Manufacturing Ain’t Noise Pollution

Covering between 10 and 25 per cent of wall surfaces with absorptive acoustic panels reduces noise levels. Photo courtesy of Primacoustic.

Everyone knows what it’s like to go into a really loud restaurant, where conversation is difficult at best. You spend your evening yelling across the table to be heard. When you get home, you are absolutely exhausted.

Your auditory system has been working double-time, doing its best to filter out unwanted noise in an effort to hear the conversation.

This same problem is ubiquitous in the workplace.

In fact, nearly 35 million people in Canada and the U.S. are exposed to hazardous noise levels every day, yet many workers and employers are simply unaware of the risks. Sound from metal stamping machines, saws, drills, CNC machines, and welding stations permeate work areas, and we naturally speak or yell louder to compensate.

As the day wears on we tire and judgment falters. Mistakes are made, productivity is reduced, and in worse cases, accidents occur.

Exposure to high levels of noise (a.k.a. sound pressure levels, or SPL) can cause both short-term and permanent hearing loss. In fact, noise- and volume-related hearing loss has been documented as one of the most widespread workplace health concerns in North America.

Tens of thousands of employees suffer from preventable hearing damage caused by high workp

lace noise levels every year.

According to the U.S. Bureau of Labor Statistics, since 2004, 125,000 workers have suffered significant, permanent hearing loss. In 2009 alone, the BLS reported more than 21,000 hearing loss cases.

In 1981 OSHA implemented regulations to protect all workers in general industry and mandated all employers to implement a hearing conservation program. OSHA regulations allows eight hours of exposure to 90 A-weighted decibels (dBA), but only two hours of exposure to 100-dBA sound levels. For reference, 90 decibels (dB) is about equal to listening to a classical music concert, and 100 dB is a loud rock concert.

Accumulated exposure over long periods can not only cause deafness, but reduced auditory sensitivity at specific frequencies.

Exposure to high SPL in manufacturing and industrial plants can also provoke physical and psychological stress, impede communication, diminish concentration, and reduce productivity.  For instance, when you are working in a noisy environment, yelling across the room to a co-worker to avoid a safety hazard becomes hard, if not impossible, creating unnecessary workplace accidents and injuries due to the inability to hear the warning call.

It should also be noted that prolonged and constant exposure to lower volumes of sound pressure can also affect hearing and cause long-term hearing damage.

Mandated hearing conservation programs are in place in most countries. These programs legally require employers to measure noise levels; provide free hearing exams, ear protection, and training; and monitor the noise levels in the work environment.

The first line of defense against excessive noise exposure should be to reduce the sound pressure to the point where the risk to hearing is eliminated or minimized. With the reduction of even a few decibels, the negative impact on hearing is reduced considerably, communication is enhanced, and noise-related irritation is greatly reduced.

With protective measures in place, manufacturers also reduce their health costs and long-term liability.

The usual first line of attack is to provide workers with protective hearing devices such as isolation headphones or earbuds.  These are required gear for a worker exposed to extreme noise. The problem, however, is that these impede communication and safety, are uncomfortable, and are effective only at certain frequencies.  Workers often stop using them and suffer the results.

In most manufacturing plants the floor is made of concrete; the ceiling is often corrugated steel; and the walls are either cinder block, tilt-up concrete, or gypsum board.  Noise from the various machines ricochets off these hard surfaces to create a cacophony of noise known as the reverberant field.

The echo self-perpetuates, and the SPLs inside the room elevate to the point where a constant din abounds.

The solution is actually quite simple: “Trap” the sound as early as possible before it echoes back into the room.  A rule of thumb is to cover between 10 and 25 per cent of the wall surfaces with absorptive acoustic panels.  Sound energy penetrates the soft panel, causing the internal fibers to vibrate, creating a thermodynamic reaction that essentially converts sound into heat.

Various types of panels are available in the market all of which perform differently.

Low-density panels, such as foam, are reasonably effective at high frequencies (above 1 kHz), but do little to control low frequencies.  In earlier times, open-cell acoustic foam was often prescribed, but because of flammability concerns, inability to meet regulatory standards, and the creation of dust from oxidization, foam panels are rarely used in industry today.

Panels made from high-density glass wool absorb a much broader frequency range and attenuate noise to a much greater degree.  In other words, facilities can get away with using fewer panels and gain better results.

The thickness of the acoustic panel also plays a role. The thicker the panel, the lower the frequency it will absorb.

For instance, a 1-in.-thick high-density glass wool panel will absorb down to about 350 Hz, which is effective in the voice range, while a 2-in.-thick panel will absorb down to 150 Hz, which can be beneficial when a large press or brake is running.

Mounting acoustic panels near offending machines will absorb the direct sound before it has a chance to expand into the room. Installation is as easy as putting up a picture. Panels are mounted to the wall and simply pressed into place.  Distributing panels throughout the available wall surfaces in the room will immediately reduce the reverberation time (RT) and quiet the entire space.

In areas where mounting panels to the wall is either a challenge or impossible, suspending specialized panels from the ceiling is an option. The advantage here is that since these are open on two sides, sound energy permeates the panel from both the front and the back, essentially doubling the performance of the panel. Creating a solid canopy over very loud machines is particularly effective.

Most facilities employ a combination of ceiling clouds or baffles in conjunction with the wall-mounted panels to contain the ambient noise and attenuate the volume of the noise.

In all cases, it is prudent to check with local building authorities to ensure the acoustic panels have been tested and approved for use. Tests such as the ASTM E84 in the U.S. and CAN/ULC-S102 provide data on fire and smoke emissions and generally categorize products that are safe as Class A.

The acoustic performance of the panel should also have been checked at an independent laboratory to confirm the manufacturer claims. This not only ensures that you get the performance needed, but also provides insurance companies with the data they need to provide proper coverage and protect from liability.

The resulting workplace will not only be a safer, it will be less stressful for the employees, improve their productivity, and reduce long-term health costs.

James Wright is a business development executive, Primacoustic, 604-942-1001, www.primacoustic.com.