[Illustration: FIG. 1]
=7. The Enclosed Stairway.=—The important consideration in the planning
of factory stairways is to provide a quick, easy, and safe egress for
the occupants in case of fire. While it is necessary to have good
liberal stairways for communication between the floors, this is not
such an important feature in factory design, from the fact that there
is little travel of employes between the floors, in a modern factory,
as each individual’s work is usually apportioned to him and confined
to a particular location, and therefore does not require him to be on
different floors during the day.
The common type of factory stairway is that designated in Fig. 1. This
shows a brick-enclosed stairway with the doors entering it direct from
the factory. Such a stairway enclosure as this should have tin-lined
doors as at _a_, which fireproof the opening. Even then the security of
a stairway of this character is not certain, from the fact that these
doors may be left open, and are open to the stairway during the egress
of the occupants. With a severe fire, therefore, on any floor, such a
stairway is likely to be filled with smoke to suffocation, and liable
to ignition from the door openings. It can therefore only be regarded
as a makeshift for a fire-escape, or fire-tower. It is also well, in
the design of such a stairway, to observe that the doors always open
outwards, and not only this, but that they open with the tide of people
coming down the stairs. For instance, in the figure the door _a_ is
opened correctly, but if the flights of steps marked _down_ and _up_
were transposed, then people coming down the flight _c_ would press
against the door at _a_ and prevent the people in the room _d_ from
getting out to the stairs and hence to safety.
[Illustration: FIG. 2]
=8. Enclosed Fire-Escape, or Stair Towers.=—Various designs for
brick-enclosed stairways of factory buildings have been recommended at
different times by the insurance companies. Two of these designs are
designated in Fig. 2 and show the elevator included, as well as the
stairway, in the tower.
A study of these plans will show that there is no direct communication
from the building to the stair tower, and that the only way by which
the stair tower may be entered is through an open balcony, which
communicates with a door in the side walls of the building, at each
floor. The brick-enclosed stair tower is shown in the figure at _a_,
the open galleries at _b_, and the door of egress from the factory at
_c_. By means of this arrangement, the occupants of each floor can,
in case of fire, go through the door in the side wall, on to the open
balcony, and into the fire-tower, thence down stairs or elevator to the
ground floor and safety. Because of the openness of the balcony, which
is surrounded with a strong rail, and partially covered by the gallery
above, the fire could hardly be sufficiently great on any floor to make
it untenantable, and no smoke or flames could communicate with the
fire-tower.
[Illustration: FIG. 3]
=9. Vestibule Fire-Tower Stairway.=—While the arrangement just
described is rational, the fire-tower is of such dimensions as would
ordinarily preclude its use in the modern building where ground space
is valuable and every inch of surface must be economized.
The best possible design, therefore, for a fire-tower is that indicated
in Fig. 3. This construction is known as the =vestibule fire-tower=,
and from the plan it is seen that this combines safety and utility
in a small amount of space. The opening marked _a_ in the plan is
always open to the weather, and the floor of the vestibule is usually
concreted and graded to a drain that connects with the rain conductor
of the roof at _b_. By this arrangement, a well-protected line of
travel is obtained between the stairway and the buildings on each
floor, the occupants of the building being protected by the parapet
wall and iron railing, as indicated at _c c_. To this vestibule from
the factory a tin-lined, or fireproof, door must be provided, so
that after the people have left one floor it can be cut off from the
vestibule.
In the construction of all fire-towers, their walls must be carried by
means of parapet walls at least 3 feet above the roof of the building,
and the roof over them must be constructed of fireproof material.
When it is required, fireproof windows may be used in the walls of
brick-enclosed fire-towers. These windows may be constructed of sheet
metal and glazed with wire glass. If it is not possible to use such
windows, a skylight may be built over the top of the tower, but this
skylight must be constructed of sheet metal, or other non-combustible
material, and glazed with wire glass.
=10. Number of Fire-Towers.=—The number of tower fire-escapes required
for factory buildings of either the first, second, or third class,
may be established according to the number of stories in height of
the building, and the floor area, in square feet, for each floor;
that is, for buildings of the first class, three or four stories in
height, having one tower, the floor area of any floor may be as much
as 20,000 square feet, while if the height of the building of the same
construction is made twelve stories, the floor area should only be
6,500 square feet.
Where two tower fire-escapes are incorporated in the plan, a building
three or four stories in height may contain as many as 25,000 square
feet in the area of one floor, but if the building were increased to
twelve stories, the floor area of each floor should not exceed 15,000
square feet.
In buildings of the second and third classes, a greater number of tower
fire-escapes should be provided, and it is good practice to supply one
tower fire-escape in a three-story building of these classes for a
floor area not exceeding 10,000 square feet, or two tower fire-escapes
should the floor area not exceed 15,000 square feet. In buildings of
this construction, of from four to six stories in height, the floor
area should not exceed, for one tower fire-escape, from 6,000 to
3,500 square feet of floor area in each floor, while with two tower
fire-escapes the maximum floor area is from 12,000 to 8,000 square feet.
=11. Location of the Fire-Tower.=—Where two tower fire-escapes are used
in a building, they must not be located near to each other, the purpose
always being to provide a second egress in case of one being cut off by
smoke or flame.
In small buildings of considerable height, it is sometimes difficult
to so arrange the plan as to provide two stairways at extreme ends
or corners of the building. In a case like this, it is frequently
necessary to extend balconies along the side of the building, entering
the fire-tower at some more distant point.