It is especially important that nobody smoke near what class of hazard?

A Smoking is not permitted near any of these.

explanation

When loading or unloading hazardous materials, keep fire away. Do not let people smoke nearby. Never smoke around:
- Class 1- Explosives
- Division 2.1 - Flammable Gas
- Class 3 - Flammable liquids
- Class 4 - Flammable Solids
- Class 5 - Oxidizers