Building systems for_interior designers phần 9 pdf

In high-rise buildings and buildings with large areas, there are places that can’t be reached by firefighters’ lad- ders and hoses. While most fire deaths occur in smaller, often residential buildings, larger commercial, indus- trial, and institutional buildings create a potential for many deaths and injuries from a single fire. High-rise buildings require an inordinate length of time to evac- uate. Stack effects can be created in high-rise buildings over 23 meters (75 ft) tall. Such buildings must have their own firefighting system. This is usually an auto- matic sprinkler system. Everybody knows that water will put out a fire. Water cools, smothers, emulsifies, and dilutes the fire. But it also damages building contents, and can conduct elec- tricity when used as a stream (less so as a spray). Water will not put out burning oil; the flammable oils will float and burn on the surface. When water hits a hot fire, the steam can harm firefighters. Despite these disadvantages, water remains one of the main ways to suppress a fire. The earliest sprinkler system consisted of a bucket of water suspended over the likely location of a fire by a black powder fuse. When a fire lighted the fuse, it blew up a powder keg and dispersed water, theoretically in the direction of the fire. Automatic sprinkler systems extinguish incipient fires before they have a chance to get out of control. The sprinkler system (Fig. 45-1) consists of a network of pipes in or below the ceiling. The pipes are connected to a water supply and have valves or sprinkler heads that are made to open automatically at a certain tempera- ture. Each sprinkler head is controlled by a plug or link of fusible metal that melts at a temperature of around 66°C (150°F). Sprinkler heads are so efficient that one to two heads can usually put out a fire. Building codes commonly allow sprinklered build- ings to have greater distances between exits, eliminating one or more stairways in a large building. By allowing larger floor areas between fire separations, some fire- resistant walls and doors may be eliminated. Buildings may be allowed to have greater overall areas and heights. Some structural elements may need less fire protection, and the building may be able to contain greater amounts of combustible building materials. Fire insurance rates are much lower for sprinklered buildings. Most fire underwriters refuse to insure a high- hazard building with no sprinkler system. However, in- surance rates may increase if water damage is a big risk. OCCUPANCY HAZARD CLASSIFICATIONS Building codes classify various occupancies according to fire hazard. These classifications are used to determine the design of sprinkler systems. 45 Chapter Fire Suppression 360 The light hazard classification is used for build- ings where it is relatively easy to provide effective fire protection. The quantity and combustibility of the building’s contents is considered to be low, and a low rate of heat release is expected from possible fires. Light hazard occupancies include apartments, audito- riums, churches, hospitals, hotels, libraries, museums, nursing homes, office buildings, restaurants, schools, and theaters. A light hazard occupancy is required to have one sprinkler head per 18.6 square meters (200 square ft), with a maximum of 4.6 meters (15 ft) be- tween supply lines and between the heads on each line. The sprinklers don’t have to be staggered along their lines. Ordinary hazard occupancies are considered to have moderate to high quantities of combustible materials, where the level of combustibility is relatively low to high. A moderate to high rate of heat release is expected. The materials may cause rapid fire development. Auto- motive garages, bakeries, laundries, and machine shops are considered ordinary hazards, as are manufacturing facilities, paper mills, print and publishing establish- ments, warehouses, and other industrial properties. Or- dinary hazard occupancies require one sprinkler per 12 square meters (130 square ft) where there is a non- combustible ceiling, and one sprinkler per 11 square me- ters (120 square ft) for combustible ceilings. The max- imum distance between lines and between sprinkler heads on a line is 4.6 meters (15 ft). Sprinklers are re- quired to be staggered if the distance between heads ex- ceeds 3.7 meters (12 ft). The quantity and combustibility of materials in extra hazard (severe) occupancies are both very high. Rapid fire development and high heat release rates are expected where volatile flammable materials are processed, stored, mixed, or dispensed. Extra hazard occupancies include aircraft hangers, chemical works, explosive plants, linoleum manufacturing plants, paint shops, and shade cloth manufacturers. One sprinkler head is required every 8.4 square meters (90 square ft) with a noncombustible ceiling, and every 7.4 square meters (80 square ft) with a combustible ceiling. Sprinkler lines and heads must