Fixed systems
Inert gas system (IGS)
On tankers it keeps the atmosphere in the cargo tanks too lean in oxygen for anything to ignite. It is prevention, not extinguishing.
Key facts
- The inert gas fills the space above the cargo and keeps the oxygen concentration below the flammability threshold of the vapour mixture.
- The key terms: the lower and upper flammable limits (LFL and UFL), the concentrations of the flammable component between which the mixture with air can ignite.
On the fire control plan
These are not bulkhead signs: a system is marked with its symbol on the fire control plan (IMO res. A.1116(30), table 3).
Legal basis
SOLAS II-2/4.5.5; FSS Code chapter 15 (inert gas systems).
This is not a legal text: when in doubt, the current wording of the Convention and the FSS Code decides.