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Confined Space & Gas Detection

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. Confined Space. Large enough to enter. Not Confined Space. Confined Space. Confined Space.

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Confined Space & Gas Detection

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  1. Confined Space &Gas Detection Level 2

  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

  3. Confined Space • Large enough to enter Not Confined Space Confined Space

  4. Confined Space • Limited means of entry and exit • Not designed for continuous worker occupancy

  5. 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

  6. 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!

  7. Typical Confined Spaces • Storage tanks • Ship compartments • Process vessels • Underground utility vaults • Storm drains • Boilers • Sewers • Tunnels • Pipelines

  8. Open Topped Confined Spaces • Pits • Degreasers • Open-topped water tanks • Ship holds • Excavations

  9. 65% of fatalities due to atmospheric hazards

  10. 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

  11. Work in confined spaces can produce dangerous atmospheric conditions • Welding • Painting • De-greasing • Scraping • Sandblasting • Mucking • Inerting

  12. 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!

  13. Hazard Measurement • Three basic kinds of atmospheric hazards • Oxygen (deficiency and enrichment) • Flammable gases and vapors • Toxic contaminants

  14. 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

  15. 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

  16. Symptoms of Oxygen Deficiency

  17. Toxic Gases and Vapors

  18. 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

  19. 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

  20. Carbon Monoxide • Produced as a by product of incomplete combustion • Associated with internal combustion engine exhaust • Vehicles • Pumps • Compressors

  21. Carbon Monoxide • Bonds to hemoglobin in red blood cells • Contaminated cells can’t transport O2 • Chronic exposure at even low levels harmful

  22. Characteristics of Carbon Monoxide • Colorless • Odorless • About the same weight as air • Flammable ( LEL is 12.5 %) • Toxic!

  23. Symptoms of Carbon Monoxide Exposure • Headaches • Fatigue • Nausea and other "Flu-like" symptoms • Loss of consciousness • Brain damage • Coma • Death

  24. 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

  25. 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!

  26. Toxic effects H2S

  27. Combustible Gases Source of ignition Oxygen Fuel

  28. Combustible Gases Source of ignition Oxygen Fuel

  29. 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

  30. Flammability Range Combustible Gases Gas Concentration LEL UEL

  31. Flammability Range Combustible Gases Gas Concentration 0 100% LEL

  32. Pitfalls in Gas Detection Two biggest pitfalls • Can the gas detector detect gas? • Will the atmosphere to be tested get to the detector?

  33. 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”

  34. “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

  35. 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

  36. 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)

  37. 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

  38. 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).

  39. Remote Sampling Techniques Stratification • Atmospheric hazards in confined spaces form layers • Test all levels (typically every 4 feet)

  40. Questions

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