| Abstract: | 火災，除了引發公共安全問題外，更造成生命財產之危害。因此各式的偵測器即被應 用於初期偵測火災的發生，希望在火災發生前期及早發現，才能有效地抑制災情擴大，而 一般大眾廣為使用的偵測器為煙霧偵測器。煙霧偵測器可分為離子式及光電式偵測器，前 者之偵測原理為在離子室一對電極中放入 α 微粒，使電極中之空氣分子離子化。因電極上 被施以一定之電壓值，造成空氣離子朝兩端極版移動，而形成電離電流。當有煙霧氣膠微 粒進入時，微粒將造成電離電流減少，在其減少量達一定值以上時，偵測器即開始作動。 而光電式偵測器之主要應用為光照射到微粒時，光會被微粒散射的原理。 根據美國消防單位統計資料中，有 10.8 % 的火災求救訊號是偵測器的誤報而引起 的，而且美國於 1993 年有記錄可查之偵測器誤報案例即高達 1,646,500 件，足見現今煙霧 偵測器的誤報率高。此種誤報狀況，會形成人們心理上的輕忽態度。是以具備一高準確性、 低誤報率之煙霧偵測器，是有效抑制災情擴大，減少生命財產損失的首要條件。各國對於 火警探測器皆有完整之測試標準，例如 CNS-8874、EN54-7、UL-268 等等。然則不同燃燒 狀況，造成迥異之氣膠微粒的粒徑分佈、粒數濃度、重量濃度以及氣膠光學特性，皆會影 響煙霧偵測器之靈敏度。因此，關於煙霧偵測器檢測標準之完整性與適用性之探討研究更 是迫切需要。 本研究針對煙霧偵測器進行一效能評估，比較各國關於煙霧偵測器檢測標準之相異處 與優缺點，以期修訂、研擬適當之煙霧偵測器檢測標準評估規範。實驗主要選擇壓克力粉 塵與碳黑為挑戰氣膠，以微粒電移動度掃瞄分徑器（ Scanning mobility particle sizer）、氣 動粒徑微粒偵測器（Aerodynamic particle sizer）及氣懸微粒質量偵測儀（Tapered element oscillating microbalance---Ambient particle Monitor, TEOM）進行氣膠濃度、粒徑 分佈之測試，以粉塵分散器（ Solid particle disperser（PALAS））產生所需之挑戰氣膠，以 Am-241 中和挑戰氣膠至波茲曼分佈。實驗中輔以氦氖雷射監測、評估氣膠光學特性。研 究結果顯示，光電式煙霧偵測器反應性，明顯受到不透光度之影響，微粒之粒徑分佈、重 量濃度與物質之折射率將直接造成煙霧偵測器之反應。研究最終希冀能進而研發高準確 性、低誤報率之煙霧偵測器，以提高公共安全。
Fire spreads uncontrolled in public will be a hazard. People died by fire, also property and goods lost in the fire disasters. However, well-established fire sensors can detect the smoke and gases produced during the early stages of developing fires. The smoke detectors have two types: the ionization-type and the photoelectric-type smoke detectors. Ionization-type smoke detectors use an ionization chamber and a source of ionize radiation to detect smoke. Inside an ionization-type detector is a source of alpha particles. They ionize the atoms of the air in the chamber. The detector senses the small amount of electrical current that these electrons and ions moving toward the plates. When smoke enters the ionization chamber, the ions attach to it. Then the smoke detector senses the drop in current between the plates and sets off the horn. On the other hand, inside the photoelectric-type smoke detectors, the light source shoots strait (or across and misses) the sensor. When smoke enters the chamber, however, the smoke particles scatter the lights and alarm the smoke detector. These smoke detectors, however, often result in frequent false sensor alarms. If this frequency is high, the tendency is to either shut down sensors, or to ignore the sensor alarms, with the potentially catastrophic consequence that an actual fire will be ignored. For this reason, an accurate, high performance, and low frequent false smoke detector can overcome the above shortcomings. The CNS-8874, EN54-7and UL-268 as a criterion normalizes the test standards of smoke detectors. However, according to the previous studies, the particle size distribution, number or mass concentration, and optical properties all affect the accuracy and performance of the smoke detector alarms. The test standards must be evaluated for its adequacy and completeness. In the study, a Solid Particle Disperser (PALAS) was used to generate challenge aerosol particles (Acrylic Powder & Carbon Black). A radioactive source, Am-241, was used to neutralize the challenge particles to the Boltzmann charge equilibrium. An Aerodynamic Particle Sizer (APS), Scanning Mobility Particle Sizer (SMPS) and Tapered Element Oscillating Microbalance (TEOM) was used to measure the number or mass concentrations and size distributions of the challenge aerosol. The Helium Neon Laser was used to measure the optical properties of challenge aerosol in the test system. The results showed the particle size distribution, number or mass concentration, and the particle reflective index all affect the accuracy and performance of the smoke detector alarms. The ultimate goals of the study are to suggest a proper normalization of testing and improve the smoke detectors. |
