Construction Noise – Pavement Interactive

Noise Basics

Healthy humans can hear audible sound with a range of 20 Hz to 20,000 Hz with a maximum intensity at 3,000 Hz. (Hz = Hertz, or cycles per second.) Frequencies below 20 Hz are called “infrasound” and above 20,000 Hz “ultrasound.” The numerical magnitude of a sound typically expressed as sound pressure level in decibles, abbreviated dB.

Distance

Distance is important, since the intensity of sound decreases inversely as the square of the distance from the source.

Δ Sound Pressure Level =

Example

r₀ = initial radius from sound source
r₁ = second radius from sound source

and if r₁ = 2r₀ then

Adding Sounds

Typically, several sources of sound occur at the same time and is not a linear function.
For example, adding one 60 dB sound to a second 60 dB sound adds to 63 dB. The formula follows:

The calculation for two 60 dB sounds is:

Energy Equivalent Sound

The Energy Equivalent Sound, or L_eq represents the same energy as the time-varying sound over the measurement period; essentially an average.
Some common time scales associated with L_eq are 24 hr, 1 hr, 1 minute, one day or night.

Formula:

Where

t₁ = start time for measurement, and
t2 = end time for measurement.

Sound Pressure and Decibles

To avoid expressing sound or noise in terms of Pascals, Pa, the decibel scale is used. The scale uses a hearing threshold of 2.0×10^-5 Pa. Sound Pressure Level (SPL) can be calculated by using the following equation:

Where

P = the measured sound pressure level
P₀ = the reference sound pressure, which is 20μPa or 2.0×10-5 Pa or 2.9×10-9 psi.

This gives a range of 0 to 120 dB (120 dB is the approximate threshold of pain).

Sound pressure typically ranges from 20 μPa to 20,000,000 μPa (0.0029 psi)

Range of Sound Pressures

Source of Sound/Noise	Approximate Sound Pressure  in µPa
Launching of the Space Shuttle	2,000,000,000
Full Symphony Orchestra	2,000,000
Diesel Freight Train at High Speed at 25 m	200,000
Normal Conversation	20,000
Soft Whispering at 2 m in Library	2,000
Unoccupied Broadcast Studio	200
Softest Sound Human can Hear	20
Source: Environmental Protection Department, Government of Hong Kong.

Using the following table, sound pressures in dB can be qualitatively compared to other sound pressure scales.

Sound Pressures in Decibels

Source	dB
Threshold of hearing	0
Rustling leaves	20
Quiet whisper at 3 ft.	30
Quiet street	50
Inside car	70
Diesel truck	100
Jet at 100 ft.	130

According to the “Fundamentals and Abatement of Highway Traffic Noise” (FHWA, 1973^[1]), a sound level change of 1 dB can barely be detected by humans, while changes of 2 to 3 dB are barely noticeable.
Also,

Change of 5 dB, readily noticeable.
Change of 10 dB perceived as a doubling in loudness.
Change of 20 dB represents a dramatic change.
Change of 40 dB represents the difference between a faintly audible sound and a very load sound.

A-Weighting Scale

The way the ear responds to sound is not proportional to sound intensity but nearly proportional to the log of sound intensity – it depends on the frequency of the sound. The human ear has peak response around 2,500 to 3,000 Hz and a relatively low response at low frequencies. To account for this, sound weighting schemes have been developed, the most common being the “A-weighting” scale.

The average person perceives a change in sound level of about 10 dB as a doubling or halving the sound’s loudness. Table 3, below, shows a relationship between dBA and “noise loudness” levels.

70 to 80 dB: 2x as loud
70 to 90 dB: 4x as loud
70 to 100 dB: 8x as loud etc.

Source: Table 3 from a noise analysis report entitled “Tijuana River Valley Regional Park, Trails and Habitat Enhancement Project,” San Diego Dept of Public Works, Prepared by Kimley-Horn and Associates, Inc. July 2005

Sound pressure levels for the lower and upper portions of frequency are reduced before being combined into one single sound pressure level value. Designated dBA or dB(A). More weight is given to frequencies starting at 1,000 Hz.

Construction Noise Facts

Construction noise comes from equipment and activities. These include motors running, tool use, and impact, among other things. Hearing loss is common among construction workers.

Hearing loss is gradual, so it may not be noticeable until the damage is already done. The ability to hear higher pitch is lost first, while the first loss that people tend to notice is the loss of the ability to hear speech. Hearing loss is also dangerous – think about what might happen if a person can’t hear someone shout or the sound of equipment behind them.

Noise can also cause tinnitis (ringing in the ears), tiredness, stress, and nervousness. Severe tinnitus can disturb the ability to sleep, and cause irritability and depression. Excessive noise raises blood pressure. Impact noises over 140 dB cause immediate nerve damage to the ear.

Noise damages hearing based on two factors: (1) level of exposure and (2) noise intensity

Exchange rate:(as stated by OSHA [http://www.ccohs.ca/oshanswers/phys_agents/exposure_can.html]) “As the sound level increases above the criterion level, Lc, the allowed exposure time must be decreased. The allowed maximum exposure time is calculated by using an exchange rate, also called a “dose-trading relation” or “trading ratio.” The exchange rate is the amount by which the permitted sound level may increase if the exposure time is halved.”

