Workplace Noise Survey

A-weighting

A frequency weighting devised to attempt to take into account the fact that human response to sound is not equally sensitive at all frequencies; it consists of an electronic filter in a Sound Level Meter (SLM), which attempts to build this variability into the measured noise level reading so that it will correlate, approximately, with the human hearing (defined in BS EN ISO 61672-1). Measurements are usually displayed as dB(A), or LAeq for sound pressure levels. 

​

C-weighting

This is a standard frequency weighting for Sound Level Meters and corresponds to the 100 Phon (perceived loudness) equal loudness contour. It is the closest to a liner or unweighted sound level value, with a relatively flat response between 63Hz and 4kHz. It is commonly used for high level noise measurements, peak sound pressure levels and correlates better with the human response to high noise levels at low frequencies (as defined in BS EN ISO 61672-1). C-weighting is used in the Control of Noise at Work Regulations 2005 for peak sound pressure measurements and are typically displayed as dB(C) or LCeq and LCPeak. CIHL Chemically Induced Hearing Loss – ototoxic substances are chemicals which result in hearing loss.

 

Decibel (dB)

The decibel is the main unit of measuring sound intensities commonly used in acoustics and is an expression of a ratio between two quantities expressed in logarithmic (log) form. It is a numbering scale used to compress a large range of values into a more manageable smaller scale. In scientific terms, the decibel is a unit for expressing the ratio of two powers (electric or acoustic) equal to 1/10 (deci) of a Bel. The threshold of hearing is 0dB and the threshold of pain is approximately 130dB dependent on frequency. In practical terms these limits are seldom experienced and typical levels lie within the range of 30dB (a quiet night-time level in a bedroom) to 80dB (at the kerbside of a busy city street).

​

Daily personal exposure level, LEP,d

This is a steady or constant level which, over 8-hours, contains the same amount of A-weighted sound energy as is received by the subject during the working day (defined in ISO 1999:1990).

​

The LEP,d is directly related to the risk of hearing damage.  

​

Weekly personal exposure level, LEP,w

The weekly personal noise exposure level for a normal week of five working days.

Equivalent continuous sound pressure level (A-weighted) LAeq

This is the continuous equivalent noise level of a time varying noise; the steady noise level (usually in dBA) which, over the measurement period, contains the same amount of (A-weighted) sound energy as the time varying noise over the same period; also called time averaged sound level.

A measure of the average sound pressure level during a period of time, in A-weighted decibels.

 

Frequency, Hertz (Hz)

The pitch of the sound, measured in Hertz.

Sound pressure is only part of the description; sound also varies in frequency and over time. Frequency is measured in Hertz (Hz) which is defined as cycles per second. The audible range for the human ear is roughly 20Hz to 20,000Hz or 20kHz, although this varies from person to person. Most audible sounds are detectable between 50Hz and 12kHz. Although, for the purpose of noise at work assessments we are mainly interested in the frequency ranged between 63Hz and 8kHz, as standardised. 

 

Advisory hearing protection zone (AHPZ)

Any area of the workplace where an employee is likely to be exposed to noise at or above the lower exposure action value (80dBA) and below the upper exposure action value (85dBA).

​

Mandatory hearing protection zone (MHPZ)

Any area of the workplace where an employee is likely to be exposed to noise at or above the upper exposure action value (85dBA).

​

Sound level meter (SLM) or sound pressure level (SPL) meter

An instrument for measuring sound pressure levels.

This instrument may be used in most work environments. A sound-level meter will generally measure in the range 10-130dB and may be connected to octave and one-third-octave band filters to analyse the frequency characteristics of the noise concerned. Sound-level meters are available with a variety of functions and levels of accuracy - it is important to be selective about this, as it has a bearing on the expense and usefulness of the data produced.

 

The microphone is the most sensitive part of the instrument, and should be protected against impacts, moisture and dust, as well as air movement - which can cause spurious responses. The instrument should be held at least one metre away from the user, or any surface to prevent errors due to reflections.

 

Sound-level meters cannot be used to measure impulsive sounds as their response time is too slow. However, impulse meters are available.

 

Sound meters must be regularly calibrated against a known standard, and routinely checked with a local calibration device before and after every use - including after a battery change.

​

Single number rating (SNR)

A single number rating system for hearing protectors expressed in dB and used as a guide to compare the potential noise reduction capability. This method requires a C-weighted average sound level measurement (LCeq) for each 'noise risk' area and the manufacturers SNR figure for the specific protector (as defined in BS EN ISO 4869-2:2018). 

             

Sound pressure level Lp

The basic measure of noise loudness, expressed in decibels, usually measured with an appropriate frequency weighting (e.g. the A-weighed SPL in dB (A).

Sound pressure level is a logarithmic measured of the root mean square (rms) sound pressure represented on the decibel scale relative to the reference sound pressure. The reference sound pressure (p0), also known as the threshold of human hearing, is 2 × 10−5Pa and a level of 0dB. This is indicated by the equation:  Lp = 20Log10(p / p0).

​

Octave band analysers

These may be used to examine the frequency characteristics of noise, and the data may be printed via a computer or plotted manually. Third-octave band analysers provide detailed analysis, and electronic analysers can give very specific data on sound energy at particular frequencies.

 

Noise dosimeter

Instrument designed to continuously measure noise exposure.  

 

Dosemeters are electronic sound-level meters with in-built clocks and data-storage facilities. In effect, they measure the total sound energy impacting on the microphone, and so to the worker under observation. 

 

The individual worker may carry personal noise dosemeters, where they will directly measure the daily noise-exposure level. The microphone should be placed within one metre of the employee's head, ideally clipped onto the lapel or brim of a safety helmet. This ensures that the dosemeter receives the same sound pressure as the employee's ear, ensuring representative measurements. Useful for measuring a highly mobile person’s noise exposure.