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PART I
INTERPRETATION AND APPLICATION

Interpretation

1. This Standard may be cited as the Standard for Inert Gas Systems.

2. In this Standard,

"inert gas" means a gas or a mixture of gases, such as flue gas, containing insufficient oxygen to support the combustion of hydrocarbons;

"inert condition" means a condition in which the oxygen content throughout the atmosphere of a tank has been reduced to 8 per cent or less by volume through addition of inert gas;

"inert gas plant" means all equipment specially fitted to supply, cool, clean, pressurize, monitor and control delivery of inert gas to cargo tank systems;

"inert gas distribution system" means all piping, valves and associated fittings to distribute inert gas from the inert gas plant to cargo tanks, to vent gases to atmosphere and to protect tanks against excessive pressure or vacuum;

"inert gas system" means an inert gas plant and inert gas distribution system, together with means for preventing backflow of cargo gases to the machinery spaces, fixed and portable measuring instruments and control devices;

"inerting" means the introduction of inert gas into a tank with the object of attaining the inert condition;

"gas freeing" means the introduction of fresh air into a tank, with the object of removing toxic, flammable and inert gases and increasing the oxygen content to 21 per cent by volume.

"purging" means the introduction of inert gas into a tank already in the inert condition, with the object of:

(a) further reducing the existing oxygen content and/or

(b) reducing the existing hydrocarbon gas content to a level below which combustion cannot be supported if air is subsequently introduced into the tank.

"topping-up" means the introduction of inert gas into a tank that is already in the inert condition, with the object of raising the tank pressure to prevent any ingress of air.

Application

3. (1) This Standard has advisory status and it is intended to cover the design and operation of:

1. inert gas systems that are required on new tankers by section 49, Fire Protection, Detection and Extinguishing Equipment Regulations and in accordance with Schedule VII, Fire Protection, Detection and Extinguishing Equipment Regulations;
2. inert gas systems that are required on existing tankers by section 49, Fire Protection, Detection and Extinguishing Equipment Regulations and in accordance with section 21, Schedule VII, Fire Protection, Detection and Extinguishing Equipment Regulations;
3. inert gas systems that are fitted but not required to comply with the requirements of section 49 of the Fire Protection, Detection and Extinguishing Equipment Regulations.

(2) For existing inert gas systems, however, the Standard is directed primarily at operational procedures and is not intended to be interpreted as requiring modifications to existing equipment other than those required on ships to which section 21, Schedule VII of the Fire Protection, Detection and Extinguishing Equipment Regulations, applies.

(3) The content of this Standard is based on current general practice used in the design and operation of inert gas systems using flue gas from the uptake of the ship’s main or auxiliary boilers and installed on crude oil tankers and combination carriers.

(4) The Standard does not exclude other sources of inert gas, such as systems incorporating independent inert gas generators, other designs, material or operational procedures; all such divergences should be carefully assessed to ensure that they achieve the objectives of this Standard.

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