OTM-7.12 Oil Tanker Manual
OTM
Inert Gas System 		Doc No.: OTM 7.12
Revision: 01
Date: 15 Oct 2024
Issued by: DPA
Approved by: MD

1. APPLICATION

This document applies to Officers onboard fully managed Tank vessels.

2. PURPOSE

The purpose of this document is to specify requirements for safe operation of Inert Gas Systems on product and crude oil tankers.

3. REQUIREMENTS

Follow ISGOTT 6th Edition chapter 7.1 (fixed inert gas system).

All oil and Chemical tankers should comply with the following guidance for carriage of cargo in inerted condition.

Ship product Above 20,000 DWT keel laid after July 1986 but before 1st January 2016 Tanker above 8,000 DWT keel laid after 1st January 2016
Cargo tanks < 3,000 m³ Cargo tanks > 3,000 m³
Crude oil IG Required IG Required IG Required
Petroleum products Flashpoint < 60°C IG Required IG Required IG Required
Chemicals Flashpoint < 60°C IG Not Required (1) IG Required (2) IG Required (2,3)
Other Liquid Substances Flashpoint < 60°C IG Not Required (1) IG Required IG Required (2,3)

1. Subject to each tank washing machine nozzle not exceeding 17.5m³/hr and total capacity of the tank cleaning machines is less than 110m³/hr.

2. For chemical tankers, the application of inert gas may take place after the cargo tank has been loaded, but before commencement of unloading and shall continue to be applied until that cargo tank has been purged of all flammable vapours before gas-freeing. Only nitrogen is acceptable as inert gas under this provision.

3. For tankers of 8,000 tonnes deadweight and upwards but less than 20,000 tonnes deadweight constructed on or after 01 January 2016, in lieu of fixed installations as required by paragraph 5.5.4.1 of SOLAS II-2, Regulation 4, the Administration may accept other equivalent arrangements or means of protection in accordance with SOLAS Regulation I/5 and paragraph 5.5.4.3 of SOLAS II-2, Regulation 4.

Note:

Note:


In the context of this matrix, the terms:

4. RESPONSIBILITIES

5. OPERATION OF INERT GAS SYSTEM

Cargo tanks must be kept inerted and under positive pressure at all times, except when required for man entry.

Warning:

Use the Inert Gas system for:

(By Gas freeing from a “Purged condition (HC=2% VOL)” to the “Gas free condition (HC=<1% LEL)”and until steady 21% by volume oxygen reading is sufficient dilution of such toxic gases to below their OEL-TWA limits will have been achieved.)

Coution:

Note:

Startup procedure

Note:

Shutdown Procedures

Safety Checks When the IG Plant is Shutdown

Possible Failures and Action to be Taken


6 CARRIAGE OF CARGOES UNDER INERTED CONDITION

Set and lock individual tank IG isolation valves as required (open or close)

Note:

Loading Operations

Note:

Discharging Operations

Coution:

Note:


7.INERT GAS EMERGENCY PROCEDURES

Additional Follow-up Action on Crude Oil Tankers

Pyrophoric iron sulphide deposits (pyrophors), formed when hydrogen sulphide gas reacts with rusted surfaces in the absence of oxygen, may be present in the cargo tanks of crude oil tankers. These deposits can heat to incandescence when coming into contact with air. The failed inert gas system must be repaired and restarted, or an alternative source of inert gas provided, before discharge from inerted tanks is resumed.

Additional Follow-up Action on Product Tankers

Tank coatings usually inhibit the formation of pyrophors in the cargo tanks of product tankers. If it is considered totally impracticable to repair the inert gas system, discharge may therefore be resumed with the written agreement of all interested parties, provided that an external source of inert gas is provided or detailed procedures are established to ensure the safety of operations.

Coution:


8.REFERENCED FORMS AND CHECKLISTS


9.APPENDICES