Caution Hearing Protection Required

What is Sound?

Sound from a human’s standpoint,

is its perception to changes in air pressure or otherwise called sound pressure. The human ear is, more or less, capable of detecting changes in air pressure at frequencies between about 20 Hz and 20,000 Hz. However, the change in air pressure must be great enough for the ear to detect. Changes in air pressure between approximately 0.00002 Pa (at 1000 Hz)  and 0.356 Pa  are somewhat typical in a day. Increases greater than 20 Pa may lead to hearing loss. Other living creatures, have different ranges.

What is sound pressure?

In a general sense, variations in air pressure are associated with the movement of air. When air moves or vibrates at the right velocity, frequency, and amplitude, local variations in atmospheric pressure are created that can be detected by an ear or “heard.” The greater the change in air pressure the greater the perceived “volume” or amplitude. A microphone is often used to measure sound pressure because it responds to changes in air pressure. When a well designed microphone is calibrated, it can be used to measure sound pressure for a wide range of frequencies. Hardware or software is often needed to determine the sound pressure for ranges of frequencies. Once analyzed one can better determine if hearing protection is needed.

When is hearing protection a good idea?

Hearing protection is needed when unwanted sound pressure is experienced by the ear, often called noise. A good time to use hearing protection. There are many definitions of unwanted noise, many defined by governments, see page on noise exposure standards. Nonetheless, excessive levels of sound pressure, even if it is from a fine music recording, can physically damage the ear and its “system.” The chart at the bottom of this page shows a wide variety of “effective” sound pressures from various sources. One commonsense way of reducing noise is to move further away; otherwise, a hear protection device ( HPD ) may be required.

Sound pressure drops off proportionally with distance.

For example, moving from 4 feet away to 8 feet reduces the sound pressure in half and moving from 4 feet to 20 feet away reduces the sound pressure to one fifth. So if it is too loud, go some place else, or get hearing protection.


Hearing protection required for some of these examples of sound pressure, in air at standard atmospheric pressure (from


Source of sound

Sound pressure* (Pa)

Sound level (dBSPL)

Shockwave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure)



Theoretical limit for undistorted sound at 1 atmosphere environmental pressure



Stun grenades



Simple open-ended thermoacoustic device[1]



.30-06 rifle being fired 1 m to shooter’s side



Rocket launch equipment acoustic tests



LRAD 1000Xi Long Range Acoustic Device at 1 m[2]



Jet engine at 1 m



Threshold of pain



Vuvuzela horn at 1 m[3]



Risk of instantaneous noise-induced hearing loss



Jet engine at 100 m



Non-electric chainsaw at 1 m[4]



Jack hammer at 1 m



Traffic on a busy roadway at 10 m



Hearing damage (over long-term exposure, need not be continuous)[5]



Passenger car at 10 m



EPA-identified maximum to protect against hearing loss and other disruptive effects from noise, such as sleep disturbance, stress, learning detriment, etc.[6]



Handheld electric mixer



TV (set at home level) at 1 m



Washing machine, dishwasher[7]



Normal conversation at 1 m



Very calm room



Light leaf rustling, calm breathing



Auditory threshold at 1 kHz[5]



*All values listed are the effective sound pressure unless otherwise stated.



Casella Cel discusses Exposure Assessment and Hearing Protection

Exposure assessment of employees working in noisy areas is necessary to ensure that harmful noise levels are not exceeded without proper countermeasures being taken. As a simple rule of thumb, if you need to raise your voice to carry on a conversation with someone, then it is likely that the noise level is around 85 dB so a sound level meter or dosimeter should be used to determine the actual decibel level. A simple instrument to check continuous noise levels in a fixed location is the CEL-240. Other simple sound level meters such as the CEL-244 can be used where noise levels have lots of variation or impulses as they will ‘integrate’ (i.e. average together) these sound pressure level fluctuations making a correct and accurate measurement more feasible. NOTE: ANY instrument used for OSHA regulatory compliance or compliance with EU directives, i.e. instruments used to demonstrate that the exposure levels are at, above or below recommended threshold limit values (TLV’s), permissible exposure limits (PEL) or daily action and exposure limit values (DEAV, DELV) must be capable of meeting the applicable ANSI and IEC standards for measurement accuracy.

Hearing Protection-Casella CEL-240

Hearing Protection-Casella CEL-240


Wikipedia discusses Regulations
Main article: Noise regulation

Environmental noise regulations usually specify a maximum outdoor noise level of 60 to 65 dB(A), while occupational safety organizations recommend that the maximum exposure to noise is 40 hours per week at 85 to 90 dB(A). For every additional 3 dB(A), the maximum exposure time is reduced by a factor 2, e.g. 20 hours per week at 88 dB(A). Sometimes, a factor of two per additional 5 dB(A) is used, however, these occupational regulations are acknowledged by the health literature as inadequate to protect against hearing loss and other health effects.

With regard to indoor noise pollution in residences, the U.S. EPA has not set any restrictions on limits to the level of noise. Rather, it has provided a list of recommended levels in its Model Community Noise Control Ordinance, which was published in 1975. For instance, the recommended noise level for indoor residences is less than or equal to 45 dB.[43][44]

Noise pollution control in residences is not funded by the federal government in part because of the disagreements in establishing causal links between sounds and health risks, since the effect of noise is often psychological and also, because it leaves no singular tangible trace of damage on the human body. For instance, hearing loss could be attributed to a variety of factors including age, rather than solely due to excessive exposure to noise.[45][46] A state or local government is able to regulate indoor residential noise, however, such as when excessive noise from within a home causes disturbances to nearby residences.


Contact us anytime by

calling or by filling out the contact form

Basic Contact Form for Renting Equipment


If you need more information on hearing protection visit the Pages tab above or Casella’s website.