In many cases it is necessary to remove existing buildings before any actual construction work can be done. The wrecking of a building appears to the casual observer to be a simple and easy task, but it nevertheless calls for experience and skill, because there are many dangers connected with it, even when the structure to be demolished is quite small; and in the case of a large structure these hazards are multiplied many times.

The prevailing tendency toward specialization in industrial and other operations has extended to demolition work, so that we now find, in many of the larger cities at all events, contracting firms which have developed organizations for handling this particular work, and have devised methods for carrying it out in a highly efficient and expeditious manner. When the services of such an organization are available it is usually economical to employ them, and the probabilities of accidents should also be reduced, as a result of the experience of the men in charge of the operations.

Whether or not demolition work is done by specialists, every such job should be supervised by a person of sound judgment, who should also be capable of handling the working force competently and effectively. The men should be selected, so far as possible, with reference to their capabilities, and each should be assigned to the particular kind of work for which he appears to be best fitted.

2. Planning The Work

Before beginning the actual work of demolition, a careful study should be made of the structure that is to be torn down, and of its surroundings; and a definite plan of procedure should be mapped out, which should thereafter be followed as closely as possible. This is specially important when haste is essential, because the work can be executed much more rapidly and safely when it proceeds in accordance with a definite scheme than when it is carried out in a haphazard manner. In formulating the plan it is necessary to consider the security of adjoining buildings, and to make adequate provision for their safety.

3. Shoring Adjoining Buildings

Extensive shoring of other buildings is often imperative, and full provision should be made for carrying out all necessary operations of this kind promptly and thoroughly, and in a safe and workmanlike way. As a rule, however, the demolition work, when done by a firm which specializes in these operations, is considered completed when the building has been razed to the sidewalk level, and such shoring operations as may be necessary in removing or altering the foundations are performed by some other contractor. The precautions to be taken in connection with work below the sidewalk level are therefore more properly included in the section describing excavation work. (See paragraph 14.) Occasionally, however, the removal of a building weakens the side walls of the structures immediately adjoining it, and to prevent possible damage in such a case, the demolition contractor may use some of the floor beams of the wrecked building to prop up these walls, until such time as permanent protection can be provided.

Furthermore, if a structure has been partially wrecked by a fire, flood, explosion, or other catastrophe, it may be necessary to shore up or brace some of the walls of the building that is to be taken down, before the wrecking operations can be safely started. A condition of this kind calls for special consideration.

4. Gas And Electricity

Make sure, at the very outset, that the gas pipes have been disconnected, and that all electric wires in the building are "dead".

Fig. 1. Flood Beams from a Demolished Building Joined Together and Used for Strengthening the Walls of Adjoining Buildings.

If a strong odor of gas is subsequently perceived, stop the work until the source of the gas has been discovered, and do not allow the men to look for it with lanterns nor with open lights of any other kind.

5. Order Of Procedure

The demolition work should always proceed systematically, story by story; and the work on the upper floors should be entirely completed before any of the supporting members or other important parts on the lower floors are disturbed. By proceeding in this orderly manner it is easy to eliminate various dangerous conditions, such as weak and unsupported walls and chimneys, towering above the workmen.