Understanding Noise: Sound Power Vs. Sound Pressure

Sound Power and Sound Pressure have been covered a few other times here on the EXAIR Blog. Once here by Brian who made the visual correlation in regards to a speaker and a musical instrument. And here by Russ who breaks down how you calculate sound power level with the below equation!
Sound Power Equation
too lou Sound Power Level Equation
All machines generate sound when they are in operation. The propagated sound waves cause small changes in the ambient air pressure while traveling. A sound source produces sound power and this generates a sound pressure fluctuation in the air. Sound power is the cause of this, whereas sound pressure is the effect. To put it more simply, what we hear is sound pressure, but this sound pressure is caused by the sound power of the emitting sound source. To make a comparison, imagine for example a simple light bulb. The bulb’s power wattage (in W) represents the sound power, whereas the bulb’s light intensity represents the sound pressure.
7179304430_8101287900_c
Light Bulb
Sound power does not generally depend on the environment. On the contrary, the sound pressure depends on the distance from the source and also on the acoustic environment where the sound wave is produced. In the case of indoor installations for example, sound pressure depends on the size of the room and on the sound absorption capacity of the surfaces. For instance, say the room walls don’t absorb all the sound but reflect parts of it, then the sound pressure will increase due to the so called reverberation effect. (reverberation time is broadly defined as the time it takes for the sound pressure to reduce by 60 dB after the sound emitting source has been shut off). OSHA puts the following limits on personnel exposure to certain noise levels:
Working in areas that exceed these levels will require hearing protection.
EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind.  If you’d like to talk about how we can help protect you and your folks’ hearing, call us. Jordan Shouse Application Engineer Send me an email Find us on the Web  Like us on Facebook Twitter: @EXAIR_JS Light Bulb image courtesy of  josh LightWork  Creative Commons License

Engineered Super Air Nozzles Improve Efficiency and Safety vs. Commercial and Homemade Nozzles

They may be inefficient, but they sure are loud…

Over the years, EXAIR has come across a variety of different types of blow-off devices.  We have seen copper tubes, pipes with a crushed end, fittings with holes drilled into them, and modular flex lines.  For compressed air use, these are very dangerous and very inefficient.  In many instances, companies will go through a mixed bag of items to make a blow-off device for their application.  It is inexpensive to do.  But what they do not realized is that these items are very unsafe and will waste your compressed air, costing you much money in the long run.

When EXAIR started to manufacture compressed air products in 1983, we created a culture in making high quality products that are safe, effective, and efficient.  Since we stand by our products, we created a program called the Efficiency Lab.  We test blow-off devices against EXAIR products in noise levels, flow usage, and force measurements.  With calibrated test equipment, we compare the data in a detailed report for the customer to review.  If we are less effective, we will state that in the report, but this is very rare.  With this quantified information, we can then determine the total amount of air savings and safety improvements that EXAIR products can offer.

With our Efficiency Lab, it is quite simple to do.  For starters, you can go to our Product Efficiency Survey on our website to give the conditions for testing.  If you wish for a side by side analysis, you can place your pneumatic device in a box and send it to EXAIR.  We will run the tests at the specified conditions or in a range of settings.  We will then return your pneumatic device back to you with a report of the comparison.  This report can be used to show managers, executives, HSE, etc. on the improvements that EXAIR can provide in cost savings and safety.

In a recent Efficiency Lab, a customer sent us a water jet nozzle that he was using to blow off product passing on a conveyor (reference photo above).  The customer supplied us with the required information to test.  They had three water jet nozzles on a manifold that had ¼” NPT male connections.  The air pressure was set at 75 PSIG (5.2 bar), and the air pattern was round.  Their annual usage for this blow-off device was 7000 hours continuous, and their electric rate for their facility was $0.10/KWh.  The reason that they sent their nozzle to EXAIR was because the operation was very loud, and they believed that they were wasting compressed air.  They asked me for a recommendation and what the payback period might be with my selection.

