UNIT 5
CONTROL MEASURES
Principles of Control:
Many different hazards are encountered by workers in Canadian
workplaces ranging from exposure to compressed gases, flammables and
explosives, corrosives, poisons, infectious materials, carcinogens,
radiation, heat, noise, vibration, and danger of physical injury.
A workplace hazard can be controlled in many different ways, depending
on the nature of the hazard and the process that causes it, however, each
control measure must meet the following requirements:
1. It must control the hazard so that workers' health is no longer
endangered.
2. It must allow workers to do their jobs without excessive discomfort, e.g.,
full rubber acid suits can be worn for emergencies or short duration jobs
but are unreasonable for long periods of time.
3. It must protect all workers who may be exposed, not just the one
handling the hazardous product.
4. It must not create a hazard for the surrounding community, e.g.,
ventilation systems should be equipped with scrubbers to remove
hazardous substances from their exhaust rather than just dump dirty air
into the neighborhood.
Location of Controls:
Hazard controls can be located at 3 places:
1. at the source, where the hazard begins
2. along the path of the hazard en route to the worker
3. at the worker
The most effective location of a control is at the source! Controls tend to be
less effective the farther they are from the source.
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At the Source
At the Worker
Along the Path
1. Control at the Source:
Control of a hazard at its source means that the hazard is :

eliminated from the workplace altogether; or

isolated (completely separated) from the worker
Control at the source is by far the best method of control, and is the only
method acceptable for control of carcinogens (cancer-causing agents).
-elimination -- means that either the operation is stopped
permanently (which is usually not practical), or a substitute is used in
place of the more hazardous material.
Examples of elimination by substitution are listed.

Benzene -- a carcinogenic substance used as a solvent in paints and
other coatings-- has been replaced by less-toxic solvents such as
mineral spirits and toluene.

Asbestos, which has been proven to cause lung cancer, has been
replaced by mineral wools such as glass fibers or rockwool in various
applications such as insulation.

Sandstone grinding wheels which give off toxic silica dust, can be
replaced by less toxic aluminum oxide wheels.

The danger of silicosis, the disease caused by silica in the lungs, can be
avoided by the use of steel shot for sandblasting.

White paint can be produced with titanium or zinc oxides instead of
highly toxic lead oxide pigments.

Water-based coatings are continually being improved to replace organic
solvent-based coatings to reduce exposure to volatile organic
compounds (VOC's), as in latex paints, varnishes, and asphalt sealers.
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Caution -- Safer is not necessarily Safe:
Even the "safer" substitutes can still
be hazardous if not handled correctly.
Although toluene is non-carcinogenic,
it, like most organic solvents, cause
liver damage in high concentrations.
SU BST IT U T ION
Recent studies of animal exposure to
fiberglass have shown some evidence
XYLENE of lung cancer like that produced by
asbestos.
BENZENE
- isolation -- means completely separating the worker from the
source or the source from the worker. Isolation
usually involves some form of "engineering
controls".
Examples of isolation follow.


Open tanks or process vessels can be
enclosed (covered) and a ventilation
system can be connected to the tank to
prevent the escape of gases.
Workers can be isolated from hazardous fumes, by buiding air
conditioned control rooms in chemical plants. With clean air being
continually pumped into the control room, a positive pressure is
maintained in the room so that only clean air escapes but no fumes
enter.
2. Control Along the Path:
Control along the path between the source and the worker is usually done
by one or more of the following methods:

local and / or general ventilation

barriers

housekeeping
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- local ventilation -- means using fume hoods, located immediately
above or near the source to draw away hazardous fumes. Local fume
hoods are common in laboratories, paint spray booths, over hot ovens
and welders. A properly designed local ventilation system can be very
effective in controlling airborne hazards in the workplace. The air from
these fume hoods should be directed through some type of
scrubber or
air purifier (e.g., electrostatic precipitator, bag house, or cyclone
separator) before exhausting the air to the neighborhood!
- general ventilation --, also called dilution
ventilation, generally uses a fan or blowers
to blow the dust or vapour away from the
worker. This dilutes the concentration to
which the worker is exposed by spreading
it through the rest of the workplace.
Obviously, this would only be an
acceptable method for non-hazardous,
nuisance dusts and odours.
- barriers -- are usually portable screens used to deflect hazardous
agents like noise, heat, sunlight, welding light, or radiation away from
workers.
- housekeeping -- means proper cleaning of the workplace, disposal
of wastes and clean-up of spills. Vacuum
cleaners should be used instead of brooms
because they remove the substance from the
workplace, while brooms may stir it up and
spread into the air where it may be inhaled by
workers.
3. Control at the Worker:
Control at the worker is the least satisfactory control method because it is
farthest from the source and does not eliminate the hazard from the
workplace. Control at the worker should be used as a last resort as when
engineering control are impossible or impractical.
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There are 2 kinds of control at the worker.

