Control of lighting should be flexible. Conveniently located, separate switches or dimmers should be installed for areas with different types of activities. It should be easy to extinguish lights for areas that are not occupied and to maintain minimal emergency lighting, for safety. Where feasible, daylighting should be used, supplemented, as needed, with artificial lighting. Light from windows can be reflected deeply into rooms, with venetian blinds, glass block, or other architectural elements. Glare and solar heat can be limited with blinds, shades, screens, or low-transmission glass. Provision should be made for decreasing or extinguishing supplementary artificial lighting when there is adequate daylight. Consideration should be given to use of photoelectric-cell sensors with dimmers for control of the artificial lighting. Maximum use of daylighting and other energy conservation measures are often essential, not only to meet the owners construction budget but also to satisfy the energy budget, or limitations on power consumption, set by building codes or state or federal agencies. Enhancing the functions performed by the power and lighting systems, the special systems in a building serve the life safety, communication, and security needs of a facility and its occupants. 15.19.1 Lightning Protection The design of lightning protection systems should conform with the standards of the American National Standards Institute, the National Fire Protection Association (Bulletin No. 780, Lightning Protection Code) and Underwriters Laboratories (Standard UL96A Master-Labeled Lightning Protection Systems). In deciding whether to provide a building lightning protection system, designers should first perform a risk assessment in accordance with NFPA 780, Lightning Protection Code. This evaluates such factors as building height, terrain, building construction, proximity to other buildings, type of occupancy, and isoceraunic level (frequency of thunderstorms). If the risk assessment warrants, a lightning protection system is designed. Protection for a building may be accomplished by several methods. An installation recognized by NFPA and UL consists of lightning rods or air terminals placed around the perimeter of the roof and on vertical projections, such as chimneys and the ridge of a peaked roof. These air terminals are bonded together and to a copper or aluminum conductor that extends down to a good electrical ground. There are also two less conventional types of installation that can be used. One involves the use of an air terminal containing a low-level radioactive source that produces a stream of ionized particles. This creates a low-resistance path that draws a lightning stroke to the air terminal, where it can be safely discharged to ground. The other type uses thousands of small air terminals spread along the high points of a structure to constantly dissipate any electrical charge in the air before it can build up high enough to induce a lightning stroke. The electrical wiring in a building is especially susceptible to the effects of a lightning stroke. To minimize these effects, a multilevel protective approach is used. Lightning arresters, which are connected from the phase wires to ground, are provided on the utility company lines and at the various voltage levels down to utilization voltage. Usually of the metallic oxide varistor (MOV) type, the arresters present a very high resistance to ground at normal system voltage, but quickly collapse to zero resistance during a lightning discharge, dissipating the discharge

type Description Comments Organic soil, highly plastic soil Low strength and high compressibility Sensitive clay Potentially large strength loss upon large straining Micaceous soil Potentially high compressibility Soil Expansive clay, silt, or slag Potentially large expansion upon wetting Liquefiable soil Complete strength loss and high deformations caused by earthquakes Collapsible soil Potentially large deformations upon wetting Pyritic soil Potentially large expansion upon oxidation Laminated rock Low strength when loaded parallel to bedding Expansive shale Potentially large expansion upon wetting; degrades readily upon exposure to air and water Pyritic shale Expands upon exposure to air and water Rock Soluble rock Rock such as limestone, limerock, and gypsum that is soluble in flowing and standing water Cretaceous shale Indicator of potentially corrosive groundwater Weak claystone Low strength and readily degradable upon exposure to air and water Gneiss and schist Highly distorted with irregular weathering profiles and steep discontinuities Subsidence Typical in areas of underground mining or high groundwater extraction Sinkholes Areas underlain by carbonate rock (Karst

4. Slightly Organic Soils. These soils typically have less than 5% organic matter. Per the Unified Soil Classification System, they have a ratio of liquid limit (ovendried soil) divided by liquid limit (not dried soil) that is greater than 0.75. Often a modifier, such as slightly organic soil, is used to indicate the presence of organic matter. Also included in Table 6.10 is the typical range of laboratory test results for the four major divisions of organic material. Note in Table 6.10 that the water content (w) increases and the total unit weight (t) decreases as the organic content increases. The specific gravity (G) includes the organic matter, hence the low values for highly organic material. The compression index (Cc) is discussed in Art. 6.5.6. Other Descriptive Terminology. In addition to the classification of a soil, other items should also be included in the field or laboratory description of a soil, such as: 1. Soil Color. Usually the standard primary color (red, orange, yellow, etc.) of the