Optimization of Fire Detection Limits for Manned Spacecraft

The ability to safely and reliably detect an incipient fire is critical to the safety of both the crew and spacecraft for manned spaceflight missions. At the same time, however, false alarms to non-fire conditions can, at best, waste valuable crew time and, at worst, create a situation where the crew fails to respond adequately to a real fire because of too many false alarms. In a recent paper, we considered the fire size (based on experimental particulate generation rates) that would trigger a particle sensing fire detector based on realistic vehicle parameters such as ventilation flow, filtration and detector set point. The results showed the importance of filtration and ventilation flow for early detection of any incipient fire.

This paper continues that work to consider background sources of indoor aerosols in addition to smoke particles. The lumped capacity model considers fire-generated particulate, smoke and toxic gases. It simplifies the flow inside the vehicle but contains the most relevant physics in a computational model that is amenable to large-scale parametric studies. In this paper, background aerosol sources such as that from clothing, Velcro and other human-generated particles are considered in addition to fire. For test cases we consider three vehicles relevant to space exploration, a node inside the International Space Station (ISS), an exploration vehicle with the specifications of the Crew Exploration Vehicle (CEV) and, for legacy purposes, the Space Shuttle. In addition to the different vehicles, we consider variations in ventilation flow and filtration and examine the likelihood of a false trigger as compared to the ability to successfully identify a fire before it reaches a size where it poses a significant threat to the crew or vehicle.