Within Class 1 (Explosives), which division represents a mass explosion hazard — meaning virtually the entire load explodes at once — with dynamite given as the example?

AAMVA CDL Manual, Section 9.3.1, Figure 9.1 (nhcdm.pdf p. 9-2); 49 CFR 173.50

The six explosives divisions (1.1-1.6) represent a scale from most to least severe detonation risk, and placarding/segregation rules differ by division. A driver who can't tell a 1.1 mass-explosion load from a 1.4 minor-explosion load can't make correct loading or emergency-response decisions.