That is going to depend on you local code. Most jurisdictions decide based on the HP of the boiler. I would contact the local boiler inspector - they should know. You can go here for some contact info:
I think that it is important to realize that boilers are really "ancient slow-moving beasts" that do not change dirction quickly. All types will continue to stay hot and generate steam for some time after the fuel supply is stopped (the most common emergency action).
If there is a problem with process steam generated, it can be dumped via a control valve ...but things stay hot.
If your concern is protection of the boiler, you should know that the redundant devices that protect against damage are required by the boiler code and state law
