Information on the sound level (2023)

sound level specifications: THE EVOLUTION OF CALM

Por John C. Dolehanty

September 2005

Q.- What is the easiest and most economical way to guarantee the tranquility of industrial facilities?

A.- Sound Level Specifications.

Many companies have suffered through the frustrating cycle of spending valuable resources quieting their facilities, only to have their efforts frustrated by purchasing and installing noisy equipment and machinery. Smart companies learn from this experience and implement sound level specifications to ensure machines and equipment are designed and built to run quietly.

Proper use of a sound level specification when purchasing new equipment is essential to any noise control and hearing protection program. The sound level specification prevents noise problems in new installations and helps reduce noise levels in older installations over time as noisy equipment is replaced with quieter equipment.

The intent of this article is to (1) explain the purpose of a machinery sound level specification and why it is important, (2) highlight the components of an effective specification, and (3) identify common pitfalls when assessing compliance with the Specifications.

Purpose of a sound level specification

An effective noise abatement program is highly dependent on a purchase specification for a working noise level. The primary purpose of a sound level purchase specification is to ensure that noise control measures are considered and implemented in the design and construction process. This ensures that the installed device meets your primary criteria of preventing/reducing employee participation in the Hearing Conservation Program (HCP). Criteria for secondary equipment may include meeting an environmental performance limit or meeting interior office limits that ensure adequate voice communications (office HVAC, etc.).

The primary purpose of the sound level specification is to help prevent noise-induced hearing loss by ensuring that employee noise exposure does not exceed 85 dBA TWA._{8 standard}. Noise exposure of a full shift (8 hour) employee of 85 dBA TWA_{8 hours}requires employers to establish and maintain an ongoing and effective hearing protection program.

With a sound level purchase specification in place, future sound mitigation efforts are generally limited to keeping the equipment and controls currently in place. Without a specification to purchase a working sound level, current and past noise abatement efforts can be thwarted when noise-producing equipment is in close proximity to areas/workers that have been silenced due to abatement efforts. noise.

OSHA does not require noise levels for equipment. If you purchase a device that causes employee exposure levels to exceed 85 dBA TWA, you haveAlsotook responsibility for maintaining an ongoing and effective hearing protection program!

The scheduled replacement of noisy equipment is the ideal opportunity to reduce noise levels. Time and resources are available for this. It is important that a sound level specification be part of the replacement process.

Use hearing conservation programs

An average sound level limit of 80 dBA is intended to prevent hearing loss related to work related noise. A sound level purchase specification that refers to an A-weighted sound pressure level at 1 meter cannot address environmental noise (perimeter/community noise) issues, nor is it appropriate to address indoor acoustics and floor intelligibility issues. speaks.

In the case of environmental concerns, reference should be made to the local noise protection ordinance. Property limits for industrial sources typically range from 55 dBA to 70 dBA. Interior acoustics are generally treated using NC and RC curve criteria. For example, open plan offices are often designed to be NC-40 compliant.

Essential components of effective sound level specifications

Limits

Factors such as regulatory limits, additional effects of additional noise sources, operator intervention, types of equipment, and available control technology are important to consider when selecting a specification noise level limit.

Many sound level purchase specifications limit the sound pressure level of new equipment to an average sound level of 80 dBA (or less) at 1 meter across the equipment/system enclosure and at any position on the operator. This limit has proven to be very effective in preventing employee exposure from exceeding 85 dBA TWA. A limit of 80 dBA was chosen to allow the introduction of a sound level of 80 dBA in areas where the current sound level is 83 dBA and has not yet exceeded a cumulative sound level of 85 dBA. (A-weighted sound levels are provided because A-weighted levels are used to assess worker noise exposure.) It should also be noted that some specific pieces of equipment have traditionally been specified in terms of sound power levels, particularly electric motors. Note that the sound power level of an electric motor (L_W) of 85 dBA is actually less than 80 dBA at 1 meter.

equipment

A Type I or II integrating sound level meter is the preferred instrument for determining the sound level of equipment. The sound level meter must be able to measure average, maximum, minimum and peak sound levels. A non-integrated sound level meter should only be used if the device in question produces a very constant (unchanging) sound level (this is rare!). The meter must be configured so that there is no lower limit threshold (to capture the full range of sound levels from the device). Also, a 3 dB slew rate (or doubling rate) is typically used. This setting more accurately reflects the actual physical level of sound propagation, in contrast to OSHA's more liberal 5 dB reference setting for worker exposure control.

An octave band (frequency) sound level meter is not usually needed, but it can be useful when measuring ultrasonic (radio frequency) sources.

measurement method

Most sound level purchase specifications are based on information from the National Machine Tool Builders Association (NMTBA).noise measurement techniques, Second Edition, January 1976. The NMTBA has been superseded by the Association for Manufacturing Technology (AMT) and they are in the final stages of approving an updated ANSI technical reference guide: B11.TR5:Sound Level Measurement Guidelines, a guide for measuring, evaluating and documenting sound levels emitted by machineryto replace the NMTBA guidance.

