Internal combustion engine exhaust safety

The exhaust must be led to the open air and kept clear of any ventilation intakes or openings through which it might enter the vessel. Employers must follow 1915.136(a) which requires that engines used below decks for pumps, generators, or blowers discharge exhaust into the open air and not toward ventilation openings. Failure to do so can allow exhaust gases to enter occupied spaces and create hazardous atmospheres.

It means the exhaust outlet must be positioned and routed so that fumes cannot be drawn into any mechanical or natural ventilation openings that lead into the vessel. Put simply, keep exhaust outlets physically separated and pointed away from air intakes or hatches so exhaust cannot flow back in. This is the requirement of 1915.136(a). Consider routing, wind patterns, and intake locations when designing or testing exhaust discharge sites.

Exhaust line joints and connections must be checked for tightness immediately after starting the engine, and any leaks must be corrected at once. This is the direct requirement of 1915.136(b). A visual and, if safe, tactile check right after startup catches leaks before they expose workers to exhaust gases.

Check joints visually for soot or spray, listen for hissing, feel (from a safe distance) for escaping air, and use a gas detector in the vicinity of joints. Employers should follow the inspection requirement in 1915.136(b). If a leak is suspected, shut down or isolate the engine if possible and repair the leak immediately. Never place bare hands close to hot components—use appropriate tools or remote detection methods.

A competent person must perform carbon monoxide testing of the atmosphere when vehicles or portable equipment exhaust below decks. 1915.136(c) requires tests be made by a competent person and OSHA's interpretation of the "competent person" role explains that such a person must be capable of recognizing and evaluating hazardous atmospheres and specifying protection measures, see the OSHA letter on competent person requirements in shipyards.

Tests must be made as frequently as conditions require to ensure dangerous concentrations do not develop. 1915.136(c) uses a performance-based phrase—"as frequently as conditions require"—so testing frequency depends on factors like engine run time, ventilation effectiveness, number and type of engines, and prior CO readings. The competent person must set the appropriate schedule based on those conditions (see OSHA's guidance on the competent person role at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18).

Employees must be removed from the compartment when the carbon monoxide concentration exceeds 50 parts per million (0.005%). This is the specific action level set in 1915.136(c). Work cannot resume until ventilation lowers CO below that allowable limit using blowers adequate in size and number.

The employer must use blowers sufficient in size and number and arranged to reduce the CO concentration below 50 ppm before work resumes. 1915.136(c) requires effective mechanical ventilation to lower CO to at-or-below the allowable limit. The competent person should evaluate blower capacity, placement, and air changes needed to restore safe levels.

No—employees shall be removed from the compartment when CO exceeds 50 ppm and may only return after blowers have reduced the concentration below 50 ppm. The clear requirement is in 1915.136(c). The competent person must confirm safe levels before allowing re-entry (see OSHA's explanation of competent person duties at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18).

No—the standard does not prescribe a specific CO monitor model or technology; it requires the competent person to make tests as frequently as conditions require under 1915.136(c). Employers should use reliable, properly calibrated instruments suitable for low-level CO detection (capable of reading around and below 50 ppm) and follow manufacturer calibration and maintenance guidance to ensure accurate readings. The competent person must select appropriate equipment as described in the OSHA letter on competent person responsibilities at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18.

While 1915.136 does not mandate records for every test, employers should document CO measurements, times, locations, personnel removed, and corrective actions to show they followed 1915.136(c). Good documentation helps demonstrate the competent person evaluated conditions and implemented ventilation and repairs per OSHA's competent person guidance at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18. Keep records in a format that helps track trends and proves prompt corrective action.

No—exhaust from fixed engines located below decks must be led to the open air and kept clear of ventilation intakes and openings; temporary discharges that could enter the vessel would violate 1915.136(a). If temporary routing is necessary for maintenance, the competent person must ensure no exhaust can enter occupied spaces and implement monitoring and ventilation controls as required by 1915.136(c). See OSHA's guidance on competent person authority at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18.

The standard does not require permanent routing of vehicle exhaust; instead, when such vehicles or portable equipment exhaust into the atmosphere below decks, the competent person must test for CO as frequently as needed and take action if dangerous concentrations develop, per 1915.136(c). For fixed-position engines below decks, 1915.136(a) specifically requires the exhaust be led to the open air clear of intakes. Use engineering controls like ventilation and routing when practicable.

Any exhaust leaks discovered upon starting the engine must be corrected at once. 1915.136(b) requires immediate repair. Until repairs are completed and the exhaust system verified tight, use ventilation and/or relocate personnel away from the area to prevent CO or other exhaust hazards.

Owners may use safe and appropriate methods—visual inspection, listening for leaks, soap-bubble tests where applicable, or gas detection—to verify tightness immediately after startup, as required by 1915.136(b). Choose methods that avoid exposing workers to hot parts or exhaust; if a pressure or soap test is used, follow safe procedures and ensure the engine is shut down and cooled if necessary.

The standard requires removal of employees from compartments when CO exceeds 50 ppm and correction by ventilation before resuming work; it does not mandate permanent removal of the vehicle. Employers can reduce CO by improving ventilation, repairing engines to reduce emissions, or changing work procedures, as allowed under 1915.136(c). The competent person should evaluate and specify the necessary protection per OSHA's competent person guidance at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18.

1915.136(c) sets a simple actionable limit: employees shall be removed when the carbon monoxide concentration exceeds 50 parts per million (0.005%). The standard does not specify averaging time; it is an exposure threshold for immediate action, so any measured concentration above 50 ppm requires removal and ventilation per 1915.136(c). The competent person should interpret measurements in context and take prompt corrective measures (see OSHA competent person letter at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18).

The employer bears the responsibility for complying with 1915.136, but the duties placed on the competent person are considered responsibilities of the employer, per OSHA's competent person definition and explanation. See 1915.136 and OSHA's letter clarifying that the competent person's responsibilities are deemed the employer's responsibilities at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18. Employers must ensure competent persons are capable and that required testing and ventilation are carried out.

No—PPE alone is not the prescribed control; 1915.136(c) requires atmospheric testing and ventilation to maintain CO below 50 ppm and removal of employees when the limit is exceeded. While respirators may be used as interim or supplemental protection under a comprehensive respiratory program where appropriate, the standard emphasizes testing and engineering controls (see 1915.136(c)). The competent person should determine necessary measures as described in OSHA's competent person guidance at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18.

1915.136(c) sets 50 ppm as the actionable concentration above which employees must be removed; the competent person cannot substitute a higher threshold for immediate removal. However, the competent person may use other occupational exposure information when planning controls and testing frequency, but must comply with the removal requirement in 1915.136(c). For guidance on the competent person's authority to specify protection measures, see OSHA's letter at https://www.osha.gov/laws-regs/standardinterpretations/2016-04-18.