Clause 18 exists to allow the minister to designate another person to do the same thing the minister himself does. What is very important to understand here is that the powers under clause 17 are very serious. I cannot emphasize that more.
They're very serious because they allow the minister, through his own decision, to order a series of very significant things in terms of “do this, do that”, and it's aimed to be done on a very urgent basis only. In other words, the power of the minister under clause 17 is circumscribed to very urgent matters.
The idea of why we need to authorize a person other than the minister is simply that the minister may not be reachable. But the fundamental principle is that this power would be used, or exercised if you want, primarily by the minister to start with, and only under very exceptional circumstances would somebody other than the minister do it.
With all due respect, I don't believe the power found in clause 17 can be delegated to the chief of a fire department or anything of that sort. Cooperation will be required from perhaps the local police or the local services, but I don't believe the power in question here should be delegated to anybody other than someone who is very close to the minister, given the seriousness of what is being done and the related accountability that must come with it.