What regulations for noise at work?

Noise at work is a nuisance that can be considered from different angles, possibly inducing (variable depending on the context):

  • with regard to workers:
    • conditions for carrying out their tasks leaving something to be desired (e.g. to concentrate)
    • difficulties in oral communication (viva voce or by telephone: to understand and be heard), not only when discretion[1] or confidentiality[2] are desirable
    • stress, fatigue and risks to physical integrity, when audible warning signals are not correctly perceived and risks of hearing loss
  • with regard to the company that employs workers:
    • degraded working atmospheres
    • decreases in the quality of productions
    • absenteeism and recruitment difficulties
    • administrative complications and costs in the event of proven occupational deafness

It is therefore permissible to consider the regulation of noise at work as a good thing for all, being - in France - based on specifications concerning:

  • the sound levels to which employees may be exposed
  • the minimum characteristics of noisy premises, in terms of soundproofing

Regulations for noise at work: specifications concerning the sound levels to which employees may be exposed

In terms of regulations for noise at work, concerning the sound levels to which employees may be exposed, Directive 2003/10/EC of the European Parliament and of the Council of 6 February 2003 on the minimum health and safety requirements relating to the exposure of workers to the risks due to physical agents (noise), transposed into French law, constitutes the reference document for:

  • the peak sound pressure (ρpeak) i.e. the maximum value of the instantaneous sound pressure measured with frequency weighting C
  • the daily noise exposure level (LEX,8h ) (dB(A) ref. 20 μPa) i.e. the time-weighted average of the noise exposure levels for a nominal eight-hour working day (taking account of impulsive noise, if any)
  • the weekly noise exposure level (LEX,8h) i.e. the time-weighted average of the daily noise exposure levels for a nominal week of five eight-hour working days

Exposure limit values and exposure action values in relation to daily noise exposure levels and peak sound pressure are set at:

  • exposure limit values: LEX,8h = 87 dB(A) and ρpeak = 200 Pa i.e. 140 dB (C) ref. 20 μPa respectively
  • upper exposure values triggering the action: LEX,8h = 85 dB(A) and ρpeak = 140 Pa i.e. 37 dB (C)ref. 20 μPa) respectively
  • lower exposure values triggering the action: LEX,8h = 80 dB(A) and ρpeak = 112 Pa i.e. 135 dB (C) ref. 20 μPa respectively

Regulations for noise at work: specifications concerning the minimum characteristics of noisy premises, in terms of soundproofing

In terms of regulations for noise at work, concerning the minimum characteristics of noisy premises, in terms of soundproofing, the Order of 30 August 1990 taken for the application of Article R. 235-11 of the Labor Code and relating to the acoustic correction of work premises is the reference document, for the decrease in sound level by doubling the distance to the source DL. The minimum values are set, according to the floor area of room S (in square meters) at:

  • in the case of a room empty of any machine or production facility:
floor area of room Sbelow 210 m2between 210 m2 and 4600 m2above 4600 m2
 DL in dB(A) 2 1,5 log10 (S) - 1,5 4
remark - S in m2 in the formula -
  • in the case of premises after installation of production machinery and equipment
floor area of room Sbelow 210 m2between 210 m2 and 1000 m2above 1000 m2
 DL in dB(A) 3 1,5 log10 (S) - 0,5 4
remark - S in m2 in the formula -

The above specifications are applicable for the construction or fitting out of work premises, where machines and devices likely to expose workers to a daily noise exposure level greater than 85 dB (A) must be installed, whether a predictive acoustic study shows it, or such a study is lacking.

Area of intervention of ITS in relation to the regulation of noise at work

The areas of intervention of ITS in relation to the regulation of noise at work vary according to the context:

  • on-site measurements of the physical parameters basing the specified limits:
    • sound pressure levels (on the one hand: peak and on the other hand: equivalent continuous)
    • decrease in sound level by doubling the distance to the source

      Such sound metrology can be carried out with own-owned acoustic measurement means by a human resource duly qualified in physical measurements (specialized in instrumental techniques), with extensive experience in the field of noise-related data acquisition and processing, as required for a diagnosis at workplaces, e.g. relation to dedicated standards
  • ISO 9612 Acoustics - Determination of occupational noise exposure - Engineering method
  • NF EN ISO 14257 Acoustics - Measurement and parametric description of spatial sound distribution curves in workrooms for evaluation of their acoustical performance

The results of the sound level measurements carried out can give rise to the preparation of noise maps, and can - like those concerning the spatial decay rates[3], be compared to the regulatory limits for a compliance review ; in addition to regulatory impositions, ITS can measure the reverberation time of work premises[4]

  • in the case of non-compliance of measurement results with regulatory specifications, (in the context of an engineering assignment) identification of areas for improvement and development of action plans:
    • calculations for sound propagation, absorption and transmission
    • simulation of noise or reverberation diminution efficiency
      • reduction of noise at source: canopies for noisy equipment, soundproofing enclosures for machines and production lines, silencers
      • limitation of the propagation of noise by means of acoustic screens (anti-noise walls) or soundproof cabins for staff
      • reduction of the reverberation rooms by the implementation of sound-absorbing materials (e.g. soundproofing wall panels, acoustic ceiling tiles and baffles suspended from the underside of roofs)

ITS has means of simulation and calculation in terms of predictive acoustics (some: analytical, others: based on ray tracing) available to a qualified human resource in building physics, with long experience of studies relating to noise reduction in an industrial environment.