be no more than 3.7 meters (12 ft) apart, and heads must be staggered if they are more than 2.4 meters (8 ft) apart. Generally, sprinkler systems are required for Factory, Hazardous, and Storage occupancies, or where large groups of people are present, as in Assembly, Institu- tional, and large Mercantile and Residential occupan- cies. The requirements are based on the number of oc- cupants, the mobility of the occupants, and the types of hazards present. Sprinkler systems are also commonly used in base- ments, windowless buildings, and high-rises. Sprinklers are often found in furnace and boiler rooms, at incin- erator, trash, and laundry collection areas, and at the tops of chutes. They are required in kitchen exhaust sys- tems and at spray painting shops or booths. Sprinklers are used in vertical openings, duct systems that exhaust hazardous materials, drying rooms, and atriums. Residences generally don’t have a water supply ad- equate for a standard sprinkler system. Toxic gases and smoke fill small residential rooms quickly, so a rapid response is essential for life safety. Many codes now re- quire fast-response sprinklers with tested ability to en- hance survival in the room where the fire originates in all residential occupancies. Such sprinklers are listed for protection of dwelling units. They are sensitive to both smoldering and rapidly developing fires, and open quickly to fight a fire with one or two heads. Most codes exempt residential bathrooms under 5.1 square meters (55 square ft), closets with a minimum dimension of less than 91 cm (3 ft), open porches, garages and carports, and uninhabited attics and crawl spaces not used for storage. Entrance foyers that are not a sole means of egress are also exempted. Residences use a special water distribution pattern, with water sprayed to walls and high enough to prevent the fire from getting above the sprinklers. They cool the gases at the ceiling level, so that fewer sprinklers need to open. The cost of residential sprinkler systems can be recovered through reduced fire insurance rates, but there is a long payback time. Fire Suppression 361 W a te r m a i n Si a mese c o nnecti o n f o r fire department W a ter fl o w initi a tes a l a r m M a in sh u t o f f Reserve water t a n k F irst floor sprinklers Second floor sprinklers S p rinkler h ead Figure 45-1 Sprinkler system. DESIGNING FIRE SUPPRESSION SYSTEMS The plumbing engineer or a sprinkler system specialist usually details the requirements for spacing sprinklers and references the appropriate codes. The design of the system considers the degree of hazard to the occupants. The maximum floor areas per head are set by hazard level. The areas covered by various types of sprinkler heads determine their approximate locations. Heads are located to detect fire readily and to discharge water over the greatest area. The sprinkler system designer consid- ers obstacles such as joists, beams, and partial height partitions. The design of the hydraulic piping that sup- plies the sprinklers is a complex process. The interior designer should work closely with the sprinkler system designer to verify sprinkler head loca- tions and provide adequate clearance at each sprinkler. Typically, a minimum of 46 cm (18 in.) must be left open below the sprinkler head deflector. The interior designer should be especially observant of this require- ment where wall cabinets or shelving are used, as in storage rooms, kitchens, and libraries. SPRINKLER SYSTEM COMPONENTS Sprinkler systems are designed to start to put out the fire and to send out an alarm simultaneously. When water flows through a sprinkler head, an alarm gong goes off outside the building. The gong alerts people outside the building to the fire, and allows the occu- pants to make additional firefighting arrangements to minimize loss and to speed the end of the fire. Turning off sprinklers as soon as possible prevents water dam- age. The alarm is often connected to a private regional supervisory office that calls the municipal fire depart- ment. All public buildings and some other buildings are required to have a fire detection and alarm system with an indicator of the location of the fire in the custodian’s office. Sprinkler systems need an adequate water supply, and standby power for water pumping. Siamese con- nections (Fig. 45-2) allow fire engines to pump water into the system from outside the building. They are in- stalled close to the ground on the exterior of a building and provide two or more connections through which the fire department can pump water to a standpipe or sprinkler system. Tall buildings may have elevated water storage tanks that can help supply water for sprinklers. Sprinkler systems require very large supply pipes, valves, and fire pumps. The valves are used to shut the system off for maintenance, system modification, or re- placement of heads that have operated after a fire. An improperly closed valve is the major reason for sprin- kler system failure. Fire