IBC Code (MSC.176(79)) · MARPOL Annex II (MEPC.118(52)) · P&A Manual & Cargo Record Book
IBC Code Chemical Tanker & MARPOL Annex II (NLS, Prewash & Stripping) Guide
Chemical tankers and Noxious Liquid Substance (NLS) carriers operate under two interlocking statutory regimes: the International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code, IMO Resolution MSC.176(79) / MEPC.119(52)) under SOLAS Chapter VII Part B and revised MARPOL Annex II (IMO Resolution MEPC.118(52)).
Complementing our CDI Chemical & LPG Inspection Guide and ISGOTT 6 Ship/Shore Safety Checklist Guide, this guide covers IBC Code Ship Types 1, 2 & 3, venting, inerting, deck foam, pump-room ventilation & Ch. 14 chemical PPE, Section 15.13 Inhibitor Certificates, and MARPOL Annex II Categories X, Y, Z & OS stripping (`75 L`), mandatory prewash, and underwater discharge rules.
Updated · Written by SeaReady in our own words. Not affiliated with OCIMF, RightShip, CDI, any MoU or any administration — always check the current official documents.
1. IBC Code Chapters 1–16: Ship Types, Containment, Venting, PPE & Overflow Control
Under SOLAS Chapter VII regulations 8–10 and IMO Resolution MSC.176(79), a chemical tanker may only carry liquid substances listed in IBC Code Chapter 17 (or assessed by tripartite agreement) that are explicitly endorsed on its International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk (§ 1.5):
| IBC Code Chapter & Requirement | Statutory Threshold / Limit | Onboard Verification & Vetting Focus |
|---|---|---|
| Certificate of Fitness & Ship Types 1, 2 & 3 (IBC Code Chs. 1, 2 & 16 / MSC.176(79)) | 5-year max validity (§ 1.5); ≥ 760 mm shell distance (§ 2.6.1); 1,250 m³ (Type 1) & 3,000 m³ (Type 2) tank limits (§ 16.1) | Every product loaded must appear by exact Chapter 17 shipping name on the International Certificate of Fitness (§ 1.5). Type 1 (most severe hazard) and Type 2 chemical tankers require cargo tanks to be sited ≥ 760 mm inboard from the bottom and side shell plating (§ 2.6.1), with single-tank cargo volume capped at 1,250 m³ on Type 1 ships and 3,000 m³ on Type 2 ships (§ 16.1). |
| Cargo Temperature Control, Controlled Venting & Tank Inerting/Padding (IBC Code Chs. 7, 8 & 9) | High-velocity vent valves ≥ 30 m/s at ≥ 3 m height (or B/3 or 6 m stack, § 8.3 & § 15.12.1); IGS ≤ 8% O₂ (Ch. 9) | Verify cargo heating/cooling return-media sampling for toxic/flammable leaks (Ch. 7), test high-velocity P/V valves and flame screens (Ch. 8), and maintain positive pressure and oxygen monitoring (≤ 8% O₂ by volume for inerted tanks or dry nitrogen padding for moisture-/oxygen-sensitive cargoes under Ch. 9 § 9.1.4). |
| Fixed Deck Foam, Pump-Room CO₂ & Pump-Room Extraction Ventilation (IBC Code Chs. 11 & 12) | ≥ 30 min alcohol-resistant deck foam (§ 11.3); 45% CO₂ (§ 11.2); ≥ 30 (or ≥ 45) air changes/hour (§ 12.1.3 & § 15.17) | Regular protein foam is prohibited on chemical tankers (§ 11.3.2); verify annual foam concentrate lab analysis certificates. Cargo pump-rooms require mechanical extraction ventilation pulling from below the floor plates providing ≥ 30 air changes/hour (§ 12.1.3), or ≥ 45 air changes/hour when carrying toxic products invoking § 15.17. |
| Cargo Gauging, Vapour Detection & High-Level / Overflow Control (IBC Code Ch. 13 & § 15.19) | Open (O), Restricted (R) or Closed (C) gauging (§ 13.1); ≥ 2 toxic/flammable gas detectors (§ 13.2); 95% / 98% alarms (§ 15.19) | Check Chapter 17 Column j for gauging type and Column k for vapour detection (F = flammable, T = toxic). At least two portable or fixed instruments must be on board for each required vapour type (§ 13.2.1). Independent high-level (95%) and overflow control (98%) visual/audible alarms and sequential valve shutdowns (§ 15.19.6–.7) must be functionally tested prior to every cargo operation (§ 15.19.4). |
| Chemical PPE, SCBA Safety Sets, Cabin Escape Masks & Decontamination Showers (IBC Code Ch. 14) | ≥ 3 complete 20-min SCBA chemical safety sets (§ 14.2.2); ≥ 15-min cabin escape masks when Column n = Yes (§ 14.3.1) | Maintain chemical-resistant aprons, gloves, boots and tight-fitting goggles (§ 14.1), ≥ 3 complete SCBA chemical safety outfits in protective lockers (§ 14.2), cabin emergency escape respiratory and eye protection for every person on board when Column n = Yes (§ 14.3.1), IMO MFAG antidotes and oxygen resuscitators (§ 14.3.2), and deck decontamination showers/eyewash protected against freezing (§ 14.3.4). |