Noise Reduction

The Noise Reduction Rating, NRR, is a single number which is required by law to be shown on the label of each hearing protector sold in the US (40 CFR, Part 211, Subpart B, Hearing Protective Devices).

Figure 3: Examples of Hearing Protection

[1] Image courtesy of www.hocksproducts.com:
1) foam earplugs 2) molded earplug 3) earmuffs 4) tapered earplug

For A-weighted measurements:
Protected dBA = Unprotected dBA – [NRR – 7]

Why – 7? This correction factor is used to account for the de-emphasis of low-frequency energy inherent to the A-weighting scale.

Example: Protector rated at 17 dB and used in a environment noise level of 95 dBA. The noise entering the ear would be expected to be about 95 – [17 – 7] = 85 dBA

Figure 4: Typical NRR Label. Recall that you deduct 7 dBA from the NRR shown on the label, or, in this case, NRR = 29 – 7 = 22

Typical equipment and their associated NRRs:

Ear plugs: NRR = 29
Headset: NRR = 22
Headset: NRR = 27
Headset: NRR = 30

The shape of the ear can affect the way earplugs fit. Each person should choose the hearing protection that is most comfortable, because ill-fitting or uncomfortable hearing protection will not be used, and therefore would offer no protection.

Construction Equipment Noise Levels

OSHA regulations for noise exposure:

Allowed to be unprotected	Allowed to be unprotected
Up to 8 hours	90 decibels
Up to 4 hours	95 decibels
Up to 1 hour	105 decibels

When noise reaches 95 decibels, OSHA requires you to work less than 4 hours without hearing protection. This does not mean that 95 decibels is a safe level of noise; 1 in 5 people exposed regularly to 90 decibels will lose some hearing, while short, very loud noises do the most harm.

Equipment	Decibels	Equipment	Decibels
Pneumatic chip hammer	103-113	Earth Tamper	90-96
Jackhammer	102-111	Crane	90-96
Concrete joint cutter	99-102	Hammer	87-95
Portable saw	88-102	Earthmover	87-94
Stud welder	101	Front-end loader	86-94
Bulldozer	93-96	Backhoe	84-93
See videos, below.

A good rule of thumb is that if people 3 feet apart need to raise their voices to speak to one another, it is too noisy and hearing protection should be used.

Also try to move around the site in the course of the day, and move from more to less noisy areas as work allows. During rest or lunch breaks, move to a quieter area.

Use hearing protection regularly. This doesn’t need to completely block voices or other noise, like backup alarms. Reduce the noise, don’t shut it completely out.

Make a yearly appointment to have a doctor check your hearing.

Washington State Noise Limitations for Construction Workers

The Washington Industrial Safety and Health Act (WISHA) sets the Permissible Exposure Limit (PEL) at 85 dBA for a 8 hour shift, while the OSHA PEL is 90 dBA for 8 hours. According to WISHA, for every 5 dBA above 85, the exposure time is cut in ½. This is referred to as exchange rates.

Figure 5: WISHA Allowable Exposure Times

WAC 296-817 Hearing Loss Prevention

According to Washington State law, the following table limits the exposure of construction workers to noise and delineates the protection required.

University of Washington

UW School of Public Health and Community Medicine has done extensive studies on construction noise, and provides brochures for most of the major construction trades.

Work shift noise level for 887 construction workers (UW study)

Category	Result (dBA)
Average full-shift noise level	81.4
Average length of work shifts	8 hr 26 min
% of full-shift average levels over 85 dBA	34%
% of full-shift average levels over 90 dBA	10%
% of work shifts with any noise over 115 dBA	52%
Average % time hearing protectors used above 85 dBA	39%
Average % time hearing protectors used above 115 dBA	34%
Note: Based on one minute samples of L_eq

Hearing protection NRR which should prevent most workers from being exposed above the 8 hour allowable limit (UW study)

Trade	NRR (dBA)
Sheet metal worker	12
Insulation worker	12
Electrician	12
Tile setter	12
Carpenter	14
Cement Mason	14
Ironworker	18
Bricklayer	22
Laborer	24
Operating Engineer	24
Masonry restoration worker	26

City of Seattle Construction Related Noise

Maximum permissible noise levels within Seattle for all types of sounds during the daytime (7 am to 10 pm).

District of Sound Source	District of Receiving Property
District of Sound Source	Residential	Commercial	Industrial
Residential	55	57	60
Commercial	57	60	65
Industrial	60	65	70

Maximum permissible noise levels within Seattle for all types of sounds for weeknights (10 pm to 7 am) and weekends and holidays (10 pm to 9 am).

District of Sound Source	District of Receiving Property
District of Sound Source	Residential	Commercial	Industrial
Residential	45	57	60
Commercial	47	60	65
Industrial	50	65	70

City of Portland, OR Construction Related Noise

Construction times allowed by the City of Portland noise code is 7 am to 6 pm Monday through Saturday, and allows for noises up to 85 dBA at a 50 ft. distance. However, Portland recognizes that some equipment cannot meet that standard (such as jackhammers, concrete saws, etc) and are exempt from the standard during the permissible construction times.

FHWA Roadway Construction Noise Model

Based on extensive calculations and measurements from Boston’s Central Artery/Tunnel project. The data base has extensive equipment data measured via A-weighted L_max at a distance of 50 ft. from the construction equipment.
Refer to the publication: FHWA-HEP-05-054, January 2006, “FHWA Roadway Construction”