UN 3358 applies to refrigerating machines and refrigerating-machine components that contain flammable, non-toxic liquefied gases classified under Class 2.1, when shipped under the International Maritime Dangerous Goods (IMDG) Code. While the UN number and class exist, these shipments are subject to a specific exemption when the conditions of IMDG Special Provision (SP) 291 are fully met.
Scope of the Special Provision
IMDG Special Provision 291 recognizes that certain refrigerating machines pose a very low risk during transport when properly designed and constructed. Under SP291, flammable liquefied gases must be fully contained within pressure retaining components of the refrigerating machine. These components must be designed and tested to at least three times the normal working pressure and constructed in a way that prevents bursting or cracking under normal conditions of transport.
This exemption only applies, when the refrigerating machine or component contains less than 12 kg of gas, it is not subject to the provisions of the IMDG Code.
Regulatory Effect of the Exemption
When all requirements of SP291 are satisfied:
- An IMO Dangerous Goods Declaration is not required
- Dangerous goods marks, labels, and placards are not required
- The shipment is treated as non-DG for IMDG compliance purposes, despite being associated with UN 3358 and Class 2.1
This exemption significantly simplifies documentation and handling, provided that the technical conditions of SP291 are met and verifiable.
Industry Best Practices
Although exempt from IMDG documentation and marking requirements, it is strongly advised that freight forwarders, NVOCCs, and shippers proactively notify the ocean carrier at the time of booking that the cargo consists of refrigerating machines shipped under the SP291 exemption.
Early disclosure helps:
- Avoid booking delays or rejections
- Prevent misclassification during carrier DG screening
- Ensure alignment with carrier-specific policies, which may still require acknowledgment of exempted dangerous goods
Shippers should retain technical documentation confirming compliance with SP291 (e.g., gas type, gas quantity, and design pressure) and make it available upon request. Transparency with carriers and logistics partners remains essential, even when the IMDG Code formally exempts the shipment.
If you have any questions about this special provision or any other ones, please reach out to DGM for further guidance. DGM also provides comprehensive hazardous material training classes that include how to correctly understand special provisions.