Deprem sonrası yangınlar
Fire following earthquake
- Tez No: 46547
- Danışmanlar: DOÇ.DR. ABDURRAHMAN KILIÇ
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 49
Özet
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Özet (Çeviri)
FİRE FOLLOWING EARTHQUAKE SUMMARY Post-earthquake fires are majör problems in affected areas and sometimes grow to such proportions that cause great damages in terms of loss of properties and casualties. This phenomenon is iraportant in cities with a large building stock composed primarily of wood and with industrial installations, such as oil refineries, large factories, chemical plants, ete. The post-earthquake fire problem is complex and involves many diverse elements. A simplified flowchart describing post-earthquake fire potential is shown in Figüre 1. EARTHQUAKE FIRES;Fires break out initially and then spread, depending on building [~~^, construction, wind, ete., before firefighting teanıs arrive.-l1 Firefighting teams fight fires but also respond to other FİREFİGHTİNG - emergencies, such as chemical spills, building collapses, ete. jFirefighting may also be impaired due to loss of water supplies, communications, ör other systems.RESULT Figüre 1. Simplified scenario for the post-earthquake fire problem The fire spread begins with the occurrence of the earthquake, which causes structural and non-structural damage to buildings, lifelines, and fire stations themselves. Structural damage also causes many of the fire safeguards we rely upon to lose their integrity. Firewalls/stops/doors, non-combustible wall and roof coverings sprinkler systems, fire alarms, ete., ali become less effective because of earthquake stress. The earth movement causes fires to break out by overturning öpen flames (candles, fireplaces, water heaters), shorting electrical circuits, arcing power lines, rupturing flammable material containers and pipelines. Many of these fires can quickly and easily be controlled and extinguished by civilians if they're uninjured, aware of the fire, able to get to it, and if they have the knowledge, and means with which to fight the fire. However, if the fires spread to the stage where they require professional firefighting services and firefighting teams can viiquickly respond, the fire can usually be contained. However, an earthquake can result in simultaneous outbreaks of dozens of fires. Fires initiated after earthquakes indicate the importance of post-earthquake fires in terms of their potential to cause structural damage. They also demonstrate the need for a more rigorous design requirement for post-earthquake fire hazard mitigation. Earthquake engineering research has been mainly focused on the area of earthquake-resistant design and evaluation of earthquake hazards in terms of building collapse, lifelines, bridge and dam failures, land-slides, liquefaction of soil. While structural safety plays an important role in seismic hazard mitigation, certain other earthquake related issues such as post-earthquake fires are equally as important. There is some reasons that may cause post-earthquake fires. These are: l.Gas leaks due to failure of pipes ör gas appliances. 2.Electrical distribution system problems. S.Flammable materials spills. 4.Overturning of burning candles, table lamps, gas grills, ete. Due to the nature and frequency of their use, gas and electrical distribution systenıs and appliances are more exposed to the risk than elements such as burning candles and lamps. A systematic formulation of the risk for ali types of fire is not easily possible. Analytical models have been used with some success to estimate the risk of appliance failure, i. e. sliding ör overturning, and interior gas piping system failure during an earthquake. Such models can be extended fiırther for the purpose of estimating the risk of fire that may occur due to appliance failure. When analytical modeling cannot easily be used, techniques based on the expert opinion data and the extrapolation of fire statistics for non-earthquake conditions can be utilized. The latter case is especially applicable when the system involved are continuously exposed to the risk. it is more appropriate to analyze the fire outbreak rate not in the relation with the rate of collapsed buildings but in the relation with the seismic intensity. it is estimated that in the case f earthquakes of less ör equal to intensity 6, the fire outbreak rate of total fires may not exceed %o 0,20, that of general fires may not exceed %o 0,15, and that of chemical fires may not exceed %o 0,05. But in the case of earthquakes of intensity 7, the possibility that the fire outbreak rate becomes much higher. The chain of events that may lead to a gas-related fire is summarized below: l)Following an earthquake, overstress in the piping system components ör overturning ör sliding of an appliance occurs. 2)Gas leak develops. 3)Leak is undetected, and gas is accumulated in an enclosed area. 4)Gas intensity in the air reaches an ignitable level. 5)An ignition source is activated. viiiThis chain of events often stops at the fourth ör fifth level. in a dwelling equipped with an automatic seismic shut-off valve, the above chain of events can practically stop at the second level. However, if a right condition persists and the above chain of events is followed to the end vvithout any interruption, a fire will develop. The right condition means development of a leak in an area susceptible to gas accumulation and fire. Potential fire causes of electrical distribution systems are ground fault, improper installation, equipment overload, loose connections, worn-out wires and electrical components, ete. An electrical distribution system is made up of these components: Branch circuit wiring, receptacle outlet and svvitches, cords and plugs, fixtures and lamps, transformers. in the event of an earthquake, the electrical distribution system is especially critical because the ground shaking can trigger displacements of electrical components and friction of wiring and cords against each other ör protruding metal edges in their vicinity. Such phenomena will increase the risk of fire. The probability of fire development depends on a variety of factors including the design of the system, the age of the electric components, installation practice, existence of faulty wiring, overloaded components, ete. The risk of fire due to an earthquake is estimated by extrapolating the risk for ordinary (non-seismic) conditions. Since the 1906 San Francisco earthquake, the threat of fire following an earthquake has been recognized as being potentially as much of a hazard as the earthquake itself. Potential fire damage following and earthquake is dependent upon many factors. Some of the most important include the amount and nature