BS 5395†2, Stair types:Category A ~
A small private stair for use by a limited number of people who
are generally familiar with the stair. For example, an internal stair
in a dwelling serving one room not being a living room or a
kitchen. Also, an access stair to a small room or equipment room
in an office, shop or factory not for public or general use. Subject
to the provisions of A.D. B, possibly a fire escape for a small
number of people. Typically, 1.300 to 1.800 m overall diameter.Category B ~
Similar to category A, but providing the main access to the upper
floor of a private dwelling. Typically, 1.800 to 2.250 m overall
diameter.Category C ~
A small semi-public stair for use by a limited number of people,
some of whom may be unfamiliar with the stair. Examples include a
stair in a factory, office or shop and a common stair serving more
than one dwelling. Typically, 2.000 to 2.250 m overall diameter.Category D ~
Similar to category C, but for use by larger numbers of people.
Typically, 2.000 to 2.500 m overall diameter.Category E ~
A public stair intended to be used by a large number of people at
one time. For example in a place of public assembly. Typically,
2.500 to 3.500 m overall diameter.Note 1: With regard to means of escape in event of a fire, minimum
widths given may be insufficient. All applications to satisfy the
requirements of Building Regulations, Approved Documents B1 and
B2: Fire safety. This has particular reference to stair clear width
relative to the number of persons likely to use the stair and
protection of the stair well.Note 2: In addition to an outer handrail, an inner handrail should be
provided for categories C, D and E.Spiral Stairs--2