Sound, it is all around at every given point of the day. Whether it is from the music we listen to, the person talking to you, your cars engine, or the wind blowing through the leaves there is no escaping it. Hearing is one of the five senses that the majority of humans rely on and should be protected at all costs and with a good understanding of what sound is, one can help mitigate damage done to their hearing. Sound can be broken down into two parts, sound power and sound pressure. But the real question is, how do these corollate to each other to become the sound that we rely on.
Sound Power (Watts) is defined as the rate at which sound energy (decibels) is emitted, reflected, transmitted or received, per unit of time. Whereas, Sound Pressure is defined as the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave. Based on these two definitions it can be determined that sound power is the cause that generates the sound wave and sound pressure is the effect or what we hear after the sound wave has traveled to the ear.
This can be summed up in a simple analogy using a light bulb. Light bulbs use electricity to generate a source of light, this means that the power required (also stated in Watts) to cause the bulb to light up is comparable to Sound Power. The intensity of the light being generated (stated in Lumens) would be the Sound Pressure. Sound Pressure is what we would typically hear or call sound. This is what is measured because that is the harmful aspect to our hearing and ears. If the Sound Pressure is high enough and the ear is exposed to it long enough, permanent damage can be done resulting in hearing loss to the point of complete hearing lose.
I have known many people who have lost there hearing either completely or a large portion of it from exposure to loud noises. EXAIR designs and manufactures quiet and efficient point of use compressed air products. These products either meet or exceed the OSHA noise Standards in OSHA Standard 29 CFR – 1910.95 (a).
If you are not sure what the noise level is in your facility check out EXAIR’s Digital Sound Level Meter. It’s an easy to use instrument for measuring Sound Pressure levels in an area.
Strings of numbers and characters can often appear daunting. For instance, if I wrote in binary code it would be a string of ones and zeros. (01000101 01101110 01100111 01101001 01101110 01100101 01100101 01110010 01101001 01101110 01100111 00100000 01101001 01110011 00100000 01000001 01010111 01000101 01010011 01001111 01001101 01000101.) That can look like gibberish and cause concern if unknown or it can make sense to programmers and people familiar with binary code.
Other alphanumeric strings may cause some concern for industry professionals. Take, for instance, OSHA standards. The OSHA standard 29 CFR 1910.95 (a) may be unfamiliar to some, and thus concerning. Many Environmental Health and Safety Engineers will recognize this code. It is an OSHA standard that revolves around the amount of time an employee is permitted to be exposed to specific sound levels. These sound levels are all based on the weighted sound level of the noise the operators are exposed to. To better understand how the octave and frequency of the sound play into this, there is a chart provided below.
The weighted sound level is the level at which a Digital Sound Level Meter will read the current level of noise within an environment. This scale is then used to move further into the OSHA directive that we focus on helping companies meet to best provide safe environments for their employees to work in.
If you notice, the lowest weighted sound level is 90 dBA, this is also the lowest-rated noise level that OSHA speaks of in 1910.95(b)(2). It has been shown that noise levels over this level for extended periods will result in permanent hearing loss. The standard then goes on to discuss the duration an employee can be exposed to noise levels even with the use of personal protective equipment as well as even impulsive or impact noise. The table of permissible time limits is shown below.
As you can see from the table above provided by OSHA, any noise level that an operator is exposed to for eight hours cannot exceed 90 dBA. Noises within an industrial environment can also be variable throughout the day. For instance, the operator stands outside of a sheet metal press and the concussive strike on the press gives off a 90 dBA strike for every stroke of the press. This would not be a continuous noise level. Maybe the operator is operating a CNC machine that is cutting a nest of parts and uses a handheld blowgun to remove debris and coolant from the parts before taking them from their fixture. This blowgun is not used continuously and therefore would not be rated as such for the exposure time. A time study would be conducted on the average length of time the operator is utilizing this gun along with the level of noise it produces during use. OSHA then gives a calculation to use to appropriately combine the sound level while the gun is being used and when it is not in use. That equation is written out below.
C1 = Duration of time for a specified noise level
T1 = Total time of exposure permitted at that level
Cn = Total time of exposure at a specified noise level
Tn = Total exposure time permitted at that level
Should the summation of the fractions for different exposures be greater than the Total Exposure fraction, the summation value should be used. As mentioned above, a time study on exposure to noise levels will be needed to obtain the information needed for this type of study. Once the study is done the process can proceed to the next level within the OSHA standard which is a hearing conservation program.
