Limiting Oxygen Concentration 

Required to Inert Jet Fuel Vapors 

Existing at Reduced Fuel Tank 

Pressures

Steven M. Summer 

August 2003 

DOT/FAA/AR-TN02/79 

This document is available to the public through the National Technical 

Information Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration

te technical note technica 
NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA aircraft certification office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center’s Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
Technical Report Documentation Page

1. Report No.

DOT/FAA/ARTN-02/79

2. Government Accession No. 3. Recipient's Catalog No.

 4. Title and Subtitle 

LIMITING OXYGEN CONCENTRATION REQUIRED TO INERT JET FUEL

5. Report Date

August 2003

VAPORS EXISTING AT REDUCED FUEL TANK PRESSURES 6. Performing Organization Code

7. Author(s)

Steven M. Summer

8. Performing Organization Report No. 

9. Performing Organization Name and Address

Federal Aviation Administration 

William J. Hughes Technical Center 

Airport and Aircraft Research and 

10. Work Unit No. (TRAIS)

Development Division 

Fire Safety Branch 

Atlantic City International Airport, NJ 08405

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

13. Type of Report and Period Covered

Technical Note 

Federal Aviation Administration 

Office of Aviation Research 

Washington, D.C. 20591 

14. Sponsoring Agency Code

 

ANM-100

15. Supplementary Notes

16. Abstract

This report discusses experiments to determine the reduction in oxygen concentration required to prevent a fuel tank explosion. 

A simulated aircraft fuel tank containing JP-8 fuel of an amount equivalent to a mass loading of approximately 4.5 kg/m3 was 

used to determine the limiting oxygen concentration (LOC) at pressures corresponding to altitudes ranging from 0 to 38 kft. In

addition, the peak pressure rise was measured at various altitudes (pressures) due to ignition occurring at O2 levels 

approximately 1% to 1.5% above the LOC. 

A wide range of ignition sources were used throughout the testing. An oil burner transformer connected to an analog timer 

provided a low power arc of both short (0.1 second) and long durations (1 second), a spark igniter taken from a J-57 engine 

provided a very short duration (175 μseconds) high powered spark, and a heated metal block was used as a hot surface ignition 

source. These varied capabilities allowed for an evaluation of the variation in the LOC due to a specific type of ignition source. 

From these tests, it was determined that the LOC at sea level through 10 kft is approximately 12% O2, while exhibiting a linear 

increase from 12% at 10 kft to approximately 14.5% at 40 kft. Tests with various sparks/arcs as ignition sources at sea level 

showed little variation in results, with the LOC ranging from 12.0% to 12.8%. Also, a heated surface capable of igniting a fuel 

air mixture proved insufficient for ignition in a tank inerted to just 14%. Peak pressures resulting from ignition at oxygen 

concentrations 1% to 1.5% above LOC values decreased as the altitude was increased to 30 kft, while the duration to reach the 

peak pressure increased. 

17. Key Words 

Fuel, Fuel tank, Flammability, Ignition, Inert, Jet-A, JP-8, 

Limiting oxygen concentration, Nitrogen inerting

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS) Springfield, Virginia 

22161.