pumps provide required water 362 FIRE SAFETY Ted’s client wanted to add a direct entrance from the street to his new retail store. The site, however, was a historic building, and the Landmark Commission in- sisted that the new door exactly mirror the appearance and location of the existing door to the building on the opposite end of the facade. This posed a problem be- cause a big brass Siamese sprinkler system connection was located right in front of the proposed new door. The placement of the door was critical to the interior design of the store, and Ted needed to have the prob- lem settled before he could finish his design. Once the contractor got into the building, he dis- covered that the piping for the sprinkler connection was tight against a granite foundation wall. The con- nection could be moved off to one side, but not com- pletely out of the way. By moving the connection as far to the side as possible, and by widening the door’s framing detail, Ted and the contractor were able to in- stall the new door where it would work from the in- side, while still being acceptable to the Landmark Commission on the outside. The result looks like it has always been there. Figure 45-2 Siamese connection. pressure in a standpipe or sprinkler system when the pressure in the system drops below a preselected value. Many code authorities will accept combining sprin- kler piping with the heating and cooling system, heat recovery system, hot and chilled water thermal storage system, or solar energy system, permitting construction cost savings. Sprinkler Heads The sprinkler head keeps the water in the system by a plug or cap held tightly against the orifice (opening) by levers or other restraining devices. The levers are held in place by the arms of the sprinkler body. In the past, the restraining device was usually a fusible metal link that melted at a predetermined temperature. More recently, a glass bulb with colored liquid and an air bubble is used. Heat expands the liquid, which compresses the air bubble until it is absorbed. Expansion continues with rising temperature until the bulb bursts at a predeter- mined temperature and releases water in a solid stream through the orifice. The deflector on the sprinkler head converts the solid stream to a spray. It is more efficient to direct the spray down and horizontally rather than up, for better water distribution near the head and more effective cov- erage below. Sprinkler head types include upright heads that sit on top of exposed supply piping (Fig. 45-3), and pen- dant heads that hang below the piping (Fig. 45-4). Side- wall sprinklers (Fig. 45-5) are usually located adjacent to one wall of smaller rooms, as in hotels or apartments, and throw a spray of water across the room, allowing an entire small room to be covered by one sprinkler head. Pendant heads may be recessed, with part of the sprinkler body concealed above suspended ceilings and the deflector below the ceiling. Flush heads have only the heat-detecting element below the ceiling. Concealed heads are entirely above the ceiling, with a cover plate that falls away in a fire. Sprinkler head finishes are avail- able in plain or polished brass, satin or polished chrome, stainless steel, and gold. The manufacturer may be able to coat ornamental pendants to match a desired decor, but sprinkler heads are never permitted to be field coated. The air around a standard sprinkler may reach around 538°C (1000°F) before the standard 175°F-rated sprinkler opens, causing a lag time. Quick-response sprinkler heads are now required throughout light haz- ard occupancies, including office buildings, motels, and Fire Suppression 363 Figure 45-4 Pendant sprinkler head. Figure 45-5 Sidewall sprinkler head. Figure 45-3 Upright sprinkler head. hotels. They are more thermally sensitive and open sooner than older styles, and are able to fight a fire with fewer open heads, causing less water damage. The quick- response sprinklers track air temperature rise. The ear- lier operation is considered to offer superior life pro- tection. They may, however, open for extraordinary heat that is not fire related. Early suppression fast-response (ESFR) sprinklers are used for specific challenging fire hazards, for exam- ple where storage is piled high. The sprinkler’s higher pressure and flow penetrate the fire’s base faster. Quick- response, early suppression (QRES) sprinklers are sim- ilar to ESFR sprinklers, but with a smaller orifice for light-hazard occupancies. They are expected to be avail- able soon for business, retail, public assembly, and ed- ucational applications. Extended coverage sprinklers are used for unob- structed construction with flat smooth ceilings and no projecting lighting fixtures or grilles. Extra-large orifice sprinkler heads emit large quantities of water where water pressures are low. Multilevel sprinklers use sprin- klers at lower levels in a space that has other sprinklers at a higher level. Normally, the lower sprinklers would