FSS Code Chapter 15 • Tank O₂ ≤8% • IG Supply O₂ ≤5% • Positive Pressure • 125% Capacity • Purge Time • Dilution Curve • Blower Capacity

Inert Gas System & Tank Oxygen Tool Purging, O₂ Dilution, Blower Capacity & Discharge Rate

Screen tanker inert-gas quality, capacity and tank oxygen in one workflow. Simple mode calculates theoretical purge exchanges and time while checking the 5% inert-gas supply limit, 8% cargo-tank oxygen limit, positive pressure and the 125% discharge-capacity relationship. Advanced adds multiple cargo tanks, sequential or parallel inerting, individual tank pressure, discharge-rate demand, delivery-unit redundancy and a live oxygen-decay curve.

Figures represent
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Need several tanks, parallel inerting or blower redundancy? Click Advanced above.The purge-time calculation is an ideal well-mixed dilution model. Real tanks can stratify and short-circuit, so onboard oxygen measurements remain controlling.
Tank oxygenTime / exchanges to target
IG quality5% O₂ supply screen
Capacity125% discharge screen

Tank Inerting

m³.
% by volume.
% by volume.
% by volume.
m³/h.
mm water gauge.

Cargo Discharge / IG Main

m³/h.
mm water gauge.
% of ideal well-mixed exchange effectiveness.

System & Regulatory Basis

m³/h.
mm water gauge.
mm water gauge.
mm water gauge equivalent.
% effective dilution versus ideal complete mixing.

IG Delivery Unit Register

For flue-gas / inert-gas-generator systems, FSS Chapter 15 normally calls for at least two blowers, subject to the specific single-blower exception for certain inert-gas-generator systems. Nitrogen systems use their compressor/generator capacity instead.

UseUnit typeRated delivery m³/hAvailable now?

Cargo Tank Register

Vapour volume is the gas space being diluted. Planned discharge rate is the cargo-volume replacement demand while the tank is discharging. Tank pressure must remain positive under the approved operating procedure.

UseVapour volume m³Start O₂ %Target O₂ %Tank pressure mmWGPlanned discharge m³/h

Inert Gas System Checks

Safety boundary: this tool models oxygen dilution only. It does not determine hydrocarbon concentration, lower/upper flammable limits, critical dilution lines, gas-freeing safety, static-electricity precautions or safe entry. Purging hydrocarbon vapour and subsequent gas freeing require the vessel’s approved procedure, gas measurements and applicable tanker/chemical-cargo guidance.
FSS Chapter 15 basis: when the FSS inert-gas requirements apply, relevant cargo tanks are to be maintained at oxygen content not exceeding 8% by volume and positive pressure; inert gas delivered to the cargo tanks is to contain no more than 5% oxygen by volume; delivery capacity is to be at least 125% of the maximum cargo discharge capacity, with a chemical-tanker acceptance route allowing discharge to be restricted to no more than 80% of IG capacity; and an IG-main low-pressure alarm is required below 100 mm water gauge. Gas exceeding 5% oxygen is to be automatically vented rather than supplied to the cargo tanks.
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