At the enquiry into the Cripplegate fire of 1897, Mr. Hatchett Smith, F.R.I.B.A., declared that the well-holes or lighting-areas in the warehouses involved, were a source of danger as constructed, and he recommended that such lighting-areas should be confined by party walls, and sealed with rolled plate-glass or pavement-lights. Windows facing the street should be glazed with double sashes, and external walls should be built with a hollow space of about two inches between them and their plastering, with an automatic water-sprinkler at the top of the hollow space. Such a plan of construction would, he contended, confine the fire to the apartment in which it originated, though it would not extinguish the fire in that room. The flooring Mr. Smith seemed to take for granted would be of concrete and fireproof.
Among other fire precautions, the introduction of the electric light in place of gas may operate as a valuable precautionary measure, especially in theatres and public places; while a strong iron curtain, to be quickly dropped down between the stage and the auditorium, is also a most valuable precaution.
But all such measures may be largely neutralized by the inflammable contents of the buildings. Some manufactures are remarkably dangerous in this respect, and the extensive storage of certain goods renders even spontaneous combustion probable. Thus, if a well-built fireproof structure contain large quantities of combustible materials, and these burn furiously, the heat evolved may be so great as to conquer almost everything in the building. Indeed, the heat in huge fires is sufficient to melt iron.
Nevertheless, the liability to fire and its destructiveness is much decreased by wise precautionary measures in building, the idea underlying them being that walls, floorings, doors, or what not should be so made as to localize the fire to the apartment in which it originated.
As with buildings, so with clothing. Here is a piece of muslin. Light it: it will not flame; it slowly smoulders. But even as the problem of building completely fireproof structures has not been solved, so also the question of fireproof fabrics has not been completely answered.
Progress, however, has been made in that direction. Methods have been adopted whereby the flaming of fabrics can be prevented, and their burning reduced to smouldering.
A solution of tungstate of soda is, perhaps, one of the best chemicals to use for this purpose, for it is believed not to injure the fibre; but for articles of clothing, borax is better suited, as it does not injure the appearance of the clothes, and it is very effectual in its operation, though it weakens the fibre. Alum, common salt, and sulphate of soda will also diminish or entirely prevent flaming; but they tend to weaken the fibre.
A simple experiment illustrates the principle. Any boy who has made fireworks, or dabbled in chemistry, knows that paper—one of the most inflammable of substances—after being soaked in a solution of saltpetre, will not flame, but smoulders quickly at the touch of fire; hence the name touch-paper, which is used to ignite fireworks.
Some of these salts, then, prevent the fabric from flaming, and also reduce the burning to slow smouldering, the explanation being apparently this,—when the fabric is dipped in solutions of certain salts, tiny crystals are deposited among the fibres on drying, and the inflammability is diminished; but the effect of the salt upon the fabric has to be considered, and some, such as sulphate of ammonia, will decompose when the goods are ironed with a hot iron.