Spacecraft Fire Safety
Fire Suppression and Response
The Space Shuttles
and the ISS have fire extinguishers but, as
with fire detectors, there are some
differences. The Shuttles use a Halon-based suppressant
for portable extinguishers and the fixed system in
the avionics bays. All modules of the ISS use carbon-dioxide
(CO2) extinguishers, except the Russian
module, which uses water-based, foam extinguishers
that are similiar to those that were used on Mir.
The Need for Additional Study
These
different approaches suggest that our understanding
of microgravity fire suppression is incomplete.
This is because there is little data on the extinction
of fires in microgravity. Design decisions for
previous spacecraft have been based primarily
on Earth-based suppression experiments. Designers
favored CO2 for the ISS because of
its effectiveness on Earth-based fires and because
it could be
removed
from the spacecraft's atmosphere by other on-board
systems. But little has been done to determine
which
agent is best for suppressing microgravity fires
while
offering the least invasiveness (post-fire
toxicology and cleanup).
Identifying the Best Suppression Agent
A
goal of the FPDS program is to develop reliable data
and guidelines for the design of fire suppression
systems in microgravity. Already, researchers
at
NASA GRC are evaluating the effectiveness of
suppressants in ground-based, reduced-gravity facilities.
These
projects have yielded new data that will direct
future work. They have also demonstrated
the need to conduct microgravity experiments on Earth
and
in
space
to properly assess the effectiveness of such
candidate suppressants as CO2, N2,
He, water mist, and micro-encapsulated
water.
 |
| The Multiuser Droplet Combustion Apparatus (MDCA)
will be used to screen the effectiveness of various
fire suppressants. |
A planned experiment
in this area will screen several of
these extinguishing
agents to assess
their performance in low-gravity. The Flame Extinguishment
experiment (FLEX) will be conducted in the Multi-user
Droplet Combustion Facility (MDCA) on the ISS and
will use a droplet to evaluate suppressant effectiveness
in reduced gravity. This simplified, spherical geometry
is beneficial because it allows detailed study and
computational analysis. Additionally, scientists
in the Microgravity Combustion Science program have
accumulated
a considerable
amount of data on droplet combustion over the years.
Deploying
Agents in Microgravity
Researchers
will explore how best to deliver the suppression
agent by performing small-scale validation experiments
and large-scale
flow simulations. The flow models will be those
developed for smoke and contaminant transport
to ensure a consistency of computational tools within
the FPDS program.
Tools for Designing Fire Suppression Systems
In
order to validate the computer models, researchers
will need to conduct long-duration, reduced-gravity
experiments to validate the conclusions. With
advanced planning, these experiments could be conducted
in the FEANICS
(Flow Enclosure Accommodating Novel Investigations
in Combustion of Solids), a mini-facility
to study the combustion of solids in the Combustion
Integrated Rack (CIR) on the ISS. If this
is possible, researchers would be able to extend
the models
to address other fuels, suppressants, and geometries
and conduct reduced gravity tests for verification.
Once researchers have identified appropriate suppressant
agents, determined the best delivery system, and
developed reliable computer models, spacecraft and
space habitat designers will have data and analysis
tools that can be used to design effective fire suppression
systems.
Products
The primary product developed in the Fire Suppression
and Response area of the FPDS program will be design
rules for suppressant systems, including the effectiveness
of suppressants, required concentrations, and dispersion
methods.
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