Gaz, yangın algılama sistemleri ve otomatik sulu söndürme

Yavuz, Selim Metin
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Fen Bilimleri Enstitüsü
Gaz tehlikeleri üç gruba ayrılamatkta olup gazların cinsine ve oluşturdukları tehlike çeşidine göre sınıflandırılırlar. Alevalabilir gazlar, bir kıvılcım veya alev kaynağıyla buluştukları zaman patlarlar. Zehirli gazlar, direk insan vücuduna zarar vererek ölüme sbebiyet verebilirler. Oksijenin azlığı yine insan sağlığıyla ilgili olup, fazlalığı ise cisimlerin tutuşma sıcaklığını düşürürler. Gazların algılanmasında çeşitli metotlar kullanılmakta. Kullanılan metodların saptanmasında algılanacak gazın türü önem kazanmaktadır. Günümüzde kullanılan algılayıcılar bazılarnı şöyle sıralayabiliriz; katalitikler, yarı iletkenler, termal iletkenler, elektrokimyasal piller. Genellikle gaz dedektörleri tehlikeli ortamlarda kullanıldıklarından, kendinden güvenlikli veya elektriksel güvenlik altına alınırlar. Bununla konuyla ilgili çeşitli standartlar geliştirilmiştir ve kullanılan cihazlar bu standartlara uygun olarak üretilmektedir. Yangın algılayıcılarıda, yangının türüne göre ilk belirtilerini algılayacak şekilde yapılırlar. Bunlar ısı, duman, alev algılayıcılar olabilir. Kullanılacak yerin özelliğine göre bu dedektörler arasında seçim yapılır. Algılayıcıların kullanılacakmahalde yerleşim şekilleride önem kazanmaktadır. Tek başına çalışan algılayıcılar olduğu gibi, bir merkezi birime bağlanarak komplike sistemlerde yapılmaktadır. Yangın söndürme sistemleride kendi içlerinde yine yangının çeşidine göre çeşitlenmiştir. Sulu söndürme, kuru kimyevi tozlarla söndürme, köpük, halon gazı veya karbondioksit gazı ile söndürme gibi. Sulu söndürme sistemlerinden olan sprinkler sistemi çokça kullanılan yöntemdir. Bu yöntemde, kullanıldığı yerdeki boru tesisatının hidrolik hesabı ve minumum su gereksinimi önem kazanmaktadır. Uluslararsı standartlarda kurulacak şişemin yerine göre sınıflandırmalar yapılmakta ve gerekli su rezervleri bu sınıflara göre belirtilmektedir. Yine de sistemin tüm hidrolik hesapları gözden geçirilmesi gerekmektedir. Sprinkler sistemide kendi içinde kullanılacak yere göre çeşitlilik göstermektedir. Normal sistemlerde sprinklerin ucunda bir bulp bulunmakta ve ortamsıcaklığı belli bir sıcaklığın üzerine çıktığı vakitte bulp kırılarak ortama su fışkırtılır. Yangın algılayıcılar ile birlikte kullanılmakta ve algılayıcılardan gelen ihbara göre çalışan çeşitlerde bu bulp bulunmamaktaıdr. Suyun 0° de donacağı göz önüne alınarak kuru tip sprinkler tesisatlanda bulunmaktadır. Sistemde kullanılan valfler ve pompalar da sisteme özgüdür.