administrative controls

personal protective equipment
- administrative controls -- are the rules and procedures that control
the worker rather than the hazard. Administrative controls can limit an
employee's exposure to a hazard by reducing the time one spends on a
particular task.
For example, once employees approach their maximum permissible
exposure, they are transferred to another job or area of
the plant. This is commonly done in large chemical
factories, where there is a large pool of skilled workers
who can do job rotation.
Medical checkups may be used for screening employees,
i.e., to hire new employees who do not have high
sensitivity to dusts (if your workplace is dusty) or to know
when to rotate employees to new locations.
Workers exposed to high temperatures may be given frequent breaks.
Cleaning and maintenance of closed chemical vats can release large
amounts of toxic material and should therefore be carried out on weekends
or at night when as few workers as possible will be exposed to the
hazards.
Administrative controls do not control hazards, they only control who shall
be exposed and for how long.
- personal protective equipment -- is the clothing, hearing
protection, respiratory protection, etc. worn by workers in the presence
of hazards.
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When it is not feasible to control the environment by
elimination, isolation, ventilation, or some other control
measure, it may be necessary for the worker to use
personal protective equipment.
Personal protective equipment is considered the
control method of last resort behind engineering and
administrative controls. Since these protective devices
do not eliminate the hazard, failure of personal protective equipment or its
misuse may lead to high worker exposure.
Personal protective equipment is used:

when engineering controls do not exist for the process or are impractical
as when a particular maintenance job is only done a few days per year.

when engineering controls are inoperative due to a temporary
breakdown

when there is an emergency, i.e., a spill or a leak.
The most commonly used personal protective equipment, (other than
safety shoes and hard hat, which are standard equipment), include:

safety glasses, monogoggles, or face shields

hearing protection

respirators and masks

chemical resistant gloves, rubber overboots, and rubber suits
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Whatever personal protective equipment
selected, it is most important that it is:
is
a) worn when needed (foremen and safety reps
need to enforce this),
b) fits properly (workers need to be fit-tested for
equipment and shown how to use it and know
when it needs cleaning or replacement), and
c) correctly chosen for the job. The MSDS sheet will
be of assistance in specifying what type of
respirator or glove is needed. Alternately, the
manufacturer or a safety supply store/catalogue can
give advice.
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Hearing Protection:
Three types of hearing protection devices are available
for use when it is impossible to reduce noise to safe
levels by engineering methods: ear plugs, ear muffs, and
"canal caps" (sound band).
- ear plugs -- are available as reusable rubber plugs or
as disposable urethane foam plastic plugs.
Both of these are designed to fit snugly into the ear canal. They work best
for reduction of high frequency noise; about 30 dB maximum reduction, but
far less for low frequency noise.
Unfortunately, plugs are generally uncomfortable to wear.
- ear muffs -- have hard plastic shells which completely cover the ear
and are sealed to the head with a soft rubber cushion.
They are held in position by a sprung headband. Although heavier and
bulkier than ear plugs, they give much better protection and are more
easily fitted. Ear muffs are available with a frame that connects tightly to
the hardhat. Many workers find that ear muffs are hot and restrictive to
wear.
-canal caps -- seal the opening of the ear canal with a soft rubber
cap which is held in place by a plastic band that fits either over the
head or under the chin. It is light weight, does not restrict motion,
and easily put on or taken off. The pressure they apply grows
uncomfortable in time, making them more suitable for short term use.
When selecting hearing protection, the aim should be to reduce noise to
below the danger level of 85 dB. The following table show the average
reduction in noise levels in dB obtained by various hearing protection at
different frequencies.
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Frequency (Hertz)
250
500
1000
2000
4000
plastic ear plugs
12
14
18
27
31
lightweight ear muffs
13
20
27
35
42
heavy weight ear muffs
25
33
39
40
45
Discomfort is the main objection to wearing hearing protection so
employers should make several different types available to employees.
The best ear protector is ultimately the one that fit the worker best and
he/she will wear.
Respiratory Protection:
Respiratory protection devices are
best
suited
for occasional /
intermittent use for jobs where other
controls (isolation, ventilation, etc.)
are insufficient. Examples include
short-term
handling
of
toxic
chemicals, spray painting operations,
grinding operations, emergency and
rescue work.
Good respiratory protection is difficult to achieve for several reasons:
- different types of hazards require different equipment
- workers are handicapped (laboured breathing, hampered speech,
discomfort)
- it is difficult to avoid leaks
Respiratory protection is needed for 3 kinds of atmospheres:
1. oxygen deficient
2. hazardous dust, mist, fumes, smoke
3. toxic gases and vapours
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There are basically 2 types of respiratory equipment:

respirators -- which remove contaminants from air

breathing apparatus -- which supplies clean air
Some are available as half-masks covering only the nose and mouth while
others are full-masks covering the entire face.
All types must fit snugly, and this makes them uncomfortable to wear. A
good seal is almost impossible for workers with beards or glasses.
- respirators -- of any kind require a minimum concentration of 16%
oxygen content for safe use.
cloth
masks
chemical-cartridge
filter masks
canister
filter masks

Cloth masks are only good for nuisance dusts because they have
leakage rates up to 15%. They are not for toxic dusts or very fine dusts
(dusts <1 micron are most damaging to the lungs).

Chemical-cartridge filter masks are half-masks which can absorb
toxic gases like acids, organic vapours, ammonia, etc. They are usually
O.K. for up to about 0.1% vapour in air and allow about 5% leakage
rates.

Canister filter masks are full-face masks with a large capacity filter
attached to the chin of the mask or to a hose connected to the mask.
These will withstand up to about 1% vapour for about 30 minutes. They
typically allow only 0.25% leakage rates.
None of these respirators are suitable for conditions which are immediately
dangerous to life and health (IDLH), because if they fail or become
exhausted (used up), the worker is in immediate danger.
5 - 10
breathing apparatus -- supplies clean air to the worker by a
airhose/airline or directly from compressed air tanks which the worker
wears on his/her back.

Airhose breathing apparatus may be supplied from a compressed air
cylinder or from an air compressor. The air compressor must be
designed and maintained to exclude oil droplets, carbon monoxide, and
dust. Airhose breathing apparatus is commonly used for sand blasting,
spray painting, welding, and cutting operations.

SCBA (self contained breathing apparatus) uses small compressed gas
cylinders worn on the back of the worker. They provide 20-40 minutes
of breathing time for escape, rescue, spill clean-up or other emergency.
These are the only equipment suitable for IDLH conditions.
self contained
breathing apparatus
SCBA
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EXERCISE FOR UNIT 5
1. Select the requirements of a good control program.
a) the cheapest
b) protects exposed workers
c) relies on "ppe" rather than ventilation and isolation
d) allows workers to do the job without additional discomfort
e) uses the most expensive technology available
f)
does not create hazards in the surrounding community
g) waits until the best technology is available before controlling hazards
2. Select the most effective control measure.
a) at the source
b) along the path
c) at the worker
3. Name 2 kinds of "control at the source".
a) ...........................................
b) .....................................................
4. Name 4 kinds of "control along the path".
a) ...........................................
b) .....................................................
c) ...........................................
d) .....................................................
5. Name 2 kinds of "control at the worker".
a) ...........................................
b) .....................................................
6. Answer the following as true (T) or false (F).
.............. a) Ear muffs provide more hearing protection than ear plugs or
canal caps (assuming that they are all fitted properly).
.............. b) Respirators such as masks and chemical filters do not protect
the worker when the oxygen level is less than 16%.
.............. c) Air hose type breathing apparatus will protect a worker when conditions are
immediately dangerous to life and health (IDLH).
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