I would like to interject a small side-step at this point. Rather than rolling straight into the implementation of PPE which is proven to be the lowest reliable factor of protection by the CDC and NIOSH. If any of these noise levels being generated are due to the use of compressed air points of use, EXAIR can potentially lower the noise of these point of use applications. In the events, open blowoffs or “band-aid” fixes are in place to keep processes running, and Engineered Solutions can easily be implemented that will reduce the noise level produced by this operation. Whether it is on the handheld Safety Air Gun in the hands of a CNC operator, or if it is a part/scrap ejector that is blowing the sheet metal press out after every strike, we have products that have proven time over time using an Engineered Solution will save air, reduce noise levels, and still get the job done.
If you would like to discuss OSHA directives revolving around compressed air, share with us a recent citation you received from an inspector for this standard, or just discuss compressed air usage in general, contact us.
What sound level do you get when you feed an EXAIR Super Air Nozzle at 80psig? What if there are two of them? Or three? Grab your scientific calculators, folks…we’re gonna ‘math’ today!
But first, a little explanation of sound power & sound pressure:
Strictly speaking, power is defined as energy per unit time, and is used to measure energy generation or consumption. In acoustics, though, sound power is applicable to the generation of the sound…how much sound is being MADE by a noisy operation.
Sound pressure is the way acoustics professionals quantify the intensity of the sound power at the target. For the purposes of most noise reduction discussions, the target is “your ears.”
The sound levels that we publish are measured at a distance of 3 feet from the product, to the side. The units we use are decibels, corrected for “A” weighting (which accounts for how the human ear perceives the intensity of the sound, which varies for different frequencies,) or dBA. Also, decibels follow a logarithmic scale, which means two important things:
A few decibels’ worth of change result in a “twice as loud” perception to your ears.
Adding sources of sound doesn’t double the decibel level.
If you want to know how the sound level from a single source is calculated, those calculations are found here. For the purposes of this blog, though, we’re going to assume a user wants to know what the resultant sound level is going to be if they add a sound generating device to their current (known) situation.
Let’s use an EXAIR Model 1100 Super Air Nozzle (rated at 74dBA) as an example, and let’s say we have one in operation, and want to add another. What will be the increase in dBA?
10 x log10[1074/10 + 1074/10] = 77.65 dBA
Now, there are two reasons I picked the Model 1100 as an example:
It’s one of our most versatile products, with a wide range of applications, and a proven track record of efficiency, safety, and sound level reduction.
We proved out the math in a real live experiment:
Why do I care about all of this? My Dad experienced dramatic hearing loss from industrial exposure at a relatively young age…he got his first hearing aids in his early 40’s…so I saw, literally up close and very personal, what a quality of life issue that can be. The fact that I get to use my technical aptitude to help others lower industrial noise exposure is more than just making a living. It’s something I’m passionate about. If you want to talk about sound level reduction in regard to your use of compressed air, talk to me. Please.
Russ Bowman Application Engineer EXAIR Corporation Visit us on the Web Follow me on Twitter Like us on Facebook
When I was visiting a supplier in Japan, our host was extremely proud of their koi pond and wanted to demonstrate something. He took us to the pond’s edge and clapped his hands. From the murky depths of the pond emerged huge koi breaking the surface with open mouths. As their reward, he tossed them a handful of fish food.
While everyone else was enamored with his ability to have trained the fish, I was awestruck with the fact that they could hear the sound of clapping deep down into the pond. No wonder dad kept telling me to be quiet or you will scare the fish away.
According to the National Wildlife Federation fish don’t have ears that we can see, but they do have ear parts inside their heads. They pick up sounds in the water through the lateral lines that runs down each side of its body and transmitted to their internal ear.
While human auditory abilities may not be as sensitive as the rest of the animal kingdom, the inner workings of our ears are very sensitive easily damaged. Listening to loud noise for long periods of time can damage the hair cells in the inner ear. Noise-induced hearing loss usually develops gradually and painlessly. We live in a noisy world and hearing loss among Americans is significant. According to the Center for Hearing and Communications, approximately 12% of the U.S. population or 38 million Americans have a significant hearing loss.