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Technically, people should not work in an
environment where the oxygen content falls below 20.9%
and never work in levels that drop below 19.5%.
Early
signs of oxygen deficiency are: pulse and respiration
rates increase as the body tries to compensate for the
decreased oxygen supply, muscle co-ordination is
decreased, and there is insensitivity to pain, emotional
changes and fatigue.
Natural
ventilation alone will often not be sufficient enough to
maintain breathable quality air. The air can be
maintained by providing mechanical ventilation (blowers
and fans) with a warning system in place, alarming if
equipment fails. This should always be noted on the
entry permit for confined spaces.
So
you’ve completed your three levels of training in
confined spaces and you feel confident to handle your
confined space work. Your company has an excellent
Confined Space Program which includes:
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Identification of confined spaces
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Identification and assessment of potential hazards,
before and while working in the confined space
-
Plan
to control and eliminate hazards
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Training for employees entering confined spaces
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Permit entry system for each confined space
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Development of an emergency plan, including training
and equipment in case an unforeseen situation occurs
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An
emergency response system
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Program review whenever there is a change in
circumstances or at least annually, to identify
program weaknesses and make any necessary changes to
the program
Remember, conditions can change quickly while inside the
confined space and sometimes hazardous atmospheres are
created by the work activities that are being carried
out. Air testing prior to entering and continuously
monitored during the confined space activity should be
carried out depending on the nature of the potential
hazards and work.
Has your
gas detection equipment been maintained recently? Some
pieces of equipment require recalibration; check the
instruction guide specific to your model to determine
how often your monitor should be recalibrated. Check
the expiry date of your gas sensors in your monitor…is
it time to order new ones? Carrying a thermometer and
hydrometer can alert you to extreme heat, humidity or
cold.
Remembering that confined spaces are distinctive and
that each potential hazard is identified and understood
from every conceivable source, allows workers to know
what safety gear and protective equipment to use, how to
use it, and how to safely perform a rescue.
Control
the confined space, don’t let it control you!
Confined
Space Incidents
In
2003, a barge was moored in New Westminster, B.C. and
was undergoing maintenance. When a supervisor working
inside a compartment in the hull failed to show up for
coffee, two workers went to check on him and never
returned. Two others followed and again, never returned,
though one took a moment to phone 911 before losing
consciousness – and dying – inside the compartment. Four
of the workers died from oxygen deprivation. The other
employee and a rescuing firefighter were injured, but
survived.
******
A
cellar-hand was overcome by carbon dioxide after
entering a 4,500 litre wine vat through a 380 mm opening
at the top vat. The juice of the crushed grapes had been
drawn off through the drainer at the bottom of the tank,
leaving crushed grape skins and seeds. The atmosphere
was inert due to the presence of large amounts of carbon
dioxide. The contributing factors included a lack of
scientific equipment to test the wine vat's internal
atmosphere and the employee appeared to lack any
knowledge of the risks associated with carbon dioxide,
including the rapidity of symptoms, onset of euphoria,
loss of muscle control and death within minutes.
(Source: Government of Western
Australia, Department Consumer and Employment
Protection)
******
The
Occupational Safety & Health Administration is
investigating an accident in a manhole at a Superior,
Wisconsin landfill that claimed four lives. The incident
started when one worker in the hole was overcome by
toxic fumes. One by one, the other three victims went to
help their colleagues and were themselves overcome. All
four were dead of hydrogen sulfide poisoning by the time
rescue workers arrived at the scene.
The men
were reportedly trying to fix a sewer in a hole that was
three feet in diameter and more than 25 feet deep at the
privately owned landfill. None of the men were wearing
respirators or safety masks, and emergency responders
found no evidence of gas detection or other safety
equipment at the accident scene.
Workplaces where oxygen depletion should be considered:
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Hospitality industry
- carbon dioxide and/or nitrogen systems are used,
often stored in poorly ventilated cellars for tapping
off beverages such as beer and soft drinks. Where
these systems are poorly maintained, leakages could
occur leading to air displacement in these cellars.
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Brewing and winemaking
- fermentation produces carbon dioxide, resulting in
displacement of air in fermentation vessels. Also,
vessels are charged with a carbon dioxide atmosphere
to minimize spoilage due to oxidation reactions.
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Farming
- offal pits and effluent tanks will often have
contaminant-rich and oxygen-poor atmospheres.
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Waste water treatment
- biological activity caused by microbes utilizes
oxygen and often produces toxic gases as by-products
of metabolism.
Sources:
http://www.osh.dol.govt.nz/publications/series/hb-24-oxygendepletion.html
http://www.efilmgroup.com/Confined-Space-Accident-Kills-4-in-Wisconsin.html
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