My colleague, Russ Bowman, wrote a blog about “Sound Power vs Sound Pressure vs Sound Pressure Level”. He discussed the logarithmic equations around sound. I will be discussing what happens when you have more than one sound source, as often heard within manufacturing plants. Sounds can be added together to determine the overall sound level that you hear. This is very important when it comes to minimizing hearing loss.
In looking at a single source of sound, sound pressure is created by the loudness of a noise. The units are measured in Pascals. The lowest pressure perceived by human hearing is 0.00002 Pa, and we can use this value as a reference point. From sound pressures, we can arrive at a sound pressure level which is measured in decibel, dB. This correlation between sound pressures and sound pressure levels are calculated by Equation 1:
L = 20 * Log10 (P / Pref)
L – Sound Pressure Level, dB
P – Sound pressure, Pa
Pref – reference sound pressure, 0.00002 Pa
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
Because human ears are sensitive to different frequencies, the sound pressure levels can be modified, or weighted, to indicate an effective loudness level for humans. This adjustment is done in two different ways; A-weighting and C-weighting. The C-weighting is for very loud noises with high peaks or sharp impacts like gunfire. The A-weighting is the most used value as the sound pressure levels are adjusted by the frequency level. For higher and lower frequencies, the change in the sound value is much greater than the mid-level frequencies that are within our hearing range. Sound measurements for safety are measured on an A-weighted scale. OSHA created a chart in the standard 29CFR-1910.95(a). It shows the noise levels over exposure times for an operator. To use the OSHA chart accurately, the total noise level in dBA should be calculated.
Hearing loss is the best known, but not the only, ill effect of harmful noise exposure. It can also cause physical and psychological stress, impair concentration, and contribute to workplace accidents or injuries.
To determine the total sound level, we can add all the sound pressure levels together by Equation 2:
Equation 2:
Where L1, L2… represents the sound pressure level in dBA for each sound source.
As an example, a manufacturing plant had an operator using a machine that had four copper tubes to blow off a cutting operation (reference photo below).
Blow off station
The decibel level for a copper tube was measured at 98 dBA. The total amount of sound that the operator was exposed to was determined by Equation 2 with four values.
L = 10 * log10 (109.8 + 109.8 + 109.8 + 109.8)
L = 104 dBA
In looking at the OSHA chart above, the operator would only be allowed to operate the machine only a little over one hour without hearing protection. In this same example, we replaced the copper tubes with an EXAIR Super Air Nozzle, model 1100SS. The noise level for each nozzle is 74 dBA at 80 PSIG (5.5 bar). By replacing all four copper tubes with Super Air Nozzles, Equation 2 becomes:
L = 10 * log10 (107.4 + 107.4+ 107.4 + 107.4)
L = 80 dBA
The total sound level is now in accordance with OSHA regulations for the operator to work all 8 hours at the machine without hearing protection.
A commonly used acronym for hearing safety is NIHL, or Noise Induced Hearing Loss. To keep your operators safe and reduce NIHL, it is important to measure the total sound level in that area. As a protocol in safety, it is a requirement to use engineering standards before purchasing personal protective equipment or PPE. For the customer above, they followed that protocol with our Super Air Nozzles. If you need to reduce noise levels in your facility, EXAIR offers a large line of blow-off products that can meet the safety requirements. You can contact an Application Engineer for more information.
At the time of writing this blog, Cincinnati is experiencing our usual 17-year brood of cicadas. Millions, if not billions, of 17-year cicadas have emerged in Cincinnati and Southwest Ohio, making spending any amount of time outside unbearable. My four-year-old’s favorite part of the day is swinging on the back porch, and he even wants to go right back inside after just a few minutes.
I stuck the EXAIR 9104 Digital Sound Level Meter inside of one of our bushes here at the office. Within a 3′ radius, I counted 10–15 cicadas crawling around pretty casually. And they were producing a whopping 90 dBA! And if i shook a branch and really got them worked up, it peeked over 101 dBA.
Now while it takes repeated exposures of sufficient duration to cause hearing loss. And in a few weeks these cicadas will be gone; you probably don’t need to worry about the 2025 cicadas affecting your hearing. Noise exposure is, however, a real issue for most manufacturing facilities. Due to this risk, OSHA strictly enforces standard 29 CFR-1910.95(a).
This directive outlines 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 is the best known, but not the only, ill effect of harmful noise exposure. It can also cause physical and psychological stress, impair concentration, and contribute to workplace accidents or injuries.
Hearing loss can occur in as little as 30 minutes when exposed to sound levels of 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 PPE protection being worn, hefty fines will soon be following. 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.
EXAIR 9104 Sound Level Meter
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! Sorry, but we will not be able to help you with your Cicada problems. We just have to let nature do its thing, and they will be gone in a few weeks. Until 2027, that is, when we get hit with the 10-year brood!
