Noise in the workplace

Tim Turney, global marketing manager, Casella, Bedford, England.

Workers in industrial settings may be exposed to noise that can cause long-term damage to their hearing. Most people understand that being subjected to a loud, instantaneous noise can damage hearing beyond repair, but employees exposed to a lower noise level over the course of their working life can suffer the same consequences. It can be difficult to understand the terminology used to measure noise and the respective limits we place on noise levels to protect employees, but employers will often work with consultants or other experts to ensure compliance. However, to improve employee engagement and awareness, having a better understanding of this terminology could help save workers from occupational hearing loss and other hearing-related diseases.

Sound is measured in decibels – a logarithmic scale that means every 3-decibel increase equates to double the amount of sound energy. This is referred to the exchange rate (Q), which, in this case, is what’s used in the United Kingdom and Europe is a Q=3. In the United States, a Q=5 is used for OSHA noise measurements. This doubling of noise energy also equates to a doubling of risk for hearing damage, making relatively small increases in decibels have a significant effect on employee health.

It depends on the local legislation, but, in general, there are two main types of “action levels,” or values. Firstly, based on exposure to noise over an 8-hour period, which, if exceeded, can cause hearing damage over the period of a working life. Suitable hearing protection must be made available for workers when there’s a daily or weekly exposure above action levels (for example, starting at 80 dB(A) for optional personal protective equipment in the EU and UK) and suitable hearing protection must be worn by employees when the daily or weekly exposure exceeds 85 dB(A). The 8-hour exposure is known as the L_EP,d in the UK, L_EX,8h in Europe and time-weighted average in the United States. These exposures are all standardized to an 8-hour workday so that individuals with different exposure times and shift durations can all be compared with the same action values.

With the 8-hour averaged action levels, employers must measure representative samples of employees’ exposure to noise. To do this, an average measurement must be taken, which in the UK is called an L_AEQ (Equivalent Continuous Sound Energy Level) and in the United States is known as L_AVG. This is a logarithmic average. This is done with a handheld sound level meter or a noise dosimeter, which can work throughout the day. In the case of the noise dosimeter, as it is worn throughout the day, it will display the 8-hour noise exposure.

An L_AEQ is the (A) weighted average, so simply being with a frequency weighting to represent how the human hears noise. If the workplace in which the sample is taken from is continuously noisy, then the measurement can be taken over the course of a few minutes, as this is a representative average of the conditions throughout the day. If the noise is more variable, longer samples will be needed to get a representative average and should be representative of where the individual exposed is located. This value is then used to calculate the exposure in line with the time that they’re in this environment.

Most people take the raw value of the measured average and wrongly take this as the 8-hour exposure level to compare it with action values – if the worker is only in an environment with this sound level for six hours and conducts other duties in quieter environments for the remaining two hours, you could be overprotecting them, costing extra money and even introducing risk.

The other action level that employers and workers should be aware of is referred to as peak noise level, exceeding this level of noise even once throughout the day can cause instantaneous hearing damage. In the UK, these action values start at 135 dB(C) and, in the United States, it’s 140 dB(Z). These are C-weighted parameters that in the UK are notated by L_Cpeak and in the United States, L_Zpeak. The “Z” and “C” in these parameters represent how the human ear responds to noise at these higher levels.

When using a measurement instrument, make sure you have the right parameters shown. Modern instruments allow you to select to a set of legislation (for example, OSHA) to ensure the right parameters and weightings are selected, so you don’t inadvertently select an incorrect parameter.

Measuring the level of noise exposure to an employee who’s stationary throughout the day is relatively easy. A handheld sound level meter can accurately collect the samples necessary to calculate the TWA across the working day.

This becomes more difficult for mobile workers who are exposed to varying levels of noise depending on their daily activities. To attain an accurate sample for these employees, a noise dosimeter should be attached to the person throughout their entire workday. With the worker wearing the device for the entire eight hours, employers can deduce their time weighted exposure by the readings taken by the dosimeter, without having to do any calculations.

As always, it’s advisable to work with experts in noise and environmental monitoring, such as industrial hygienists, and use monitoring equipment that’s accurate and reliable.

Editor's note: This article represents the independent views of the author and should not be considered a National Safety Council endorsement.