Smoke properties from different materials were determined using detectors to measure
different particulate sizes and their relative abundances in order to describe the overall smoke
distribution. A substantial portion of the
aerosol mass is in particles that are larger
than 1 micron. Teflon smoke is comprised
primarily of particles having diameters
less than 1 um. The effect of aging is
consistent with particle coagulation with
limited wall loss; the overall number
count decreases substantially while the
mass concentrations remain relatively
steady. This is reasonable given the
broader size distribution for silicone
smoke containing significant numbers of
both large and small particles. Although
the arithmetic mean diameters are all in
the 100 to 200 nanometer (nm) range,
interpreting particle sizes by only 1
statistic can be deceptive due to the
nature of the particle size distribution. In
general, since the mass increases with the
cube of the diameter, the larger particles do not affect the arithmetic mean diameter (AMD) as
much as they affect the light scattering signal that corresponds with the particle mass.
Consequently, although the AMD for silicone rubber is 227 nm, almost half the particle mass is
larger than 1000 nm. The lamp wick showed similar behavior in the experiment (Urban 2009).
All samples produced significant numbers of sub-micron particulate that are better detected
using an ionization smoke detector, however a light scattering detector would perform very
well for most of the cases. Depending on the conditions, results suggest broader smoke
particulate size distributions can be produced from pre-fire overheat events, thus detection
methods that can measure a wider spectrum of particulate size might show more successful
and reliable detection. Spacecraft and associated missions outside of low-Earth orbit will
require increased reliability of fire detection systems in addition to robust false alarm
resistance. Given the constrained space on any spacecraft, the target for the fire detection
system is necessarily the early phase and not established flaming fires; consequently, the
primary target for detection is the pre-fire heating products and not the soot and ash. This
research will help to improve design of future detectors (Urban 2009).
PUBLICATION(S)
Mulholland G, Meyer M, Urban DL, et al. Pyrolysis smoke generated under low-gravity
conditions. Aerosol Science and Technology. March 6, 2015;49:310-321. doi:
10.1080/02786826.2015.1025125.
ISS015E26265 – View of Smoke and Aerosol
Measurement Experiment (SAME) hardware in the
Microgravity Science Glovebox (MSG) in the US
Laboratory/Destiny. SAME aims to test the performance of
ionization smoke detectors and evaluate the performance
of the photoelectric smoke detectors.