All confined spaces and many enclosed spaces require atmospheric testing before entry as well as periodic re-testing, depending on operations and conditions in and around the space.
OSHA specifies testing procedures. [29 CFR 1915.12]
Those qualified to conduct these tests include:
The Shipyard Competent Person or a Marine Chemist may conduct initial tank entry testing and hotwork testing. However, if the space contains flammable or combustible liquids or gases, a Marine Chemist must issue a certificate before hot work begins. If the Shipyard Competent Person finds a toxic atmosphere above the OSHA Permissible Exposure Limit (PEL), additional testing by the certified marine chemist or certified industrial hygienist is required and additional controls must be implemented to prevent excessive exposures. Controls typically include ventilation and personal protective equipment (PPE). [29 CFR 1915.12(c)(3)]
Safe Atmospheres |
According to OSHA, the following are acceptable atmospheric conditions for entry:
- Oxygen concentrations between 19.5 percent and 22.0 percent by volume. [29 CFR 1915.12]
- Flammable gas and vapor concentrations less than 10 percent of the Lower Explosive Limits (LEL). [29 CFR 1915.12]
- Toxic vapor, gas, and particulate concentrations less than the OSHA Permissible Exposure Limits (PELs) (8-hour time-weighted average PELs). [29 CFR 1915.12]
An employee may not enter a space in which the oxygen content by volume is less than 19.5 percent or more than 22.0 percent except for emergency rescue or for a short duration in order to install necessary ventilation
equipment, provided that:
- The oxygen content within the space is monitored continually by volume. [29 CFR 1915.12(a)(3)]
- Respiratory protection and other appropriate PPE and clothing are provided in accordance with the PPE section of 29 CFR 1915. [29 CFR 1915.12(a)(3)]
An employee may not enter a space in which the concentration of flammable vapors or gases is equal to, or greater than 10 percent of the LEL, except for emergency rescue or for a short duration in order to install necessary ventilation equipment, provided that:
- No ignition sources are present.
- The atmosphere in the space is monitored continuously. [29 CFR 1915.12(b)(3)]
- Atmospheres at or above the upper explosive limit (UEL) are maintained. [29 CFR 1915.12(b)(3)]
- Respiratory protection and other appropriate PPE and clothing are provided in accordance with the PPE section of 29 CFR 1915. [29 CFR 1915.12(b)(3)]
An employee may not enter a space in which the concentration exceeds a PEL or is immediately dangerous to life or health (IDLH), except for emergency rescue or for a short duration in order to install necessary ventilation equipment, provided that:
- The oxygen content within the space is monitored continually by volume. [29 CFR 1915.12(c)(3)]
- Respiratory protection and other appropriate PPE and clothing are provided in accordance with the PPE section of 29 CFR 1915. [29 CFR 1915.12(c)(3)]
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Shipyard Competent Person |
 Figure 3: Shipyard Competent Person testing a confined space before entry.

Figure 4: Testing and visual inspection
ensure atmospheric conditions within the space are maintained after the
certificate is issued.

Figure 5: Rudder

Figure 6: Testing equipment.

