CMC Confined Space Entry Requirements 3 — Questions and Answers
Question 1: Who is responsible for testing a confined space atmosphere immediately prior to worker entry under NFPA 306?
- The ship captain or master
- A marine chemist or competent person designated under OSHA 1915 (Correct answer)
- Any crew member with PPE
- The port safety officer
Correct answer: A marine chemist or competent person designated under OSHA 1915
NFPA 306 requires a marine chemist or competent person to test the atmosphere before entry.
Question 2: What hazard class does hydrogen sulfide (H₂S) present in confined spaces aboard vessels carrying crude oil?
- Oxygen-enriching hazard
- Toxic and flammable gas hazard (Correct answer)
- Asphyxiant-only hazard
- Corrosive vapor hazard
Correct answer: Toxic and flammable gas hazard
H₂S is both highly toxic and flammable, presenting dual hazards in crude oil cargo tanks.
Question 3: Under OSHA 29 CFR 1915.12, what is required when workers must enter an oxygen-deficient atmosphere?
- Increase natural ventilation before entry
- Supply air respirators or SCBA must be used (Correct answer)
- Workers must sign a hazard acknowledgment form
- Entry is permitted with a buddy system only
Correct answer: Supply air respirators or SCBA must be used
OSHA 1915.12 mandates supplied-air respirators or SCBA for entry into oxygen-deficient spaces.
Question 4: A space on a vessel is designated 'Not Safe' by the marine chemist. Under what condition may workers enter?
- After the shipowner grants written permission
- Only after the marine chemist or competent person re-tests and re-designates the space as safe (Correct answer)
- After 24 hours of continuous forced ventilation
- With full encapsulating suits and SCBA only
Correct answer: Only after the marine chemist or competent person re-tests and re-designates the space as safe
A 'Not Safe' space may only be re-entered after the marine chemist or competent person re-tests and changes the designation.
Question 5: What does the term 'inerting' mean in the context of vessel confined space safety?
- Removing all workers and locking out the space
- Filling the space with an inert gas to prevent flammable atmospheres (Correct answer)
- Applying rust-inhibiting coatings to tank walls
- Reducing oxygen to 16% for fire suppression
Correct answer: Filling the space with an inert gas to prevent flammable atmospheres
Inerting involves introducing an inert gas (such as nitrogen or CO₂) to displace oxygen and prevent flammable mixtures.
Question 6: Which instrument is specifically required to detect flammable vapors in a confined space before entry?
- Photoionization detector (PID) only
- Combustible gas indicator (CGI) calibrated for the relevant vapor (Correct answer)
- Oxygen meter only
- pH meter for liquid residues
Correct answer: Combustible gas indicator (CGI) calibrated for the relevant vapor
A combustible gas indicator calibrated for the specific vapor present is required to assess flammable gas hazards.
Question 7: What is the maximum allowable oxygen concentration in a vessel's confined space before it is considered oxygen-enriched and hazardous?
- 21.0%
- 22.0%
- 23.5% (Correct answer)
- 25.0%
Correct answer: 23.5%
OSHA 1915 considers atmospheres above 23.5% oxygen as oxygen-enriched, creating increased fire and explosion risk.
CMC Confined Space Entry Requirements 3
Who is responsible for testing a confined space atmosphere immediately prior to worker entry under NFPA 306?