## Understanding Decibels & Why OSHA Pays Attention to Your Noise Exposure

In the simplest of metric terms, a decibel is one-tenth of a bel.  But, historically, bel was a unit created to honor Alexander Graham Bell who invented the telephone.  In the early days with telephone wires, they noticed that the signal strength would decay over a long distance.  In order to determine power requirements to connect people for communications, they determined that they could use the ratio of power levels.  As a start, it had to be based on a minimum amount of power required for a person to hear on the telephone.  They found that the signal power level to generate an angular frequency of 5000 radians per second would be that minimum value as determined by an average number of people.  They used this mark as a reference point in the ratio of power levels.  Because of the large variations in values, they simplified the equation on a base-10 log scale and dividing the bel unit by 10.  Thus, creating the measurement of decibel.

Today, this same method is used to measure sound.  Like frequency waves that travel through the telephone wires, pressure waves travel through the air as sound.  This sound pressure is what our ears can detect as loudness, and it has a pressure unit of Pascals (Pa).  As an example, a small sound pressure would be like a whisper while a large sound pressure would be like a jet engine.  This is very important to know as high sound pressures, or loudness, can permanently damage our ears.

With sound pressures, we can determine the Sound Pressure Level (SPL) which is measured in decibels (dB).  Similar to the equation for the telephone power signals above, the SPL also uses a ratio of sound pressures in a base-10 logarithmic scale.  For a minimum reference point, an average human can just start to hear a sound pressure at 0.00002 Pa.  So, the equation for measuring sound levels will use this minimum reference point as shown in Equation 1.

Equation 1:

L = 20 * Log10 (p/pref)

where:

L – Sound Pressure Level, dB

p – Sound pressure, Pa

pref – reference sound pressure, 0.00002 Pa

Why is this important to know the decibels?  OSHA created a chart in 29CFR-1910.95(a) that shows the different noise levels with exposure times.  This chart was created to protect the operators from hearing loss in work environments.  If the noise level exceeds the limit, then the operators will have to wear Personal Protection Equipment (PPE), or suffer hearing damage.  EXAIR offers a Sound Level Meter, model 9104, to measure sound levels in decibels.  It comes calibrated to accurately measure the sound to determine if you have a safe work environment.

There is a term that is used when it comes to loud noises, NIHL.  This stands for Noise Induced Hearing Loss.  Once hearing is damaged, it will not come back.  To keep your operators safe and reduce NIHL, 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 can be used to contact EXAIR if you have any questions.

John Ball
Application Engineer
Email: johnball@exair.com

Photo of Telephone by Alexas_FotosCC0 Create Commons

## How To Solve A Problem with Compressed Air

In my (almost) six years as an EXAIR Application Engineer, I’ve learned a great many things about the capabilities of our products.  The way we do business sure does make it easy:

• We readily share application information, as a team.  If you ask me a question, you’re asking all of us.  It does neither of us any good if I tell you something MIGHT work if one of my team knows it WON’T – or if someone knows what else DOES work.  If we can offer a solution, we will.
• We’ll test your product, free of charge.  This is a popular way of finding out which Line Vac is best for conveying a particular product, for example.
• If you’re considering a quiet, safe, and efficient EXAIR product as an upgrade, we’ll test your current product in our award winning Efficiency Lab, so you can compare accurate performance data and analyze the expected benefits…which can be dramatic.  Try us on that.

• We’ll let YOU test our product, risk-free.  All catalog products come with a 30 Day Unconditional Guarantee.  We invite you to put it through its paces for up to a month.  If it’s not working out, we’ll arrange return for full credit.
• We’ll do the math.  But first, a disclaimer: strictly comparing the force or flow of an engineered product to an open-end blow off won’t always tell the tale.  Our Intelligent Compressed Air Products are creating a laminar flow which won’t generate as high of a force/thrust as open-end blowing (which is turbulent by nature,) but is MUCH more conducive to efficiency and noise reduction, as well as similar (if not improved) performance.  But back to the math: if you know the metrics you need to meet for spot cooling (like a Vortex Tube, Adjustable Spot Cooler, Cold Gun, etc.) or for liquid spraying (the liquid flow rate and/or pattern size & shape from an Atomizing Spray Nozzle, for instance,) or the heat load that a Cabinet Cooler System can handle, we’ll do the calculations and specify the appropriate product.

Regardless of the application, if it can be solved with compressed air, it’s very likely that we have a great solution.  Call me to find out how we can help.

Russ Bowman
Application Engineer
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