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Confined Space &Gas Detection

Level 2

Definition of a Confined Space

• Large enough for worker to enter

• Are not designed for continuous worker occupancy

• Limited openings for entry and exit

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Confined Space

• Large enough to enter

Confined Space

Not Confined Space

Confined Space

• Limited means of entry and exit

• Not designed for continuous worker occupancy

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Permit Required Confined Spaces

• One or more of the following: • Hazardous atmosphere (known or potential)

• Material with the potential for engulfment

• Inwardly sloping walls or dangerously sloping floors

or• Contains any other serious safety hazard

Permit Required Confined Spaces

Required atmospheric testing• Oxygen• Flammable gases and vapors• Any known or potential toxic contaminants

The above tests shall be done with a calibrated direct-reading instrument, and in that order

• Before entry it is mandatory to determine that the CS atmosphere is safe!• Periodic monitoring is also required• Monitor and ventilate continuously (recommended)

Monitoring determines the air is safe, ventilation keeps it that way!

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Typical Confined Spaces

• Storage tanks

• Ship compartments

• Process vessels

• Underground utility vaults

• Storm drains

• Boilers

• Sewers

• Tunnels

• Pipelines

Open Topped Confined Spaces

• Pits• Degreasers• Open-topped water tanks• Ship holds• Excavations

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65% of fatalities due to atmospheric hazards

193234276Total

15621Other12

91010Eye injury1101515Insufficient maneuverability1033033Ingress / egress 912627Falls inside Confined Space801515Struck by falling objects7

16016Engulfment610310Caught in / crushed by machinery 5

9211Electrical shock or electrocution4322023Explosion or fire at point of entry3154915Explosion or fire in CS 2

787280Atmospheric condition in CS1

DeathsInjuriesEventsAccident TypeRef

Alternate Entry Procedures

• If a hazard cannot be eliminated, but can be controlled by continuous forced air ventilation, then alternate entry procedures can be used

• Paragraph (c)(5)(i) lists the conditions under which alternate entry procedures can be used

• Benefits:

– Substantially lower equipment requirements

– No attendants required

– Solo entries permitted

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Work in confined spaces can produce dangerous atmospheric conditions

• Welding

• Painting

• De-greasing

• Scraping

• Sandblasting

• Mucking

• Inerting

Confined Space Entry

• Monitor and ventilate continuously– Many accidents result from changes in the

CS atmosphere which occur after the entry is initiated

– Monitoring determines the air is safe, ventilation keeps it that way

– The only way to pick up changes before they become life threatening is to monitor continuously!

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Hazard Measurement

• Three basic kinds of atmospheric hazards

– Oxygen (deficiency and enrichment)

– Flammable gases and vapors

– Toxic contaminants

Oxygen

• Composition of fresh air– 78.1 % Nitrogen

– 20.9 % Oxygen

– 0.9 % Argon

– 0.1 % All other gases• Water vapor

• CO2

• Other trace gases

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Oxygen

• Oxygen Deficiency – Most widely accepted definition: Air is oxygen deficient

whenever concentration is less than 19.5%

– OSHA has determined that the leading cause of deaths in confined spaces is asphyxiation

Symptoms of Oxygen Deficiency

Convulsions, gasping respiration, cessation of breathing, cardiac arrest, symptoms immediate, death within minutes

- 0%6%

Nausea, vomiting, inability to move, loss of consciousness, and death

- 6%10%

Disturbed respiration, poor circulation, worsening fatigue and loss of critical faculties, symptoms within seconds to minutes

- 10%12%

Impaired judgment, increased pulse and respiration, fatigue, loss of coordination

- 12%19.5%

Oxygen content in fresh air20.9%

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Toxic Gases and Vapors

Permissible Exposure Limit (PEL)

• Determined by OSHA

• Sets limits for legal unprotected worker exposure to a listed toxic substance

• Force of law in USA!

