When a fire is said to be “under control”, it means it’s no longer spreading and is currently contained. It does not mean that the fire is out yet. This is just one evaluation, or size-up, that can be made of a fire. Once it’s under control, that’s when they would move on to overhaul operations.
Some other stages a fire may be in during size-up include:
Incipient Stage: This is the beginning of a fire. It’s still small and may simply be put out with a handheld extinguisher.
“Smoke Showing”: Maybe not an “official” size-up term, but this means smoke can be seen from outside the structure. The fire may still be small, but it’s likely on the way to growing into more.
Working Fire: This has moved past the incipient stage and may be considered a “real fire”. It is considered “working” when it’s in the process of being suppressed. It will probably not be able to be put out by a single fire company. Instead, departments that are usually part of a pre-planned mutual aid may be called in, either to bring more engines or trucks, or to stand by in case they are needed.
Well Involved/Fully Involved: Fire, heat, and smoke are so wide-spread that interior access may be delayed until fire streams can be applied.