Depends on who the chair is and what their role is. Ideally the chair should be someone who can get things done (Head of Operations etc). It should never be the H&S person.  If the meeting is not quorate then I’d postpone the meeting rather then have some non-entity running it as it then just becomes a talking shop and there is no point in having that. If this is happening routinely then you need to look at management commitment to H&S.    

You don't say if it's a unionised or non-unionised context which does affect some of the consultation requirements and practices.  However, in either case it is possible to change the TOR, although I suggest this would best be agreed by the committee itself rather than being unilaterally changed.  So I'd put it to them as a proposal (preferably when quorate!) and with the agreement of the union if unionised.