Noise Limits for Sleep Environments

FMN Contributing Author

Sound while you sleep has a big impact on the sleep you get. Two aspects of noise in the sleep environment need to be considered.  The first aspect is the baseline level of continuous noise.  If the sound frequencies in the noise are perfectly constant and not unpleasant, we can usually get used to the noise and eventually sleep right through it. This concept is used in white noise generators.  White noise contains all of the audible frequencies, and when it is played over the background noise in the sleep environment, it turns all the noise into a constant set of sound frequencies with the background noise fading right in. For most people, this means better sleep.  Some people, however, find white noise unpleasant.  Here is a sample of white noise: . If you find white noise unpleasant, pink noise might be a little more bearable: . Pink noise focusses a little more on the lower frequencies.  If you like pink noise, you might like brown noise even more: , it focusses even more on the more pleasant lower frequencies.

As a Fatigue Manager you could suggest that your workforce use one of these noise types to drown out background noise in their sleep environments to improve their sleep.  Or, if you are designing a nap room or sleep space for them, you could add one of these noise types to the space (check this sound machine out) but, just be careful how loud you make the noise.  According to the World Health Organization[1], and others [2], the maximum volume of constant noise should be 40 dBA. So you can’t just keep turning up the white noise to drown out any background noise.  When background noise is too loud, earplugs or sound proofing the sleep environment might be necessary…or if possible and even better, get the people or machines making the noise to be quiet!

The second aspect of noise that needs to be considered is the level of intermittent noise in the sleep environment.  When noise is not constant, it seems that a 10 dBA increase from the average noise level is the waking threshold [2, 3]. This means that even if the level of constant noise is less than 40 dBA, if it intermittently fluctuates louder by 10 dBA, it will disrupt sleep.

Taken together, these limits suggest that all noise should be confined to lower than 40 dBA and any fluctuations should be confined to less than 10 dBA variations for all sleep environments.  If you go beyond these limits, the sleep your workforce obtains may not be as efficient and fatigue risk will increase.  This is because noise during sleep leads to more awakenings, longer periods of wakefulness after falling asleep and shorter periods of deep sleep[4] and less REM sleep[5]. These are all hallmarks of poor quality sleep[6].