What is a Decibel?
Understanding the decibel scale may be complicated. Probably the most straightforward definition may be found at How Stuff Works. It states:
“The decibel scale is a little odd because the human ear is incredibly sensitive. Your ears can hear everything from your fingertip brushing lightly over your skin to a loud jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound. That’s a big difference!
On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB.”
Noise in the Laboratory
The OSHA standard for occupational noise is 90 dBA for an 8-hour time weighted average; this level of noise is the threshold for permanent hearing damage. With respect to noise in the laboratory, in a recent fact sheet on laboratory noise, OSHA stated: “The recommended upper limit for noise for speech to be intelligible is 55 dBA.”
- Lab Manager Magazine published an article last July, Can You Hear Me Now?. It summarizes the state of noise in the analytical laboratory, and cites a standard of 53 decibels (translated from another measurement scale, NC, aka noise criterion) for background noise for an analytical laboratory. The article suggests ways to measure the level of noise.
- Another Laboratory Magazine article, Laboratory Acoustics, has suggestions on laboratory design that help.
- The National Institutes of Health Office of Research Facilities recommends a maximum noise level of 40-45 NC (NC45 is equivalent to 45-55 decibels) in research laboratories, as stated in their Design Policy and Guidelines, published in 2003.
Noise and Health
Very few laboratories have noise levels that permanently damage hearing, at 90 decibels. However, evidence is growing that significantly less noise affects speech communication and reduces ability to perform cognitive tasks.
Many studies in occupational settings reveal that workers exposed to high levels of industrial noise for 5–30 years have increased blood pressure and statistically significant increases in risk for hypertension, compared to workers in control areas.
The World Health Organization published a number of reports in the late 1990’s that reported many effects of noise, other than hearing loss. “Among the cognitive effects, reading, attention, problem solving and memory are most strongly affected by noise.”
A review of the health effects of noise by researchers led by Dr. Mathias Basner, entitled “Auditory and non-auditory effects of noise on health“, published in October 2013 in the medical Journal Lancet, reports “Investigators have repeatedly noted that noise exposure increases systolic and diastolic blood pressure, changes heart rate, and causes the release of stress hormones (including catecholamines and glucocorticoids).”