The more servers that are added to a datacentre, the more cooling that centre is likely to need. And the more cooling those servers require, the more "whoosh" is generated. Whoosh, for the uninitiated, is the annoying noise of fans and humming power supplies that can feel like a pressure in your head.

Datacentre workers live with this noise. It's part of the job, part of the culture. But there may be reason to start giving the noise issue more attention: datacentre consolidations and the adoption of high-density equipment -- both big industry trends -- are bringing more equipment and denser and hotter systems into datacentres.

There's a dearth of scientific data assessing noise trends in datacentres, its health consequences and the impact on productivity. Noise is simply taken for granted by datacentre managers who spend little, if any, time measuring sound levels. For the most part, datacentre workers just learn to deal with it.

"It's pretty loud, it's pretty stressful," said computer operator Bruno Skiba, who works at a financial services firm and wears ear protectors similar to those used on a firing range.

Noise, of course, varies from centre to centre, system to system. It's now fairly common for datacentre workers to spend a lot of time off the datacentre floor and manage systems in separate rooms.

And on a system level, noise can vary. While some racks may have high-speed, whinny fans, some Itanium-based servers from Hewlett-Packard have larger fans that are less noisy. Skiba's firm recently got a delivery of those quieter servers.

Taken in concert, the noise generated from all the equipment in a datacentre can be distracting. That fact prompted datacentre workers at C I Host, a Dallas-based hosting company, to get Bose noise-cancelling headphones to help make the work environment comfortable, said Christopher Faulkner, CEO at C I Host.

"The noise -- the pressure on their head, if you will -- is very distracting and causes serious issues with [workers] being able to concentrate and do their jobs," said Faulkner.

Faulkner said he's never measured the noise in his datacentre, something that wouldn't be surprising to Tad Davies, executive vice president of the Brick Group, a St. Louis-based company that designs and builds datacentres. Davies said he can recall only one IT manager who asked for sound level measurements. "It's been, universally, an issue that has not been brought up," he said.

Davies, without naming the customer, shared a schematic of the datacentre showing the decibel levels taken in 12 different places in the facility. The lowest was 70 dB and the highest 79 dB. The highest levels were recorded near HVAC equipment. At these levels, you have to talk loudly to be heard, but they are considered safe levels under US Government standards.

By comparison normal conversation is about 60 dB; a power lawn mower is about 90 dB, a jet engine at takeoff, 140 dB, according to the US National Institute for Occupational Safety and Health. The US Government sets workplace standards for noise, and doesn't require action until workers are exposed to average noise levels of 85 dB or greater during an eight-hour day.

Dr. Peter Rabinowitz, a member of the American College of Occupational & Environmental Medicine's Sensory Perception Committee, said he is unaware of any datacentre-specific research on noise. While OSHA sets standards for action, low frequency noise coming off fans and air handling systems can affect concentration and produce fatigue, he said.

"In general, I think people like to work in a fairly quiet workplace," said Rabinowtiz.

There is no single agreed-upon decibel level standard for protecting workers who must deal with the constant din of datacentre noise. But if workplace noise reaches 85 decibels (dB) it triggers some steps under law in the US. By contrast, Europe's workplace protections begin at the 80dB level.

The question is: who's measuring? There is a dearth of studies on noise in the datacentre, said Mark Stephenson, a senior research audiologist and coordinator National Institute of Occupational Safety & Health (NOISH) hearing research. NOISH is part of the US centres for Disease Control and Prevention.

"I'm not aware of studies that have demonstrated that working in a datacentre exposes you to hazardous noise," Stephenson said. "However, there certainly could be something out there.

"The trend toward larger and larger facilities would have a slow incremental increase in the noise level, so it's possible that something like [crossing the legal threshold for action] would creep up," said Stephenson.

If the noise level reaches 85dB over an eight-hour day, that should trigger some monitoring under Occupational Health and Safety Administration regulations. If noise levels hit 90dB then companies are required to take steps to protect workers' hearing.

Whether noise is an issue for an IT manager depends on the type of datacentre. In some future scenarios -- think of it as the ultimate lights-out datacentre -- the facility might be, in total, a computer: a highly interconnected operation that's remotely managed, with self-healing, self configuring systems that's rarely entered by personnel. Noise won't matter as much.

But most datacentre operations are far from the lights-out ideal and are run by people like Nick Martin, the IT manager at Taco Metals, a maker of marine products. Martin has been in IT since the 1970s and said noise reduction has always been important to him. He likes quiet. He especially likes to talk on the telephone with a vendor when he's working on some equipment, something that was impossible in his datacentre.

Martin replaced his ceiling tiles with sound deadening acoustic tiles and installed the same tiles on some of the datacentre's walls. "It really knocked the sound down quite a bit," he said.

Using a headset, Martin said it now is quiet enough to "go from my office to the computer room working with the Microsoft tech flawlessly so there is no interruption in tech support." That matters a lot, he said, because it helps avoid downtime.

There is a lot that can affect noise levels. Lower-power chips, for one, can reduce energy needs and cooling requirements. But working against low power chips is a trend toward putting more of them in compact systems: A 5kW rack might get replaced with a 20kW rack as part of a server consolidation.

The level of attention paid to noise reduction by manufacturers can vary. Some vendors put acoustic silencers on their racks, although these racks may cost more. And equipment can be designed to reduce noise, but that manufacturing priority depends on the customer.

Although vendors are aware of noise issue, buyers aren't pressing them to make it an important consideration in design, said Don Beaty, a consulting engineer. Beaty has headed the American Society of Heating, Refrigerating and Air-Conditioning Engineers's Technical Committee TC 9.9 for mission critical facilities, technology spaces and electronic equipment.

"If (users) are not pushing back on the manufacturers, why would the manufacturers spend the money or make that a main criterion?" said Beaty, referring to noise levels. "They are applying their own value system instead of their customers'.'"

More vendor focus on the issue would lead to improvements, said Beaty. "A base design would include more noise mitigation."

But vendors would also be concerned about whether noise mitigation increases power needs, or whether things like acoustic doors make equipment harder to work on, he said.

Wade Vinson, a thermal strategist at HP, said datacentres are up against regulatory limits on the amount of noise they can generate, forcing datacentre managers to put in hearing protection programs. "In many ways, servers being quieter can be a competitive advantage for some companies," he said.

Vinson also noted that trying to keep fan power down -- by using aerodynamic fans with variable speed controls that adjust to server load -- can reduce total power use, a major consideration of IT managers. "We have a big incentive to keep fan noise down and that's to save power," he said.

As users upgrade to larger servers, and bring more power and air conditioning into their datacentres, "...for the first time they are going to start to be more cognisant of the noise levels as they try to increase the density of equipment," said Vinson.

Robert Rosen, a CIO at one of the agencies that makes up the National Institutes of Health, and past president of the IBM user group SHARE, recalls working with large VAX servers that were so loud "we couldn't even think in that room." Today, he has installed special carpeting in his server room that prevents static electricity and reduces sound levels. If vendors make noise reduction a consideration, that would be a good move, he said. But Rosen said he won't sacrifice system performance for airflow improvements.