Minimum air gap A, in Away from a wall* Close to a wall* Lavatories with effective openings not greater than 1/2-in diameter 1.0 1.50 Sink, laundry trays, and goose neck bath faucets with effective openings not greater than 3/4-in diameter 1.5 2.25 Overrim bath fillers with effective openings not greater than 1-in diameter 2.0 3.00 Drinking fountains with a single orifice not more than 7/16 in in diameter or multiple orifices with a total area of 0.150 in2 (area of a 7/16-in-diameter circle) 1.0 1.5 Effective openings greater than 1-in * Side walls, ribs, or similar obstructions do not affect the air gaps when spaced from inside edge of spout opening a distance c greater than three times the diameter of the effective opening for a single wall, or a distance greater than four times the diameter of the effective opening for two intersecting walls (see figure). Vertical walls, ribs, or similar obstructions extending from the water surface to or above the horizontal plane of the spout opening require a greater air gap when spaced closer to the nearest inside edge of spout opening than specified in note* above. 2
effective opening. 3
effective opening. when the basic fixture is a lavatory served by as 11/4-in trap, the average flow during discharge is 7.5 gal /min. So a bathtub that discharges 15 gal /min is rated as two fixture units (2
7.5). Thus, a tabulation of fixture units can be set up, based on an assumed basic unit. A specific number of fixture units, as listed in Table 14.4, is assigned to each type of plumbing fixture. These values take into account: Anticipated rate of water flow from the fixture outlet, gal /min Average duration of flow, min, when the fixture is used Frequency with which the fixture is likely to be used The ratings in fixture units listed in Table 14.4 represent the relative loading of a water-distribution system by the different types of plumbing fixtures. The sum of the ratings for any part or all of a system is a measure of the load the combination of fixtures would impose if all were operating. The probable maximum water demand, gal /min, can be determined from the total number of fixture units served by any part of a system by use of graphs shown in Fig. 14.4. The demand obtained from these curves applies to fixtures that are used intermittently. If the system serves fixtures, such as air-conditioning units, lawn sprinklers, or hose bibs, that are used continuously, the demand of these fixtures should be added to the intermittent demand. For a continuous or semicontinuous flow into a drainage system, such as from a pump, pump ejector, air-conditioning system, or similar device, two fixture units should be used for each gallon per minute of flow. When additional fixtures are to be installed in the future, pipe and drain sizes should be based on the ultimate load, not on the present load. The required domestic-water pipe sizes should be determined by application of the principles of hydraulics. While economy dictates use of the smallest sizes of pipe permitted by building-code requirements, other factors often make larger sizes advisable. These factors include: 1. Pressure at the water-supply source, usually the public main, psi 2. Pressure required at the outlets of each fixture, psi 3. Loss of pressure because of height of outlets above the source, pressure loss due to friction caused by the flow of water through water meters and backflow preventers, and friction from water flow in the piping 4. Limitations on velocity of water flow, ft / s, to prevent noise and erosion 5. Additional capacity for future expansion (normally 10% minimum) 14.9.1 Method for Determining Pipe Sizes 1. Sketch all the proposed risers, horizontal mains, and branch lines, indicating the number and the type of fixtures served, together with the required flow 2. Compute the demand weights of the fixtures, in fixture units, using Table 14.4 3. From Fig. 14.4 and the total number of fixture units, determine the water demand,

Adhesives used for bonding wallboard may be classified as stud, laminating, or contact or modified contact. Stud adhesives are used to attach wallboard to wood or steel framing or furring. They should conform with ASTM C557. They should be applied to supporting members in continuous, or nearly so, beads. Laminating adhesives are used to bond gypsumboards to each other, or to suitable masonry or concrete surfaces. They are generally supplied in powder form, and water is added on the site. Only as much adhesive should be mixed at one time as can be applied within the period specified by the manufacturer. The adhesive may be spread over the entire area to be bonded, or in parallel beads or a pattern of large spots, as recommended by the manufacturer. Supplemental fasteners or temporary support should be provided the face boards until sufficient bond has been developed. Contact adhesives are used to laminate gypsumboards to each other, or to attach wallboard to metal framing or furring. A thin, uniform coat of adhesive should be applied to both surfaces to be joined. After a short drying time, the face board should be applied to the base layer and tapped with a rubber mallet, to ensure overall adhesion. Once contact has been made, it may not be feasible to move or adjust the boards being bonded. Modified contact adhesives, however, permit adjustments, often for periods of up to 1/2 hr after contact. Also, they generally are formulated with greater bridging ability than contact adhesives. Modified adhesives may be used for bonding wallboard to all kinds of supporting construction. See also Arts. 11.26.2 to 11.26.4 and 11.27. 11.26.2 Single-Ply Gypsumboard Construction A single-ply system consists of one layer of wallboard attached to framing, furring, masonry, or concrete (Fig. 11.23). This type of system is usually used for residential construction and where fire-rating and sound-control requirements are not stringent. Maximum spacing of supports should not exceed the limits specified in Table 11.10. Nail Attachment. Spacing of nails generally is determined by requirements for fire resistance and for firmness of contact between wallboard and framing necessary to avoid surface defects. Spacing normally used depends on whether single nailing or double nailing is selected. Double nailing provides tighter contact, but requires more nails. In either method, one row of nails is driven along each support crossed by a board or on which a board end or edge rests. The spacing applies to the centerto- center distance between nails in each row. In the single-nailing method, nails should be spaced not more than 7 in apart for ceilings and 8 in apart for walls (Fig. 11.25). In the double-nailing method, pairs of nails are driven 12 in c to c, except at edges or ends, in a special sequence (Fig. 11.26). First, one nail of each pair is