Fire Safety Science Digital Archive

The purpose of an automatic fire detection system is the fast and reliable detection of arising fires in order to keep damages as low as possible. The European Standard EN54 defines a series of tests to prove and certify the functionality of smoke detectors, i.e. to prove that the detector is able to detect a fire in a prescribed period of time. Unfortunately the complex problem of avoiding false alarms is not completely addressed. In contrast to the well standardised methods for the evaluation of the detection capability of a smoke detector, there is a lack of a reproducible and representative test method concerning the false alarm susceptibility with regard to nuisance aerosols. The consequences of false alarms should not be underestimated, as they may cause several costs to the operator, especially in airborne applications. Several approaches are possible to reduce the false alarm susceptibility of smoke detectors, e.g. different wave lengths and scattering angles. Unfortunately the developer has no test methods to quantify improvements due to new developments. This paper presents a new approach for the test of smoke detectors regarding their susceptibility to false alarms due to nuisance aerosols, like steam and dust. Fog and spray tests in the developed set-up are planned. The presented test apparatus is a helpful tool for developers as well as for test houses during the developing and certification process. System designer will have a decision criterion to find an adequate detector for a specific place of installation. Target of the project was the development of a standardised test method for sensitivity tests of fire detectors to hazardous substances. The presented test apparatus has been developed in a cooperation of Airbus and the University of Duisburg-Essen and can contribute to a test standard. The design is similar to the EN54 test duct, however due to its small volume of only around 32 l the duct is much smaller, easier to clean, portable and cheaper. For an accurate and reproducible aerosol feeding the duct has been combined with a commercialised particle generator. The particle generator Palas RBG 1000 disperses a pre-defined amount of standardised dusts. With the developed duct, detector tests under different flow directions and velocities can be performed in the same way as with the EN54 test duct. An optical reference measurement of the aerosol concentration is performed by a light extinction path in the infrared range. The duct allows a qualitative statement on the sensitivity of the tested detector regarding nuisance aerosols with reproducible results. Also a slow pollution with dust of the measuring chamber can be emulated. The achieved results of this study are a promising first step in the development of a new test standard.