To limit the probability that an insufficient run
in a curved flight will not provide adequate support for users' feet,
which could lead to:
- persons falling during normal use -- when traffic flow
is likely to be lower than for exit stairs during an emergency and
users are likely to have the option of using the wider portion of
the treads, or
- persons falling in an emergency -- when traffic flow
is expected to be limited because of the presence of exit stairs as
an alternate or the limited occupancy in a dwelling unit, and users
are likely to have the option of using the wider portion of the treads
-- which could lead to delays in the evacuation or movement of persons
to a safe place, which could lead to harm to persons.
This is to limit the probability of
harm to persons.