be inhibited by the action of the higher sprinklers. Flow control sprinklers close automatically when ceiling temperatures are reduced, saving water and damage. A new development is a single head that may provide mul- tiple types of sprays. Larger droplets penetrate the fire while a finer spray cools ceilings. Sprinkler System Piping The most common and simplest piping system for sprin- klers is a wet-pipe system. Wet-pipe systems contain water at a sufficient pressure to provide immediate, continuous discharge through the sprinkler heads that open auto- matically in the event of a fire. They are used in spaces with air temperatures above 4°C (40°F). The affected sprinklers are opened by sensitive elements in the heads and immediately emit water. Wet-pipe systems must be drained in order to change the location of a sprinkler head, adding expense and inconvenience to the project. A dry-pipe system contains pressurized air or nitro- gen that is released when a sprinkler head opens, al- lowing water to flow through the piping and out the opened nozzle. Dry-pipe systems are used in unheated areas where wet-pipe systems might freeze, such as load- ing docks, cold-storage areas, and unoccupied buildings. Dry-pipe systems require compressed air, a heated main control valve housing, and pitched piping to allow drainage after use. A preaction system is a dry-pipe system with air in the pipes, with water flow controlled by a valve oper- ated by separate heat or smoke detection devices more sensitive than the ones in the sprinkler heads. The pre- action valve holds water back until heat or smoke opens it, sounding an alarm and filling the pipes with water. Preaction systems are used where building contents are sensitive to water damage. The early alarm allows the fire to be extinguished manually without using the sprinklers in computer rooms, retail stores, and muse- ums. The delay can allow the fire to grow rapidly, how- ever, by as much as 30 percent within 60 seconds, thus requiring 30 percent more water to extinguish it. A deluge system uses open sprinklers on dry pipes. When a heat and smoke detection system opens the del- uge valve, the system floods with water and all heads emit water. This releases a huge quantity of water. Del- uge systems are used for areas with a risk of extremely rapid fire spread, like aircraft hangers and places where flammable liquids are stored or used. A circulating closed-loop system is a wet-pipe sys- tem with larger sprinkler piping. The system circulates water for the heating, ventilating, and air-conditioning (HVAC) water heat pumps. Temperatures must stay be- tween 49°C (120°F) and 4°C (40°F). Sprinkler System Damage Control The space with sprinklers should have adequate water drainage during and after the fire. When fire hoses and sprinklers overshoot the fire area, the building and its contents sustain water damage even where there is no fire. The water drains to lower building levels, so floor drains should be provided to safely carry this water away from the building. Provisions for drainage of water can include scup- pers in exterior walls, which are less likely to clog than floor drains. Scuppers should have hoods to control birds and insects. Salvage covers can protect sensitive objects and direct water toward drainage points. A read- ily accessible outside valve that controls all the normal sources of supply to the system can cut off water promptly when it is no longer needed. STANDPIPES AND HOSES Standpipes are water pipes that extend vertically through the building to supply fire hoses (Fig. 45-6) at every floor. Wet standpipes contain water under pressure and 364 FIRE SAFETY are fitted with fire hoses for emergency use by building occupants. Dry standpipes do not contain water, but are used by the fire department to connect fire hoses to a fire hydrant or pumper truck. Separate water reserves, upfeed pumping, or fire de- partment connections feed standpipes. They provide emergency firefighting before the fire department arrives, and are also used for full-scale firefighting. The water supply can be turned on automatically or manually. OTHER FIRE SUPPRESSION SYSTEMS For buildings where water would cause irreparable dam- age to the building contents, expensive systems are avail- able that discharge an inert gas or powder over the flames. These systems are used in libraries, museums, and art galleries. Commercial kitchens use dry chemical systems for grease fires. The exhaust plenum and duct system be- comes grease coated and the kitchen’s high operating temperatures create a fire hazard. A flash fire in a cook- ing appliance can ignite grease in the duct. A dry chem- ical system with a sodium bicarbonate base is sprayed into the plenum chamber and ducts, extinguishing the fire in seconds. The system automatically cuts the sup- ply of heat to the stove or appliance, whether it is gas or electric. Grease fires can distort a duct, allowing grease to spill into concealed spaces in walls and