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Trade Exam · Module 6

Confined Space Awareness

Lesson 4 of 8~20 minFree previewCurrent as of September 2026Leer en español

Septic tanks, sewer manholes, lift stations, vaults and water mains can kill in minutes. This lesson covers what makes a space a confined space and a permit-required confined space under Cal/OSHA (Title 8 Sections 1950 to 1962 for construction, Section 5157 for general industry), the hazardous atmosphere limits (oxygen 19.5 to 23.5 percent, flammable gas over 10 percent of the LFL), testing order, the entrant, attendant and entry supervisor, the permit, and rescue.

Key Takeaways

  • A confined space is large enough to bodily enter, has limited or restricted entry or exit, and is not designed for continuous occupancy (Section 1951).
  • A permit-required confined space also has, or could have, a hazardous atmosphere, an engulfment hazard, a trapping configuration, or another serious hazard (Section 1951).
  • A hazardous atmosphere includes oxygen below 19.5 percent or above 23.5 percent and flammable gas, vapor or mist over 10 percent of its lower flammable limit (Sections 1951, 5157).
  • Test the atmosphere in this order: oxygen first, then combustible gases and vapors, then toxic gases and vapors (Section 1953(a)(5)(C)).
  • At least one attendant stays outside the space for the whole entry and does not go in until relieved by another attendant (Sections 1953(a)(6), 1958(a)(4)).
  • The entry supervisor checks the permit, authorizes entry, confirms rescue is available and ends the entry when conditions change (Section 1959).
  • Non-entry rescue with a harness and retrieval line is required unless it would increase risk; a mechanical retrieval device is needed for vertical spaces more than 5 feet deep (Section 1960(c)).
  • Hydrogen sulfide is heavier than air, collects in sewers and manholes, and deadens the sense of smell at high levels, so never trust your nose (OSHA).

Why This Matters

Plumbers work in and around some of the most dangerous spaces on any job: septic tanks, sewer manholes, lift stations, sumps, valve pits, water mains and utility vaults. The air inside can be short on oxygen or full of hydrogen sulfide or methane, and the person who goes in without testing, or goes in after a collapsed coworker without equipment, may not come back out.

For construction work, Cal/OSHA's rules are in Title 8 Sections 1950 to 1962, "Confined Spaces in Construction." The general industry rule, Section 5157, uses the same definitions and atmosphere limits. One exception to know: excavations and trenches are covered by the excavation orders (Article 6), not by the construction confined space article (Section 1950(b)).

Confined Space vs. Permit-Required Confined Space

A confined space (Section 1951) is a space that:

  • Is large enough and so configured that an employee can bodily enter it;
  • Has limited or restricted means for entry and exit; and
  • Is not designed for continuous employee occupancy.

Section 1950 lists examples that plumbers see all the time: pits (pump, valve and equipment pits), manholes (sewer, storm drain and utility), tanks, sewers, storm drains, water mains, precast manhole units, lift stations and cesspools.

A permit-required confined space (permit space) is a confined space that has one or more of these:

  • Contains or could contain a hazardous atmosphere;
  • Contains material that could engulf an entrant (liquid or flowable solid);
  • Has an inside shape that could trap or asphyxiate an entrant, such as inwardly converging walls or a floor that slopes down to a smaller cross-section; or
  • Contains any other recognized serious safety or health hazard.

Before work begins, a competent person identifies all confined spaces where the employer's workers may work, and which of them are permit spaces (Section 1952(a)). Workers are warned by danger signs or an equally effective method, and anyone not authorized is kept out (Section 1952(b) and (c)). An employer whose workers will enter a permit space needs a written permit space program (Section 1952(d)).

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