Many manufacturing plants have a strong focus on safety for their workers. One major safety concern that is commonly overlooked is noise. Occupational Safety and Health Administration, or OSHA, has a directive that defines the noise exposure over a time-weighted average; 29CFR 1910.95(a). For an eight-hour day, the maximum noise level is 90 dBA. The Center for Disease Control, CDC, reports that “approximately 18% of all manufacturing workers have hearing difficulty”1.
What is sound? In the simplest of terms, a decibel is one-tenth of a bel. Historically, bel was a unit created to honor Alexander Graham Bell, who invented the telephone. Like the frequency waves that travel through telephone wires, pressure waves travel through the air as sound. This sound pressure is what our ears can detect as loudness. EXAIR offers a Digital Sound Level Meter, model 9104, that is calibrated and can measure sound in decibels. It is very important to know the sound level, as it can permanently damage your ears.
Here is a test for you. If you go and stand in your plant, you can probably hear loud noises coming from your compressed air system. EXAIR has an engineered product to solve most of them. On the Hierarchy of Controls for NIOSH, Personal Protection Equipment, PPE, is the least effective. A better control would be to isolate your operators from the hazard with an engineered product. EXAIR can offer that solution for many of your blow-offs and pneumatic discharges to reduce noise levels. This would include; but not be limited to; Super Air Nozzles, Safety Air Guns, Super Air Knives, and Super Air Amplifiers.
Let’s look at a ¼” open copper tube. It can create a sound level of over 100 dBA. They are commonly used because they are readily available and inexpensive to make. But they waste a lot of compressed air, as well as creating a hazard for your operators. Just by adding a model 1100 Super Air Nozzle to the end of the copper tube, we can reduce the noise level to 74 dBA at 80 PSIG (5.5 bar). Wow! Not only will it remove the hazard, but it will reduce the amount of compressed air usage; saving you money. Here is a quick video to show the importance of the EXAIR Super Air Nozzles.
At EXAIR, we have a statement, “Safety is everyone’s responsibility.” EXAIR manufactures engineered products with high quality, safety, and efficiency in mind. To keep your operators safe, EXAIR offers many different types of blow-off products that are designed to decrease noise to a safe level. So, here’s to Alexander Graham Bell for creating the telephone, which you can use to contact an Application Engineer at EXAIR. We will be happy to help to reduce your sound levels.
We are all familiar with sounds in everyday life. Some sounds are pleasant, and some sounds can be destructive. Sound has exponents of pressure, power, and intensity. In this blog, I will go over each one to see how we perceive sound and are affected by it.
Sound pressure is what our ears pick up. The small bones in our ears detect pressure changes with our eardrums to convert to noise signals. In looking at a single source, sound pressure is created by sound waves. . In looking at a single source, sound pressure is created by sound waves. The units are measured in Pascals. The lowest pressure perceived by human ears is 0.00002 Pa, and we can use this value as a reference point. Depending on the frequency, pain can occur at 65 Pa. We can arrive at a sound pressure level which is measured in decibels, dB. This correlation between sound pressures and sound pressure levels is calculated by Equation 1.
Equation 1:
L = 20 * Log10 (P / Pref)
L – Sound Pressure Level, dB
P – Sound pressure, Pa
Pref – reference sound pressure, 0.00002 Pa
Sound pressure has to be measured at a certain distance. Like a wave in a pond, the farther the distance, the smaller the waves. Most standards are set at 1 meter away. As an example, the sound pressure from a passenger car as heard from the roadside is 0.1 Pa. With Equation 1, we can get the following decibel level:
L = 20 * Log10 (0.1Pa / 0.00002Pa) = 74 dB
Sound power deals with the amount of energy that is generated at the source, which is independent of distance. There is an old saying, “if a tree falls in the forest and no one is nearby, does it make a sound?”. Well, it does. Even though you may be too far away from the source to detect the sound pressure waves, it still creates a sound. Sound power is important to measure noise in different locations around the source. This will help to ensure proper protection for the workers in the different areas. The unit of measure for sound power is watts (W). Equation 2 shows the formula to calculate sound power levels. This equation also uses a reference point which was determined by a standard to be 1 pW or 1 * 10-12 Watts.
Equation 2:
LN = 10 * Log10 (p / pref)
LN – Sound Power Level, dB
p – Sound power, W
pref – reference sound power, 1 * 10-12 W
As an example, a jet engine can generate roughly 1 watt of sound power. From Equation 2, we get a sound power level of
L = 10 * Log10 (1 W / 1 * 10-12 W) = 120 dB
To avoid confusion with sound pressure levels, we usually use the unit of bel (B) rather than decibel (dB). So, the jet engine would produce a sound power level of 12 Bel.
