Hazardous atmospheres on vessels

This rule covers any space on a vessel where the employer knows or has reason to believe a hazardous atmosphere or substance may exist, except where separate rules in 1918.94 apply. See 1918.93(a).

• If a space is covered instead by one of the specialty provisions listed in 1918.94 (for example, carbon monoxide or certain fumigated cargoes), apply that specific section rather than 1918.93(a).

A designated and appropriately equipped person must test the atmosphere of any space that the employer knows or has reason to believe contains, or has contained, a hazardous atmosphere, and testing must be done prior to employee entry. See 1918.93(b).

• "Designated and appropriately equipped" means the employer must assign a trained person who has the right instruments (for example, oxygen, combustible gas/LEL, and toxic-gas monitors) and the training to use them.

Yes — when mechanical ventilation is used to maintain a safe atmosphere, a designated person must test the atmosphere to ensure it is not hazardous. See 1918.93(c).

• Testing should be performed both after ventilation has begun and as necessary during the work to confirm the atmosphere remains safe.

Persons entering a space containing a hazardous atmosphere must be protected by respiratory and emergency protective equipment that meets the requirements of the maritime subpart J. See 1918.93(d)(1) and general OSHA respiratory requirements at 29 CFR 1910.

• Equipment commonly required includes respirators or self-contained breathing apparatus (SCBA), rescue gear, and any emergency equipment specified by the employer’s procedures and applicable respiratory standards.

Workers entering hazardous atmospheres must be instructed about the hazards, precautions, and how to use protective and emergency equipment; additionally, standby observers who are similarly equipped and instructed must continuously monitor those inside the space. See 1918.93(d)(2).

• The employer’s instruction should include how to recognize warning signs, alarm responses, and emergency rescue procedures.
• Standby observers must remain in communication with entrants and be prepared to initiate rescue.

Except for emergency or rescue operations, employees are not permitted to enter atmospheres identified as flammable or oxygen-deficient (less than 19.5% oxygen); those who enter only for emergency operations must be instructed about the dangers and must use self-contained breathing apparatus. See 1918.93(d)(3) and the OSHA interpretation clarifying oxygen-deficient atmospheres at https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.

• OSHA’s Respiratory Protection Standard considers oxygen-deficient atmospheres to be those with oxygen below 19.5% by volume; entry into such atmospheres is immediately dangerous to life or health unless appropriate SCBA and procedures are used.

To prevent inadvertent entry, appropriate warning signs or equivalent means must be posted at all means of access to spaces identified as hazardous, flammable, or oxygen-deficient. See 1918.93(d)(4).

• In addition to signs, employers should consider physical barriers, locked hatches, and written entry permits where appropriate.

Designated employees must clean up asbestos cargo spillage and must be protected as required by the asbestos standard in general industry, 1910.1001; see 1918.93(e).

• Note: OSHA has explained that many remediation activities involving asbestos-containing building materials may fall under the construction asbestos standard [29 CFR 1926.1101], so employers should confirm which asbestos standard applies to the specific cleanup task; see the OSHA interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14.

A "designated person" is an employee chosen by the employer who is trained, equipped, and authorized to test atmospheres and, when necessary, enter hazardous spaces; the employer should document the designation, training, and equipment provided. See 1918.93(b) and 1918.93(d).

• Documentation should include the person’s name, training records (what they were trained to test and how to use monitors and PPE), the instruments assigned, and any written procedures or entry permits used by the employer.

The employer’s designated tester should use instruments to check oxygen concentration, flammable gas/explosive limits (LEL), and likely toxic gases; testing must be done before entry and during ventilation as needed. See 1918.93(b) and 1918.93(c).

• Typical equipment includes a calibrated multi-gas monitor for O2, LEL, H2S, CO, and other site-specific toxic gases; employers must ensure instruments are maintained and calibrated according to manufacturer instructions.

No — even when mechanical ventilation is used, a designated person must make tests to ensure the atmosphere is not hazardous. See 1918.93(c).

• Relying solely on ventilation without atmospheric testing risks missing pockets of hazardous air; continuous or periodic testing may be necessary depending on conditions.

Personal gas monitors are useful for detection and worker warning, but entrants into atmospheres identified as hazardous must be protected by respiratory and emergency equipment meeting subpart J; entry into flammable or oxygen-deficient atmospheres (below 19.5% O2) is prohibited except for emergencies when self-contained breathing apparatus (SCBA) must be used. See 1918.93(d)(1) and 1918.93(d)(3) and the OSHA interpretation on oxygen-deficient atmospheres at https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.

• Use personal monitors as part of the safety program, but provide and require the correct respirator or SCBA when the hazard requires respiratory protection.

An atmosphere with oxygen content below 19.5% by volume is considered oxygen-deficient and, except for emergency/rescue situations, employees must not enter such atmospheres. See 1918.93(d)(3) and the OSHA interpretation addressing oxygen-deficient atmospheres at https://www.osha.gov/laws-regs/standardinterpretations/2024-07-16.

• For emergency entries into oxygen-deficient spaces, entrants must be trained and use self-contained breathing apparatus.

The standard prohibits employee entry into any atmosphere identified as flammable except for emergency or rescue operations; 1918.93 does not set a numeric LEL threshold, so employers must identify flammable atmospheres by appropriate testing and hazard criteria. See 1918.93(d)(3).

• Employers should use calibrated combustible gas/LEL instruments and site-specific procedures to determine when an atmosphere is flammable and therefore off-limits to routine entry.

Entrants and standby observers must be instructed about the hazards present, the precautions to take, and the use of protective and emergency equipment before entry. See 1918.93(d)(2).

• Training should cover how to use respirators or SCBA, alarm and communication procedures, rescue roles, and how to respond to changing atmospheric readings.

Standby observers must continuously monitor the activity of employees inside the hazardous space and must be similarly equipped and instructed to initiate rescue if needed. See 1918.93(d)(2).

• Monitors should be able to observe entrants, maintain reliable communication, read monitoring equipment, and be trained and equipped to summon or perform rescue.

For emergency or rescue entries into flammable or oxygen-deficient atmospheres, persons must be instructed in the dangers and must use self-contained breathing apparatus (SCBA) for entry. See 1918.93(d)(3).

• SCBA provides independent breathable air and is generally required when oxygen is below safe levels or when toxic or unknown flammable gases are present.

The special rules in 1918.94 (for carbon monoxide, fumigated grains, fumigated tobacco, other fumigated cargoes, and certain fish catches) apply instead of 1918.93 for those specific situations identified in 1918.93(a).

• Before applying 1918.93 procedures, check whether the space falls under one of the 1918.94 subsections (see 1918.94(a–e)).

In addition to posting appropriate warning signs at all access points per 1918.93(d)(4), employers should use physical barriers, locked access points, written entry permits, and controlled access procedures to prevent inadvertent entry.

• Combining visual warnings with locks, access-control procedures, and supervisory checks provides layered protection against accidental entry.

While 1918.93(e) requires that designated employees clean up asbestos cargo leaks and be protected under 1910.1001, OSHA has explained that many remediation activities involving asbestos-containing material may fall under the construction asbestos standard [29 CFR 1926.1101]; employers should determine which asbestos standard applies to the specific cleanup activity. See 1918.93(e) and the OSHA interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-11-14.

• If the cleanup resembles construction-type remediation (abatement, demolition, or repair involving ACBM), follow [29 CFR 1926.1101]; for other scenarios, the general industry standard 1910.1001 may apply.