SafetyQuestion 330 of 360
A plumber's gas meter reads the oxygen level inside a sewer vault. What is the acceptable oxygen range for safe entry under Cal/OSHA?
a.19.5% to 23.5%
b.10% to 30%
c.5% to 15%
d.Any level above 12%
Explanation
Under Title 8 §5157, the atmosphere is safe for oxygen only between 19.5% (oxygen-deficient below this) and 23.5% (oxygen-enriched above this). Below 19.5% a worker can lose consciousness; above 23.5% the enriched atmosphere greatly increases fire risk. Readings outside this range mean the space must be ventilated and retested before entry.
Law Reference: Cal/OSHA Title 8 §5157Practice all 360 questions free — no signup required.
Related questions on this topic
- A worker asks why a 5-foot trench needs protection when the walls 'look solid.' What fact best explains the danger of an unsupported trench wall?
- A plumber must enter a municipal sewer manhole to clear a blockage. Under Cal/OSHA §5157, why is this classified as a permit-required confined space?
- Before entering a sewer vault, a plumber lowers a multi-gas meter to test the atmosphere. In what order must the atmosphere be tested?
- Testing a sewer manhole, the meter shows the flammable gas reading as a percentage of the Lower Explosive Limit (LEL). Below what LEL reading does Cal/OSHA generally consider the flammable atmosphere acceptable for entry?
- During a permit-required confined space entry into a sewer, Cal/OSHA requires an attendant. What is the attendant's primary role?
- A plumber notices a rotten-egg smell while opening a sewer cleanout, then the smell fades. What toxic gas is this most likely, and why is the fading smell dangerous?
Last reviewed: · editorial process
PrepPass Editorial Team · Verified against California CSLB C-36 Plumbing Trade Examination · How we review