These alternative arrangements broadly fall into
two groups. Firstly, those people potentially most
at risk from a fire, usually those closest to where
the alarm was activated, will be immediately
evacuated, while others in the premises are
given an alert signal and will only evacuate if
it becomes necessary. This is generally called
a phased evacuation and the initial movement,
depending on the layout and configuration
of the premises, can be either horizontal
or vertical.