• Individual states free to enact stricter, but never less conservative limits

• Given in “Parts-per-Million” (ppm) concentrations

– 1 % = 10,000 ppm

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Permissible Exposure Limits

• “Parts-per-Million” (ppm) concentrations

– 1.0 ppm the same as:

• One automobile in bumper-to-bumper traffic from Cleveland to San Francisco

• One inch in 16 miles

• One minute in two years

• One ounce in 32 tons

• One cent in $10,000

Carbon Monoxide

• Produced as a by product of incomplete combustion

• Associated with internal combustion engine exhaust

• Vehicles

• Pumps

• Compressors

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Carbon Monoxide

• Bonds to hemoglobin in red blood cells

• Contaminated cells can’t transport O2

• Chronic exposure at even low levels harmful

Characteristics of Carbon Monoxide

• Colorless

• Odorless

• About the same weight as air

• Flammable ( LEL is 12.5 %)

• Toxic!

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Symptoms of Carbon Monoxide Exposure

• Headaches

• Fatigue

• Nausea and other "Flu-like" symptoms

• Loss of consciousness

• Brain damage

• Coma

• Death

Hydrogen Sulfide

• AKA sewer gas

• Produced by anaerobic sulfur fixing bacteria

• Especially associated with:

– Raw sewage

– Crude oil

– Marine sediments

– Tanneries

– Pulp and paper industry

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Characteristics of Hydrogen Sulfide

• Colorless

• Smells like “rotten eggs” (at low concentrations)

• Heavier than air

• Corrosive

• Flammable (LEL is 4.3 %)

• Soluble in water

• Extremely toxic!

Toxic effects H2S

Immediate respiratory arrest, loss of consciousness, followed by death

1000 PPM

Death in 30 min. – 1 hr. 500 – 700 PPM

Eye inflammation, respiratory tract irritation after 1 hour, loss of consciousness with time

200 – 300 PPM

Rapid loss of smell10 – 100 PPM

Smell0.01 – 0.1 PPM

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Combustible Gases

OxygenFuel

Source of ignition

Combustible Gases

OxygenFuel

Source of ignition

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Combustible Gases

• Lower Explosion Level (LEL)– 100% LEL is the concentration of combustible gases or

vapors which will explode is sufficient oxygen and a source of ignition is present

– A combustible hazard exist when the levels exceed 10% LEL

Combustible Gases

LEL UEL

Flammability Range

Gas Concentration

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Combustible Gases

0 100% LEL

Gas Concentration

Flammability Range

Pitfalls in Gas Detection

Two biggest pitfalls

• Can the gas detector detect gas?

• Will the atmosphere to be tested get to the detector?

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Verification / Calibration

• Verify accuracy on a regular basis to guard against any unexpected loss of sensitivity

• The safest course of action is to expose the sensors to known concentration test gas before each day’s use!

• Never exceed 30 days between verification of sensor accuracy

• Verification is also called “Bump Test”

“Bump” Test Vs. Calibration

• A “bump” test only provides verification of sensor performance

• Only necessary to adjust sensor sensitivity if readings are off by more than 10%(Reading that are too high are not a safety concern)

• Calibration includes adjustment

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Pre-entry Methods

• Lowering the gas detector into the space to obtain readings in diffusion mode

• Using a sample-draw system to draw a sample out of the space

Diffusion Method

• Enable the Peak-hold feature to allow the monitor to latch on to the worst case measurements

• Turn on the flash-lights built in to the detector is available

• Allow the detector to be at each level to be tested long enough obtain a stable reading (20-30 seconds)

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Remote Sampling Methods

• Always test sampling system for leakage and proper flow be for sampling the remote space

• Hand squeeze aspirators can be tested in just seconds by blocking the inlet and observe that the aspirator remains deflated till the blockage is removed.

• Motorized pumps should be tested by blocking the inlet at activating the low flow alarm

Remote Sampling Techniques

• Make sure to sample long enough for the sample to reach the sensors

– Motorized Systems: 1 Sec / Foot or 3 Sec / Meter

– Manual Systems: 1 Squeeze /Foot or 3 Squeezes per Meter

• Make sure to sample for sufficient additional time to make the sensors stabilize (20-30 seconds).

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Remote Sampling Techniques

Stratification

• Atmospheric hazards in confined spaces form layers

• Test all levels (typically every 4 feet)

Questions