# Industrial noise

Industrial noise, or occupational noise, is often a term used in relation to environmental health and safety, rather than nuisance, as sustained exposure can cause permanent hearing damage. Industrial noise is a hazard traditionally linked to heavy industries such as ship-building and associated with noise-induced hearing loss (NIHL), a form of occupational hearing loss. Modern thinking in occupational safety and health further identifies noise as hazardous to worker safety and health in many places of employment and by a variety of means.

Noise can cause hearing impairment at long-term exposures of over 85 decibels (known as an exposure action value), and it also acts as a causal factor for stress and raises systolic blood pressure.

Noise can be a causal factor in work accidents, both by masking hazards and warning signals, and by impeding concentration. Noise acts synergistically with other hazards to increase the risk of harm to workers. In particular, noise and dangerous substances (e.g. some solvents) that have some tendencies towards ototoxicity may give rise to rapid ear damage.

A-weighted measurements are commonly used to determine noise levels that can cause harm to the human ear, and special exposure meters are available that integrate noise over a period of time to give an Leq value (equivalent sound pressure level), defined by standards.

## Reduction

Acoustic quieting is the process of making machinery quieter by damping vibrations to prevent them from reaching the observer.

Noise decreases as distance from its source increases. When two identical noise sources are side by side producing a recorded noise of, say, 100 dB(A) the reduction in noise from removing one of the noise sources is about 3 dB, resulting in 97 dB(A). When the distance to a noise source is doubled the recorded noise level is reduced by 6 dB, sometimes called the Rule of 6.

The noise attenuation in decibels at a distance from the source $d$, knowing the SPL at distance $d_0$, is $20log_{10}\left(\frac{d}{d_0}\right)$. If the distance is doubled, i.e. $\left(\frac{d}{d_0}\right)=2$, the attenuation becomes 6.02 dB (6 for most practical purposes).

## Regulation

Since the hazards of occupational noise exposure were realised, programs and initiatives such as the US Buy Quiet program have been set up to regulate or discourage noise exposure. The Buy Quiet initiative promotes the purchase of quieter tools and equipment and encourages manufacturers to design quieter equipment.[1]

Industrial noise can also be regulated by legislation. A 2012 Cochrane review found low-quality evidence that legislation reduced industrial noise both immediately and in the long-term.[2]