Can one imagine that Research and Development, or even compatibility tasks can be carried out properly in a sound environment characterized by a sound pressure level of 80 dB(A) which would comply with the applicable noise regulations?

Because the regulations only provide minimum requirements, from the point of view of the safety and health of employees, it is permissible, in some contexts, to consider being a little more ambitious in terms of acoustic comfort of the work premises and workplaces ; recourse can then be made to ITS for a personalized study of the acoustic comfort of all workplaces (including individual or collective offices, i.e. open spaces and associated spaces such as company restaurants for which there are reference standards, although not - in general - of mandatory application[5]).

In addition, in addition to its consulting activity, ITS markets all the soundproofing solutions (components and systems) for workspaces that meet regulatory requirements relating to noise.

Spread the word !


[1] situation obtained when an effort is required to understand the content of a conversation; then, the conversation is not a source of distraction

[2] situation obtained when even with an effort to understand a conversation, it remains incomprehensible

[3] slope in decibels of the spatial sound decay curve in a given distance range, when the distance to the source doubles

[4] time interval required for the reduction in a ratio of 1 million to 1 of the sound pressure after interruption of a sound source

[5] Acoustics - Offices and associated areas - Acoustic performance levels and criteria by type of area

What are the input data useful for the simulation of the dissipation (absorption) of an acoustic structure ?

The input data useful for the simulation of the dissipation (absorption) of an acoustic structure are mainly the type of fluid, its thermodynamic state (pressure, temperature, density), and also - of course - intrinsic characteristics of each layer.

In a concrete and exhaustive way, the evaluation of the dissipation of an acoustic structure (absorbing sound - either as panel or lining for walls or roof in a room or as filling in a noise reduction device that a silencer is -) requires knowledge of the following input data (listed in the order of their input for a calculation with the SILDIS® software Module 2 / 2+ Prediction of acoustic performance of plane partitions and walls :

  • temperature
  • pressure
  • (in case of the presence of a porous medium):
    • (as a minimum) resistivity, porosity, (and, if known) tortuosity, thermal and viscous characteristic lengths (or else designation of the nature - e.g. rock, glass, basalt, polyester, ceramic wool or foam to be precised -, trade name and density)
    • thickness
  • (in the event of the presence of a surfacing, if it is not modeled as a porous medium):
    • superficial air flow resistance
    • weight per unit area
    • thickness
  • (in the event of the presence of a perforated protection, if it is not modeled as a porous medium):
    • designation of the geometry of the holes (e.g. circular, square, slot-shaped perforation) and their arrangement (e.g. square, hexagonal, staggered)
    • diameter or side of holes / width of slots
    • center distance (for slots only)
    • perforation rate
    • thickness
    • (optionnal) mass density, the consideration of this parameter allowing, in some contexts, to improve the accuracy of prediction

In the event that it is not clean dry air, the additional following input data (for gas at silencer operating conditions) would be required:

  • individual constant
  • adiabatic constant
  • density
  • speed of sound
  • dynamic viscosity
  • specific heat at constant pressure
  • thermal conductivity

This is the list of useful input data to simulate the dissipation / sound absorption of an acoustic structure in linear regime. In the nonlinear regime, the characteristics of the acoustic excitation (nature, sound pressure levels per frequency band) must also be considered.

How to carry out the depollution of exhaust gases from internal combustion engines with an SCR process ?

Products of a combustion process, the exhaust gases from internal combustion engines contain atmospheric pollutants such as nitrogen oxides (NOx):

  • nitric oxide NO
  • nitrogen dioxide NO2

It is well known that these molecules are toxic, posing serious health problems (e.g. concerning the respiratory system of humans), and that they have harmful effects for the environment (e.g. contributing to the phenomenon of acid rain).

The depollution of combustion engine exhaust gases is possible in particular through Selective Catalytic Reduction (SCR).

It is a question of causing chemical reactions specific to recombining (with nitrogenous compounds) the molecules constituting the undesirable gases that NOx are, to obtain compounds as harmless as nitrogen (N2) and water (H2O) usually contained in (wet) air. [1]

Urea CO(NH2)2 in aqueous solution is a nitrogenous compound widely used for the Selective Catalytic Reduction (SCR) of nitrogen oxides (NOx) contained in the exhaust gases of industrial engines.