Figure 7: Sample Competent Person Record.
Shipyard employers must designate competent persons who possess the following minimum criteria: [29 CFR 1915.7(c)]
- Ability to carry out instructions and perform tests as directed by the Marine Chemist.
- Understanding of appropriate 29 CFR 1915 standards.
- Knowledge about the structure, location, and spaces in which work is performed.
- Ability to perform tests, calibrate and use test equipment, interpret test results, and maintain test records.
- Ability to inspect, test, evaluate spaces, and determine the need for further evaluation by a CIH or CMC.
A Shipyard Competent Person (SCP) is qualified to perform the following tasks:
- Visually inspect and test the following spaces to determine the atmosphere's oxygen content before employees enter the space. [29 CFR 1915.12(a)(1)]
- Spaces that have been sealed.
- Spaces containing, or that have previously contained, combustible or flammable
liquids or gases.
- Spaces containing or that have previously contained liquids, gases, or solids
that are toxic, corrosive, or irritating.
- Spaces that have been fumigated.
- Spaces that contain, or that have previously contained, materials or residues of materials that create
an oxygen-deficient atmosphere.
- Visually inspect spaces containing, or that have previously contained, combustible or
flammable liquids or gases before employees enter the spaces to:
- Determine the presence of combustible or
flammable liquids within these spaces.
- Test to determine the
concentration of flammable vapors and gases within these spaces. [29 CFR 1915.12(b)(1)]
- Visually inspect spaces containing, or
that have
previously contained liquids, gases
or solids that are toxic, corrosive, or irritating before employees enter the space to:
- Determine toxic,
corrosive, or irritant residues within these spaces.
- Test air concentrations for toxic, corrosive, or irritant materials
within
these spaces. [29 CFR 1915.12(c)(1)]
- Test spaces before hot work and ensure that no
concentrations of flammable vapors equal to or greater than 10 percent of the LEL
exist: [29 CFR 1915.14(b)]
- Dry cargo holds.
- Bilges
- Engine and boiler room spaces where a CMC
or CGAP
certificate is not required
- Vessels and vessel sections for which a CMC or CGAP
certificate is not require.
- Visually inspect and test each space certified as "Safe for
Workers" or "Safe for Hot Work" as often as necessary to
ensure that atmospheric conditions within these spaces is maintained within
the conditions established by the certificate, after the certificate has
been issued. [29 CFR 1915.15(c)]
- Determine the flammability of preservative coatings on any surface before
welding, cutting, or heating is performed. [29 CFR 1915.53(b)]
- Test the atmosphere for explosive vapors in spaces in which the metals are coated with soft and greasy preservatives before and immediately after beginning welding, cutting, or heating. [29 CFR 1915.53(e)(1) and 29 CFR 1915.53(f)].
- Visually inspect structural voids such as skegs,
bilge keels, fair waters, masts, booms, support stanchions, pipe
stanchions, and railings, and test them for the presence of flammable
liquids or vapors before welding, cutting, heating or brazing. [29 CFR 1915.54(c)]
- Calibrate and maintain test equipment. [29 CFR 1915.7(c)]
The Shipyard Competent Person (SCP) must complete the Competent Person Record, which must be posted. This record identifies conditions of spaces designated as "Safe for Hot Work" or "Safe for Workers." Spaces that are designated "Not Safe for Workers" or "Not Safe for Hot Work" or "Enter with Restrictions" must have warning signs and labels posted at the entrance of the space. [29 CFR 1915.16] The shipyard must maintain and make available a roster of shipyard competent persons. [29 CFR 1915.7(b)(2)(i)]
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Certified Marine Chemist |

Figure 8: Marine Chemist tests confined space prior to entry.

Figure 9: Certified Industrial Hygienist (CIH)
A Marine Chemist is one who possesses a current Marine Chemist Certificate issued by the National Fire Protection Association. [NFPA 306: Control of Gas Hazards on Vessel Sections] The NFPA specifies training and certification requirements.
Tasks performed by the Marine Chemist include:
- Testing for flammable, combustible, and toxic atmospheres before beginning hot work operations in spaces, adjacent spaces, and pipelines, which contain flammable or combustible liquids or gases. [29 CFR 1915.14(a)]
- Testing to confirm that inerting of spaces containing flammable and combustible materials has been effective. [NFPA 306, Section 3-2.1]
- Testing of spaces that are IDLH or cannot be ventilated to comply with OSHA PELs until the space can be certified "Enter with Restrictions" or "Safe for Workers." [29 CFR 1915.12(c)(3)]
- Approving the use of inerting medium (such as nitrogen, carbon dioxide, etc.) and personally supervising the introduction of the inerting medium into the space. [NFPA 306, Section 3-2.1]
Marine Chemist certificates shall be posted and accessible nearby during the operations and available for inspection (such as for OSHA, workers, and supervisors, and so forth) for a period of three months after the completion of work. [29 CFR 1915.14 (a)(2)]
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Certified Industrial Hygienist (CIH) |

Figure 10: Certified Industrial Hygienist (CIH).
An Industrial Hygienist (IH) has the appropriate training, education, and experience to recognize, evaluate, and control occupational and environmental health hazards. A Certified Industrial Hygienist (CIH) has met the requirements of the American Board of Industrial Hygiene (ABIH). A CIH performs the following task:
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Coast Guard Authorized Person (CGAP) |
A Coast Guard Authorized Person is authorized by the Coast Guard to conduct inspections for hot work, instead of a Marine Chemist. [29 CFR 1915.14(a) and 29 CFR 1915 Subpart B Appendix B]
Note: If a Marine Chemist is not available, the Coast Guard Captain of the Port can authorize personnel to perform this work.
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