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I know the title used to be HAZID, but I though I would babble on about HAZOPs.
So, what do you need for HAZOPs? At a minimum, the P&IDs. Layouts might be useful. If you want to bring in design basis data, be my guest, though what usually happens is that the consultant process engineer or delegate retrieves the data from their offices during the breaks.
You need to prepare blank HAZOP sheets that will be filled up as the review continues. Wait, that’s old school. Nowadays you have a scribe who types out whatever the review team churns out. For a greenhorn, this is a stressful job. Apart from having your mistakes broadcast for all to see, you have to keep up with what the team says, understand technical terms, and sometimes perform editing as the review goes on. If the scribe has a strong personality, they might just take over from the official facilitator.
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Wata - Malaysian Oil and Gas Engineer 
How a HAZOP is run largely depends on how strong the personalities of the three parties involved (similar to a wrestling match) ie the attacker (client), the defender (consultant) and the referee( facilitator). A strong attacker means, that defender gets body slammed, and are left with 10000 action items to incorporate into the design in 2 days. A strong defender means no matter how crap or unoperable the design is, it will still be built and the close out action are done by the attacker. A weak referee normally results in a free for all where everyone rips the design and does whatever they want