Material identification, physical hazards and compatibility
A dangerous-goods transport decision begins with the actual material and its reliable transport information. A familiar commercial name, an attractive package or the absence of a strong smell does not establish classification. Distinguish the material identity, transport description, principal and subsidiary hazards, quantity and condition before assessing the proposed movement.
A classification is not a complete operating plan
The Chinese framework points to the applicable dangerous-goods road-transport rules and relevant special provisions. International model concepts help explain technical language but are not automatically a Chinese operating permission. Use the current applicable entry and requirements rather than assume an older GB edition, an overseas placard or a remembered exception controls every shipment.
A principal hazard does not erase subsidiary hazards. A material may be both toxic and flammable; a gas may threaten life through oxygen displacement even if it is not combustible. A corrosive label does not mean that two corrosive products are compatible. Evaluate the actual substances and relevant compatibility information rather than grouping everything with the same broad class into one harmless load.
Interpret physical properties carefully
Volatility concerns how readily a substance enters the vapor phase; flash point and ignition sources concern a different part of the fire problem. A low flash point does not mean ignition is impossible below it in every real process or mixture. An oxidizer can intensify combustion without serving as the ordinary fuel. A water-reactive material requires its own response information, not a universal instruction to add water because the incident is hot.
Density information also needs context. A heavier-than-air vapor may accumulate in low places, but wind, temperature, confinement and the release itself affect the actual cloud. Do not enter a depression or confined space because a distant observer cannot smell anything. A simple density comparison is a recognition exercise, not a prediction of a guaranteed safe boundary.
Read supplied data as supplied data
In a worked exercise, a stated concentration, permitted temperature or compatibility table is an explicit input. Apply its units and conditions, and state the conclusion supported by that information. Do not convert a hypothetical number into a current national limit. Missing identity, conflicting documentation or an abnormal package condition requires resolution through the actual responsible process rather than a guessed classification or unauthorized test.