| Cargo Inhibition Certificates & Dedicated Cargo Sample Locker (IBC Code § 15.13, § 16.2 & § 16.5) | Mandatory Certificate of Protection before loading (§ 15.13 & § 16.2.3.6); cell-divided ventilated sample locker (§ 16.5) | Never load a self-reactive or polymerising monomer (e.g., styrene, methyl methacrylate, vinyl acetate, acrylic acid) without the manufacturer’s Certificate of Protection (§ 15.13). Stow retained cargo samples strictly inside the ventilated, cell-divided sample locker in the cargo area (§ 16.5) with a complete disposal log. |
2. MARPOL Annex II: 4-Category NLS System (X, Y, Z, OS), 75-Litre Stripping & Prewash
Under revised MARPOL Annex II (IMO Resolution MEPC.118(52)), every Noxious Liquid Substance is assigned to Category X, Y, Z or OS (Regulation 6). Ships constructed on or after 1 January 2007 must achieve a water-tested stripping efficiency leaving no more than 75 litres of residue in each cargo tank and its associated piping (Regulation 12.4):
| MARPOL Annex II Category / Rule | Stripping & Prewash Mandate | Operational & Cargo Record Book Verification |
|---|---|---|
| Category X — Major Hazard to Marine Resources or Human Health (MARPOL Annex II Reg. 6.1.1 & Reg. 13.6) | Discharge to sea prohibited; mandatory prewash to shore reception facility before leaving unloading port | After unloading a Category X cargo, the tank must undergo a mandatory prewash in accordance with the approved P&A Manual before the ship leaves the unloading port, discharging all prewash washings to a shore reception facility until effluent concentration is ≤ 0.1% by weight (Reg. 13.6.1.1). A Government-authorised surveyor must endorse the Cargo Record Book entry (Reg. 13.6.1.3). |
| Category Y — Hazard to Marine Resources or Human Health (MARPOL Annex II Reg. 6.1.2 & Reg. 13.7) | ≤ 75 L stripping limit (Reg. 12.4); mandatory prewash if High-Viscosity (≥ 50 mPa·s) or Solidifying substance | Non-solidifying, low-viscosity Category Y cargoes stripped to ≤ 75 litres may have tank washings discharged at sea under Reg. 13.2. However, if a Category Y substance is Solidifying (unloaded at < MP + 5°C for MP < 23°C, or < MP + 10°C for MP ≥ 23°C, Reg. 1.15) or High-Viscosity (≥ 50 mPa·s at unloading temperature, Reg. 1.7) — or inside persistent-floater areas (Reg. 13.7.1.4) — a mandatory prewash to shore reception is required before departure. |
| Category Z — Minor Hazard & Other Substances (OS) (MARPOL Annex II Reg. 6.1.3, Reg. 6.1.4 & Reg. 13.2) | ≤ 75 L stripping limit for Cat. Z (ships built ≥ 1 Jan 2007); OS (IBC Ch. 18) outside Annex II discharge restrictions | Category Z residues stripped to ≤ 75 litres may be discharged en route under Reg. 13.2 (ships constructed before 1 Jan 2007 may discharge below the waterline or above waterline if approved). Other Substances (OS) listed in IBC Code Chapter 18 present no harm to marine resources when discharged as bilge or ballast washings. |
| Four En-Route Underwater Discharge Criteria (MARPOL Annex II Reg. 13.2 & Reg. 12.10) | Speed ≥ 7 knots (≥ 4 kn non-self-propelled) · Underwater discharge outlet · ≥ 12 nm from land · Depth ≥ 25 m | Every permitted at-sea discharge of Category X (post-prewash residuals), Y or Z tank washings must simultaneously satisfy all four Reg. 13.2 conditions: (1) ship proceeding en route at ≥ 7 knots; (2) discharged below the waterline through the underwater discharge outlet (Categories X & Y) not exceeding the maximum design rate in the P&A Manual; (3) distance ≥ 12 nautical miles from the nearest land; and (4) water depth ≥ 25 metres (with special restrictions in the Antarctic Area where any NLS discharge is prohibited under Reg. 13.8). |
3. High-Risk Chemical Cargo Traps: Inhibitors (§ 15.13), Compatibility & Sample Lockers (§ 16.5)
During CDI vetting, SIRE 2.0 Chapter 8, and Port State Control inspections on chemical tankers, inspectors focus heavily on five operational records:
- Cargo Compatibility Matrix & Adjacent Stowage (IBC Ch. 16): Verify that the onboard cargo stowage plan checks chemical reactivity across common bulkheads, double-bottom tanks, vent headers, and heating coils using the USCG Chemical Data Guide (CHRIS) or company reactivity matrix. Reactive cargoes must be separated by a cofferdam, void space, pump-room, or tank containing a mutually compatible cargo.