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified

21. No. of Pages

 30

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY vii 

1. INTRODUCTION 1 

1.1 Background 1 

1.2 Aviation Fuel Specification and Characteristics 1 

1.3 Scope of Experiments 3 

2. EXPERIMENTAL APPARATUS 4 

2.1 Test Article 4 

2.2 Pressure Measurement 6 

2.3 Vapor Measurement 6 

2.3.1 Hydrocarbon Analysis 7 

2.3.2 Oxygen Analysis 8 

2.4 Ignition Sources 8 

2.5 Spark/Arc Energy Calculation Method and Results 8 

3. EXPERIMENTAL PROCEDURES 10 

3.1 Methane Validation Tests 10 

3.2 JP-8 Liquid Fuel Tests 10 

4. DISCUSSION OF RESULTS 11 

4.1 Methane Validation Tests 11 

4.2 JP-8 Liquid Fuel Tests 12 

4.2.1 Long Duration Oil Burner Transformer Tests 12 

4.2.2 Engine Spark Igniter Tests 19 

4.2.3 Short Duration Oil Burner Transformer Tests 21 

4.2.4 Hot Surface Vapor Ignition Tests 21 

5. CONCLUSIONS 22 

6. REFERENCES 22 

APPENDIX A—COMMERCIAL AND MILITARY AVIATION FUEL SPECIFICATIONS

iii
LIST OF FIGURES

Figure Page 

1 Typical Flash Point Temperatures of Jet A and Jet B Fuel Blends 2 

2 Typical Industry-Accepted Plots of Jet Fuel Flammability Limits 3 

3 Schematic of Experimental Setup (Plan View) 5 

4 Thermocouple Locations 6 

5 Ullage Vapor Sampling System 7 

6 Voltage and Current Traces of (a) J-57 Engine Igniter and (b) Oil Burner 

Transformer Ignition Sources 9 

7 Experimental Methane LFL Data 12 

8 Limiting Oxygen Concentration Data Results—Aluminum Plate Relief 

Mechanism 13

9 Limiting Oxygen Concentration Data Results— Foil Diaphragm Relief 

Mechanism 13

10 Limiting Oxygen Concentration Data Results—Minimum/Maximum Values for 

Ignition and Nonignition 14 

11 Limiting Oxygen Concentration Data Results—Fuel-Air Ratio and Fuel Vapor 

Concentration vs Oxygen Concentration (Sea Level) 15 

12 Limiting Oxygen Concentration Data Results—Fuel-Air Ratio and Fuel Vapor 

Concentration vs Oxygen Concentration (10 kft) 15 

13 Limiting Oxygen Concentration Data Results—Fuel-Air Ratio and Fuel Vapor 

Concentration vs Oxygen Concentration (20 kft) 16 

14 Limiting Oxygen Concentration Data Results—Fuel-Air Ratio and Fuel Vapor 

Concentration vs Oxygen Concentration (30 kft) 16 

15 Limiting Oxygen Concentration Data Results—Fuel-Air Ratio and Fuel Vapor 

Concentration vs Oxygen Concentration (38 kft) 17 

16 Peak Pressure Rise vs Altitude at O2 Concentrations 1%-1.5% Above the LOC 18 

17 Ignition Time Duration vs Altitude at O2 Concentration 1%-1.5% Above the LOC 18 

iv
18 Engine Igniter Test Results (Sea Level) 20 

19 ASTM D 86 Distillation Curves and Flash Point (FP) Data of JP-8 and Hexane 

Mixtures 20

LIST OF TABLES 

Tables Page 

1 Altitude-Pressure Data 4 

2 Estimated Spark/Arc Energies 9 

3 Nonvented, Full Vessel Ignition Pressure Results 19 

4 Short Duration Oil Burner Transformer Test Results 21 

5 Hot Surface Vapor Ignition Test Results 21 

v/vi
EXECUTIVE SUMMARY

Aircraft fuel tank protection has become of great interest within the aviation community since

the fatal accident of TWA 800, a B747, over East Moriches, NY, in July 1996. The National 

Transportation Safety Board determined that the “probable cause of the TWA flight 800 accident 

was an explosion of the center wing fuel tank (CWT), resulting from ignition of the flammable 

fuel-air mixture in the tank.” As a result, the Federal Aviation Administration (FAA) is currently 

conducting research aimed at reducing or eliminating the flammability exposure time of high 

flammability fuel tanks. Much consideration is being given to the design and optimization of a 

system involving nitrogen inerting. In this process, nitrogen or nitrogen-enriched air would be 

used to reduce the oxygen concentration within the fuel tank to a level at which ignition could

not be supported by flammable ullage vapors. This type of system has been implemented in 

several military aircraft; however, high cost and weight factors combined with low-reliability

factors make those designs impractical for transport category aircraft. Recent advances in gas 

separation technologies may make it possible to design an economic and reliable means of

inerting commercial aircraft fuel tanks. However, in order to optimize such a system, more data 

concerning fuel flammability and inerting gas requirements were needed. The goal of the 

research effort discussed herein is to determine the oxygen concentration necessary to render the 

fuel tank ullage inert. This value is termed the limiting oxygen concentration (LOC). 

