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Confined Space |
A confined space is a space which
has any one or more of the following:
Limited openings for entry and exit,
Poor ventilation,
An area that is not designed for continuous employee
occupancy, but large enough that a worker can enter and perform an assigned
task.
The
following areas are examples for confined spaces:
Boiler
Furnace
Pipeline
Pumping station
Reaction or process vessel
Septic tank
Sewage digester
Sewer
Silo
Storage tank
Confined Space Entry:
Confined
space entry means the action by which a person passes through an opening into a
permit required confined space and work will follow.
Entry Permit:
Entry
permit means the written or printed document that is provided by the employer
to allow and control entry into a permit space and that contains the
information on the purpose of the entry, date and the authorized duration of
the entry permit, authorized entrants within the permit space, the hazards of
the permit space to be entered, the measures used to isolate the permit space
and to eliminate or control permit space hazards before entry, the results of
initial and periodic tests, etc.
Confined Space Training:
Training
should be provided to each employee:
Before the employee is first assigned duties,
Before there is a change in assigned duties,
Whenever permit space conditions change that expose an
employee to a hazard of which they have not been previously trained,
Whenever the employer has reason to believe either that:
o
There
are differences from the permit space entry procedures, or
o
That
the employees do not understand the procedures.
The
Employee is required to be thoroughly trained in the duties as required
by regulations. New or revised procedures must be discussed for compliance and
worker safety.
The
Employer is required to certify that the required training has been
completed. The certification will contain each employee's name, signature and
the date of training. The certification should also be available for inspection
by employees and their representatives.
Unfavorable Natural Ventilation:
The
air inside a confined space can be very different from the outside because it
may not be moving freely. Deadly gases may be trapped inside the confined
space. This is especially true if the space is used to store or process chemicals
or organic substances which may decay. There may not be enough oxygen inside
the confined space to support life. Also, the air could be so oxygen rich that
is likely to increase the chance of a fire or explosion. The following
atmospheric conditions are possible in a confined space:
Oxygen-deficient atmosphere
Oxygen-rich atmosphere
Flammable atmosphere
Toxic atmosphere
Oxygen-deficient Atmosphere:
An
oxygen-deficient atmosphere has less than 19.5 % of available oxygen. Any air
less than 19.5 % oxygen should not be entered without an approved SCBA
(Self-contained Breathing Apparatus) as shown in Figure 1.
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Figure 1. Self-contained Breathing Apparatus
The
oxygen level in a confined space can decrease because of work, such as:
Welding
Cutting
Brazing
Certain chemical reactions such as rusting
Bacterial action such as
fermentation.
The
oxygen level is also decreased if oxygen is displaced by another gas such as
carbon dioxide or nitrogen or oxygen may settle to the bottom of a confined
space due to the existence of lighter gases generated in the confined space.
Total displacement by another gas will result in unconsciousness, then death.
Oxygen-enriched Atmosphere:
An oxygen -enriched atmosphere has oxygen content above 23.5 % and
may contribute to a fire or explosion.
Oxygen-enriched
atmospheres may be created by a number of situations, such as leaking oxygen
equipment or the use of certain chemicals.
Flammable Atmospheres:
A
flammable atmosphere occurs when a flammable gas, vapor or mist in excess of
10% of its LEL (Lower Explosive Level) is detected. Two things make an
atmosphere flammable:
The oxygen content
A flammable gas, vapor or dust in the proper mixture.
Toxic Atmospheres:
The
following list describes toxic atmospheres and is also used as a guideline for
assessing toxic atmospheres:
Liquids, residues or sludge from material previously
stored,
Toxic materials absorbed into the walls which give off
toxic gases or vapors when they are removed or cleaned,
Hazardous gases produced by decay or accumulation because
they are heavier than air,
Materials used or produced by the work being performed (for
example: cleaning solvents, paints, and welding fumes),
Materials used or produced by working near a confined space
which can enter and accumulate in the space.
Testing the Atmosphere:
Testing
the air is the most important part of a confined space entry procedure.
Therefore, special test equipment is used to analyze the air. The proper tests
must be used before anyone enters the space or before an entry permit to work
in any confined space is received.
Some
gases or vapors are heavier than air. It is necessary to test all areas (top,
middle and bottom) of a confined space with their proper equipment to determine
what gases are present. Tests should be performed outside the space, just
inside the space, one-foot down and every four-feet
thereafter. If the testing shows oxygen deficiency or the presence of toxic
gases or vapors, the space must be ventilated and re-tested before the workers can
enter. If ventilation is not possible and entry is necessary, workers must have
respiratory protection.
The
confined space air is tested for the :
Oxygen level
Presence of flammable gases or explosive materials
Presence of toxic gases and vapors
Obvious physical hazards
The
air of a confined space is always tested first from OUTSIDE the confined space.