At EXAIR, we have a statement that says, “Safety is everyone’s responsibility.” EXAIR builds its name around manufacturing safe and protective compressed air products. In the United States, we have an organization called the Occupational Safety and Health Administration (OSHA) that enforces governmental directives for safe and healthy working environments. They do training, outreach programs, and educational assistance for manufacturing plants to reduce injuries and fatalities. They can also enforce these directives with heavy fines for violations. With compressed air systems, the two most common violations are 29CFR 1910.242(b) for dead-end pressure/chip shielding and 29CFR 1910.95(a) for maximum allowable noise exposure.
Unsafe Nozzle
Here is an example of a nozzle that is dangerous. As you can see, there is only one path where the air can pass through. Other similar types of blow-off devices that would fall into this same group would include copper tubes, flexible lines, and open pipes. They are dangerous as compressed air cannot escape if it is blocked by your body or skin. If operated above 30 PSIG (2 bar), these nozzles could penetrate the skin and create an air embolism within the body, which can cause bodily harm or death. This is a hazard that can be avoided by using EXAIR Super Air Nozzles and Safety Air Guns. The nozzles are designed with fins, which allow the air to escape and cannot be blocked by your skin. So, you can use the EXAIR Super Air Nozzles safely above 30 PSIG (2 bar) and remain OSHA compliant.
Unsafe Air Gun
To counteract the dead-end pressure violation, some nozzle manufacturers create a hole through the side of the nozzle (reference photo above). This will allow the compressed air to escape, but now the issue is noise levels. With an “open” hole in the nozzle, the compressed air is very turbulent and very loud. The National Institute for Occupational Safety and Health (NIOSH) states that 70% to 80% of all hearing loss within a manufacturing plant is caused by compressed air. OSHA created a chart to show the maximum allowable noise exposure. This chart shows the exposure time and noise limits before hearing protection is required. The EXAIR Super Air Nozzles, Super Air Knives, and Super Air Amplifiers are designed to have laminar flow, which makes them very quiet. As an example, the model 1210 Soft Grip Safety Air Gun has a sound level of only 74 dBA, well under the noise exposure limit for 8 hours.
One of the last things that companies think about when purchasing compressed air products is safety. Loud noises and dead-end pressure can be missed or forgotten. To avoid any future fines or having to purchase additional personal protective equipment (PPE), it will be much safer to purchase EXAIR products. If you would like to improve the safety of your facility and reduce energy costs, an Application Engineer at EXAIR can review your current blow-off devices. Remember, safety is everyone’s responsibility.
I was once on a local theater’s website, ordering tickets to an upcoming show that my wife and I were excited to see. I had the option to pay online and have a digital code emailed to me in lieu of a real live paper ticket. Can you believe they wanted to charge me almost $2 A TICKET for that?!? I adamantly refused (by that I mean I clicked the mouse extra hard on the “Will Call” button before completing my payment)…and saved that $4 (almost) for something REALLY important.
The night of the show, there was a 20-minute line at the Will Call window. Folks who had opted for the digital code were doing a quick scan with their smartphones and walking straight into the theater. I used the $4 I saved to partially pay for a $10 glass of wine from a concession kiosk in the lobby, as a peace offering for my lovely bride. That was indeed “something REALLY important.”
Another time, I was ordering a sump pump backup system for our house. I had the option of paying extra for the deluxe system, which came with all the fittings and a special tool to make installation a bit easier. Even though the ‘deluxe’ system adder was probably a bit more than the cost of the fittings from my local hardware store, I paid the “convenience fee” and got the deluxe system anyway. For the record, during the installation, I realized I would have bought an incorrect fitting at the local store which would have forced an emergency trip while I had the water turned off in my whole house. THAT was an inconvenience I was glad to have avoided.
Similarly, you can buy any EXAIR product with, or without, accessories that’ll make for simpler installation, improved performance, and to ensure it does what you want it to do. Some of these are product-specific, but many are suitable (and recommended) for use with any of our products:
Filter Separators
Good engineering practice calls for point of use filtration for any compressed air operated device. Even if you have the best intake & discharge filters on your air compressor, trace amounts of contaminants can sneak through, pipes can rust, and water vapor that the dryer doesn’t catch can condense. Particulates can build up and eventually clog the tight clearances in many engineered compressed air products, and if you’re using air for cleaning, drying, etc., keep in mind that whatever’s in your air will get on your product. Moisture isn’t always as big of a deal, but it can freeze inside Vortex Tubes, Spot Cooling Products, Cold Guns, and Cabinet Cooler Systems. That’s why we include Filter Separators in our Air Knife, Air Wipe, Static Eliminator Products, Line Vac, Adjustable Spot Cooler, Cold Gun, and Cabinet Cooler System Kits.