The tests were conducted at the FAA William J. Hughes Technical Center, Atlantic City 

International Airport, Atlantic City, NJ, in a facility capable of creating pressures corresponding 

to altitudes ranging from 0 to 38 kft. From these tests, it was determined that the LOC at sea

level through 10 kft is approximately 12% O2, with a linear increase from 12% at 10 kft to 

approximately 14.5% at 40 kft. Tests with various sparks and arcs as ignition sources at sea 

level showed little variation in results, with the LOC ranging from 12.0% to 12.8%. Also, a 

heated surface capable of igniting a fuel air mixture proved insufficient for ignition in a tank 

inerted to just 14%. Peak pressures resulting from ignition at oxygen concentrations 1% to 1.5%

above LOC values decreased as the altitude was increased to 30 kft, while the duration to reach 

the peak pressure increased. Further experiments to examine the trend of peak pressure rise as a 

function of both altitude and oxygen concentration are needed. The results contained in this 

report should be useful in the design, sizing, and optimization of future aircraft inerting systems 

and add to the overall knowledge base of jet fuel flammability characteristics. 

vii/viii
1. INTRODUCTION.

1.1 BACKGROUND. 

Aircraft fuel tank protection has become of great interest within the aviation community since

the fatal accident of TWA 800, a B747, over East Moriches, NY, in July 1996. The National 

Transportation Safety Board (NTSB) determined that the “probable cause of the TWA flight 800 

accident was an explosion of the center wing fuel tank (CWT), resulting from ignition of the 

flammable fuel/air mixture in the tank [1]”. The NTSB [1] further concluded that contributing 

factors to the accident were that the design and certification of the aircraft required only the 

preclusion of all potential ignition sources in order to prevent a fuel tank explosion. No 

measures were taken to reduce heat transfer or inert the fuel tank. 

In several aircraft configurations, including the B747, the environmental conditioning system 

packs are located beneath the CWT. The hot bleed air from this system, passing directly 

underneath of the tank, is the driving force behind the generation of flammabable fuel vapor in

the ullage. In fact, the Aviation Rulemaking Advisory Committee’s Fuel Tank Harmonization 

Working Group [2] found that heated CWTs contain a flammable fuel-air mixture 30% of the 

total flight time as compared with only 4%-6% of the flight time for unheated CWTs and 2%-4% 

for typical unheated main wing tanks. 

The Federal Aviation Administration (FAA) is currently conducting research aimed at reducing 

or eliminating the flammability exposure time of CWTs. Much consideration is being given to 

the design and optimization of a system involving nitrogen inerting. In this process, nitrogen or 

nitrogen-enriched air would be used to reduce the oxygen concentration within the fuel tank to a 

level at which ignition could not be supported by the flammable vapors. Inerting systems have 

been implemented in several military aircraft; however, high cost and weight factors of those

designs combined with low reliability factors make military designs impractical for transport 

category aircraft. Recent advances in gas separation technologies may make it possible to design

an economic and reliable means of inerting aircraft fuel tanks. However, in order to optimize 

such a system, more data concerning fuel flammability and inerting gas requirements are needed

throughout the operational envelope of a fuel tank, including various possible ignition sources. 

1.2 AVIATION FUEL SPECIFICATION AND CHARACTERISTICS.

In the United States, specific requirements relative to aviation turbine fuel properties is set forth

by the American Society of Testing and Materials (ASTM) Standard D 1655. This standard 

limits itself to the commercial grade fuels Jet A, Jet A-1, and Jet B. Jet A and Jet A-1 are the

most commonly used aviation fuels, differing only in their freezing point (-40°C for Jet A and 

-47°C for Jet A-1). Both are derived from kerosene and have a relatively high flash point, set at 

a minimum of 38°C (100°F). 

Jet B fuel, on the other hand, is rarely used today. Jet B is essentially the same as JP-4, a 

standard U.S. military fuel that was used until 1988 when a transition to JP-8 (a fuel which is

very similar to Jet A) was initiated [3]. In addition, the U.S. military also currently uses the 

high-flash point (60°C), kerosene-based JP-5 fuel for Navy carrier-based aircraft. While ASTM 

D 1655 does not control the specifications for these military fuels, a listing of their 

1
corresponding requirements can be found in the Handbook of Aviation Fuel Properties [4]. 

These specifications, for JP-4, -5, and -8, as well as those from ASTM D 1655 for Jet A, Jet A-1, 

and Jet B, are given in appendix A of this report for convenience. 

The fuel used in the experiments discussed within this report was JP-8, which can be treated 

approximately as Jet A (see appendix A). With regards to the chemical composition of Jet A, 

ASTM D 1655 states that these fuels “shall consist of refined hydrocarbons derived from

conventional sources including crude oil, natural gas liquids, heavy oil, and tar sands.” There are 

no provisions given for the exact composition of the fuel, and as such, the properties of any 

given fuel batch can vary from that of any other, provided that they meet the minimum 

specifications set forth in ASTM D 1655. This lack of a definitive composition results in fuels

that consist of hundreds of chemical species. 

Regarding the flammability properties of aviation fuels, the two most widely used parameters are 

the fuel’s flash point and flammability limits, given in terms of altitude and temperature data. 

The flash point of a liquid fuel is defined as the lowest temperature, at atmospheric pressure, at 

which sufficient vapor is released by the fuel to support ignition. The current standardized 

methods for determining the flash point are ASTM D 56 and ASTM 3828. Both methods place a 

sample of fuel in a closed cup and heat it at a constant rate. A small flame is introduced into the 

cup, and the lowest temperature at which ignition is observed is referred to as the flash point. 

Figure 1, as taken from reference [4], shows a graph of approximate flash points versus blends of 

Jet A and Jet B fuels. 

Fuel Composition by Volume

Flash Point (ASTM D93) 

Temperature °C

FIGURE 1. TYPICAL FLASH POINT TEMPERATURES OF JET A AND 

JET B FUEL BLENDS 

2
The flammability limits of a given fuel provide more information than the flash-point

measurement, especially when presented as regions of flammability in terms of altitude and fuel 

temperature. At any given altitude (pressure), a fuel will have a lean (or lower) flammability 

limit (LFL) and a rich (or upper) flammability limit. Within these limits, ignition of vapors may 

occur, while outside the limits there should be no observed combustion phenomenon. Over the 

years, there have been numerous experiments to determine the flammability limits of aviation 

turbine fuels. A typical plot of these limits, including ignition energies, for Jet A and Jet B fuels 

is shown in figure 2, as taken from reference [3]. 

FIGURE 2. TYPICAL INDUSTRY-ACCEPTED PLOTS OF JET FUEL

FLAMMABILITY LIMITS 

Both the flash point and flammability limits given above assume isothermal and equilibrium 

conditions, not taking into account such things as possible condensation of the fuel vapor and 

variation of the ullage composition. In order to provide useful data for fuel tank inerting 

requirements, data on the reduction of fuel flammability as a function of oxygen depletion are

needed. 

1.3 SCOPE OF EXPERIMENTS.

The purpose of the experimental research discussed in this report is to further quantify the 

oxygen concentrations required to protect against the ignition of JP-8 fuel vapors at altitudes 

ranging from 0 to 38 kft. This data will aid in the design of nitrogen inerting systems for use in 

aircraft fuel tanks. Throughout the experiments, the lowest oxygen concentration resulting in 

ignition of the ullage fuel vapors is referred to as the limiting oxygen concentration (LOC). 

3
2. EXPERIMENTAL APPARATUS.

2.1 TEST ARTICLE. 

The experiments discussed within this report were conducted at the FAA William J. Hughes 

Technical Center’s Pressure Fire Modeling Facility. This facility houses a 10-m3

 vessel capable 

of withstanding a maximum working pressure of 650 psi. An attached vacuum pump evacuated 

the chamber to pressures corresponding to desired altitudes. The pressures corresponding to 

each altitude tested can be found in table 1. 