The name gas comes from the word chaos which neatly summaries the main feature of the state simplest of matter. A gas is a swarm of particles moving randomly and chaotically constantly colliding with each other and the walls of any container. The real volume of the particles is minute compared to the total space which they occupy and this is why gases fill any available volume and are redily compressed. The average speeds of gas molecules are of the order of 100s of meters per second and they are colliding with each other billions of times per second. This is why gases mix rapidly and why they exert pressure. This constant motion is easily demonstrated by releasing a small amount of odorous gas in a room. Within seconds the gas can be smelt in all parts of the romm. These properties apply to substances which are normally gaseous and to vapours from evaporated liquids. A volume of any gas at the same temperature and pressure contains the same number of molecules irrespective of what the gas is. This means that measuring gas by volume is very convenient. Gas measurements at higher levels are in % (volume) and at lower levels parts per million, pmm (vplume). Whilst different gases have different densities, they do not totally separate into layers according to their density. Heavy gases tend to sink and light gases tend to rise, but their constant motion means that there is continuous mixing (i.e they do not behave like liquids). So in a room where there is a natural gas (methane) leak, the gas will tend to rise because it is lighter than air but the constant motion means that there will be a considerable concentration at floor level. This will happen in perfectly still conditions but if there are any air currents, the mixing will be increased. IX Air is a mixture of gases, typically : Nitrogen 77,2% Oxygen 20,9% Water 0,9% Vapour Argon 0,9% Carbon Dioxide 0,03% Other Gases 0.07% Because its analysis is reasonably constant, it is usually considered as a single gas which simplifies the measurement of toxic and flammable gases for safety and health applications. The methods of as analysis are as follows : 1- Catalytic Detection This method is used to detect almost all explosive gases and to analyses all polyatomic gases(not diatomic gas) which doesn't have absaption strips in infrared (02.N2.H2...)- 2-Unscattering Infared Absarption. This method allows the continuous monitoring of gases within the infrared bands 2 and 10 Mm. 3 -The Chromatography Gas Phase. This method the constituents of the gas mixture are separated.Most of the gases could be dosed by this method. But the realization of this method is complex. 4-The continuous Coulometry. It is a electrochemical method of dosing. There are two types of coulomety; direct and indirect. All consistent gases formed by purchaser solution, can be directly or after a preliminary reaction to be insusceptible, can be dosed by coulometry: f S02, H2 O, N02, NO, CO2, CO... 5-The Electrochemistry With Liquid Or Belled Electrolyte this method is based on established current measurement between a sensing electrode and a counter electrode. Oxygen and toxic gases like CO2, H2 S, SO2, NO, NO2, H2, HCN... could be dosed by this method. 6-The Electrochemistry with solid Electrolyte Certain metallic oxides become conductive when they are heated to a high temperature. This the main principle which is used for the electro-chemistry with solid electrolyte method. This method is used exclusively to analyses oxygen. 7-The Paramagnetic. This technique is based on the magnetic properties of gases, this method is used to detect principal oxygen and paramagnetic gases: NO, NO2... 8-The Conductimetry This method used to dose all susceptible gases which can give a ionizable compound ( by direct solution or after chemical transformation ) which can vary the conductivity of the chosen reactive. Most frequently: - gases giving acid solutions: HCL, HF... -anhdrides of acids: SO2, 02. - gases giving basic solutions: NH3. 9-The Colourimetry This method permit the measuring of gas concentration by evalvation of colour in tensity, by increased optical absorption. We could use this method to dose all gases immediately coloured or sus ceptible to give a coloured compound after reaction, dissolution or absorption in a surrounding. 1 0-The Semi-Conductors Measurement relias on the induced variations of electric conductiviy, by gas absorption on the surface of a metallic oxide. This technique is used to detect toxic and explosive gases. 1 1-The Thermal Conductivity This method relies on a variation of thermic conductivity of a hot material in contact with another. To analyses flammable and toxic gases this method is used. 12-The Chemiluminescence Certain chemical reactions operants at room temperature give luminous emissions which can be used for dosing the gas participaking in the reactions. To dose the toxic gases like NO, O3, P... this method should be used. Do to its high sensitivity, this method is usually used for the measuring of atmospheric pollution, however this method may be very expensive. XI 13-The Photoaacoustical Detection An infrared monochromatic ray is sended through a surrounding within circular the analyses gas. The wavelength is chosen depending on the absorption of the gas. Detection of CO2, the aromatic compounds and the organop hosphore gases (wargas) is possible by using this method. I4-The Pohotoionosation A.U.V. beam is used to ionize the molecules of the gas. The aromatic compounds are dosed by this technique. 