Sound Power Level and Sound Pressure

Energy…all day (and night) long, we humans are surrounded by – and bombarded by – all kinds of energy. Sometimes, the effects are pleasant; even beneficial: the warmth of the sun’s rays (solar energy) on a nice spring day is the sure-fire cure for Seasonal Affective Disorder, and is also the catalyst your body needs to produce vitamin D. Good things, both. And great reasons to get outside a little more often.

Sometimes, the effects aren’t so pleasant, and they can even be harmful. Lengthy, unprotected exposure to that same wonderful sun’s rays will give you a nasty sunburn. Which can lead to skin cancer. Not good things, either. And great reasons to regularly apply sunblock, and/or limit exposure if you can.

Sound is another constant source of energy that we’re exposed to, and one we can’t simply escape by going inside. Especially if “inside” is a factory, machine shop, or a concert arena. This brings me to the first point of today’s blog: sound power.

Strictly speaking, power is energy per unit time, and can be applied to energy generation (like how much HP an engine generates as it runs) or energy consumption (like how much HP a motor uses as it turns its shaft) For discussions of sound, though, sound power level is applied to the generation end. This is what we mean when we talk about how much sound is made by a punch press, a machine tool, or a rock band’s sound system.

Sound pressure, in contrast, is a measure of the sound power’s intensity at the target’s (e.g., your ear’s) distance from the source. The farther away you get from the sound’s generation, the lower the sound pressure will be. But the sound power didn’t change.

Just like the power made by an engine and used by a motor are both defined in the same units – usually horsepower or watts – sound power level (e.g. generation) and sound pressure (e.g. “use” by your ears) use the same unit of measure: the decibel.  The big difference, though, is that while power levels of machinery in motion are linear in scale, sound power level and pressure scales are logarithmic.  And that’s where the math can get kind of challenging.  But if you’re up for it, let’s look at how you calculate sound power level:

Sound Power Level Equation

Where:

Wis reference power (in Watts,) normally considered to be 10-12 W, which is the lowest sound perceptible to the human ear under ideal conditions, and

W is the published sound power of the device (in Watts.)

That’s going to give you the sound power level, in decibels, being generated by the sound source.  To calculate the sound pressure level:

Sound Power Level to Sound Pressure Equation

Where:

Lis the sound power level…see above, and

A is the surface area at a given distance.  If the sound is emitted equally in all directions, we can use the formula for hemispheric area, 2πrwhere r=distance from source to calculate the area.

These formulas ignore any effects from the acoustic qualities of the space in which the sound is occurring.  Many factors will affect this, such as how much sound energy the walls and ceiling will absorb or reflect.  This is determined by the material(s) of construction, the height of the ceiling, etc.

These formulas may help you get a “big picture” idea of the sound levels you might expect in applications where the input data is available.  Aside from that, they certainly put into perspective the importance of hearing protection when an analysis reveals higher levels.  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.

 

Compressed Air and Safety

Warning

Compressed air is generally considered the fourth utility in industrial, commercial and back-yard settings.  It is used to power pneumatic equipment, cleaning surfaces, conveying materials, etc.  The compressor reduces the volume inside a chamber to increase the pressure.  The compressed air typically is contained in a reservoir tank for distribution to pneumatic equipment and devices.  Since air is a compressible fluid it has stored energy; and, if not used properly, it can be hazardous.  Most people perceive compressed air as harmless, but this is untrue.  It can be very dangerous.  Here are some potential risks when using compressed air:

  1. If the air pressure against the skin becomes greater than 30 PSI, air can penetrate through the membrane and cause an embolism which could be fatal.  The term used is Dead-End pressure, any end-use nozzle or blowoff product cannot exceed 30 PSI dead-end pressure.
  2. Hearing damage can occur from exposure to loud noises from compressed air exhausting from pneumatic equipment or devices.
  3. Proper use of Safety Air Guns and Safety Air Nozzles is a must. They should not be modified or tampered with.  For example, tying the trigger on an air gun for continuous blowing or modifying the nozzle to get a different blowing pattern.
  4. Compressed air can generate high velocities which can shoot chards of debris. The accelerated fragment can injure any part of the body even from bounce-back.
  5. If the air pressure is higher than the recommended rating for the equipment, uncontrolled eruptions can occur which can send broken pieces everywhere.
  6. When air hoses or lines are laying on the floor, near pinch points, or degrades from the environment, a break can occur causing unrestrained hose “whipping”.

Some safety precautions can be followed in your area when using compressed air products.  They may seem basic, but they are commonly overlooked.

  1. Verify that all compressed air components are rated to be used for the maximum line pressure.
  2. Use shut-off valves nearby to isolate the system from the main compressed air line.
  3. Have general inspection on your compressed air system to check for pipe degradation, leaks, faulty pneumatics, etc.
  4. When you go to repair items attached to the compressed air line, make sure to use proper lockout procedures to isolate and remove the hazardous energy.
  5. Remember that compressed air is not a toy and use proper PPE when required.
  6. If any pneumatically operated product is damaged, remove it from service and either repair it or replace it.
EXAIR Products

In 1970, Occupational Safety and Health Administration, OSHA, was enacted by the Department of Labor.  This organization was created “to ensure safe and healthful working conditions for working men and women”.  They created a set of laws and standards that they enforce with heavy fines and reoccurring visits if not followed.  The Department of Labor lists these laws under title 29 in the Code of Federal Regulations (CFR).  For general industry, these safety regulations are under part 1910 of 29 CFR.  To give a few examples, 29 CFR 1910.242b gives the explanation about dead-end pressure.  Under 29 CFR 1910.95a shows the maximum allowable noise exposure.  The reason that I noted these two OSHA standards as they are commonly overlooked with Safety Air Guns, and commonly fined by OSHA for improper nozzles.

