The object in planning x-ray protection for any installation is to reduce the x-ray intensity at all positions where personnel will be stationed to a value such that no one will receive more than 0.1 r during any 24-hour period. No hard and fast rules need be laid down for accomplishing this; the methods to be used are best left to the ingenuity of those making the plans. Almost any space can be made safe against x-rays by the use of lead or concrete walls of sufficient thickness, though in practice such an installation would probably be considered prohibitively expensive, especially when protection against very penetrating radiation is required. The alternative is to consider other methods of protection to be used in addition to radiation barriers. In the interest of economy, full consideration should therefore be given to all three of the following factors: (1) distance from barrier to x-ray source; (2) direction of x-ray beam; (3) radiation barriers.<br />Distance from Barrier to X-Ray Source: The intensity of any beam of x-rays falls off inversely as the square of the distance from the x-ray tube target. This holds true for all x-radiation regardless of its penetrating power. For example, a twofold increase in distance from the tube target results in a fourfold decrease in the x-ray intensity; a tenfold increase in distance reduces the intensity to 1.0 per cent of its initial value. By making the distance from the x-ray source to all operating stations as great as possible, a saving can be effected in the cost of lead sheet, concrete, or lead-glass. Such savings increase rapidly as the penetrating power of the radiation goes up, for then progressively thicker barriers are required to reduce a given beam to, let us say, 1.0 per cent of its initial value. Regardless of what the radiation quality may be, however, the same percentage reduction can be brought about by increasing the distance tenfold.<br />For reasons of economy, first consideration should, therefore, be given to the matter of distance between the x-ray source and all occupied spaces in the immediate vicinity. The x-ray room should be as far removed as conditions will permit from all offices, laboratories, and shops where workers remain throughout the working day. Where occupied rooms must be near the x-ray space, it is good practice to place them on opposite sides of a corridor. Inside the x-ray room, the tube should be placed as far away as possible from all operators, consideration being given to the use for which the radiation is intended and to the space available for the purpose. In neither medical nor industrial x-ray rooms can full advantage be taken of the saving possible through increasing the distance from the x-ray source; it may be necessary to watch a patient during treatment or to palpate a patient during a fluoroscopic examination; in industrial radiography and fluoroscopy within protected cabinets, the presence of nearby operators may be essential<br />