Catch-all for substances dangerous in transport but not fitting Classes 1-8 (e.g., asbestos, dry ice, lithium batteries, env. hazardous).
Regulatory detail & full definition
Lithium batteries (UN 3480, 3481, 3090, 3091) are the most-shipped Class 9 today and have driven major rule changes (state of charge limits, packaging tests). Marine pollutant designation (UN 3082, 3077) also Class 9. Common in containers; segregation more relaxed than Classes 1-8.