Safety is everyone’s responsibility, and EXAIR products can be a key.  If you would like to discuss how to improve your workplace, you can contact an Application Engineer at EXAIR.     Because hazards and fines can be detrimental to your company when it comes to compressed air safety.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Photo: Attention Warning Sign by Peter-LomasCreative Commons: CCO

 

 

Engineered Air Nozzles Reduce Noise Levels and Outlet Pressure, Meeting OSHA Requirements

“My operators are complaining that our air guns are too loud, how can you help me?” – is a very common inquiry we receive here at EXAIR on almost a daily basis. Many open end blowoffs or air guns fitted with nozzles that have cross drilled relief holes create high pitch wind shear, resulting in excessive noise levels, sometimes exceeding 100+ dBA. This not only is a safety concern but also an OSHA violation.

Variety of Air Nozzles that produce dangerously loud noise levels

Loud noises and the length of exposure time can lead to significant health concerns such as long term hearing loss, increased stress levels and potential injury due to lack of concentration. The Occupation Safety and Health Administration (OSHA) introduced Standard 29 CFR 1910.95(a) as a way to protect workers from job related injuries associated to potentially dangerous sound levels. Per the Standard, at 90 dBA an operator is limited to a maximum of 8 hours of constant exposure. As noise levels increase, the allowable exposure time decreases, in some cases slowing production, costing a company on their bottom line.

 

EXAIR’s Air Nozzles are engineered so they entrain surrounding air across the profile of the nozzle, which produces a smoother airflow, ultimately reducing wind shear, resulting in much lower sound levels, meeting the OSHA Standard.

Illustration showing the air travel of our Super Air Nozzles

 

In addition, our Air Nozzles also meet the OSHA Standard 1910.242(b) for 30 PSI dead end pressure. All of our engineered Air Nozzles provide a relief or a safe path for the air to exit if the nozzle were to be blocked or pressed against an operator’s body so the exiting air pressure will never reach 30 PSIG.

All of EXAIR’s Air Nozzles are available with standard NPT threads to easily adapt to existing air guns. We also off our full line of Safety Air Guns which are fitted with our engineered nozzles, providing an “off-the-shelf” OSHA compliant solution. For help selecting the best product to replace your existing device or if you have a new application you would like to discuss, give us a call at 800-903-9247.

Justin Nicholl
Application Engineer
justinicholl@exair.com
@EXAIR_JN

 

Safe Trip

Just getting back in the swing of things after being on vacation last week. My family, along with my mother, went on a 7 day Eastern Caribbean cruise which included 3 days at sea and 3 days at different ports. Our port stops included the Bahamas, San Juan Puerto Rico and the island of St. Maarten. My wife and I have cruised several times and have already visited these islands, but with this cruise being our son’s and my mother’s first, we thought we would try to experience some different things.

Our last port was St. Maarten, where “we” (my wife and mother) planned our day of shopping and having an authentic lunch at a local restaurant. With the shopping portion of the day complete, we started asking locals for a good place to have lunch. We met a local who ran his own taxi company and recommended we have lunch at Maho Beach but it was going to be a 20 minute taxi ride. When we arrived, for some reason the area seemed somewhat familiar and then it hit me…. I’ve seen this place on TV! Their airport sits right on the edge of the island and arriving and departing planes basically fly right over your head while sitting at the restaurant/bar or swimming at the beach.

People line up along the road and fence line and wait for the next plane (the restaurant/bar has arrival and departure screens and will yell out when a large commercial jetliner is approaching), making it a very crowded area. Due to the potential jet blast coming from the engines there are safety signs posted that people ignore. I did ask one of the restaurant/bar managers if safety is such a concern, then why do they allow people to line up and he said “all they can do is warn people, if they want to subject themselves to injury, then that’s on them”. I don’t want to see anyone getting hurt, but I must admit, it is a little humorous to see people get blown all over the beach. Needless to say, we stood a good distance away.

St Maarten02_Maho Beach38Safety signmaho-beach-st-maarten

In all seriousness, safety should be a primary concern. Is your plant currently practicing safety when dealing with compressed air? Open pipes, tubes or drilled pipe can consume large amounts of compressed air, and exceed the pressure and noise level thresholds outlined by OSHA. And we are all aware that personnel don’t always abide by the safety rules – much like ignoring a safety sign.

At EXAIR, our customer’s safety is of utmost importance. All of our intelligent compressed air products meet or exceed the OSHA standard 1910.242(b) for safety.  This means that you can still operate the devices at 80 psig while not having to worry about an operator injuring themselves with the compressed air.  This is not just for one product line, but ALL of the compressed air products that we manufacture.

EXAIR products also meet or exceed the OSHA standard 29 CFR 1910.95(a) for maximum allowable noise exposure levels.   The chart for allowable noise level exposure is below. Occupational hearing loss is a serious issue in manufacturing, in fact, it is the most commonly recorded illness is manufacturing. Engineering controls, like replacing open air lines with engineered air nozzles, are one of the top recommendations to solve the problem. Engineering controls can effectively eliminate the problem of people forgetting, refusing, or ignoring safety processes.

OSHA Noise Level

By implementing the EXAIR engineered solutions into your facility you can effectively lower the noise level cause by unsafe compressed air blow offs and possibly eliminate the need for hearing protection all together.   In my experience any time an operator doesn’t need to wear hearing protection or you can make their surrounding environment a little quieter, they tend to be a little happier which, always leads to better production. Again, many resources back this up, loud noise can also create physical and psychological stress.

These are just two of the standards that EXAIR will never take a vacation on.   Every product that EXAIR designs must be safe for operator operations, whether that be through pressure output or through the noise level it creates.

Contact one of our applications engineers to see how we may be able to improve similar safety concerns at your facility.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN