愈是現代化的都市，地下管線系統愈趨複雜，而其重要性可由神戶大地震的經驗得知，當維生管線因強地動而震損，天然氣不斷外洩造成都市陷入一片火海，而自來水系統同樣遭到破壞，無水可供救災及民生使用，這對災民而言無疑是雪上加霜。天然氣管線系統可能受到外力作用或因腐蝕而發生破管，造成管線內壓力下降，流量因此重新分佈而無法正常供給。更有甚者，由於天然氣為可燃性氣體，當其濃度達到爆炸濃度，一點點的熱源便會引起氣爆。因此，天然氣洩流量評估對於災害防救之重要性不可言喻。
本研究首先收集並修正台北地區現有天然氣管線系統相關圖資，然後以商用軟體進行天然氣管網分析，分析結果與若干實測供氣量比對，藉以更新用戶端的需求流量。最後考慮兩種不同管線破壞方式，對每個500 m×500 m的網格做洩流量評估。第一種破壞方式考慮靠近網格中心的最大管徑管線意外破管，第二種破壞方式由耐震規範評估各網格因強地動所造成之災損數目。本研究之洩流量分佈結果不僅可做為瓦斯公司日後管線維修、更新及系統改良之用，並可做為天然氣管線災損防護規模評估的參考依據。

The underground pipeline system is much complicated in a modern city, and its importance was evidenced after the Kobe earthquake. When lifelines were damaged under this powerful earthquake, the escaping of natural gas caused city in flames everywhere. Meanwhile, there was no water supply enough for the disaster relief and livelihood because of destroyed pipelines. The victims in this situation have without no doubt one misfortune after another. Pipes of natural gas are possibly broken by external force or corrosion. The pressures in the pipelines then should be low down, so that the natural gas would be supplied abnormally due to flow redistribution. Moreover, a little bit of heat source may cause explosion when the concentration of natural gas reaches a critical limit. Therefore, the leakage evaluation of natural gas is very important in the urban disaster reduction.
At first, the data of locations and properties associated with the pipelines and facilities of natural gas in the Taipei city is collected and corrected. Then, this study performs the pipe network analysis of natural gas with the help of a powerful software. The results are compared with some recorded ones in order to update the flow demands at user joints. Finally, the leakage flow in each grid of 500 m by 500 m is evaluated according to two different cases of pipelines damage. The first one assumes an accidental break occurred at the pipe of the largest diameter near the center of each grid. The second one considers the number of breaks in each grid due to the ground motion specified in the seismic code. The distribution of leakage flow found in the study offers a reference not only in the maintenance, replacement, and upgrade of the pipe system, but also in evaluating the loss-protecting scale of disasters caused by the damaged pipe system of natural gas.

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