ceilings. As a result, fire suppression nozzles are located in hoods over cooking areas and in ducts. Systems that don’t use water are available for elec- tronic data storage areas, paint dip tanks and spray booths, petroleum storage, securities vaults, and trans- former rooms. These systems use carbon dioxide, halon, high-expansion foam, or dry chemicals. Mist systems have been used for shipboard fires in the past, and are now being considered for other uses as well. A mist system allows a faster initiation of the alarm and a quicker response to the fire than a sprinkler sys- tem. By using smaller volumes of water, they reduce damage. The mist poses no safety threat to firefighters and allows more building ventilation during the fire. It eliminates residues from clean-agent gases such as halon. The system doesn’t have to be refilled with expensive gases, and can be returned to service more quickly after use. Mist system heads are spaced more closely together and are more sensitive to heat than sprinkler heads. They operate by heat extraction and oxygen displacement and block radiant heat. Intumescent materials, which expand rapidly when touched by fire, create air pockets to insulate the surface from the fire, or swell material to block openings through which fire and smoke could travel. Intumescent paints, caulks, and putties are available, as are 6-mm ( ᎏ 1 4 ᎏ -in.) thick sheets with a variety of facing materials. FIRE SUPPRESSION AGENTS We have already mentioned some of the fire suppres- sion agents that are used in these various suppression systems. Here is some more information on the subject. Halon Halogenated hydrocarbons, commonly known as halons, are flame-extinguishing gases that are stored as liquids. Until the mid 1990s, the most common was Halon 1301, which provided lightweight, space-saving fire suppression for commercial aircraft, computer rooms, museums, li- braries, telephone exchanges, and kitchens. Halon 1301 extinguishes fire without leaving a residue to damage electronic components. Because it doesn’t displace oxy- gen, it causes little harm to people. Fire Suppression 365 Figure 45-6 Standpipe system hose rack. Halon 1301 is now known to be a long-lived and sig- nificant threat to the stratospheric ozone layer, and pro- duction was phased out in 1994. Mists, foams, and in- erting gases and clean agents have replaced it. The inerting gases and clean agents protect building contents more than the building structure and leave no sticky residue. Clean Agent Gases Replacements for Halon 1301 are being developed that use hydrochlorofluorocarbons (HCFCs) and hydrofluo- rocarbons (HFCs). These chemicals are confined to vi- tal spaces such as control rooms, computer and com- munications facilities, and emergency response centers. FM-200® works like halons but does not cause ozone depletion. It has a much shorter atmospheric life- time and presents less of a threat of greenhouse gas and global warming. FM-200 leaves practically no particu- lates or oily residue to damage electronic instruments and does not conduct electricity. It is noncorrosive and colorless. FM-200® displaces only around 7 percent of the air in a space, and has acceptable toxicity levels, mak- ing it relatively safe for firefighters. Foams Fire suppression foams consist of masses of gas-filled bubbles. Because they are lighter than water and flam- mable liquids, they float on the surfaces of burning liq- uids to smother and cool fires and seal in vapors. The foam won’t harm aircraft or delicate machinery. Low-expansion foam extinguishes burning com- bustible liquid spills or tank fires. High-expansion foam and medium-expansion foam are used for indoor fires in confined spaces. They fill enclosures such as base- ment room areas and the holds of ships. They also can be used to control liquefied natural gas spill fires and to help disperse the resulting vapor cloud. Fire suppression foams will conduct electricity, and can’t be used for electrical fires. Firefighters need to use self-contained breathing apparatus and a lifeline to en- ter a foam-filled passage. Carbon Dioxide Carbon dioxide prevents the ignition of potentially flammable mixtures and extinguishes fires involving flammable liquids or gases. It absorbs combustion energy, and reduces the temperature of the flame and vapor mixture below the level necessary to sustain combustion. Carbon dioxide smothers fires by displacing oxygen, and is limited to use in tightly confined spaces without people or animals. It is appropriate for use in display cases, mechanical and electrical chases, and unventilated areas above suspended ceilings or below raised floors. Carbon dioxide is used in data centers, telecommunica- tions equipment spaces, and electrical equipment rooms where water would damage the contents. Carbon dioxide is stored as a liquid in cylinders un- der great pressure. It is noncombustible and won’t react with most substances. It does not conduct electricity, and doesn’t normally