（Please explain the difference between Primary Hazard and Subsidiary Hazard. ）
Q.
When a certain dangerous goods has a multiple hazard, we are to determine the “Primary Hazard” and the “Subsidiary Hazard”. Kindly explain the criteria to determine which is the “Primary” and which is the “Subsidiary” hazard. For instance, why is an Oxygen bottle have RNG as Primary and ROX as Subsidiary Hazard. Does more mass determine that it is Primary? Or, other hazard produced by added external action (e.g. heat or other external means) are to be determined as Subsidiary Hazard? Kindly advise. (28 Feb 21)
A.
The definition of “Primary Hazard” and “Subsidiary Hazard” is as written, word by word. “Primary Hazard” is the “Predominant Hazard” and “Subsidiary Hazard” is the “Other Accompanying or Co-existing hazard”. For instance, UN1072 Oxygen, compressed as well as UN1007 Air, refrigerated liquid have Division 2.2 Non-Flammable Non-Toxic Gas (RNG) as “Primary Predominant Hazard” and Division 5.1 Oxydizer (ROX) as “Co-existing Subsidiary Hazard”. Mixtures have multiple hazards. Multiple hazards are not necessarily the fruit of added external causes.
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