#### § 171.066 Calculation of permeability for Type I subdivision.

(a) Except as prescribed in [paragraph (b)](/on/2024-09-23/title-46/section-171.066#p-171.066(b)) of this section, the following permeabilities must be used when doing the calculations required to demonstrate compliance with [§ 171.065(a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)), [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)), and [(c)](/on/2024-09-23/title-46/section-171.065#p-171.065(c)):

(1) When doing calculations required to demonstrate compliance with [§ 171.065(a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) and [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)), the uniform average permeability given by the formulas in Table [171.066](/on/2024-09-23/title-46/section-171.066) must be used.

(2) When doing calculations required to demonstrate that compartments on opposite sides of a main transverse watertight bulkhead that bounds the machinery space comply with [§ 171.065(c)](/on/2024-09-23/title-46/section-171.065#p-171.065(c)), the mean of the uniform average permeabilities determined from Table [171.066](/on/2024-09-23/title-46/section-171.066) for the two compartments must be used.

(b) If an average permeability can be calculated that is less than that given by the formulas in Table [171.066](/on/2024-09-23/title-46/section-171.066), the lesser value may be substituted if approved by the Commanding Officer, Marine Safety Center. When determining this lesser value, the following permeabilities must be used:

(1) 95% for passenger, crew, and all other spaces that, in the full load condition, normally contain no cargo, stores, provisions, or mail.

(2) 60% for cargo, stores, provisions, or mail spaces.

(3) 85% for spaces containing machinery.

(4) Values approved by the Commanding Officer, Marine Safety Center for double bottoms, oil fuel, and other tanks.

(c) In the case of unusual arrangements, the Commanding Officer, Marine Safety Center may require a detailed calculation of average permeability for the portions of the vessel forward or aft of the machinery spaces. When doing these calculations, the permeabilities specified in [paragraph (b)](/on/2024-09-23/title-46/section-171.066#p-171.066(b)) of this section must be used.

(d) When calculating permeability, the total volume of the ‘tween deck spaces between two adjacent main transverse watertight bulkheads that contains any passenger or crew space must be regarded as passenger space volume, except that the volume of any space that is completely enclosed in steel bulkheads and is not a crew or passenger space may be excluded.

Table [171.066](/on/2024-09-23/title-46/section-171.066)—Table of Uniform Average Permeabilities

| Location | Uniform average permeability |
| --- | --- |
| | 10 (a−c) |
| Machinery space | 85 + \_\_\_\_\_\_\_\_\_\_ |
| | v |
| | 35(a) |
| Volume forward of machinery space | 63 + \_\_\_\_\_\_ |
| | v |
| | 35(a) |
| Volume aft of machinery space | 63 + \_\_\_\_\_\_ |
| | v |
| | |
| --- | --- |
| For each location specified in this table— | |
| a = volume below the margin line of all spaces that, in the full load condition, normally contain no cargo, baggage, stores, provisions, or mail. | |
| c = volume below the margin line of the cargo, stores, provisions, or mail spaces within the limits of the machinery space. | |
| v = total volume below the margin line. | |

[CGD 79-023, [48 FR 51017](https://www.federalregister.gov/citation/48-FR-51017), Nov. 4, 1983, as amended by CGD 88-070, [53 FR 34537](https://www.federalregister.gov/citation/53-FR-34537), Sept. 7, 1988; USCG-2014-0688, [79 FR 58287](https://www.federalregister.gov/citation/79-FR-58287), Sept. 29, 2014]