damage sensitive electronic equip- ment. There is no residue to clean up after use. After use, the carbon dioxide gas escapes to the atmo- sphere at levels that pose a significant danger to build- ing occupants and firefighters. Smoldering embers may ignite again after being suppressed by carbon dioxide. PORTABLE FIRE EXTINGUISHERS Since portable fire extinguishers are movable and don’t require access to plumbing lines, they are usually specified by the interior designer on interior projects. Portable fire extinguishers are used to extinguish fires at an early stage. They are rated for the class of fire they are designed to fight. How many are required and where they must be located depend on the hazard classification of the occupancy. They must be located in conspicuous places along ordinary paths of egress. Fire extinguishers may be surface mounted or recessed within the wall us- ing a special cabinet with a vision panel. The extinguisher must be visible at all times, must be tested regularly, and must have an approved label. This presents a challenge to the interior designer, since fire extinguishers and related equipment are bright red and in highly visible locations. It may be a good idea to show this equipment on your interior elevations, so that your client (or you yourself) isn’t surprised by the final appearance of the room. The typical home fire extinguisher is not designed to fight large or spreading fires, because it will run out in eight seconds or less. A fire extinguisher must be rated as the correct type for the fire that you need to put out. The extinguisher must have adequate force to fully ex- tinguish the fire. Locate the extinguisher where it is both quick and safe to get in case of fire. Someone who has the strength and knowledge to use it properly and with- out hesitation must handle the fire extinguisher. Building codes specify which occupancies and types 366 FIRE SAFETY of building uses require fire extinguishers. Most occu- pancies do require extinguishers, and some specific ar- eas within buildings have special requirements. Com- mercial kitchens and smaller kitchens and break rooms in commercial spaces require extinguishers. NFPA 10, Portable Fire Extinguishers provides guidelines for types and locations of extinguishers. Generally, no occupant may be more than 22.9 meters (75 ft) from a fire ex- tinguisher where they are required. The interior designer needs to be familiar with the codes and related Americans with Disabilities Act (ADA) requirements for portable fire extinguishers. If a fire suppression system is to be used by the building’s oc- cupants, it must be mounted at accessible heights and located within accessible reaches from a front or side wheelchair approach. Fire suppression equipment may not protrude more than 102 mm (4 in.) into the path of travel. This requirement may eliminate bracket- mounted fire extinguishers and surface mounted fire protection cabinets in some areas. Fire extinguishers are classified by types represented by letters. They also have force ratings indicated by numbers. The higher the rating number, the more ex- tinguishing agent the unit contains, and therefore the larger the fire it should be able to put out. A higher force number also means a heavier extinguisher. Type A devices are exclusively for use on ordinary combustibles such as wood, cloth, or paper. They are quite dangerous if directed at burning grease or ener- gized electrical equipment. Type A units use water, foam, or multipurpose dry chemicals to put out the fire. They vary from Class 1A to Class 40A. Type B extinguishers are for use on flammable liq- uids, including oil and grease. They employ carbon diox- ide, dry chemicals, or wet chemical foam to suffocate flames. In the past, they also used halogenated agents. They include Class 5B to Class 40B. Type C units are for energized electrical equipment. They use nonconductive dry chemicals or carbon diox- ide. A combination type BC extinguisher is available for use in kitchens and other locations where both flam- mable liquids and electrical wiring might be involved in a fire. Type ABC is a multipurpose dry chemical extin- guisher that usually uses ammonium phosphate. ABC extinguishers can be used on any kind of fire, but are not ideal for electrical fires, as they leave a hard residue that causes damage to electrical equipment. Type D uses dry powders such as graphite or sodium chloride to put out fires in combustible metals. The spe- cific combustible metal the extinguisher is to be used on is printed on the nameplate. Fire Suppression 367 We have looked at how we can design to prevent fires from starting and spreading. We have explored the ways that we can get people safely out of a building in the event of a fire. We have also examined how to put out a fire once it starts. Now let’s explore the systems that detect fires and alert us to their presence. FIRE DETECTION A fire progresses through four stages: incipient, smol- dering, flame, and