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.
Hearing loss due to high noise levels is a common problem in many industrial facilities. Without the use of proper PPE, hearing loss can occur quickly. This is a serious concern as hearing loss is permanent and once the damage is done there’s no way to reverse it. Due to this risk, OSHA strictly enforces standard 29 CFR-1910.95(a).
This directive discusses the effects of noise and limits exposure based on the dBA. The table below indicates the maximum allowable exposure time to different noise levels. Sound levels that exceed these levels should first be addressed by proper engineering controls such as isolating the source of the sound from personnel or replacing the cause of the sound with something like an engineered compressed air nozzle. When such controls aren’t feasible, proper PPE must be worn to protect the operator.
Hearing loss can occur in as little as 30 minutes when exposed to sound levels 110 dBA or greater. Operators have a tendency not to use PPE as directed, if an OSHA inspector comes to your facility and notices that the sound levels exceed the maximum allowable level without protection hefty fines will be soon to follow. In this example from the United States Department of Labor, a company was fined a total of $143,000 for failing to protect their employees.
In order to identify the places or processes in your facility that are causing the problems, you’ll need a tool to measure the sound level. EXAIR’s easy to use Digital Sound Level Meter allows you to measure and monitor the sound level pressure in a wide variety of industrial environments. The source of the loud noise can then be identified and isolated so that corrective action can be taken. For compressed air related noise, EXAIR manufactures a wide variety of engineered compressed air products that can reduce the sound level dramatically. In many cases, EXAIR products are capable of reducing noise levels by as much as 10 dBA. Since the dBA scale is logarithmic, this equates to cutting the sound level in half!
If there are processes within your facility that are above these limits, and you’d like to eliminate relying on proper PPE, give an Application Engineer a call. We’ll help walk you through the selection process and make sure that when the OSHA inspector comes knocking you’re prepared!
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.
If I put a 10 pound weight on a scale, the scale will read 10 pounds. If I put another 10 pound weight next to it, the scale with now read 20 pounds.
If I have $10 bill in my pocket…well, that’s a LOT more cash than I usually carry. But if I somehow come into possession of another $10 bill and put it in my pocket, now I have $20. And it probably won’t be for long.
If there’s an EXAIR Model 1100 Super Air Nozzle supplied with compressed air at 80psig, and my Sound Level Meter is reading a level of 74 dBA, and I hook another one up right next to it, my Sound Level Meter now reads about 78 dBA.
Wait, what? Did we just break math there? You, and your ears, will be happy to know that there’s perfectly valid math behind the third (as well as the first two) statements above. The third one’s just a little different, that’s all.
See, sound power (that’s “how loud” sound is, as measured at the point of generation) and sound pressure (“how loud” it is, as measured at the point where it’s heard) are both quantified in units called decibels. And, unlike mass or wealth (the first two examples above), which are linear & additive, measurement of sound power & pressure is done on a logarithmic scale. That means simple arithmetic won’t work…we have to use a logarithmic equation to ‘add’ those sound levels together. It looks like this:
Where “SL1”, “SL2”, “SL3”, etc., are the sound levels, in decibels, for the “noisemakers” in question. So, for the two Model 1100 Super Air Nozzles, generating 74 dBA each:
10 x log10[1074/10 + 1074/10] = 77.65 dBA
And just to prove the math works, we made a video of a real live test:
All EXAIR Intelligent Compressed Air Products are engineered & manufactured to be safe, efficient, and as quiet as possible. If you’d like to find out more, give me a call.
Russ Bowman, CCASS
Application Engineer EXAIR Corporation Visit us on the Web Follow me on Twitter Like us on Facebook
