IASFPWG – Atlantic City, NJ Nitrogen Inerting Requirements – A Lit. Review International Aircraft Systems Fire Protection Working Group Atlantic City, NJ October , 2002 Steve Summer Project Engineer Federal Aviation Administration Fire Safety Branch, AAR-422

IASFPWG – Atlantic City, NJ Background  Recent tests at the Tech Center produced inerting requirement data as a function of altitude.  This data contradicts the typical requirement of 9% O 2 used by the military, but a literature search shows that it does not contradict any previous data on the subject.

IASFPWG – Atlantic City, NJ

IASFPWG – Atlantic City, NJ 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.

IASFPWG – Atlantic City, NJ Ref. Kuchta (1986)

IASFPWG – Atlantic City, NJ 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% O 2 were sufficient to suppress ignition except for one.

IASFPWG – Atlantic City, NJ 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.

IASFPWG – Atlantic City, NJ Previous Jet Fuel Data  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)

IASFPWG – Atlantic City, NJ 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% O 2 were due either to a disparity in ignition criteria or excessive safety factors added onto the experimental data.