Scope and definitions for subpart

This subpart applies to confined and enclosed spaces and other dangerous atmospheres both on vessels and in land-side shipyard operations, regardless of geographic location. See the Scope and application in 1915.11(a) for the full coverage statement.

A "space" includes areas on a vessel, vessel sections, or within a shipyard such as cargo tanks or holds, pump or engine rooms, storage lockers, tanks containing flammable or combustible liquids/gases/solids, rooms in buildings, crawl spaces, tunnels, and accessways. This is the definition in 1915.11(b).

• Treat the entire bounded area as the atmosphere of the space; hazards anywhere inside the bounds count toward assessments.

An "adjacent space" means any space bordering the subject space in all directions (including corners, diagonals, decks, tank tops, and bulkheads), and it matters because all adjacent spaces must be controlled to prevent spread of fire or flammable atmospheres when determining if hot work is allowed. See the definition of "adjacent spaces" in 1915.11(b).

• For a space to be "Safe for Hot Work," the rule requires that "All adjacent spaces have been cleaned, or inerted, or treated sufficiently to prevent the spread of fire." See 1915.11.
• Don’t assume nearby spaces are inert — verify and document their condition before permitting hot work.

Grinding, drilling, abrasive blasting, or similar spark-producing operations are considered "hot work" unless they are physically isolated from any atmosphere that contains more than 10 percent of the lower explosive limit (LEL) of a flammable or combustible substance. This is stated in 1915.11(b).

• If your operation can’t show physical isolation from atmospheres above 10% LEL, treat it as hot work and apply the hot work controls.

An "oxygen-deficient atmosphere" is one with less than 19.5 percent oxygen by volume, and that threshold is used to classify atmospheres for entry, respiratory protection, and IDLH considerations. See the definition in 1915.11(b).

• OSHA’s interpretation on HVAC/Oxygen-deficient atmospheres clarifies use of the 19.5% criterion in workplace settings; see the letter at Oxygen-deficient atmospheres in HVAC (2024-07-16) for further context about civilian employee coverage and respiratory protection application.

A space is "Safe for Workers" when oxygen is at least 19.5% and below 22.0% by volume; it is "Safe for Hot Work" only if oxygen does not exceed 22.0% and flammable vapors are below 10% of the LEL, plus other conditions are met. See the definitions in 1915.11(b).

• "Safe for Hot Work" also requires residues/materials not capable of producing higher concentrations during hot work and that adjacent spaces have been cleaned/inerted/treated to prevent fire spread.

An "inert or inerted atmosphere" means either (1) oxygen is at or below 8.0% by volume (or at or below 50% of the oxygen needed to support combustion, whichever is less), or (2) the space is flooded with water and vapor concentration above the water line is less than 10% of the LEL. See the definition in 1915.11(b).

• If you use inerting, document the method and monitoring used to maintain the inerted condition before allowing entry or hot work.

IDLH means an atmosphere that poses an immediate threat to life or is likely to cause acute or immediate severe health effects or prevent self-rescue. See the definition in 1915.11(b).

• Treat IDLH atmospheres as requiring the highest level of respiratory protection and rescue planning under OSHA standards and applicable shipyard procedures.

"Labeled" means the space is identified with a sign, placard, or other written communication (including pictograms) that provides information on the status or condition of the work space. See the definition in 1915.11(b).

• Use clear labels that show whether a space is "Safe for Workers," "Safe for Hot Work," "Enter with Restrictions," or "Not Safe for Workers/Hot Work" as appropriate.

A space is designated "Enter with Restrictions" when a Marine Chemist, Certified Industrial Hygienist (CIH), or shipyard competent person specifies that entry is permitted only if engineering controls, personal protective equipment, clothing, and time limits are followed as they direct. See the definition in 1915.11(b).

• The responsible qualified person must document the required controls and limits and communicate them to entrants and attendants before entry.

A "visual inspection" requires a physical survey of the space, its surroundings, and contents to identify hazards like restricted access, residues, unguarded machinery, and piping or electrical systems. See the definition in 1915.11(b).

• Visual inspection is a required step to decide classification (Safe for Workers/Hot Work, Enter with Restrictions, Not Safe) and to plan controls.

The atmosphere of a space is defined as the entire area within its bounds, meaning monitoring must represent conditions throughout the bounded space and not just at a single point. See the definition in 1915.11(b).

• When air conditions can vary within a space, take multiple samples or continuous monitoring at representative locations before and during entry.

The Lower Explosive Limit (LEL) is the minimum vapor concentration in air below which flame propagation will not occur in the presence of an ignition source; it’s used to set safety thresholds (e.g., the 10% LEL criterion for hot work). See the LEL definition in 1915.11(b).

• Practical rule: keep flammable vapors below 10% LEL for hot work, and monitor continuously when there is any chance of vapor release.

"Not Safe for Hot Work" denotes a space where hot work may not be performed because conditions do not meet the criteria for "Safe for Hot Work." "Not Safe for Workers" denotes a space where employees may not enter because conditions do not meet the criteria for "Safe for Workers." See these defined terms in 1915.11(b).

• If a space is labeled "Not Safe..." do not enter or perform hot work until a Marine Chemist, CIH, or competent person documents corrective actions that render the space safe.

A "Marine Chemist" is someone who holds a current Marine Chemist Certificate issued by the National Fire Protection Association and can evaluate and certify spaces for hazardous atmospheres, hot work, and safety for entry. See the definition in 1915.11(b).

• Marine Chemists often set restrictions, specify monitoring, and sign off when a space is "Safe for Hot Work" or requires special controls.

When a space is "flooded with water" for inerting, the definition requires that the vapor concentration in the free space above the water line be less than 10% of the LEL for the flammable/combustible material to qualify as inerted. See the inert/inerted atmosphere definition in 1915.11(b).

• Verify and record vapor readings above the water line; do not assume flooding alone is sufficient without measurement.

A "Vessel section" means a sub-assembly, module, or other component of a vessel being built, repaired, or broken, and the definition matters because the subpart’s confined-space and atmospheric rules apply to these sections just as to whole vessels. See the definition in 1915.11(b) and the Scope in 1915.11(a).

• Apply the same atmospheric testing, labeling, and entry procedures to vessel sections during construction or repair.

A Certified Industrial Hygienist (CIH) is an industrial hygienist certified by the American Board of Industrial Hygiene, and a shipyard may rely on a CIH to evaluate toxic atmospheres, set permissible exposure controls, or designate an "Enter with Restrictions" status. See the CIH definition in 1915.11(b).

• Use a CIH for complex toxic exposures when technical exposure assessment and written controls are needed.

"Entry" means the action by which a person passes through an opening into a space, and it triggers all entry-related requirements (testing, labeling, attendant, rescue planning) for that confined or enclosed space. See the definition in 1915.11(b).

• Even partial entry (any part of the body entering the space) counts as entry and requires compliance with the subpart’s controls.

A "Nationally Recognized Testing Laboratory (NRTL)" is an organization recognized by OSHA that tests and lists or labels equipment and materials that meet the criteria in [29 CFR 1910.7(b)(1)–(4)(ii)], and the NRTL definition is referenced in 1915.11(b) while full criteria appear in 1910.7 and its subsections such as 1910.7(b).

• Use equipment listed by an NRTL where the subpart or other OSHA standards require listed equipment for hazardous locations.