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ISO 27991:2025 — CO2 Marine Transport: Measurement, Emergency Response and Documentation
Supplemental Requirements for CO2 Shipping Operations
1. Scope and Relationship to ISO 27971
ISO 27991:2025 supplements ISO 27971 with additional requirements for CO2 ship transport specifically addressing measurement and verification of cargo quantity and quality, emergency response planning, personnel competency, and documentation requirements. While ISO 27971 covers vessel design and operational procedures, ISO 27991 focuses on the transactional and regulatory aspects of CO2 marine transport, including custody transfer metering, sampling protocols, and reporting formats for CCS accounting purposes.
The standard is particularly relevant for CCS projects where CO2 is shipped across national boundaries or where the transfer of CO2 between multiple parties creates requirements for accurate quantity and quality determination. It aligns with the broader ISO 27914 (CO2 storage) and ISO 27919 (CO2 enhanced oil recovery) standards to create a complete CCS value chain framework.
ISO 27991 fills a critical gap in CCS standardization by addressing the commercial and regulatory interface of CO2 shipping. As cross-border CO2 transport increases, standardized custody transfer procedures become essential for carbon accounting and regulatory compliance.
2. Custody Transfer Measurement
ISO 27991 specifies comprehensive requirements for custody transfer metering of CO2 during ship loading and unloading operations. The standard requires that all CO2 transfers be measured using custody-grade metering systems with maximum permissible error (MPE) of +/- 0.25% for quantity and compliance with ISO 10790 for Coriolis flow meters. Metering systems must be calibrated at actual operating conditions (pressure, temperature, CO2 composition) rather than water-calibrated, as CO2’s compressibility and density characteristics differ significantly from water at typical shipping conditions.
For CO2 quality determination, the standard specifies sampling frequency (minimum one sample per cargo tank per loading operation), analytical methods (gas chromatography for composition, Karl Fischer titration for water, and specific methods for trace impurities). Quality shall be verified both at loading and unloading to establish a complete quality chain of custody.
| Parameter | Measurement Method | Maximum Permissible Error | Sampling Frequency |
|---|---|---|---|
| CO2 quantity | Coriolis flow meter + DCS | +/- 0.25% | Continuous |
| CO2 purity | Gas chromatography | +/- 0.5 mol% | Per cargo tank |
| Water content | Karl Fischer / CRDS | +/- 5 ppmv | Per cargo tank |
| Temperature | PT100 / RTD | +/- 0.2 C | Continuous |
| Pressure | Pressure transmitter | +/- 0.1% of span | Continuous |
Accurate custody transfer measurement protects all parties in the CCS value chain. A 0.25% measurement error on a 20,000-tonne CO2 shipment represents 50 tonnes of CO2, equivalent to approximately $2,500-5,000 at current carbon pricing levels.
3. Emergency Response and Personnel Competence
The standard requires detailed emergency response plans specific to CO2 marine transport, addressing CO2 release scenarios including cargo tank rupture, piping failure, overpressure events, and collisions. Emergency plans must include gas dispersion modeling results, exclusion zone definitions, evacuation procedures, and coordination with port authorities and national maritime rescue services. Regular drills (at least every 6 months) are mandatory, with scenarios covering both onboard and ashore response.
Personnel competency requirements include specific training on CO2 properties and hazards, cargo system operation, emergency procedures, and first aid for CO2 exposure. The standard defines three levels of competency: basic CO2 awareness (all crew), CO2 cargo operations (deck officers and engineers), and CO2 emergency response (designated emergency team members). Certification under the STCW convention with additional CO2-specific endorsements is recommended.
Unlike LNG or LPG, CO2 has specific physiological hazards that require specialized training. CO2 concentrations above 10% cause unconsciousness within minutes, and above 20% cause immediate collapse. Emergency responders must use self-contained breathing apparatus for all CO2 release scenarios.
4. Documentation and Regulatory Compliance
ISO 27991 specifies documentation requirements including cargo manifests, shipping documents, quantity and quality certificates, calibration records, and incident reports. For cross-border CO2 transport, the standard requires compliance with applicable international maritime regulations (IMO MARPOL, SOLAS) and national CO2 transport regulations. The cargo manifest must include CO2 composition, quantity, origin, destination, and intended use (storage vs. utilization).
For CCS accounting under international frameworks (e.g., EU ETS, Article 6 of the Paris Agreement), the standard specifies minimum reporting requirements to ensure that CO2 shipped across boundaries can be properly accounted for and attributed to the correct emission source and storage site. This includes chain-of-custody documentation with digital signatures and timestamping.
Incomplete documentation of CO2 shipments can result in regulatory non-compliance and financial penalties under emissions trading schemes. The standard requires that all documentation be retained for a minimum of 10 years and be available for audit by regulatory authorities on request.
5. Frequently Asked Questions
Q: How does ISO 27991 differ from ISO 27971?
ISO 27971 covers vessel design and operational procedures for CO2 ship transport. ISO 27991 supplements this with custody transfer metering, quality verification, emergency response planning, personnel competency, and documentation requirements.
ISO 27971 covers vessel design and operational procedures for CO2 ship transport. ISO 27991 supplements this with custody transfer metering, quality verification, emergency response planning, personnel competency, and documentation requirements.
Q: What measurement accuracy is required for CO2 custody transfer?
Coriolis flow meters with maximum permissible error of +/- 0.25% are required. Meters must be calibrated at actual CO2 process conditions, not water-calibrated.
Coriolis flow meters with maximum permissible error of +/- 0.25% are required. Meters must be calibrated at actual CO2 process conditions, not water-calibrated.
Q: Is ISO 27991 applicable for cross-border CO2 shipping?
Yes, this is a primary application. The standard specifically addresses international CO2 transport with requirements for chain-of-custody documentation and compliance with international maritime regulations.
Yes, this is a primary application. The standard specifically addresses international CO2 transport with requirements for chain-of-custody documentation and compliance with international maritime regulations.
Q: What are the key CO2 hazards addressed in the standard?
Acute toxicity (CO2 asphyxiation), low-temperature freeze burns from refrigerated CO2, high-pressure hazards, and dry ice formation during operations. Each hazard has specific mitigation requirements.
Acute toxicity (CO2 asphyxiation), low-temperature freeze burns from refrigerated CO2, high-pressure hazards, and dry ice formation during operations. Each hazard has specific mitigation requirements.