The probe is placed or lowered inside the confined space. Tests must be done at
different atmospheric levels because certain toxic vapors and gases are heavier
or lighter than air. It is possible that the air of a confined space is safe at
one level but toxic at another.
NOTE:
When testing for atmospheric hazards, test first for oxygen, then for
combustible gases and vapors, and then for toxic gases and vapors.
Combustibles,
toxins and oxygen levels are measured differently. For example:
Explosive
or combustible gases and vapors are measured on a scale from 0% to 100%, which
is the LEL (Lower Explosive Level). LEL is the smallest amount of gas that can
cause an explosion. (Remember that 10% of LEL is the maximum allowable limit).
The
oxygen level is a measure of the percentage of oxygen in the air; the measure
will be a figure between 0% and 100% . (Remember that
the safe oxygen levels are between 19.5 % and 23.5 %)
Toxic
contaminants are measured in terms of the number of parts of contaminants in a
million parts of air (ppm), or milligrams per cubic
centimeters (mg/cm3).
Even
if the air has been tested safe, the work to be done may change the air,
especially hot work. Hot work (welding, cutting, burning, etc.) may:
Fill a confined space with toxic welding fumes
Reduce the oxygen supply
Replace the oxygen with flammable gases
Create an oxygen enriched environment.
Procedures for Atmospheric Testing:
Atmospheric
testing is required to evaluate hazards of the permit space and to verify that
the area is safe to enter. Th following procedures
should be completed before entry :
Evaluation Testing: The atmosphere of the confined space should be analyzed
using equipment of sufficient sensitivity and specificity to identify and
evaluate any hazardous atmospheres. Evaluation and interpretation of these
data, and development of the entry procedure, should be done by, or reviewed
by, a technically qualified professional (e.g. OSHA consultation service, or
certified industrial hygienist, registered safety engineer, certified safety
professional, etc.) based on evaluation of all serious hazards.
Verification Testing: The atmosphere of a permit space which contain
a hazardous atmosphere should be tested for residues of all contaminants
identified by evaluation testing. The test results are then recorded on the
permit.
Duration of Testing: Testing should be done for the minimum response time of
the test instrument specified by the manufacturer.
Testing Layered Atmospheres: When monitoring air that may be
layered, testing should be done approximately every 4 feet in the direction of
travel and to each side. If a sampling probe is used, the worker should adjust
by slowing down to accommodate the detector response time.
Order of Testing: A test for oxygen is performed first because most combustible
gas meters are oxygen dependent and will not provide reliable readings in an
oxygen deficient atmosphere. Combustible gases are tested for next because the
threat of fire or explosion is both more immediate and more life threatening,
in most cases, than exposure to toxic gases and vapors. If tests for toxic
gases and vapors are necessary, they are performed the last.
Confined Space Ventilation:
Blower/Fan: Ventilation by a blower or fan
may be necessary to remove harmful gases and vapors from a confined space.
There are several ways for ventilating a confined space. The method and
equipment depend on the size of the openings, the gases and the way to vent the
air.
When
flammable gases/vapors have displaced the oxygen level but exceeded the UEL,
ventilation may dilute them until they have reached an explosive concentration.
Also, if inert gases are used in a confined space, the space should be well
ventilated and re-tested before a worker may enter.
Common
Methods: A common
method of ventilation requires a large hose; one end attached to a fan and the
other lowered into an opening. The air intake should be placed in an area where
only the fresh air can be drawn into the confined space. Ventilation should be
continuous where possible, because in many confined spaces the hazardous
atmosphere will form again when the flow of air is stopped.
Recirculation: Care should be taken to assure
that the exhausted air is not recirculated back into
the ventilation current. Therefore, intake and exhaust points should be well
separated and monitored. When forced ventilation is used, the spare air should
be periodically tested to ensure that the ventilating is preventing the buildup
of a toxic air.
Ventilation
Equipment: In confined
space work, ventilating equipment is used to supply fresh air to the confined
space, which replaces the hazardous or explosive conditions with safe
atmosphere. The proper ventilation is vital for making a safe confined space
entry. The standard ventilating unit:
Should be portable
The blower should be able to move at least 600 CFM of air
Should have two 10-foot sections of lightweight, flexible
duct
Must have an explosion-proof motor
All
ventilating equipment should be assembled and tested before use. After using
the equipment, it should be thoroughly cleaned and stored to protect it from
moisture and dirt.
Other
Hazardous Conditions that may Exist in a Confined
Space:
Engulfment
Falling objects
Temperature extremes
Moving or driven equipment
Electrical hazards
Process liquids, steam, water
Isolation
Last Update: January 9, 2007
By: Serdar
Z. Elgun