IACS: Cargo Tank Vent Systems and Selection of Electrical Equipment

The International Association of Classification Societies (IACS) has revised the Unified Interpretations of the cargo tank vent systems and the selection of electrical equipment.

This Unified Interpretations document (UI SC70 Rev4 Corr1 CLN) was published on 1 April 2023.

This document refers to the interpretation of SOLAS II-2/11.6.2.2 and SOLAS II-2/4.5.4.3.1.

According to SOLAS regulation II-2/11.6.2, the requirements for openings for small flow caused by thermal variations are as follows:

6.2 - Openings for Pressure Release:

1. The openings must be positioned with the maximum height possible above the cargo tank deck to ensure the widest dispersal of flammable vapors. The height should not be less than 2 meters above the cargo tank deck.
2. The openings should be located at the farthest distance feasible, but not less than 5 meters, from the nearest air intakes, enclosed spaces containing a source of ignition, and deck machinery and equipment that may pose an ignition hazard. It is important to note that openings such as those for the anchor windlass and chain locker are considered ignition hazards.

For tankers built on or after January 1, 2017, the arrangement of these openings must comply with regulation 4.5.3.4.1.

Interpretation:

The classification of areas must be conducted according to the principles outlined in IEC 60092-502:1999.

A1 - Zone 1:

Areas on the open deck or semi-enclosed spaces on the open deck that are within 3 meters of cargo tank ventilation outlets, allowing the flow of small volumes of vapor or gas mixtures caused by thermal variation, are categorized as Zone 1, as specified in IEC 60092-502:1999 paragraph 4.2.2.7.

A2 - Zone 2:

Areas located within 2 meters beyond the zone specified in A1 are considered Zone 2 (instead of the 1.5 meters defined in IEC 60092-502:1999 paragraph 4.2.3.1).

A3 - Electrical Equipment in Hazardous Areas:

Electrical equipment or cables should generally not be installed in hazardous areas. However, if necessary for operational purposes, electrical equipment may be installed in accordance with IEC 60092-502:1999.

As stated in SOLAS regulation II-2/4.5.3.4.1:

• The openings and air intakes must be positioned at a minimum horizontal distance of 10 meters from enclosed spaces containing a source of ignition, as well as deck machinery and equipment that may pose an ignition hazard.

Interpretation:

Similar to the previous section, the classification of areas must adhere to the principles defined in IEC 60092-502:1999.

B1 - Zone 1:

Areas on the open deck or semi-enclosed spaces on the open deck that fall within a vertical cylinder of unlimited height and a 6-meter radius centered upon the outlet, as well as within a hemisphere of 6-meter radius below the outlet, which allow the flow of large volumes of vapor or gas mixtures during loading, discharging, or ballasting, are categorized as Zone 1, as specified in IEC 60092-502:1999 paragraph 4.2.2.8.

B2 - Zone 2:

Areas situated within 4 meters beyond the zone specified in B1 are classified as Zone 2, as indicated in IEC 60092-502:1999 paragraph 4.2.3.2.

B3 - Electrical Equipment in Hazardous Areas:

As a general rule, electrical equipment or cables should not be installed in hazardous areas. However, if it is essential for operational purposes, electrical equipment may be installed in accordance with IEC 60092-502:1999.

Notes:

1. Revision 4 of this UI (Unified Interpretation) must be uniformly implemented by IACS (International Association of Classification Societies) on ships contracted for construction on or after July 1, 2022.
2. The term "contracted for construction" refers to the date when the contract to build the vessel is signed between the prospective owner and the shipbuilder. For more detailed information regarding the date of "contract for construction," please refer to Procedural Requirement (PR) No. 29.

For more information, please see the document below (available only to subscribers):

Cargo Tank Vent Systems and Selection of Electrical Equipment