Q.How do we know the ship we are going to join is safe ?

If you joining a ship then you must be having its name/ship particulars. From that find out other data from web like history, cassification society and previous names if any.

If classed by recoganized classification society then that will be safe. We can have n number of other things to check and many exception but basically ship in class is safe.

One important check is knowing the flag of the vessel. Vessel with flag from FOC can be red flag and then you can start to check who are the managers and check from the PSC databases if that vessel has any past history of dentions or deficiencies.