heat. Different types of fire and smoke detectors are designed to indicate problems at each of these stages. Incipient Stage Detectors Combustion produces microscopic particles when a fire is just starting. Ionization-type particulate detec- tors (Fig. 46-1) are designed to detect these particles by noticing a reduction in the electrical current flow and to set off an alarm. Ionization-type detectors work best indoors where there is stagnant air, where the air velocity is low, and where there is little visible smoke with large particles. Ionization-type detectors respond best to fast-burning flaming fires, which need a fast re- sponse and produce less smoke. They should not be installed on warm or hot ceilings, or in kitchens, bak- eries, workshops with open flames or burners, or where there are concentrated engine exhaust fumes. They need periodic cleaning to remove dust, and reg- ular recalibration. Because the incipient stage of a fire also changes the gas content of the air, gas sensing fire detectors are often used along with particulate detec- tors. Incipient stage detectors cover between 14 square meters (150 square ft) and 84 square meters (900 square ft), depending on the type of detector and the situation. Wilson cloud chamber type detectors are sensitive to microscopic particles in the early stages of a fire but insensitive to dust. They use continuous air sampling and give few false alarms. Wilson cloud chamber de- tectors require piping and are expensive in small in- stallations. The price becomes competitive when over 30 detection points are needed. These detectors are used in high-value installations like museums, data process- ing spaces, libraries, clean rooms, and facility control rooms. 46 Chapter Fire Detection and Alarms 368 Smoldering Stage Smoke detectors have become increasingly important as finishes and furnishings become more flame resistant and therefore more likely to smolder for a long time without flame at temperatures too low to trigger sprinklers. NFPA 72, Household Fire Warning Equipment, and NFPA 101, Chapter 22 regulate the use of residential smoke detec- tors. The goal should be to provide sufficient time to evac- uate residents and to take countermeasures. The particles in smoke at the smoldering stage are large enough to be visible to the eye. Photoelectric smoke detectors use a beam of light projected to a photo-sensor. When the beam is broken by smoke, the alarm goes off. Dust, dirt, or heavy fumes can obscure both the photocell and the lamp, which along with ag- ing of the lamp results in false alarms. Photoelectric smoke detectors require continuous maintenance and periodic recalibration. They are used for smoldering fires and smoky fires from plastics and chemicals. Projected beam photoelectric smoke detectors (Fig. 46-2) can cover even greater distances. They use a beam transmitter and beam receiver mounted on the walls on opposite sides of the space somewhat below the ceiling. They are used in spaces with high ceilings, such as atri- ums, churches, malls, and auditoriums, where spot-type detectors are difficult to reach for maintenance. Pro- jected beam detectors can be physically shielded for use in very dirty, corrosive, humid, hot, or cold areas. The range from the transmitter to the receiver is from 9 to 92 meters (30–300 ft). Units are spaced 9 to 18 meters (30–60 ft) apart. Projected beam photoelectric smoke detectors are expensive. They must have an unobstructed view, which may be a problem with exposed ductwork or pendant lighting fixtures. Scattered light photoelectric smoke detectors are also called photoelectronic or Tyndall-effect detectors. A beam of pulsed light-emitting diode (LED) light is di- rected at a photocell. If the light is scattered by parti- cles, it strikes an alarm cell. Scattered light detectors are not sensitive to normal dust, dirt, or light source de- preciation and do not require continual maintenance. They are used for commercial and high-quality resi- dential construction. Laser beam photoelectric devices are scattered light type detectors that use a very high-sensitivity laser diode source. They are able to differentiate between smoke and dust particles, but work best in clean environments. Air sampling detection systems sample air through- out a space by using piping with holes at sampling points. A fan powers them, and the piping is zoned to indicate the area of the problem. A basic residential system places a listed smoke de- tector outside and adjacent to each sleeping area, in each sleeping room, and at the head of every stair, with at least one on every level including the basement. Com- bined smoke and heat detectors are recommended in the boiler room, kitchen, garage, and attic. An alarm in any detector should set off an alarm in all audible and visible units. Codes specify which occupancies require smoke de- tectors but don’t always give specific locations, so the Fire Detection and Alarms 369 Ph o t o electric sm o ke d etect o r for smolderin g sta ge I o niz a ti o n p articulate d etect or Ionization particulate d etect o r with m icroprocessor ad j usts sensitivity to envir o nment a l conditions, for inci p ient sta g e detectio n Figure 46-1 Automatic fire detectors. Figure 46-2 Pair of projected beam smoke detectors. [...]