A.
There were many items that already had a UN number but not shown on the DGR. These were items that were forbidden for air transport and was considered not needed to be shown on the DGR. However, intermodal transport had become more and more common, and it was felt not desirable to have items that are shown on the IMDG (ocean transport) and ADR (road transport) and not reflected in the IATA DGR. Items such as UN1372 Fibres, animal; UN1372 Fibres, vegetable; UN2216 Fish meal/scrap, stabilized; UN1327 Hay, UN3497 Krill meal; UN1856 Rags, oily and others are added to DGR 4.2 List of Dangerous Goods. These are all Forbidden for air transport. These items are generally self-combusting (classified as 4.1 or 4.2) as with fermentation, they gather heat and at a critical temperature they ignite. There was a case where an ocean shipment of crab shell meal from Canada to Japan burst into fire enroute.