It starts with the client approaching the shipping line for hazardous cargo acceptance.. Most lines have their specific templates for the haz cargo request.. Here is the “generic” format of the hazardous cargo request.. Client is required to fill up ALL fields in this sheet and send to the shipping line.. 
The shipping line (who normally have a specialised haz desk or haz cargo centre) will check if all the information provided is correct.. Assuming that all the info provided is right, they will then check the status of the vessel that is nominated to carry this haz cargo.. 
Usually each vessel has a fixed quota of how many and what type of haz cargoes can be carried on board.. This varies from ship to ship, line to line, port to port and depends also on the cargo that is already on board..
If the haz desk then ascertains that this nominated ship can carry this type of hazardous cargoes, it will give the go ahead to the export desk/client that the haz cargo is acceptable..
Only after this is done, the haz booking can be made firm and client will be given the container release.. So to all the shippers and forwarders out there, if a shipping line says that it cant carry the haz on a specific vsl but confirms to carry on the next vsl, this is the reason.. Each ship is different in terms of stowage and carrying capacities.. 
Once the container is packed according to the haz specifications, the container is moved to the container terminal within the stack period as usual.. A Haz CTO needs to be passed for all haz containers moving into the ports.. This is for the port to identify that this container is a hazardous container and provide the required special stow within the port area for the same.. Client must also affix the CORRECT haz labels on all 4 sides of the container WITHOUT FAIL.. Port will NOT accept any haz container into the port without the labels..
Concurrent with the movement of the haz container, the haz packing declaration (also known as Dangerous Goods Packing Certificate, Packing Declaration) must also be filled up by the client and sent to the shipping line.. As with the haz cargo request, each line has its own template of haz packing declaration.. Here is the “generic” format of hazardous packing declaration.. 
This haz packing declaration is a VERY VERY IMPORTANT document both for the ship and the shipping line, the client and the ports, specially when it comes to the various types of hazardous cargoes being handled.. 
The shipper must take due care and diligence while filling up the same as misdeclaration of the same has serious consequences on the lives of many of the people in the port, ship and transporters who handle this container along its route from Point A to Point B.. All the fields in this declaration play a vital role and none of it must be excluded for the benefit of all concerned..
One copy of this hazardous packing declaration is always available on board the ship.. The shipping line also submits a separate hazardous cargo manifest detailing ALL hazardous cargoes that are on board each of which will have its own hazardous packing declaration.. 
The shipping line personnel also verify that the details provided in the haz packing declaration is the same as the details provided at the time of haz cargo acceptance.. 
We can summarise the process as below :

  • haz cargo acceptance sent to shipping line
  • shipping line authenticates the same
  • shipping line checks haz space on the vessel
  • shipping line confirms acceptance
  • client packs the container and affixes the correct haz labels
  • haz cto is passed and container goes into the port/terminal
  • client fills up the haz packing declaration and gives a copy to the shipping line
  • shipping line provides the haz packing declaration to the ship along with haz cargo manifest