- Inhibited Cargoes & Oxygen Dependence (IBC § 15.13 & § 16.2.3.6): Many inhibitors (such as TBC in styrene monomer or MEHQ in acrylates) require a small dissolved oxygen concentration (typically 5%–8% O2 in the vapour space) to remain active. Inerting such a tank to 0% O2 with pure nitrogen deactivates the inhibitor and risks catastrophic runaway polymerisation — always follow the Certificate of Protection.
- Procedures and Arrangements (P&A) Manual & Prewash Endorsement (MARPOL Annex II Regs. 13 & 14): Every prewash, tank-washing cycle, and en-route discharge must follow the exact washing machine cycle times, nozzle pressures, water temperatures, and underwater outlet rates calculated in the Administration-approved P&A Manual.
- Cargo Sample Locker Inspection (IBC § 16.5): Cargo samples must never be stored in the Chief Officer’s cabin, ship’s office, or paint locker. Check that the dedicated sample storage space inside the cargo area has cell dividers preventing bottle breakage, chemical-resistant shelving, mechanical ventilation, and an up-to-date sample log recording retention dates and safe disposal.
- Deck Decontamination Showers, Eyewash & MFAG Antidotes (IBC Ch. 14): Test deck decontamination showers and eyewash stations before every cargo manifold connection (verifying trace-heating / recirculation loop operation in sub-zero weather under § 14.3.4) and verify that the ship’s hospital holds the exact IMO MFAG (MSC/Circ.857) chemical antidotes for every product currently on board.
Questions seafarers ask
What must be included on an IBC Code Section 15.13 Certificate of Protection (Inhibitor Certificate)?
Under IBC Code § 15.13.3 and § 16.2.3.6 (IMO Resolution MSC.176(79)), cargoes that require an additive to prevent polymerisation, decomposition, oxidation, or self-reaction must be accompanied by a manufacturer’s Certificate of Protection handed to the Master before loading begins. It must state: (1) the name and amount (concentration) of additive present; (2) whether the additive is oxygen-dependent (which dictates whether the tank must be ventilated or inerted/padded with < 8% O2 or low-oxygen gas); (3) the date the additive was put in the product and its duration of effectiveness; (4) any temperature limitations qualifying the additive’s effective lifetime; and (5) the action to be taken should the length of the voyage exceed the effective lifetime of the additive. Under § 16.2.3.6, the Master must refuse to accept the cargo if this certificate is not provided.
When does a Category Y chemical cargo require a mandatory prewash to a shore reception facility under MARPOL Annex II?
Under MARPOL Annex II Regulation 13.7.1.3 and Regulation 13.7.1.4 (IMO Resolution MEPC.118(52) as amended), a Category Y cargo requires a mandatory prewash to a port reception facility before the ship leaves the unloading port whenever: (1) the unloading is not carried out in accordance with the approved P&A Manual (so stripping efficiency to ≤ 75 litres cannot be verified); (2) the cargo is a High-Viscosity Substance (viscosity ≥ 50 mPa·s at the unloading temperature, Reg. 1.7); (3) the cargo is a Solidifying Substance (unloading temperature is less than 5°C above its melting point for substances with MP < 23°C, or less than 10°C above its melting point for substances with MP ≥ 23°C, Reg. 1.15); or (4) the cargo is a high-viscosity or solidifying persistent floater unloaded inside the North-West European waters, Baltic Sea, Western European waters, or Norwegian Sea areas.
What are the MARPOL Annex II Cargo Record Book retention and entry rules?
Under MARPOL Annex II Regulation 15 and Appendix 2 (IMO Resolution MEPC.118(52)), every ship certified to carry Noxious Liquid Substances in bulk must maintain a Cargo Record Book (in hardcopy or as an Administration-approved Electronic Record Book under Res. MEPC.312(74)). Entries must be made on a tank-to-tank basis without delay for loading (Code A), internal transfer (Code B), unloading (Code C), mandatory prewash (Code D — countersigned by the Government surveyor), tank cleaning other than mandatory prewash (Code E), discharge into the sea of tank washings (Code F), ballasting of cargo tanks (Code G), discharge of ballast water from cargo tanks (Code H), and accidental or exceptional discharge (Code I). Each completed operation is signed by the officer in charge, each page is signed by the Master, and the book must be retained on board for 3 years after the last entry (Reg. 15.5).
Why must cargo unloading temperatures and stripping blow-downs be logged on chemical tankers?
During Port State Control and CDI / SIRE 2.0 inspections, the inspector cross-checks the Cargo Record Book (Code C unloading and Code E/F washing/discharge) against the cargo heating log and P&A Manual. If the ship discharged washings of a Category Y cargo (such as palm oil, fatty acids, or phenol) at sea without performing a shore prewash, the ship must prove from contemporaneous manifold/tank temperature records that the unloading temperature stayed strictly above the Solidifying threshold (MP + 5°C or MP + 10°C) and that the viscosity at that temperature was < 50 mPa·s.
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