Catch-all for substances dangerous in transport but not fitting Classes 1-8 (e.g., asbestos, dry ice, lithium batteries, env. hazardous).
In practice
Class 9 'miscellaneous dangerous substances' covers lithium batteries (UN3480/3481), magnetic substances, environmentally hazardous substances, and many specific UN numbers. Lithium-battery fires on container ships are an industry-wide concern; carriers tighten declaration audits.
Regulatory detail & full definition
IMDG Class 9 is the catch-all classification for miscellaneous dangerous substances and articles that present a transport hazard but do not fall within Classes 1 to 8 - for example asbestos, dry ice, environmentally hazardous substances and lithium batteries. Lithium batteries (UN 3480, 3481, 3090, 3091) are the most-shipped Class 9 goods today and have driven major rule changes such as state-of-charge limits and tougher packaging tests. Marine pollutants (UN 3077, 3082) are also Class 9; segregation is generally more relaxed than for Classes 1 to 8.