In its design, a mill for any standard line of manufacture is not a
building whose arrangements and proportions are fixed upon at the whim
of the owner, but it must conform to certain conditions of dimensions,
stability, light and application of power to satisfy the requirements
essential for furnishing every advantage necessary for producing the
desired results at the lowest cost.
The destructive consequences attending fire in such buildings, whose
iron and masonry construction is called fireproof, show that some other
form of construction is necessary to obtain the desired results of
minimizing the annual cost of the maintenance of the invested capital,
as represented by insurance, depreciation, interest and taxation. There
is little incentive for entering into unusual expenses in the
construction of a manufacturing building for the purpose of increasing
its resistance to fire, unless the additional interest on such increase
in the investment is to be met by a corresponding reduction in the
annual cost of the fire-hazard. In addition to these questions,
involving the annual maintenance of the plant, the increase in the
expense of the building above a certain point may prove poor management,
by locking up capital for too long a time, and may tend to prevent the
improvements in arrangement and construction which are necessary for the
most advantageous manufacturing.
The method of mill building known as slow-burning construction combines
the advantages of low initial cost and great resistance to destruction
by fire, the final result being that the manufacturing is housed at the
minimum annual cost. The fundamental principle of such construction is
to mass the material in such a way that there shall not be any concealed
spaces about the structure, and that the number of projections of
timbers, which are more easily ignited than the flat surfaces, shall be
reduced as far as possible; that iron portions of the structure shall
not be exposed to the heat of any fire in the contents of the building,
and furthermore, that the isolation of the various portions, both in
respect to that of one building to another and of the various rooms and
stories of the same building, shall be as complete as is feasible.
The most important feature is that of the mill floors, which should be
laid on beams, generally of Southern pine, 12 x 14 inches, or two inches
larger when required by unusual loads or longer span than twenty-two
feet. These beams are placed from eight to ten feet apart between
centres.
At the columns, beams rest on cast-iron caps.
The support from one column to the next should be made by cast-iron
pintles, preferably those whose section is in the form of a Greek cross,
as that presents advantages in the way of securely joining them to the
timber beams. At the top of the pintle, a cast-iron plate should support
the base of the column above.
Timber columns are preferred to those of iron, unless the load is
greater than can be sustained by timber.
The floor planks for this type of floor are generally made of spruce
plank from three to four inches in thickness, grooved on both edges and
joined together by hardwood splines. These floor-planks should be two
bays in length, breaking joints at least every four feet.
Above this the top floor, of 1-1/4 or 1-1/2 inch hardwood, is laid, and
in some instances the resistance of the floor to fire is greatly
increased by laying a coat of plaster on the floor-plank before the top
flooring is built. But the general method of increasing the resistance
of the floor to fire is by covering the floor and beams on the under
side with plaster laid on wire-lathing.
Such a mill floor and columns, while possessing in a very high degree
features which offer resistance to the fire, being weakened by the
temperature only to a slight extent as they are slowly burned away under
the exposure to a very severe fire, also possess the merit of great
economy, both as regards the low price of construction, and in that the
floor is thinner in comparison with joisted floors of equal strength,
saving in this respect, for every floor in a building, about ten inches
in height of wall, stairs, belting, steam-pipes, and all vertical
connections reaching from floor to floor, a saving which amounts to
considerable in the total cost of a building.
The division of mills into various portions by means of fire-walls is
frequently not so efficient as assumed, by reason of the lack of
fire-doors to satisfactorily fulfil the purpose of resisting fire. The
best form of fire-door is that made of two thicknesses of matched
boards, placed at right angles to each other and nailed together, being
covered on the outside with tin, securely locked together and held to
the door by numerous hanging-strips. The door should be secured to the
hangers by means of bolts, and not screws, and the rail upon which it
runs strongly bolted to the wall. When closed, such a door should fit
into a jamb and be securely held in this manner against the wall. Such
doors are frequently hung upon an inclined track, and, by some
application of highly fusible solder at the catch, are so arranged that
they will be closed by the heat of a fire, if not closed by hand.
In this treatment of the arrangement of buildings to resist fire,
consideration has not been given to the cost of land, which is, of
itself, an important factor in determining what arrangement will be the
most expedient for an establishment. Where land is expensive, or there
are limitations in the space suitable for building, it is frequently
necessary to build mills and shops higher than would be warranted by
good judgment under other conditions; but where circumstances will
permit it, the one-story mill has been very successful, not merely in
immunity from fire, and very low cost per square foot of floor, but also
in the advantages of manufacturing, particularly in regard to cost of
supervision and movement of the stock in process of manufacture. These
are questions which must be determined, not merely in regard to the
various processes of manufacture, but the individual needs of each
concern; the position of the fire-risk in the matter being that the
hazard of a building increases very rapidly with its height, and to some
extent with its area.
The extension of one-story buildings over too large an area will not be
commended, and certainly, as regards the question of fire, it has a
tendency to place too large a property in direct exposure to a very wide
hazard.
Some textile mills have been built in the form of the block letter U,
this form having been decided upon as giving the conditions of lowest
resultant cost. One wing, two stories in height, contains weaving; the
other wing, three stories in height, contains carding and spinning,
while the engine is placed in the connecting building. The pickers and
the boilers are in outside buildings, so placed that they will not
interfere with future extensions of the building into the form of the
block letter H.