WATCH YOUR SOUND DOSAGE

If you don't watch your sound dosage, you might become hard of hearing. Research now shows that exposure to excessive sound, not aging, makes people lose their hearing.

NOTE: See addendum at bottom of page for new discoveries and special cautions on hearing loss from low frequency and subsonic sound.


Introductory:
Making correct measurements

In order for these regulations to be interpreted properly, the measurement must be correctly made. There are errors in many of the laws, because the laymen who wrote them do not understand acoustics.

The table at right states the correct setting of the sound pressure level (SPL) meter for measuring sound and noise levels at the location of the listener (or at the distance specified in the law), not at the location of the sound source. Many laws incorrectly specify the A weighting when the B or C weighting is more appropriate. Using the A weighting for loud sounds is appropriate only if the listener is a far enough away from the source that the level at the listener has dropped into the A weighting range, but the measurement is taken a lot closer to the source.

If the reading is being taken for protection of hearing, it should be taken as close to the source as unprotected people can approach. If the reading is being taken for protection of adjacent property owners from sound annoyances, the readings should be taken at the property lines.

WEIGHTINGS

SPL LEVELCORRECT WEIGHTING
above 85 dBC (reading in dBC)
55 dB to 85 dBB (reading in dBB)
below 55 dBA (reading in dBA)

Selecting the correct weighting

It is important to use the correct weighting for the sound levels being measured. Each weighting is valid only inside the specified range. Attempting to use a weighting outside its range gives erroneous readings. Such false readings cause the readings to be higher or lower than the real SPL levels. Use the correct weighting.

Many otologists think the weighting curves should be adjusted to add sounds which are not perceived as loud, but which do cause hearing damage.

Right now, sounds below 20 Hz are not even represented in the weighting curves, because most ears do not sense them as sounds. But enough acoustical energy in the subsonic area can cause pain, and can cause hearing loss beginning in the 4 KHz area in some individuals.

Many SPL meters do not have a B weighting selection. If a sound falls within the B weighting range, it can be measured with this procedure:

  • Take an A weighted reading
  • Take a C weighted reading
  • Find the arithmetic mean of the two readings obtained.

The OSHA Regulation

The OSHA (Occupational Safety and Health Administration) guidelines for sound exposure say that workers may be exposed to the following levels of sound pressure (SPL) for the following time periods (but only ONE of these levels in any 24 hour period). In addition, hearing protection is required to be available at any level above 85 dB SPL. Many otologists feel that the OSHA guidelines do not provide enough protection. (See below for the NIOSH scale.)

A formula for calculating these times (using an ordinary scientific calculator) follows:

OSHA max time (hr):
O_time = 2 ^ ((105 - SPL) / 5)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

OSHA dose:
O_dose = time (hr) * 2 ^ ((SPL - 105) / 5)

Where:
* is multiplication
/ is division
^ is exponentiation

OSHA

LEVELOSHA MAX TIME
> 115 dB SPLNONE
115 dB SPL15 minutes
110 dB SPL30 minutes
105 dB SPL1 hour
102 dB SPL1.5 hours
100 dB SPL2 hours
97 dB SPL3 hours
95 dB SPL4 hours
92 dB SPL6 hours
90 dB SPL8 hours
Extension (not in OSHA regs):
87 dB SPL12 hours
85 dB SPL16 hours (protection)
82 dB SPL24 hours (continuous)

OSHA permitted exposure times


The NIOSH Recommendation

NIOSH (National Institute for Occupational Safety and Health) and ANSI (American National Standards Institute) have adopted a stricter standard based on equal amounts of energy. Here is their scale of the amount of sound a person may be exposed to in a 24 hour period:

A formula for calculating these times follows:

NIOSH max time (hr):
N_time = 2 ^ ((94 - SPL) / 3)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

NIOSH dose:
N_dose = time (hr) * 2 ^ ((SPL - 94) / 3)

NIOSH-ANSI

LEVELNIOSH MAX TIME
> 115 dB SPLNONE
115 dB SPL28 seconds
112 dB SPL56 seconds
109 dB SPL1 minute 52 seconds
106 dB SPL3 minutes 45 seconds
103 dB SPL7 minutes 30 seconds
100 dB SPL15 minutes
97 dB SPL30 minutes
94 dB SPL1 hour
91 dB SPL2 hours
88 dB SPL4 hours
85 dB SPL8 hours
82 dB SPL16 hours
80 dB SPL24 hours (continuous)

NIOSH recommended maximum exposure times


The EPA Recommendation

EPA (Environmental Protection Agency) has adopted a yet stricter standard based on equal amounts of energy. But it seems to be based on removing annoyances, rather than hearing protection, since no person in the audience of a concert could hear the music. Here is their scale of the amount of sound a person may be exposed to in a 24 hour period:

A formula for calculating these times follows:

EPA max time (hr):
E_time = 1.5 * 2 ^ ((82 - SPL) / 3)

A formula for calculating the portion of the maximum dose used by a given sound exposure follows:

EPA dose:
E_dose = time (hr) / 1.5 * 2 ^ ((SPL - 82) / 3)

EPA

LEVELEPA MAX TIME
> 97 dB SPLNONE
97 dB SPL3 minutes
94 dB SPL6 minutes
91 dB SPL11 minutes 15 seconds
88 dB SPL22 minutes 30 seconds
85 dB SPL45 minutes
82 dB SPL1 hour 30 minutes
79 dB SPL3 hours
76 dB SPL6 hours
73 dB SPL12 hours
70 dB SPL24 hours (continuous)

EPA recommended maximum exposure times


COMPARING THE STANDARDS

LEVELOSHA MAX TIME NIOSH MAX TIMEEPA MAX TIME
> 115 dB SPLNONE NONENONE
115 dB SPL15 minutes 28 secondsNONE
112 dB SPL22 minutes 45 seconds 56 secondsNONE
109 dB SPL34 minutes 28 seconds 1 minute 52 secondsNONE
106 dB SPL47 minutes 38 seconds 3 minutes 45 secondsNONE
103 dB SPL1 hour 20 minutes 7 minutes 30 secondsNONE
100 dB SPL2 hours 15 minutesNONE
97 dB SPL3 Hours 30 minutes3 minutes
94 dB SPL4 hours 36 minutes 1 hour6 minutes
91 dB SPL7 hours 2 hours11 minutes 15 seconds
88 dB SPL10 hours 30 minutes 4 hours22 minutes 30 seconds
85 dB SPL16 hours (protection) 8 hours45 minutes
82 dB SPL24 hours (continuous) 16 hours1 hour 30 minutes
79 dB SPL24 hours (continuous) 24 hours (continuous)3 hours
76 dB SPL24 hours (continuous) 24 hours (continuous)6 hours
73 dB SPL24 hours (continuous) 24 hours (continuous)12 hours
70 dB SPL24 hours (continuous) 24 hours (continuous)24 hours (continuous)

Comparison between the standards


CALCULATING YOUR EXPOSURE

But how do you figure out your exposure if you are exposed to different levels of these sounds for different periods of time?

Here is one way to calculate your total dose to damaging sound (using the NIOSH levels):


Example: You are exposed to:

91 dB SPL - 1 hour
88 dB SPL - 3 hours
85 dB SPL - 4 hours

Is your total dose too large?


A spreadsheet is ideal for figuring these doses. Using the same example:

*ABCD E
1SPLHoursDose C formula shown
2911.5 =B2*2^((A2-94)/3)
3883.75 =B3*2^((A3-94)/3)
4854.5 =B4*2^((A4-94)/3)
5
Sum:1.75 =Sum(C2:C4)
6
NIOSH:DANGER =IF(C5>1,"DANGER","SAFE")
7



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Spreadsheet for figuring NIOSH doses

Manually calculating NIOSH doses:

dose1 = 1 * 2 ^ ((91 - 94) / 3)
dose1 = 1 * 2 ^ (- 3 / 3)
dose1 = 1 * 2 ^ (-1)
dose1 = 1 * .5
dose1 = .5

dose2 = 3 * 2 ^ ((88 - 94) / 3)
dose2 = 3 * 2 ^ (-6 / 3)
dose2 = 3 * 2 ^ (-2)
dose2 = 3 * .25
dose2 = .75

dose3 = 4 * 2 ^ ((85 - 94) / 3)
dose3 = 4 * 2 ^ (-9 / 3)
dose3 = 4 * 2 ^ (-3)
dose3 = 4 * .125
dose3 = .5

Sum the doses:
total_dose = dose1 + dose2 + dose3
total_dose = .5 + .75 + .5
total_dose = 1.75

This is larger than 1, so there is a very large chance of damaging hearing.


ADDENDUM

NEW DISCOVERIES ABOUT HEARING LOSS

Recent research has indicated two new facts about hearing loss:

  1. NO SUCH THING AS AGE-RELATED HEARING LOSS

    Age related hearing loss is now thought to not exist. Instead, what was thought to be age-related hearing loss has now been found to be acquired hearing loss from cumulative exposures to the loud sounds of steam trains, firearms, and factories.

  2. HEARING DAMAGE FROM LOW FREQUENCY AND SUBSONIC SOUND

    Extremely low frequency sounds do not follow the tables above, because the weighting curves used for the sound measurements above are based on audibility. But it is now thought that frequencies under 60 Hz, and especially those approaching DC impulse transients, cause hearing damage, even though they are not very audible. This damage begins in the "rock range", starting between 4 KHz and 6 KHz, and expanding in frequency range as exposure continues. So the following precautions should be taken:


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