Automatic Drain Filter Separators come in sizes from 1/4 NPT to 1-1/4 NPT, for compressed air flows up to 400 SCFM.
Oil Removal Filters
These aren’t always needed, but we have them if your application calls for it. Some of the “usual suspects” are food & Pharma (see above “whatever’s in your air will get on your product”), blowoff prior to painting (the smallest amount of oil on the surface causes a phenomenon known as “fish eye” and it looks exactly like that sounds), or when your compressor is known to have oil carryover.
When properly installed downstream of an Automatic Drain Filter Separator (left,) an Oil Removal Filter (center) will provide clean, oil free air to the Pressure Regulator (right) and all downstream components.
Pressure Regulators
One of our Six Steps To Optimizing Your Compressed Air System is to control the air pressure at the point of use to minimize air consumption. In other words, find the supply pressure for your product that gets the job done, so you don’t use any more compressed air than you have to. Like the Filter Separators above, these come with many EXAIR Intelligent Compressed Air Product Kits.
Pressure Regulators “dial in” performance to get the job done without using more air than necessary.
Mounting Brackets and Coupling Kits
Most of our Filter Separators, Oil Removal Filters, and Pressure Regulators can be attached to a wall, panel, etc., with a Mounting Bracket, and can actually be attached to each other with a modular Coupling Kit. These parts simplify the installation, ensure they are oriented correctly, and minimize the chance for air leaks.
Filters (left) and Pressure Regulators (center) can be mounted using Brackets, and they can be connected together with Modular Couplers (right).
Silencing Mufflers
Many EXAIR products are engineered to develop a boundary layer of low velocity air flow that greatly reduces the sound level during operation. Other products use a venturi mechanism to draw a vacuum (Reversible Drum Vacs and E-Vac Vacuum Generators) or a Vortex Tube to generate cold air flow. The air flow from these products cannot be subjected to back pressure, and, without anything to mitigate the sound pressure generated by the rapid pressure drop as the air exits, they can be quite loud. For these, we have Silencing Mufflers that, except for the largest & most powerful of these products, reduce the sound level to be compliant with OSHA Standard 1910.95 Maximum Noise Exposure Limits.
From left to right… Reclassifying Mufflers offer the highest noise level reduction, eliminate oil mist, and come in sizes from 1/8 NPT to 1 NPT. Sintered Bronze Mufflers are low cost and compact, with threads from #10-32 to 1-1/2 NPT. Straight Through Mufflers use an internal sleeve of sound reducing foam, with threads from ¼ NPT to ¾ NPT, with male threads on one end and female threads on the other. Heavy Duty Mufflers have an aluminum shell and an internal stainless steel screen that keeps contaminants like rust from being ejected in a dangerous way. We have them in ¼ NPT and ¾ NPT sizes.
Solenoid Valves (left) are available for 120VAC, 240VAC, and 24VDC in sizes from 1/4 NPT to 1 NPT. We offer manual Ball Valves in sizes from 1/8 NPT to 1-1/4 NPT.
Swivel Fittings, Stay Set Hoses, and Magnetic Bases
EXAIR Super Air Nozzles are threaded for installation with common air pipe & hose fittings. If the pipe isn’t pointed in the exact right direction, a Swivel Fitting gives you 50° of adjustability. If the pipe isn’t quite close enough to what you want to blow off, Stay Set Hoses come in lengths of 6″ to 36″, and when bent to aim the Air Nozzle, they ‘stay set’, as advertised, until they need to be moved. If a pipe doesn’t exist and you need to run an air hose from the nearest drop on the header, Magnetic Bases can support the Air Nozzle and a Stay Set Hose to get the air where you want it. They even have shutoff valves to turn them off when they’re not in use (that’s a good thing; see above).
Save installation time AND get your blowoff pointed in the right direction!
Hoses and Compressed Air Fittings
If you need one of the aforementioned air hoses to reach a Magnetic Base or to supply a Safety Air Gun, we have two diameters to choose from – 3/8″ ID (1/4 MNPT threads on the ends) and 1/2″ ID (1/2 MNPT threads on the end), and we can make them to any length you need. And, while our selection probably isn’t quite as comprehensive as your local piping supply shop, we stock a number of pipe nipples, Couplers, Reducers, Tees, and Elbows that are commonly used with our products. So – like my backup sump pump deluxe kit, we can put all the fittings you may require in the same box for you.
Contact an Application Engineer if you have ANY questions about how to properly supply compressed air to your EXAIR products.
At EXAIR, we’re here to make sure you get the most out of our products, and your compressed air system. If you need accessories to help with that, give me a call.
Russ Bowman, CCASS
Application Engineer Visit us on the Web Follow me on Twitter Like us on Facebook
