What is the maximum amount of any SINGLE class of hazardous material that may be carried on a bus, even when that material is otherwise allowed?

AAMVA CDL Manual, Section 4.2.2, p. 4-2

The 100-pound per-class cap exists alongside the 500-pound total cap to prevent any single type of hazardous material from concentrating in dangerous quantities near passengers, even while the load stays under the overall weight limit.