Meet with the contractor to view their existing H&S Management System and site specific H&S Plan. Be aware they may not have one, in which case they should be asked to prepare one and submit it to you as soon as possible.
Actively enquire as to what arrangements they have in place and then form a view about whether or not their system and plan are satisfactory. If you don't think that is the case, discuss the amendments you may require, or seek specialist advice.