Every single apartment I've lived in in Stockholm has had a single stairwell, and it's not something I've ever thought about because no-one thinks of it as an issue. But on the other hand, those stairwells are always concrete and stone and marble, and fire regulations forbid you from storing anything in the stairwells or outside your apartment.
Take my current Stockholm apartment, there's a four-storey drop from the balcony to the ground and a single stairwell, which would apparently horrify every North American.
But the walls are concrete. The walls between apartments are concrete or drywall. There's four apartments per landing. The apartment doors are made of steel. And the stairwell is empty and marbled, so there's nothing that can burn in the stairwell, and it's very difficult for fire to spread from one apartment to the others. There's no sprinkler system, but I think there's a fire extinguisher on each landing.
Not a problem.