IMSBC MHB Classification Criteria
IMSBC section 9.2.3 in full: the seven MHB codes, the UN Manual of Tests and Criteria methods behind them, and the OH residual category.
Materials hazardous only in bulk is the classification the IMSBC Code applies to a Group B cargo whose hazard arises from carriage in bulk rather than from the substance being a dangerous good in packaged form. The table at section 9.2.3.1.5 gives seven codes: CB combustible solids, SH self-heating solids, WF solids that evolve flammable gas when wet, WT solids that evolve toxic gas when wet, TX toxic solids, CR corrosive solids and OH other hazards.
The full article will set out the criteria at 9.2.3.2 to 9.2.3.7 code by code, together with the UN Manual of Tests and Criteria procedures each turns on, so that a reader can see why a given cargo carries the codes it does rather than taking the assignment on trust.
It will also cover the OH category at 9.2.3.1.4, which is residual and captures hazards the other six do not describe, and which is why wood pellets carry OH despite self-heating and why an MHB set can combine several codes with and/or.