Sound intensity is defined as sound power per unit area; it is commonly measured in Watts per square meter, W/m2. The formula is shown in Equation 3.
Equation 3:
I = p / A
I – Sound Intensity W/m2
p – Source power, W
A – Area from source, m2
From the sound source, the sound intensity is developed by the direction the sound “flows” through a particular area. If you have ever seen a band trying to setup their sound system, they take into account walls, the size of the room, open areas, speaker angles, etc., to enhance the sound. The sound pressure, or loudness, will travel through a median at a distance, which could encounter walls, machines, ceilings, etc. Let’s look at the sound power of the jet engine above at 1 Watt. If a plane was flying 1,000 meters (3,300 feet) above your head, you could find the sound intensity. First, sound travels in all directions; so, we will use the surface area of a sphere, 4πr2 to calculate the area. Since the source is at the center, the distance to the person will be the radius. So, at 1,000 meters, the area will be 4 * 3.14 * (1,000 m)2 = 12,560,000 m2. We can deduce from Equation 3 that
I = p / A = 1 W / 12,560,000 m2 = 7.96 * 10-8 W/m2.
To correlate this to the sound intensity level, which your ears perceive, it is measured in decibels, dB, and is represented by Equation 4.
Equation 4:
Li = 10 * Log10 (I / Iref)
Li – Sound Power Intensity, dB
I – Sound intensity, W/m2
Iref – reference sound intensity, 1 * 10-12 W/m2
With the example above of the jet engine that is 1,000 meters above our head, we can calculate the sound level that our ears can hear. From Equation 4, we have
Li = 10 * Log10 (7.96 * 10-8 W/m2 / 1 * 10-12 W/m2) = 49 dB
Hearing loss is permanent; and it is the most recorded occupational illness in manufacturing plants. The Occupational Safety and Health Administration (OSHA) is the enforcement agency responsible for determining and fining companies that violate this directive; 29 CFR 1910.95(a). To keep your operators safe, it is important to measure the sound level of your pneumatic equipment. NIOSH, or the National Institute for Occupational Safety and Health, uses a Hierarchy of Controls for dealing with safety issues. And the Engineering Controls is more prevalent on this chart than purchasing personal protective equipment or PPE (reference diagram above). EXAIR manufactures these engineered products for safety, noise reduction, and cost savings. They are known as the Intelligent Compressed Air Products®. To minimize any hearing loss with personnel, EXAIR has a variety of Super Air Nozzles, Safety Air Guns, Super Air Amplifiers, and Super Air Knives that can reduce the sound levels to a safe level. And as a bonus, it will save you money by reducing your compressed air usage. You can talk with one of our Application Engineers if you wish to reduce the surrounding sound levels with your pneumatic blow-offs.
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 Wave
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).
The OSHA Standard for how long someone can be exposed to a certain noise level
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.
EXAIR’s Digital Sound Level Meter
If you have questions about the Digital Sound Level Meter, or would like to talk about any of the quiet EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR or any Application Engineer.
Cody Biehle Application Engineer EXAIR Corporation Visit us on the Web Follow me on Twitter Like us on Facebook
Sound Power… When I hear that term all I can think of is the classic commercial Maxell®Sound made in 1983. I was only a year old when that commercial graced the presence of everyone’s TV. I did see it throughout the years and recall recording Casey Kasem’s Top 40 on Maxell cassettes. Then, in college it was a classic poster you would see around the dorms.
1(Maxell / Retrontario, 2009)
Needless to say, this does show sound power and sound pressure which is the point of this blog. This video however is not an industrial environment that most of us are accustomed to when worrying about the sound power / sound pressure within an environment.
If you observe the video above the speakers and the driver of the speakers is the generator of sound power. That is the energy rate emitted by a source. This power then begins to fill a space which is equivalent to the sound intensity. This is because the sound energy has a direction that is given to it, think of the speaker. The speaker gives the sound energy a vector to travel. Then when the vector hits surfaces that is the sound intensity.
This sound intensity can then be interpreted as the sound power transfer per unit of surrounding surface at a distance. This will then give the information needed to convert the information to the Sound Pressure level. This is the force of a sound on a surface area perpendicular to the direction of the sound.
With this information we can then observe the logarithmic unit (or value) used to describe the ratio of sound power, pressure, and intensity, the decibel. The decibel is what all industrial hygienists and safety personnel are concerned with. In the end, all of this is started at the point of power generation, when observing compressed air blowoffs, this is the exit point of air from the device. If you optimize the point of use device to use the least amount of compressed air and be the most efficient then the amount of sound power being generated and eventually being measured as decibels at an operator’s work station, then the result will be lower ambient noise levels.
