Tinnitus or "ringing in the ears" is my constant companion due to spending long hours in shipboard engine rooms during my six years of military service. A friend also has tinnitus, but his diagnosis is very different from mine. An ear, nose, and throat doctor told my friend (who has been a contract network engineer for 25 years) that spending long hours in data centers could very well be the reason for his tinnitus.
I remember my first time in a data center; I could not imagine spending eight hours a day in that environment. Still, until my friend mentioned his tinnitus, I assumed noise levels in data centers were acceptable.
Current OSHA standards
When it comes to noise-exposure guidelines in the workplace, two government agencies get involved: the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH). NIOSH provides recommendations about occupational safety and health, whereas OSHA creates and enforces the regulations.
The slide in Figure A, from this paper (PDF) by Patricia A. Niquette, AuD provides recommended and permissible exposure times to different noise levels.
The 85 dBA range (circled in red) is important to those who work in data centers for a number of reasons. The fact that OSHA requires monitoring of workspaces where noise levels approach 85 dBA implies that it is a significant threshold. Yet, that significance seems moot compared to the disparity between OSHA's Permissible Exposure Limit and NIOSH's Recommended Exposure Limit at 85 dBA — 16 hours vs. 8 hours, respectively.
The bottom of this OSHA report lists how other organizations regulate noise exposure, including the World Health Organization. It appears most countries have noise exposure limits similar to what OSHA requires.
Tad Davies, executive vice president of The Bick Group Inc., a company that designs and builds data centers, recalls in this Computerworld article, only one time when an IT manager asked for noise-level measurements in a Bick Group constructed data center. The readings ranged from a low of 70 dBA to a high of 79 dBA.
Data indicates hearing loss is cumulative
In Niquette's paper, she cites a 2009 study by Sharon G. Kujawa and M. Charles Liberman that questions previously held beliefs about our ability to recover from noise trauma. The scientists found that certain parts of the inner ear (i.e., the basal region of the cochlea) do not recover and exhibit dramatic degeneration when exposed to high noise levels (Figure B).
Kujawa and Liberman also point out, "This kind of damage is undetectable using current test methods, and damage is not seen until weeks or months after the exposure." Niquette put it more bluntly, "The implication of this research is that noise can produce subclinical damage that goes undetected, progresses unnoticed, and finally manifests itself long after the fact."
No cure for noise-related hearing loss, but it is preventable
Hearing disorders caused by medical reasons (even tinnitus) can be cured by removing the underlying cause, but that is not the case if prolonged exposure to excessive noise caused the hearing impairment. My friend doesn't want to make his tinnitus worse so now he wears noise-cancelling headphones when working in data centers.
The technology used in noise-cancelling headphones has been around since the 1950s, with notable advances being made recently. One example is Brigham Young University's Acoustics Research Group under the auspices of Dr. Scott Sommerfeldt and their development of Active Noise Control (ANC). From the group's website:
"Active Noise Control (ANC) is based upon the principle that two sounds of equal amplitude and opposite phase cancel each other out, leaving silence."
To get an idea of how ANC works, consider the noise pattern at the right (image courtesy of nongnu.org). Using a microphone, ANC captures the noise, creates a duplicate noise pattern of equal strength but 180 degrees out of phase, and then sends the cancelling noise to a speaker —all in real time.
Dr. Sommerfeldt has used ANC to quiet everything from operator cabins on heavy earth-moving equipment to cooling fans used in computers.
To help those who work in data centers, Dr. Sommerfeldt and the Acoustics Research Group have been working with C7 Data Centers, an outsourcing service with several large data centers, affording Sommerfeldt and his team ample opportunities to test ANC (PDF).
Tinnitus sucks, so please err on the side of caution when it comes to hearing loss. If OSHA decides to rethink and decrease exposure limits tomorrow, it won't help those of you dealing with noise in data centers today.
Share your experiences
Does your company monitor the noise levels in its data centers? If you work in a data center, do you suffer from hearing loss? How do you try to prevent hearing loss and/or slow hearing loss progression? Post your thoughts in the discussion.
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