Spacecraft Fire Safety
Fire Prevention and Material Flammability
Material flammability
may be the most critical element of an effective
fire prevention program. Tests to
assess material flammability have been in place since
the early days of manned spaceflight and today materials
are screened for use in spacecraft using a suite
of 18 tests defined in NASA-STD-6001: Flammability,
Odor, Offgassing, and Compatibility Requirements
and Test Procedures for Materials in Environments
that Support Combustion (PDF; 350 KB).
The Primary Test
 |
| Material being tested
for flammability according to procedures spelled
out in NASA-STD-6001, Test 1. |
The most important flammability screening test
is Test 1, the “Upward Flame Propagation” test.
It is conducted in a normal gravity environment,
with ambient conditions (gas composition and
pressure) equal to that of the worst-case environment
to
which the material could be exposed. As shown
in the diagram on the right, a vertical strip
of material
(typically 5 cm wide, 33 cm long, and of the
worst-case thickness) is ignited at the bottom
and scientists
measure how far the flame spreads up the strip.
The material fails the test when more than 15
cm burns or flaming debris drips onto a piece
of paper
placed 20 cm below the sample.
Additional Tests
Test 1 was designed to represent a worst-case assessment
of material flammability aboard spacecraft. However,
research conducted in microgravity has shown that
burning materials behave quite differently under
the non-buoyant conditions of microgravity than
under gravity-driven convection conditions. Materials
that fail Test 1 may still be used on spacecraft
but must undergo further testing and analysis according
to NASA-STD-6001. One of the additional tests -- ”Heat
and Visible Smoke Release Rates” -- uses
a standard cone calorimeter (a special lab instrument
that uses an oxygen-consumption technique to measure
the rate of heat release of materials) to provide
data on ignition delay times and burning rates
of materials. However, this test is also affected
by gravity-induced buoyancy, so the relationship
between these data and the behavior of materials
in microgravity is not known.
It is important for the FPDS program to develop
material flammability tests that yield data from
which the flammability of the material in microgravity
can be determined. A second critical task for this
program is to evaluate the flammability of materials
in atmospheres that may be used in exploration spacecraft
and habitats. Both of these tasks must take the gravity
level (microgravity during transit between the Moon
or Mars; 1/6 normal gravity on the Moon, and 3/8
normal gravity on Mars) into account in order to
ensure that the best and safest possible material
is used in spacecraft and space-based habitations.
Products
The
major products of this effort are:
and Accessibility Certification