THE WESTERN CANADIAN LUMBER WORKER

SAFETY PAGE

NOISE

By ANDY SMITH
Regional Safety Director

Noise has been defined in
many ways. Technically,
sound is defined in terms of
variations in pressure, stress,
particle displacement, particle
velocity, and others propa-

gated in an elastic media.

RAPID
PULSATIONS

In less technical terms, and
from the ordinary viewpoint
of hearing, sound can be de-
fined as rapid pulsations in air
pressure produced by a vi-
brating source. To most of us,
it is simply anything that we
hear. Noise is generally
thought of as an unpleasant,
unwanted sound. Noise may
or may not be harmful to
hearing, depending on _ its
character and conditions of
exposure.

Noise is a problem in our
industry for two most import-
ant reasons, One, because
some industrial noises can
damage the ears of those ex-
posed to it. Two, because in-
dustrial noise may contribute
to the cause of accidents
through interference with
hearing voice communica-
tions and warning signals.

To understand how noise
eauses loss of hearing it is
necessary to understand
something of the structure of
the human ear. Contrary. to
popular opinion, industrial
noise does not really harm the
eardrum, but does its damage
in the inner ear. There are of
course exceptions to this rule.
If the human ear is exposed
to sudden violent noises such
as the sound of a nearby ex-
plosion, pressure of these
noises can tear a hole in the
eardrum. Cases such as this
are rare, and even when they
do occur prompt, effective
medical treatment can often
undo the damage.

CANNOT BE
REPAIRED

The inner ear, however,
cannot be repaired once it
has been damaged. The me-
chanism of the inner ear,
seated deeply in the skull, re-
ceives sound impulses from
the three-boned structure of
the middle ear. When the
sound waves strike the ear-
drum it vibrates. These vibra-
tions are carried to the

BEST ANSWER
™ IS EAR PROTECTION

watery fluid of the inner ear,
and are converted into nerve
impulses by a delicate struc-
ture which consists of hair-
like vibration pickups. Over-
stimulation of these hairs by
noise can cause them to
wither, and when this hap-
pens nothing now known can
restore them. The hair cells
convert the sound through
nerve impulses to the brain
and when they are damaged
hearing suffers accordingly.
It is recognized that an in-
dustrial worker who is sur-
rounded by noise all day be-
comes less efficient in his job
—less alert, more inclined to
be careless, than he would be
without the incessant din.
Noise has a noticeable effect
on a worker’s nervous sys-
tem, increasing blood pres-
sure and muscular contrac-
tions, which results in exces-
sive fatigue, and interference
with the reception of danger
signals and auditory com-

‘munications have also been

attributed to high-level in-
dustrial noises.

DANGEROUS
TO HEARING

All of these things of course
have a serious effect on gen-

“eral safety. However, some

controversy surrounds the
answer to the question of in-
dustrial noise. Various sounds

‘or noise levels have been ad-

vanced as an amount of noise
above which continued ex-
posure will be dangerous to
hearing.

It ‘has been claimed that
if the over-all noise level does
not exceed 85 decibels, no in-
jury to hearing results. A
noise level of more than 85
and less than 100 decibels
may harm the ear of a highly
susceptible individual after a
long period of exposure.
Noise levels above 100 deci-
bels may do permanent dam-
age after long exposure to the
ears of these persons.

As the decibel rate of noise
rises, the damage it can do
increases, of course. A noise
level in excess of 130 decibels
may do permanent damage to
the ear of a normal person,
even after relatively short ex-
posure.

Frequencies of the offend-
ing sounds or noise must be-
considered too. All noises
send out sound waves which
vibrate various speeds or
times per second, The num-
ber of vibrations per second
or, more simply, the number

of times the sound waves
emitted exert a -pulsating
pressure on the ear each
second, is the frequency of
the sound.

Average hearing response -

is to frequencies from about
15 cycles per second to 15,000
cycles per second. The range
of a piano can give an idea
of frequencies of various
sounds. The 88 keys of a
piano range from the low
note of 27.5 cycles per second
to the high note, which has a
frequency of 4,186 cycles per
second. The male voice

ranges from a basso’s low of
80 cycles per second to the
high of a tenor — approxi-
mately 300 cycles per second.
Female soprano voices com-
monly reach 850 cycles per
second,

I feel that all of our opera-
tions merit a noise survey,
and undoubtedly we would
find that there are complaints
where no one dreamed a noise
problem existed.

A fairly accurate rule of
thumb would be when two
people with normal hearing
have trouble conversing at
arm’s length. The need for a
noise-measurement survey is
apparent. This rule of thumb
does not mean that a noise
hazard is or is not present,
but does indicate the need for
measurements.

The key words in solving
industrial noise problems are
reduction, isolation, protec-
tion. Reduction of the noise
is of course the best solution.
If reduction proves impracti-
cal, attempts should be made
to isolate the area from which
serious noises emanate. Then,
since even in isolated areas
men must work machines,
personal protection should be
made available. Enclosures,
either partial or complete,

can be built around
areas of machines. If
isolation is
should be designed

by someone familiar with

principles of acoustics or it-

may not be effective.

acoustical materials have |

made this job a great deal
easier than it once was

but ~

even these must be used in ~

accordance with the sound-

deadening principles in-
volved.

In any case, isolation from
noisy areas or machines us-
ually does little for the men
who must operate the ma-
chinery or work in the area.
For these, personal protection
is the best answer. There are
two types of ear protectors—
the ear-insert plug type and
the over-the-ear cushion type.
Each type has its specific use,
each is designed to do a cer-
tain kind of job. each has ad-
vantages not embodied in the
other. A great deal of scien-
tific research has yet to be
done in the development of
these ear protection devices.

Only by determining the
kind of problem encountered
in the operation can the de-
termination of which type is
best be arrived at.

The Working Man's
3 Best Friends:

(1) A cool head

(2) Steady hands

and

(3) Well-shod feet
(DAYTON'S of course)

‘NO BETTER BOOT
AT ANY PRICE

a

-» ARTTSTRY IN

DAYTONS

“4
aM
4

’

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