placed, starting at the middle of the board and then proceeding toward edges and ends. Next, the second nail is driven 2 in from the first. Finally, the first set of nails placed should be given an extra hammer blow to reseat them firmly. Single-nailing spacing should be used for edges or ends at supports. FIGURE 11.25 Wallboard attached to wood framing with single nailing. FIGURE 11.26 Wallboard attached to wood framing with double nailing. Starting at the middle of the board, one person nails rows 1 to 4, and a second person. rows 2A to 4A (solid dots). Then, again starting at the middle of the board, they drive the second set of nails (open dots). Finally, they reset the first set of nails with a blow on each nail. Screw Attachment. Fewer screws than nails are needed for attachment of wallboard. With wood framing, Type W screws should be spaced 12 in c to c for ceilings. Spacing should not exceed 16 in for studs 16 in c to c, or 12 in for studs 24 in c to c. With metal framing, spacing of Type S screws should not exceed 12 in for walls or ceilings. Adhesive Nail-on Attachment. With this method, at least 50% fewer nails are required in the middle of the wallboard than with conventional nailing. Also, a stiffer assembly results. The first step is to apply stud adhesive to framing or furring in beads about 1/4 in in diameter. Each bead should contain enough adhesive so that it will spread to an average width of 1 in and thickness of 1/16 in when wallboard is pressed against it, but there should not be so much adhesive that it will squeeze out at joints. If joints are to be treated, an undulating or zigzag bead should be applied to supports under joints. If joints are to be untreated, as is likely to be the case for predecorated wallboards, two parallel beads should be applied near each edge of the framing. Along other supports a single, continuous, straight bead is adequate. Adhesive, however, should not be applied to members, such as diagonal bracing, blocking, and plates, not required for wallboard support. The number and spacing of supplemental fasteners needed with adhesives depend on adhesive properties. Stud adhesives generally require only perimeter fasteners for walls. One fastener should be driven wherever each edge or end crosses a stud. For edges or ends bearing on studs, fasteners should be spaced 16 in c to c. The same perimeter fastening should be used for ceilings, but in addition, fasteners should be spaced 24 in c to c along all framing crossed by the wallboard. Where perimeter fasteners cannot be used, for example, with predecorated wallboard for which joint treatment is unnecessary or undesirable, prebowing or temporary bracing should be used to keep the wallboard pressed against the framing until the adhesive develops full strength. Bracing should be left in place for at least 24 hr. Prebowing bends in wallboard so that the finish side faces the center of curvature. The arc is employed to keep the board in tight contact with the adhesive as the board is pressed into place starting at one end. 11.26.3 Multi-Ply Gypsumboard Construction A multi-ply system consists of two or more layers of gypsumboard attached to framing, furring, masonry, or concrete. This type of system has better fire resistance and sound control than can be achieved with single-ply systems, principally because of greater thickness, but also because better insulation can be used for the base

Dry chemicals are effective on surface fires, especially on flammable liquids. When used on Class A fires, they do not penetrate into the burning material. So when a fire involves porous or loosely packed material, water is used as a backup. The major effect of dry chemicals is due almost entirely to ability to break the chain reaction of combustion. A minor effect of smothering is obtained on Class A fires. Fires that are likely to rekindle are not effectively controlled by dry chemicals. When these chemicals are applied to machinery or equipment at high temperatures, caking can cause some difficulty in cleaning up after the fire. Dry chemicals can be discharged in local applications by hand-held extinguishers, wheeled portable equipment, or nozzles on hose lines. These chemicals can also be used for extinguishing fires by total flooding, when they are distributed through a piped system with special discharge nozzles. The expellant gas is usually dry nitrogen. Dry powder extinguishing agents are powders effective in putting out combustible- metal fires. There is no universal extinguisher that can be used on all fires involving combustible metals. Such fires should never be fought by untrained personnel. There are several proprietary agents effective on several metals, but none should be used without proper attention to the manufacturers instructions and the specific metal involved. For requirements affecting handling and processing of combustible metals, reference should be made to National Fire Protection Association standards NFPA 48 and 652 for magnesium, NFPA 481 for titanium, NFPA 482M for zirconium, and NFPA 65 and 651 for aluminum. (The SFPE Handbook of Fire Protection Engineering, and Automatic Sprinkler Systems Handbook, National Fire Protection Association, Quincy, Mass.) 3.5.8 Fire Detection Every fire-extinguishing activity must start with detection. To assist in this, many types of automatic detectors are available, with a wide range of sensitivity. Also, a variety of operations can be performed by the detection system. It can initiate an alarm, local or remote, visual or audible; notify a central station; actuate an extinguishing system; start or stop fans or processes, or perform any other operation capable of automatic control. There are five general types of detectors, each employing a different physical means of operation. The types are designated fixed-temperature, rate-of-rise, photoelectric, combustion-products, and ultraviolet or infrared detectors. A wide variety of detectors has been tested and reported on by Underwriters Laboratories, Inc. See Art. 3.5.1. Fixed-Temperature Detectors. In its approval of any detection device, UL specifies the maximum distance between detectors to be used for area coverage. This spacing should not be used without competent judgment. In arriving at the permitted spacing for any device, UL judges the response time in comparison with that of automatic sprinkler heads spaced at 10-ft intervals. Thus, if a device is more sensitive than a sprinkler head, the permitted spacing is increased until the response times are nearly equal. If greater sensitivity is desired, the spacing must be reduced. With fixed-temperature devices, there is a thermal lag between the time the ambient temperature reaches rated temperature and the device itself reaches that temperature. For thermostats having a rating of 135
F, the ambient temperature can