A precious alloy e.g. tungsten W or vanadium V on a support based on titanium oxide TiO2 often serves as a catalyst for chemical reactions which generally occur at temperatures between 250°C and 520°C.

The depollution of exhaust gases from internal combustion engines can then be carried out by means of metal cassettes whose internal, porous parts allow the circulation of their mixture with the nitrogenous compound.

A Selective Catalytic Reduction (SCR) module - requiring a continuous supply of urea, with dosage managed by the means of an automaton and of sensors - can thus complete the noise reduction devices of an exhaust line that reactive (i.e. whose operating principle is based on changes in the geometry of the internal parts with chambers) or dissipative (i.e. whose effectiveness is linked to the presence of porous materials that absorb sound) silencers are.

Although it is generally a very distinct sub-assembly, the Selective Catalytic Reduction (SCR) module can, in somes cases, be combined with a silencer to obtain an assembly offering the features of limitation of emissions of polluting compounds and of noise.

The dimensioning of such components of an industrial combustion engine exhaust line (including for gensets) must be the subject of an overall study, taking into account the combination of :

  • in terms of acoustics: the insertion loss of each component (for silencers, depending on their design: at low and/or medium and/or high frequencies; for the SCR Selective Catalytic Reduction device: only at high frequency)
  • in terms of aerodynamics: the total pressure loss of each component (it is not uncommon for it to be of the same order of magnitude)
  • in terms of general arrangement: the size of each component (it is not uncommon for it to be of the same order of magnitude, and for the part dedicated to the mixture between the nitrogen compound and the exhaust gases - upstream of the reactor – to have to be combined with a primary silencer in view of compactness)

Experience counts to offer in all contexts an optimized solution for high-performance equipment built to last, for the pollution control of industrial combution engines exhaust gases with a Selective Catalytic Reduction (SCR) process of nitrogen oxides (NOx) such as for noise reduction.


[1] the principle of depollution of combustion engine exhaust gases by means of a Selective Catalytic Reduction (SCR) process is based on the following typical chemical equations :

2 NO + 2 Nacfq + 1/2 O2 → 2 N2 + 3 H2O
NO2 + 2 Nacfq + 1/2 O2 → 3/2 N2 + 3 H2O
NO + NO2 + 2 Nacfq → 2 N2 + 3 H2O
Description

Which noise reduction of control valves ?

When it comes to limiting noise emission due to discharge, noise reduction of control valves can be obtained by means of a suitable silencer, installed in the end of the piping line.

Such silencers are generally composed of a diffuser (upstream) and of a dissipative stage (downstream).

The diffuser is a perforated element, at which a change occurs (that is desired to be downwards) of the turbulence noise and shock noise, the presence of small diameter perforations causing a peak in noise generation for  high frequency. In addition, the presence of the diffuser causes a total loss of pressure on which attention must be paid (*).

The dissipative stage, in turn, consists of a lining (preferably: with high sound absorption), often used as filling of splitters, sometimes concentric (else: transverse), allowing for noise attenuation in a frequency range more or less extended namely depending on the acoustic characteristics of the porous medium and of its possible surfacing, on the geometry of the dissipative stage and on the nature and passage speed of the fluid.

In addition, the presence of the dissipative floor causes a total loss of pressure (usually less compared to that of the diffuser) on which attention must be paid (*) and generates self noise for which it is important to make sure that it is compatible with the noise reduction target to be considered as part of a project for which the implementation of a silencer is envisaged.

* Especially vis-à-vis the operating conditions of the valve on the downstream pressure which affects (upward)

Link to learn more about control valves noise calculation

What are the main parameters influencing control valve noise ?

Control valves (a fortiori when operating under conditions of high pressure drop) can contribute significantly to industrial & process plant noise, namely due to aerodynamic noise generation depending on valve data & process data, main parameters being as follows:

  • Valve inlet absolute pressure
  • Valve outlet absolute pressure
  • Liquid pressure recovery factor of a valve with or without attached fittings
  • Pressure differential ratio factor of a control valve with or without attached fittings at choked flow
  • Valve style modifier
  • (Required) Flow coefficient
  • Acoustic power ratio or Valve correction factor for acoustical efficiency
  • Molecular mass of flowing fluid
  • Inlet absolute temperature
  • Density of fluid at inlet
  • Specific heat ratio
  • Mass flow rate
  • Strouhal number
  • Outlet absolute temperature
  • Density of fluid at outlet
  • Speed of sound at downstream conditions
  • Valve outlet diameter
  • Internal downstream pipe diameter
  • Contraction coefficient for valve outlet or expander inlet

When valve style modifier is not an available explicit input data, additional parameters must be accounted

  • Area of a single flow passage 
  • Wetted perimeter of a single flow passage
  • Number of independent and identical flow passages in valve trim

When flow indicators are not available explicit input data, additional parameters must be accounted

  • Liquid pressure recovery factor of a valve without attached fittings
  • Upstream inside pipe diameter

Links to learn more about control valves noise calculation

More Articles