Model 1101

I recommended the model 1101 Super Air Nozzle as our standard round pattern with a ¼” NPT male connection.  With our engineered design, the Super Air Nozzle can entrain the “free” ambient air into the air stream to generate a hard-hitting force; using less compressed air.  Also, with this suggestion, they will not have to redesign their blow-off station; just remove the water jet nozzles and replace them with the Super Air Nozzles.  We tested the water jet nozzle, and we found that it used 17.5 SCFM (496 SLPM) at 75 PSIG (5.2 bar).  The noise level was measured at 91.2 dBA for a single nozzle.  As a comparison, the model 1101 Super Air Nozzle will only use 13.3 SCFM (376 SLPM) of compressed air at 75 PSIG (5.2 bar); and, the noise level was reduced to 73 dBA for each nozzle.

The first thing that is important to me is safety.  High noise levels will cause hearing damage.  OSHA generated a standard 29CFR-1910.95a with a chart for Maximum Allowable Noise Exposure.  To calculate the noise level for three nozzles, I will reference a previous blog that I wrote: “Measuring and Adding Sounds”.  With three water jet nozzles, the total sound is 96 dBA.  From the OSHA table above, the usage without hearing protection is less than 4 hours a day.  With the Super Air Nozzles, the noise level will be 78 dBA for all three nozzles; well below the requirement for 8 hours of exposure.  It is difficult to put a monetary value on safety, but using PPE should never be the first step as a solution.

For the annual savings and the payback period, I will only look at the electrical cost.  (Since the Super Air Nozzle is using less compressed air, the maintenance and wear on your air compressor is reduced as well).

The air savings is calculated from the comparison; 17.5 SCFM – 13.3 SCFM = 4.2 SCFM per nozzle.  With three nozzles, the total compressed air savings will be 12.6 SCFM for the blow-off station.  An air compressor can produce 5.36 SCFM/KW of electricity at a cost of $0.10/KWh.  For an annual savings, we have the figures from the information above; 7000 hours/year * 12.6 SCFM * $0.10/KWh * 1KW/5.36 SCFM = $1,645.52/year.  For the payback period, the model 1101 Super Air Nozzle has a catalog price of $44.00 each, or $132.00 for three.  The customer above did not disclose the cost of the water jet nozzles, but even at a zero value, the payback period will be just under 1 month.  Wow!

Not all blow off devices are the same.  With the customer above, they were able to reduce their noise levels and compressed air consumption.  If your company decides to select an unconventional way to blow off parts without contacting EXAIR, there can be many hidden pitfalls; especially with safety.  Besides, if you can save your company thousands of dollars per year as well, why go with a non-standard nozzle?  If you have a blow off application and would like to compare it against an EXAIR product, you can discuss the details with an Application Engineer.  What do you have to lose?

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Know What to Look For – Are Your Compressed Air Guns OSHA Safe?

One of the easiest ways to find out if your compressed air guns are safe for operation is by looking at the nozzle.  First, take your current compressed air gun and disconnect it from the compressed air line.  Second, look directly into the end of the nozzle where the air comes out.  If you can see the inside of the nozzle, then your air gun or blow-off device is unsafe.  Nine out of ten compressed air guns are considered to be dangerous.  In this blog, I will go through the dangers and violations of compressed air guns and nozzles that are very common in the market place.

Occupational Safety and Health Administration, OSHA, is an organization that enforces standards for safe and healthy working environments.  They have training, outreach programs, and educational assistance for manufacturing plant.  But, they will also enforce these standards with heavy fines for violations.  The two most common violations with compressed air guns and nozzles are 29CFR 1910.242(b) for dead-end pressure/chip shielding and 29CFR 1910.65(a) for maximum allowable noise exposure.  If you are unfortunate in receiving an audit, the OSHA agent will target your compressed air guns and blow-off devices.

Unsafe Nozzle

Here is the first example of a nozzle that I would like to discuss.  As you can see, there is only one opening where the air can come out from the nozzle.  Other types of nozzles that would fall into this category will include copper pipes, extensions, or worn nozzles.  They are dangerous as the compressed air cannot escape if it is blocked by your skin.  An air embolism could occur within the body which can cause bodily harm or death.  If operated above 30 PSIG (2 bar), these nozzles would violate the OSHA 29CFR 1910.242(b) for dead-end pressure.  This is a hazard which can be avoided by using EXAIR Super Air Nozzles and Safety Air Guns.  The nozzles are designed to utilize fins to allow air to escape and not penetrate your skin.  With EXAIR products, you will not violate this standard even if you go above the 30 PSIG (2 bar).

