Precombustion Fire Alarm

Response Patterns Induced by Thermally Generated Vapors for Various Wire Types Observed on the 38-Sensor Array Used in the Kamina E-Nose

Figure 2. Response Patterns Induced by Thermally Generated Vapors for Various Wire Types Observed on the
38-Sensor Array Used in the Kamina E-Nose
(Data is presented as a radial plot in which the response for each of the 38 sensors is plotted as a distance from the origin. Vapors are identified by comparing the response patterns of a sample vapor to previously measured patterns stored in memory. The pattern for PVC is readily and easily distinguishable from Kapton and Teflon. Although similar, there is sufficient difference between Teflon and Kapton for identification of the wire type.)

Frequently, one of the earliest indicators of a pending electrical fire caused by equipment failure is the overheating of wires. Wires and other electrical cables are usually encased in a plasticlike insulating material. Modern wire insulation is made from organic polymers. One common insulation material is polyvinyl chloride (PVC). For the Shuttle and other space applications, a higher-grade insulation is typically used such as Teflon or Kapton. As the wires heat up, chemical vapors are emitted from the insulation. These compounds consist of residues left over from the fabrication process (e.g., solvent residues, additives, low-molecular-weight oligomers) and of thermal degradation products of the insulation itself. Since the chemical composition and fabrication process differ for the various insulating materials, each wire type will have a unique profile for its thermally generated vapors. This chemical distribution is indicative of the insulation material itself. Vapor outgassing begins before the development of smoke or soot. Thus, chemical monitoring for selected signature vapors can provide notice of a pending fire prior to actual combustion. This in turn can provide warning to allow shutdown of operations before major damage can occur. The observation of selected chemical signatures would indicate a thermal excursion in electrical circuitry. The task is not so much to identify the signature compounds but to observe their presence and to confirm their uniqueness to the system under study. Figure 1 illustrates the experimental apparatus for the thermal generation of vapors from various wire types.		As the wire heats up, gaseous products are generated. Electronic nose (E-nose) instruments installed within the chamber detect the generated vapors. Figure 2 shows the response pattern of the Kamina E-nose to the thermal vapors of various wire types. Clearly, each wire type induced a unique response. The Sam Detect E-nose also exhibited an equally impressive response to vapors generated from heated wires. Modeling of the Sam Detect data resulted in well-separated 2-dimensional projections indicating that thermal degradation of the various wire types can be identified via chemical monitoring. Key accomplishments: Designed and built the apparatus for the controlled thermal outgassing and degradation of various wire types. This system was interfaced with the E-nose technologies. Tested two E-nose instruments (Sam Detect and Kamina) and identified promising technologies for continued developments. Modeled data that confirms a degree of selectivity. Contact: R.C. Young (Rebecca.Young-1@ksc.nasa.gov), YA-C3, (321) 867-8765 Participating Organization: Dynacs Inc. (Dr. W.J. Buttner and Dr. B.R. Linnell)
Figure 1. Experimental Apparatus for the Thermal Generation of Vapors From Various Wire Types (The wires are heated via a power transformer. This process is typically carried out in an enclosure to allow access to the vapors by an E-nose. Various E-nose technologies (not shown) were used in this study and were mounted within the chamber during the heating process.)
Figure 2. Response Patterns Induced by Thermally Generated Vapors for Various Wire Types Observed on the 38-Sensor Array Used in the Kamina E-Nose (Data is presented as a radial plot in which the response for each of the 38 sensors is plotted as a distance from the origin. Vapors are identified by comparing the response patterns of a sample vapor to previously measured patterns stored in memory. The pattern for PVC is readily and easily distinguishable from Kapton and Teflon. Although similar, there is sufficient difference between Teflon and Kapton for identification of the wire type.)