Generally average (L_equalizer) Sound levels are measured at a distance of 1 meter along the perimeter of the equipment/system along with all operator positions. The sound level meter should be placed 1.5 meters from the ground (according to the hearing range of an average person), unless there is a defined operator position at other heights.

Sound level measurements should be made under typical operating conditions and should cover the worst operating conditions. Most devices experience this under load, but some systems actually generate higher noise levels when idle. Furthermore, the sound level must be averaged over several cycles of the device to ensure that the measured values ​​are representative.

The background noise level (during the test) should always be as low as possible, preferably 10 decibels or more below the specified limit. Background levels that are 10 decibels or more below the device level are acoustically insignificant. The background noise level should be measured prior to device testing and then subtracted from the device noise level.

Common Conformity Assessment Mistakes

Many companies feel that their sound level specification protects them from noisy equipment. Unfortunately, due to a lack of acoustic expertise and sometimes improper use of the device, it is not uncommon to find incorrectly documented sound level data. These mistakes and oversights can be costly to both vendors and end users of the equipment.

equipment

calibration- The measuring devices must be calibrated before and after the on-site measurement sessions (with a portable calibrator). If the meter does not calibrate within ±1 decibel after the measurement session, the meter measurements should be repeated. In addition, the measurement devices must be recalibrated annually in a certified testing laboratory. The integrating sound level meter and its associated field calibrator must always have a stamp indicating that their laboratory calibration can be traced back to the National Institute of Standards and Technology (NIST). Meter calibration documentation should always accompany any written report.

A common mistake is using the wrong gauges. Whenever possible, an integrating sound level meter should be used. A non-integrated sound level meter should only be used when sound levels are neither fluctuating nor stable.

Construction- The sound level meter must be correctly configured. Typically this would involve: setting the rate of change to 3dB, setting the threshold to 0dB (or the lowest possible setting), setting the dynamic range so that sound levels are essentially even between high and low levels, and set the measurement metric to L_equalizer(average level). Ideally, the meter should also simultaneously measure the following metrics: sample time, L_Maximum, yo_Minimum, me too_summit. A dosimeter is often used to document equipment sound levels. That in itself is not a problem.AndThe meter is set up correctly. Remember that the standard dosimeter setup is for documenting employee exposure.noEvaluation of the sound level of the devices.

Another common mistake is when the wrong device conditions are measured. Sound level measurements should be representative of typical (or, in some cases, worst case) production/operating conditions. If these conditions are not possible, a simulation/graph can be used. For example, multiple sources can be measured separately and then mathematically combined to get the total sound level. (Remember to remove the undertone from each individual source measurement.)

It is worth noting that equipment measurements are very different from a measurement of employee noise exposure. The use of typical employee dosimeter equipment/techniques may result in incorrect information. Typical employee exposure measurements (OSHA) use a lower limit threshold of 80 dBA with an exchange rate of 5 dB. An 80 dBA threshold setting integrates all sound levels below 80 dBA as 0 dBA in this setting. This incorrect setting usually results in artificially low sound levels.

Minutes

A common measurement error occurs when the meter is placed too close to the device in the belief that this will provide a good sample (such as an air sample). Since sound pressure is a function of distance from the sound source, the location of the meter is critical.

The background level should be subtracted from the measured device sound level. Optimally, the background should be at least 10 dBA below the sound level of the device. The background noise level variability should be stable as the background noise level approaches the device noise level.

Perimeter sound levels should never be averaged; They should be treated as independent data points. And remember, decibels are logarithmic values ​​and cannot be manipulated using standard arithmetic means.

Key to successfully using the sound specification

The key to successfully using a sound level specification to minimize the deleterious effects of noise in an industrial facility is to create a partnership between the buyer and the supplier. Key elements of this partnership include:

• Timed coordination- Addressing noise issues before equipment is placed in service leads to more effective noise abatement efforts.
• Training- Does your company provide supplier training to help them understand your specification and perform conformance assessments?
• documentation- Do you provide suppliers with guidelines and formats for documenting measurement locations, meter settings, duration of each sample, and calibration history?
• Rating and comments- Assessing vendor capabilities and providing feedback on compliance efforts provides a foundation for improving both specification compliance and consistent data delivery.

Remember: A sound level purchase specification can only be effective if it is consistently applied and enforced. A good rule of thumb to remember: Equipment vendors' efforts to meet purchasing sound level specifications reflect the same commitment they make to enforcing them!

Mr. Dolehanty is president of Phase To, Inc. and has over 18 years of experience in the hearing protection and noise control fields. You can contact Mr. Dolehanty at (517) 886-9379 and atjohndolehanty@phaseto.com.