Federal regulations require that aircraft cargo compartment smoke detection systems be certified by testing their operation in flight. For safety reasons, only simulated smoke sources are permitted in these certification tests. To provide insight into smoke detection certification in cargo compartments, this research investigates the morphology, transport and optical properties of actual and simulated smoke sources.
Experimental data show the morphology of the particulate in smoke from flaming fires is considerably different from simulated smoke. Although the detection of smoldering fires is important as well, only a qualitative assessment and comparison of smoldering sources was possible; therefore, efforts were concentrated on the quantitative comparison of smoke from flaming fires and smoke generators. The particulate for all three different flaming fires was solid with similar morphological properties. Simulated smoke was composed of relatively large liquid droplets, and considerably different size droplets can be produced using a single machine. Transport behavior modeling showed that both the actual and simulated smoke particulates are sufficiently small to follow the overall gas flow. However, actual smoke transport will be buoyancy driven due to the increased temperature, while the simulated smoke temperature is typically low and the release may be momentum driven. The morphology of the actual and simulated smoke were then used to calculate their optical properties. In contrast to the actual smoke from a flaming fire, which is dominated by absorption, all of the extinction for the simulated smoke is due to scattering. This difference could have an impact on detection criteria and hence the alarm time for photoelectic smoke detectors since they alarm based on the scattering properties of the smoke.