Studies of noise-exposed populations clearly indicate that time spent working in noisy workplaces may lead to Noise-Induced Hearing Loss (NIHL). According to Basner et al (2013) NIHL can be caused by sound pressure levels higher than 75 to 85 dBA in industrial settings. It’s the combination of sound pressure levels and exposure time, however, that is critical in most cases.

Data on the impact of hearing loss varies from one region to another; however, in the USA it has been estimated that over 11% of the total workforce reports varying degrees of hearing difficulty. Of the reported hearing difficulties, approximately 25% can be attributed to workplace exposure (Tak and Calvert, 2008).

A 2013 US study concluded that circa 18% of noise-exposed workers have material hearing impairment (Masterson et al, 2014) as deﬁned by the National Institute for Occupational Safety and Health (NIOSH, 1998) criterion. Furthermore, an international review of NIHL concluded that occupational noise exposure causes between 7% and 21% of the hearing loss among workers (Lie et al, 2016).

Assessing noise exposures

In most jurisdictions noise levels are averaged during surveys using a metric known as the Equivalent Continuous Sound Pressure Level (Leq). The Leq value describes an equivalent steady noise level, i.e., the unfluctuating noise level at each measurement position that would have an equivalent energy level to the actual fluctuating noise over the duration of the sampling interval.

Leq is always an ‘equal energy measure’ corresponding to the 3 dB exchange rate, never to any other exchange rate (Marsh and Richings, 1998). In the USA, however, OSHA prescribes the use of a Time Weighted Average (TWA) noise exposure and in order to measure this an LAvg noise index is used.

In the USA LAvg is specified in Occupational Safety and Health Administration (OSHA) legislation and it is defined as ‘the average sound level over the measurement period’ and normally a Threshold Value is used during the calculation of LAvg where any levels below the Threshold Value are not included (OSHA, 2016). With some noise monitoring instrumentation, results in terms of both LAvg and LAeq are given.

The International Organization for Standardization (ISO) Standard 1999 (ISO, 2013) defines the index referred to as the noise exposure level normalised to a nominal 8-hour working day, which is designated LEX, 8h.

In simple terms, the LEX, 8h is a measure of the average noise energy a person is exposed to during a working day. It is determined by the average noise level and the amount of exposure time accumulated (A-weighted sound energy) during the working day.

Critical global differences

The following paragraphs look at the critical differences between European and USA legislation.

In the EU, wide-ranging legal obligations arise when the LEX, 8h of any employee exceeds 80 dBA (this is known as the Lower Exposure Action Value (LEAV). More onerous obligations arise in the EU when an employee’s LEX, 8h exceeds 85 dBA, which is known as the Upper Exposure Action Value (UEAV).

Under current Occupational Safety and Health Administration (OSHA, 2003) regulations, workers are not permitted to be exposed to an 8-hour time-weighted average (TWA) equal to or greater than 90 dBA. In effect this appears to be equivalent to an LEX, 8h of 90 dBA. To put this into context, however, at LEX, 8h levels of 90 dB one fifth of all workers will become ‘socially handicapped’ by the time they retire (Robinson, 1987). The higher the noise exposure, the greater the likelihood and severity of damage.

While OSHA regulations require employers to implement a Hearing Conservation Programme if workers are exposed to levels higher than an 8-hour TWA of 85 dBA, there is a very important difference between EU and USA assessment methodology. This is because OSHA uses a 5 dB exchange rate, meaning the noise energy doubles with each additional 5 dB. The exchange rate which is predominantly used worldwide (and the one recommended by NIOSH, 2016) is 3 dB. This means that workers in the US can be exposed to much higher levels of noise for much longer than their European counterparts.

In the USA the principal regulations concerning occupational noise in the manufacturing, utilities and service sectors (CFR 1910.95) provide for a Permissible Exposure Level of 90 dBA. In contrast to this, EU legislative requirements are markedly more stringent with extensive controls and obligations arising at 80 dBA (the LEAV).

Throughout the EU, employers are compelled to introduce Hearing Conservation Programmes when the LEX, 8h exceeds 80 dBA (the Lower Exposure Action Value) and this requirement does not apply in the USA until the 8-hour TWA exceeds 85 dBA.

EU employers are compelled to reduce the exposure of workers as far as is reasonably practicable by means of technical and/or organisational measures when the LEX, 8h exceeds 85 dBA (Directive 2003/10/EC). This is obviously more onerous than the US requirement that feasible administrative or engineering controls must be initiated when the TWA exceeds 90 dBA (CFR 1910.95). Furthermore, when considering the need for engineering or administrative controls, only those exposures to sound levels greater than 90 dBA are used in the USA calculation. It is therefore clearly evident that EU noise control criteria are more protective of workers’ hearing.