FORCED IGNITION AND FLAME SPREAD TEST (FIST)
Ignition delay tests use
samples that are 30 mm long, 30 mm wide and 10 mm thick. The dimensions were
deemed adequate to compare the results to those of the LIFT methodology.
Samples are flush mounted in the bottom surface of the duct below the
radiant heaters and with their downstream edges adjacent to the wire igniter.
Forced flow velocity and oxygen concentration are set, data acquisition is
started and the heaters powered to their predetermined setting.
Sample heating may be monitored with surface thermocouples, IR or video
cameras. The time from exposure of the sample to the radiant flux to the
observation of flashing followed by continuous burning is defined as the
flashing and ignition time, respectively. Extinguishing the flames with a
nitrogen flow ends the experiment.
Flame spread experiments use
samples that are 130 mm long, 30 mm wide and 10 mm thick. A decaying heat
flux is imposed on the sample surface to determine the variation of the
flame-spread rate with incident heat flux. Samples are flush mounted in the
bottom surface of the duct below the radiant heaters and with their downstream
edges adjacent to the wire igniter. Forced flow velocity and oxygen
concentration are set, data acquisition is started and the heaters powered to
their predetermined setting. Sample
heating may be monitored with surface thermocouples, IR or video cameras. The
igniter is immediately powered to ignite the downstream edge of the sample.
Flame spread rates are determined by evaluating IR and video images using
Spotlight data processing software. Extinguishing the flames with a nitrogen
flow ends the experiment.
Mass loss experiments use ignition
delay samples sized 30 x 30 x 10 mm and measure continuous mass loss for the
standard ignition delay tests described above and for long duration tests of
pyrolysis without ignition. The tests proceed as indicated in the ignition delay
protocol above with the addition of a data logging scale below the sample. At
the start of each test, the scale is zeroed within a few seconds of heater
activation and after mass readings have stabilized.
Mass loss data is collected at 0.5-second intervals and with a
sensitivity of 0.05 mg. The area around the FIST experiment is closed to foot
traffic, lab doors are closed and oxidizer flow velocity is closely monitored to
minimize fluctuations in mass readings due to pressure changes. Mass logging is
terminated after ignition or at the end of the timed test period.
Figure 10 shows the sample holder used for mass loss experiments and its
placement in the flow tunnel.
