Nitrogen Inerting Requirements A Lit. Review

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Nitrogen Inerting Requirements A Lit. Review

• International Aircraft Systems Fire Protection
  Working Group
• Atlantic City, NJ
• October 30 - 31, 2002

Steve Summer Project Engineer Federal Aviation
Administration Fire Safety Branch, AAR-422
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Background

• Recent tests at the Tech Center produced inerting
  requirement data as a function of altitude.
• This data contradicts the typical requirement of
  9 O2 used by the military, but a literature
  search shows that it does not contradict any
  previous data on the subject.

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Background

• Values lower than 11 12 have arisen due to two
  things
• A difference in ignition criteria
• Pressure rise should be used as criteria, as
  overpressurization is what will cause
  catastrophic failure.
• Safety factors added on to experimental values
• Data has been taken at stoichiometric levels with
  a large ignition source (worst-case scenario), so
  a certain amount of SF is built into the data.

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Ref. Kuchta (1986)
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Previous Jet Fuel Data

• Sam Zinn (1971) Examined data as far back as
  1946 from Boeing, Bureau of Mines, U of Cal.,
  WADC, Convair, and Wright Pat
• All found levels of between 11 12 O2 were
  sufficient to suppress ignition except for one.

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Previous Jet Fuel Data

• Stewart Starkman (1955) determined a level of
  9.8
• Criteria for ignition was any visual flame front.
• It is noted in their report that at times, flame
  occurred with little to no pressure rise.
• Their data does however verify the trend of
  decreasing inerting requirements as altitude
  increases.

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Previous Jet Fuel Data

• Kuchta_at_Bureau of Mines (1970) suggested a SF of
  20 be added on to the LOC value.
• It appears that this is where the current
  military standard of 9 has come from.
• This added SF might not be needed as the tests
  were performed under worst-case conditions (i.e.
  stoich. mixture, large ignition source)

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Conclusions

• A literature search of previous experimental data
  shows excellent agreement with the current
  dataset that was obtained.
• All reported levels that were lower than 11
  12 O2 were due either to a disparity in ignition
  criteria or excessive safety factors added onto
  the experimental data.