Hi mrkjd
Why not take the specific legislation out of the equation?
You shouldn't really be THAT bothered about whether activity X is subject to DSEAR or not, but rather assess the risks and mitigate them "so far as reasonably practicable".
If you do that assessment and activity X is subject to DSEAR you can comply with the requirements of DSEAR without even mentioning the acronym!
Nothing in DSEAR says that the risk assessment has to be entitled "DSEAR assessment" so why not simply refer to it as "Risk Assessment for whatever scope you define"?
So, the risk assessment(s) for activity X could be a single assessment that considers ALL the risks of activity X or a fire and explosion risk assessment (and thence DSEAR assessment) for activity X or a fire and explosion risk assessment for activity X within a wider context or various other options.
John Elder raises the broader issue of scope.
Clients don't like "scope creep" as it has a tendency to have risk of budgets going out of the window and so need control mechanisms.
Some Consultants/Contractors operate on the basis that scope creep is what makes the difference between breaking even and making a healthy profit, partly as when scope creep happens the Consultant/Contractor already appointed is likely to be an a bidding list of one for any "additional works".
I wrote "Some" not "All" and I am certainly not suggesting that John might be amongst the "Some".
I do think that it makes sense to broaden the scope of an initial DSEAR or whatever assessment so that the assessor looks at the broader picture of what is around EACH activity X.
But the potential for "scope creep" can be managed by splitting the assessment into parts. An initial sweep, a report on a scoping study and then the Client has the choice to ask the Consultant/Contractor to now make proposals for such further work as the Client deems appropriate having received the scoping study report or the Client has the choice to now go out to tender.
It might well be that the scoping study report poses questions about whether the competencies of the Consultant/Contractor are sufficient for what is needed for part or all of what is needed next.
As example the scoping survey might indicate that a need a fire suppression system for areas A, B and C, which might be entirely separate or interlinked systems. The Client may not need their initial "DSEAR or whatever" assessor for this, but rather a Contractor who can do a bespoke design and installation, possibly with a separate contract for someone to do the contract administration to oversee that the fire suppression Contractor does what it has said on the tin.
Might be that the Client ALSO needs more detailed "DSEAR or whatever" assessment of other areas which might be procured in parallel with the fire suppression system(s).
Horses for courses.