of combustible material available for the spread of fire, response capacity of the local fire departments and weather conditions at the time of the fire. Natural gas systems have been the focus of considerable attention as potential sources of fire despite the lack of evidence in recent earthquakes. The number of fires in past earthquakes is relatively low. Experience shows that natural gas can be linked to only a fraction of the earthquakes that occur following an earthquake. Electrical, chemical and other sources of ignition for outweigh those from natural gas. Experience in past earthquakes has shown that a majority of fires related to natural gas can be attributed to partial ör total structural collapse and shifting ör toppling of unanchored gas appliances and equipment. Without structural collapse, risks of gas üne damage during earthquakes can be greatly reduced with relatively simple anchoring details. The fire and explosion risk associated with earthquakes may be explained with the different parameters. These are intensity of the event (I), the general human factor (Ho), material factors (m), the pressure under which liquids and gases are stored ör processed (p), the temperature at which materials are kept (t), the average residence time of material during storing ör processing (tav), reaction velocity (rv), passive safety measures (sm), active safety procedures (s?), technical failure factors (tech), construction material factor (cm), ignition sources (I), distribution factor (d). They are examined in the following parts. ixEarthquakes, besides causing very great economic strife to developing countries in particular, also cause substantial social upheavals within the country. Damages caused by earthquakes in underdeveloped ör developing countries are seen to be öne hundred times greater than that sufFered by developed countries. The damage caused by earthquakes in large urban areas, in particular, are manifested in both social and economic spheres. An empirical formula developed in Japan can be used to estimate the number of earthquake-related fires. The empirical formula is shown that: fN0.6041 7 = 0,003152C,CJ-^- Ntop(1) \l^topj Y=Number of earthquake related fires. C,=Coefficient depending on time (l(Night), 0,75 (Daytime)). C^CoefScient depending on season (l(Winter), 0,5 (Summer)). N=Number of collapsed ör heavily damaged houses. N^Total number of wooden buildings in the district. in order to estimate the number of earthquake related fires in Bursa and istanbul we prepared a hypothetical earthquake scenario. it is feared that a strong earthquake affecting istanbul might occur along Marmara fault zone. If that should happen it is thought the seismic intensity in istanbul would be IX ör VIII. istanbul, the capital of three majör empires, the Roman, the Byzantine and the Ottoman, is the only city in the world which is built upon two continents. Industry means jobs and the concept of finding work is what draws much of the population of Asia Minör to istanbul. Glassware, textiles, leather, cigarettes, chemicals, building materials, spare parts, food cover vast areas in ör near the city. 45% of the industrial complexes in Turkey are situated in istanbul and here 60% of the exported industrial products are produced. it must be stressed here that research regarding earthquakes has declared the site of the city of istanbul as a first degree earthquake zone. Istanbul's streets are often narrow and streep and many are comprised of staircases. There are cantless streets which are in accessible to motorized vehicles. The acquisition of sufficient water supplies is also often difficult, if not impossible. Homes and industrial sites are built adjacent to each other. Many depots of flammable materials and workshops can be found in order neighborhoods. To date Turkey has not experienced many fires that have occurred as a result of earthquake. in the record available to us there is only limited information regarding fires that have transpired due to earthquake. in the last majör Erzincan earthquake in Xwhich a total of 1751 work places and 21546 homes were damaged, only two fires broke out and neither caused extensive damage. The principal reason why fire has not been a major factor in Turkish earthquakes is that the structures in those areas which have experienced major earthquakes during the past recent years have been primarily constructed of concrete, earth and stone. As these structures entirely collapse during an earthquake, they cover the fire source and resulting dust also chokes off the supply of oxygen. Another main reason why fire has not been a major factor is that the most recent earthquakes have occurred in regions which are not industrially developed. This work has pointed out that earthquake-caused fires primarily occur in industrial and commercial facilities and in wooden buildings. An earthquake of magnitude 7.5 will cause 203 fires. A summary of the results of that study is given in Table 1. Table 1 Number of Earthquake Related Fires in Istanbul Fires occuring within large industrial concerns were not included in this work. Our prediction is that ifa large-scale earthquake does occur in Istanbul, the death toll XIand number of buildings destroyed will be especially high in squatter neighborhoods and that fires will break out in some industrial and commercial centers and in wooden structures. Istanbul will also experience major damage to its road, water, electrical and sanitation systems. It has been determined that in areas experiencing intensity IX earthquakes, at least 25% of all electrical and telephone lines will be cut and that there will be at least 15 breaks along every one hundred kilometers of water, gas and sewage lines. The reasons is given in the next parts. Turkey has published earthquake regulations which include provisions to be taken in construction. The high cost of such provisions is, however, the primary reason why they are not enforced. Although the enactment of such provisions reduces the acceptable risk due to earthquake and increases security, the cost of such provisions also increases. The regulations need to be revised so as to decrease the high expense. Uncontrolled construction should not be allowed. In order to ensure the fire safety of the city, measures first must be taken to provide fire safety to buildings and steps must be taken to improve utilities, the water, roads and traffic of the city. Efforts to strengthen the fire department in terms of both education and technology must continue unimpeded. Those district which are at high risk for fire and for natural disasters must be identified and steps must be taken to bring more efficient organizations into operation. Xll
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