... automatic fire signaling systems or fire alarm systems are required The codes specify required systems and provide testing data An electrical engineer will be involved in the design of an extensive fire alarm system With a protected premises fire alarm system, the alarm sounds only in the protected building Protected premises systems are used for privately owned facilities If a building were unoccupied,... cost of automatic systems is high, but the reduction in labor and increased speed result in a short payback period and a rise in efficiency There are four major types of systems for material handling in commercial and institutional buildings They include vertical lift car-type systems, horizontal and vertical conveyors, pneumatic systems, and automated and track-type container delivery systems VERTICAL... also very good in any large building where people may not be familiar with the building, evacuation procedures, or the alarm system This includes hotels and convention centers, where visitors often ignore or misunderstand bells and horns High-rise office buildings require emergency voice alarm communication systems The system should allow full control of transmission and building- wide distribution of... up to 454 kg (1000 lb) at speeds up to 107 meters (350 ft) per minute The maximum cart size is around 81 cm (32 in.) wide by 173 cm (68 in.) long by 178 cm (70 in.) high 390 Materials Handling 391 PNEUMATIC SYSTEMS 12345 67 89 Figure 49- 1 Automated dumbwaiter Automated dumbwaiters are also called ejection lifts Institutional and other facilities use them for rapid vertical movement of relatively large... use for carrying information on paper Pneumatic tube systems are reliable, rapid, and efficient They are relatively low cost if installed during the initial building construction Pneumatic tube systems consist of single or multiple loops of tubes 57 to 152 mm 1 (2ᎏ4ᎏ–6 in.) in diameter A single large, noisy compressor pressurized older systems Newer systems are computer controlled with a small blower... quiet The newer systems can be of unlimited length The carriers within the tubes travel at 7.6 meters (25 ft) per second Pneumatic trash and linen systems provide for rapid movement of bagged or packaged trash and linen from numerous outlying stations to a central collection point Health codes require separate systems for trash and linen Linen systems are commonly used in hospitals Trash systems are found... Manual pull station 372 FIRE SAFETY partment Remote station protective signaling systems are used for private buildings like offices and stores that are unoccupied for longer periods and where the owners don’t want to rely on outside observers for notification Proprietary fire alarm systems are found in large, multibuilding facilities, like universities or manufacturing facilities A visual display... hazardous occupancies, fire alarm systems are tied to an audio system This intercom system directs occupants out of the building, and may also give the location of the emergency Industrial facilities have manual stations at points of egress, and horns instead of bells or gongs because of the high noise level IX P a r t CONVEYING SYSTEMS 47 C h a p t e r Elevators Any multistory building needs ways to get... systems are found in many types of buildings, often along with trash compactors The pneumatic trash or linen system consists of large pipes under negative pressure, with loading stations throughout the building The pipes are 41, 46, or 51 cm (16, 18, or 20 in.) in diameter They carry one load at a time at 6 to 9 meters (20–30 ft) per second The compressors for trash and linen systems are large and very noisy... point-to-point or loop system with simple controls or a complex system with loops and branches operated by a centralized computer Automated container delivery systems are easy to retrofit into a building, due to their small size and flexible track layout  392 CONVEYING SYSTEMS In another variation, floor tapes below the carpet invisibly route robotic battery-powered vehicles The vehicles can connect to elevators . firefighting before the fire department arrives, and are also used for full-scale firefighting. The water supply can be turned on automatically or manually. OTHER FIRE SUPPRESSION SYSTEMS For buildings. protective signaling systems are used for private buildings like offices and stores that are unoccupied for longer periods and where the owners don’t want to rely on outside observers for notification. Proprietary. critical locations and are fo- cal points for circulation paths. Interior designers are often involved in selecting the finishes for elevator cabs and lobbies, and for the but- tons and indicators in