15-The Optic Fibre In This field, the efforts have been concentrated on the methane detection. The earliest application for gas detection equipment arose in coal mines, where naturally occuring Methane (Firedamp) in congun with air was readily ignited, by flame propugation from sparks, unpretected flames, explosion and faulty electrical apparatus. Invention of the first reliable gas detection method was in the first reliable gas detection method was in the early 1 800 s. This method, the flame safety lamp, is still used in coal mines. During the intervenig 1 80 years, many new principles and techniques have been developed and employed. As a result of this growth a British Standard has been published and this defines for the first time a common-philosophy for instrumentation used in this field. The areas of primaryconcern are the nature of the workplace, location and the plant environment, and also whether the gas is toxic or combustible and, either lighter or heavier than air. Gases vapours can be dangerous for three. They can be Toxic, Asphyxiating or Flammable. Toxic gases are those gases which can cause sickness or in extreme cases can be fatal, effects can be caused by contact with the skin, ingestion, inhaling. One of the more common meas of detecting toxic gases is by the "Draeger tube method". There is also the impregnated paper tape method. Dvring the last few years efforts have been made to be more reliable and specific in detecting toxic gases, the use of semiconductors metal oxide detector was probably the first step. In human beigos lack of oxygen can lead, to loos of cancentration, coma and death. Oxygen defficiency can be caused in a number of ways, by fires, chemical reactions or by air being displaced by another and usually heavy gas(i.e. CO2). Early oxygen sensor were lange heavy devices, but in recent years a new type of sensor has been developed known as the "electro-chemical". Of all the all the sensors manufactured for the detection of flammable gases, perhaps the SMRE pellistor, over a period of time, has proved the most reliable. xn Automatic fire detectors consist of two types of detectors; heat detectors and smoke detectors. Heat detectors are the oldest type of automatic fire detection device. A sprinkler can be considered a combined heat-activated fire detectors exhavsting device when the sprinkler system is provided, with overflow indicators connected to the fire alarm control system. Although heat dedectors and have the lowest false alarm rate of all automatic fire detectors, they are also the slowest in detecting fires. A smoke detector will detect most fires much more rapidly than heat detector. Automatic fixed extinguishing systems are the most effective means of controlling fires in buildings. As soon as a fire starts, it produces a variety of environmental changes that can be used to detect its presence. Human beings are excellent fire detectors since they possess senses of smell, sight, and touch. Also, they possess a computer capable of comparing the signals from these various sensors against previous knowledge and experience. This aids in the discrimination between friendly and hostile fires. But since man's senses are also unreliable due to the need for frequent rest and relaxation, and since his sense of smell is compensating, a number of mechanical, electrical, and electronic devices have been developed to mimic human senses in the detection of the environmental changes which are created by fire. The most common elements of a fire that can be detected are heat, smoke (aerosol particulate), and light radiation. Complicating the matter is the fact that not all fires produce all of the elements and non-fire conditions can also produce similar ambient conditions. It is the job of the fire protection engineer to decide which of the elements produced by a fire might be expected from hostile fires and which similar ambient conditions might be expected from non-fire conditions. Even if all of these elements are present in a given fire, the magnitude of the different elements must exceed some background level during the fire development. It is also helpful to determine which element will appear first. This is especially true if life safety is involved. The rapid growth of business and industry in the nineteenth century and the resultant increase in fire hazards and property values brought about the need for more adequate protection against fire. Hose streams were useful, but the difficulty of reaching a fire through smoke and heat has often been demonstrated. Unless a fire was discovered in its early stages, such simple fire protection as water pails, standpipes, and hose equipment proved inadequate. Although fire control was made easier by improved building construction, comparatively little headway was made in reducing fire loss involving delayed detection until the advent of the automatic sprinkler. Automatic sprinklers are devices for automatically distributing water upon a fire in sufficient quantity either to extinguish it entirely or to prevent its spread in the event that the initial fire is out of range of, or is of a type that cannot be completely extinguished by, water discharged from sprinklers. The water is fed to the sprinklers through a system of piping, ordinarily suspended from the ceiling, with xiu the sprinklers placed at intervals along the pipes. The orifice of the fusible link automatic sprinkler is normally closed by a disk or cap held in place by a temperature-sensitive releasing element. The forerunners of the automatic sprinkler were the perforated pipe and the open sprinkler. These were installed in a number of mill properties from 1850 to 1880. The systems were not automatic the discharge openings in the pipes often clogged with rust and foreign materials, and water distribution was poor. Open sprinklers, an improvement over perforated pipes, consisted of metal bulbs with numerous perforations attached to piping and intended to give improved water distribution. This system was only slightly better than the perforated pipe. The idea of automatic sprinkler protection, whereby heat from a fire opens one or more sprinklers and allows the water to flow, dates back to about 1860. Its practical application in the United States, however, began about 1878 when the Parmelee sprinkler was first installed. This sprinkler, while very crude when compared with modern devices, gave generally good results and proved conclusively that automatic sprinkler protection was both practical and valuable.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1995
Anahtar kelimeler
makine mühendisliği, gazlar, otomasyon, uzaktan algılama, yangın, mechanical engineering, gases, automation, remote sensing, fire