approach to handling unforeseen issues
- adherence to schedules and cost control
It is precisely these factors that prompt many other clients to engage the expertise of ITS and its business partners for similar industrial noise reduction projects, not only in Europe (covering engineering - including acoustic metrology where required - and turnkey construction and installation, unless only site supervision is wished).
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