Safety Air Gun

To counteract the dead-end pressure violation, some nozzle manufacturers created a hole through the side of the nozzle (Reference photo below).  This will allow for the compressed air to escape, but, now the issue is noise level.  With an “open” section in the nozzle, the compressed air is very turbulent and very loud.  They state that 70% to 80% of all hearing loss within a manufacturing plant is caused by compressed air.  For this, OSHA 29CFR 1910.65(a) was created to show the maximum allowable noise exposure.  This chart shows the time and noise limits before requiring hearing protection.  The EXAIR Super Air Nozzles are designed to have laminar flow which is very quiet.  With our typical Safety Air Gun, model 1210, the sound level is only 74 dBA; well under the noise exposure limit for 8 hours.

Unsafe Air Gun

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.

Why do I bring these points up?  Because safety is everyone’s responsibility.  The National Institute for Occupational Safety and Health, NIOSH, has an overview of how to handle hazards in the workplace.  They call it the Hierarchy of Controls (click).  This is a means to best protect workers from dangers.  The most effective way is by eliminating the hazard or substituting the hazard.  The least effective way is with Personal Protective Equipment, or PPE.  For your unsafe compressed air nozzles and guns, EXAIR can help by substituting the hazardous air gun and nozzle with an engineered solution designed with safety in mind.

In my opening statement, I explained a quick and easy method to determine if your compressed air guns are dangerous.  To keep your company compliant and safe, EXAIR offers a variety of different types of nozzles and Safety Air Guns to best fit your requirement.  If you find that you are using hazardous blowing equipment, you can contact an Application Engineer to find a safe and effective alternative.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Protect Personnel from Noise with Engineered Products

Sound can be defined as vibrations that typically travel as an audible wave through mediums that can be a gas, liquid or solid. For this blog we will concern ourselves with sound travelling through a gas (atmosphere) in an industrial setting.

Sound is energy that travels in waves and is measured by its frequency (cycles per second) and amplitude (intensity). A common unit of measurement for sound energy is the decibel. The decibel (abbreviated with dBA) is a unit-less number that is based on the logarithm of a known measured quantity to a reference quantity. Without reciting the equation for every increase of 3 dBA is a doubling of sound energy or twice as loud.

Since our focus is on industrial sound one might question why be concerned at all, after all sound emanates from most machines and devices. The reason for concern is that there are OSHA regulations regarding the amount of time workers can be exposed to different levels of sound in their workday as illustrated below. These limits are in place to protect personnel from Noise Induced Hearing Loss or NIHL. When the damage to anyones hearing is caused by their profession, it is also referred to as Occupational Hearing Loss or OHL.

After monitoring for noise, NIOSH and the CDC next recommend administrative controls to minimize or eliminate the noise hazard (click for their helpful PDF). This would include the use of noise reducing EXAIR products like Super Air Nozzles, Air Knives and Air Amplifiers.

dBA Chart.JPG
OSHA Maximum Allowable Noise Exposure

When considering the many items in an industrial setting that produce loud sounds the list would be exhaustive. Many of them simply produce loud sounds that can’t be eliminated or reduced while on the other hand there are some that can. Some of the noisiest offenders that plants have control over are air powered tools and open tube blow-offs.  Eliminating inefficient methods of part blow off & part cleaning with an engineered solution allows a company to significantly reduce the level of sound in their plant, improve worker safety and save money on compressed air consumption.

Employers are required to provide hearing protection to employees whom are exposed to sounds above 90 dBA on a Time Weighted Average (TWA). Without digressing into the formulas TWA calculates a workers daily exposure to occupational sounds by taking into account the average levels (in dBA) and the time exposed to different levels.  This is the how OSHA assesses workers exposure and what steps should be taken to protect the workers.

To conclude, plants need to be mindful of the OSHA regulations for sound levels, time of exposure and that hearing protectors wear out. Earmuff seals can lose their elasticity and reduce their effectiveness and the soft pre-molded earplugs can wear out in a day and need replaced.  Keep a good supply on hand and OSHA suggests letting workers with noisy hobbies take them home for protection off the clock!

If you would like to discuss reducing noise or any EXAIR product, I would enjoy hearing from you…give me a call.

Steve Harrison
Application Engineer

Send me an email
Find us on the Web 
Follow me on Twitter
Like us on Facebook