Confined spaces compliance guidelines

An oxygen concentration between 19.5% and 20.8% by volume is generally acceptable for entry; values below 19.5% or above 20.8% should prompt investigation and corrective action. See 1915.12(a)(3) for the guidance that 20.8% is the normal sea-level value, 19.5% is the lower limit for acceptable entry, and anything above 20.8% requires finding and correcting the cause before entry. Additional note: during hot work the agency allows up to 22% to account for instrument error, but the cause of excess oxygen must still be removed before unsafe operations begin; see 1915.16(b).

Measurable flammable vapors below 10% of the lower explosive limit (LEL) are too lean to burn but still may indicate that flammable vapors are being released and could reach hazardous levels over time, so you should investigate and eliminate the source before entry. See 1915.12(b) which explains that atmospheres at or above 10% LEL are considered hazardous in confined spaces and that lower readings still require investigation because conditions can change.

If a flammable substance is present below 10% LEL but above its OSHA permissible exposure limit (PEL), you must address the toxic exposure (for example with ventilation, respiratory protection, or other controls) before allowing entry or work. The appendix points out this exact situation and refers you to the toxic atmosphere provisions in 1915.12(c) and highlights the concern in 1915.12(b)(6).

Monitoring frequency depends on factors such as temperature, the type of work being done, elapsed time since certification, whether the space is unattended, and whether the vessel has been moved or trimmed; there is no single fixed interval. The compliance guidelines explain that 1915.13(b) (and the appendix discussion) require the competent person to set monitoring frequency based on conditions like higher temperatures (which increase vaporization), work that stirs residues, elapsed time since a Marine Chemist certificate, unattended periods, work breaks, and ballasting or trimming.

Yes — you must retest the tank's atmosphere before entry if it was left unattended because conditions could have changed (for example, another barge could have dumped product into it). The appendix explicitly advises retesting after a tank is left unattended and refers to the monitoring and testing responsibilities in 1915.13(b) and 1915.13(b)(4).

Grinding, drilling, or abrasive blasting are not always considered 'hot work'—it depends on whether the operation introduces ignition sources into a hollow structure or an atmosphere that could support combustion; for example, abrasive blasting on the external hull generally does not require pumping and cleaning of tanks. The appendix discussion of 1915.11(b) gives examples where such operations do not constitute hot work and emphasizes that hot work precautions are needed when void spaces, tanks, or hollow structures could contain flammable atmospheres.

Before performing hot work on any hollow structure, you must test the void space and take appropriate precautions based on the test results. The compliance guidance for 1915.11(b) specifically advises testing void spaces and taking measures (ventilation, purging, cleaning, or other controls) to ensure safe atmospheres prior to hot work.

If measurements show toxic contaminants above acceptable limits, you must take corrective actions such as stopping entry, ventilating, providing respiratory protection, or otherwise controlling exposures until concentrations are at or below required levels. The appendix refers you to the toxic atmosphere provisions in 1915.12(c) and the related paragraphs 1915.12(c)(2), 1915.12(c)(3), and 1915.12(c)(4) for the specific compliance options and controls.

An oxygen-enriched atmosphere increases the range and speed at which materials will burn, so you must correct any enrichment before hot work; the standard allows detection instruments to read up to 22% oxygen to account for instrument error but you must investigate and eliminate the source of enrichment. The appendix warns that oxygen over 20.8% broadens flammability and expressly discusses hot work precautions in 1915.14(a) and 1915.14(b), and notes the allowance up to 22% for instrument error as described in the guidance and related 1915.16(b).

If the entire vessel is in the same unsafe condition, you can comply by posting signs with appropriate warning language at the gangway and at all other access points to the vessel. The appendix explains this compliance option and references the sign requirements in 1915.16(a) and 1915.16(b).

Yes — a competent person may evaluate exposures for chemicals without an OSHA PEL and specify necessary protections and precautions to ensure worker safety. OSHA's interpretation clarifies that the competent person, as defined in Part 1915, is empowered to recognize and evaluate exposures and to specify protections, and refers directly to the agency's letter on this topic: Competent person requirements in shipyards.

Before re-entering a tank after a break or at the end of a shift you should check for equipment left inside and re-monitor the atmosphere if necessary, because torches or hoses left behind can change oxygen or gas levels. The appendix highlights this issue and directs employers to the monitoring responsibilities in 1915.13(b).

Because ballasting, trimming, or moving the vessel can expose or shift trapped product or residues and change the tank atmosphere, you must retest the atmosphere after such moves and before entry. The appendix specifically warns that vessel movement can expose previously trapped cargo and requires rechecking as part of the monitoring duties in 1915.13(b).

Common situations include pipelines that were not blanked or disconnected opening, vessel shifting that releases trapped product, and residues releasing vapors; each can take a low reading toward or above 10% LEL over time and should be investigated. The appendix lists these examples and explains the hazard in 1915.12(b).

If a confined space measures flammable vapors at or above 10% LEL, you must treat it as hazardous for confined space entry and take controls (ventilation, purging, or prohibiting ignition sources) or follow the applicable entry procedures before allowing work. The appendix makes clear that atmospheres at or above 10% LEL are considered hazardous in confined spaces; see 1915.12(b)(3) and the broader 1915.12(b).

An instrument reading up to 22% oxygen may be tolerated as an allowance for instrument error, but you must investigate and remove the source of excess oxygen before performing hot work. The guidance explains that while 20.8% is the normal value and over-enrichment is hazardous, the standard permits readings up to 22% to account for instrument error, and requires finding and correcting the cause prior to hot work; see 1915.12(a)(2) and 1915.16(b).

No — ordinary sunglasses are not adequate for the intense radiant energy produced by welding or torch cutting; you must provide welder's hoods, helmets, goggles, or safety spectacles with the proper shaded lenses for those operations. OSHA's interpretation on shipyard eye and face protection explains that "potentially injurious light radiation" refers to intense radiant energy from welding and cutting and that ordinary sunglasses do not provide the necessary protection; see the interpretation at Shipyard eye and face protection and the general shipyard standards in 1915.