TABLE 1. ALTITUDE-PRESSURE DATA 

Altitude

(kft) 

Pressure 

(psia)

0 14.70

10 10.25

20 6.97

30 4.61

38 3.22

The vented fuel tank test article placed within the 10-m3

 vessel was approximately 0.25 m3 (9 ft3) 

in volume. It was equipped with 12 K-type thermocouples, sample lines for hydrocarbon and 

oxygen vapor sampling, thermostatically controlled hot plates with a capacity of 1650 watts, and 

a 6-in.-diameter mixing fan used to ensure a homogeneous ullage vapor mixture. A fuel pan, 

measuring 9.5 by 9.5 in., was placed in the center of the fuel tank. A 10- by 10-in. opening in 

the fuel tank’s roof was fitted with interchangeable pressure relief mechanisms of either a springloaded 1/4-in.-thick aluminum plate or a foil diaphragm.

The aluminum plate mechanism was used in the early phases of testing to gain general 

knowledge of the LOC at each altitude, while the diaphragm was used to more accurately

determine the LOC. In the case of the aluminum plate, an ignition was said to occur if there was 

noticeable movement of the plate; whereas, with the latter mechanism, ignition was said to occur 

if the diaphragm was ruptured during the test. Ignition was also evident from the appearances of

flames of various size and color. 

In addition, two piezoresistive pressure transducers installed in the tank were used at oxygen 

concentrations approximately 1%-1.5% above the LOC at each altitude. These tests were

performed in hopes of providing more knowledge of the pressure rises associated with these lowlevel oxygen tests so as to increase confidence that any chemical reactions near the LOC would

not result in pressure increases that might impact the structural integrity of the tank. 

A bank of nitrogen bottles, connected to the fuel tank and controlled via a solenoid valve, served 

the dual purpose of controlling the ullage oxygen concentration and extinguishing any flames

resulting from ignition of the ullage vapors. In addition, a bottle of 100% methane was 

connected to the fuel tank, for use during the validation tests, in which the LFL for methane was

determined and compared to published data [5]. 

4
The 12 thermocouples were used to record liquid fuel, ullage, and tank wall temperatures for the

purpose of test monitoring and for use in future fuel vapor modeling work. Two thermocouple 

trees, placed within the tank, held a total of four ullage thermocouples. There were two 

thermocouples on each tree, which were placed a third of the way up from the bottom of the tank

and a third of the way down from the top. Two thermocouples were placed on the floor, directly 

above the two heating elements, and one in the middle of the floor, directly under the fuel pan, in 

between the two heating elements. In addition, one thermocouple was used to record the liquid 

fuel temperature, and another thermocouple was placed at the center of each sidewall. 

A spark/arc gap was located in the front left corner of the fuel tank. This gap consisted of two 

1/16-in.-diameter tungsten electrodes that used a micrometer for gap width control and 

adjustment springs for electrode alignment. The gap width was set at approximately 7 mm

throughout testing as this has been shown to be the optimum electrode spacing for ignition 

testing with methane [6]. Throughout testing, these electrodes were powered by two different 

spark/arc generators—an arc generating oil burner transformer and a J-57 engine spark igniter. 

In addition to these two ignition sources, a hot surface was also used in a brief set of tests 

concerning hot surface vapor ignition (HSVI). All of these ignition sources are discussed in

detail in section 2.4 of this report, and a discussion of the methods used and results of energy 

calculations of the spark/arc generators is provided in section 2.5. 

All test equipment was controlled through solid-state relays, powered by toggle switches located 

within a trailer directly outside the test facility. The trailer also housed all computer and data

acquisition equipment. Schematics of this test setup, including thermocouple placements, are 

shown in figures 3 and 4. 

Video

Camera THC

Analyzer

Right Test Track

Left Test Track

10 m Pressure 

Vessel

3 Analyzer Bypass

Sample Line O 

Analyzer 2

Heater

Spark

Source

Fan

= Thermocouple Feedthrough

N Lines 2

House

Air Line

Pressure Transducers

FIGURE 3. SCHEMATIC OF EXPERIMENTAL SETUP (PLAN VIEW) 

5
Left T/C Tree Right T/C Tree

Liquid JP-8 Fuel Fuel Pan

= Thermocouple Bead

6.0" 6.0"

FIGURE 4. THERMOCOUPLE LOCATIONS 

2.2 PRESSURE MEASUREMENT.

Two piezoresistive pressure transducers were used in testing at ullage oxygen concentrations 

approximately 1%-1.5% greater than the determined LOC at each altitude. A Kulite model

XT-130 and an Endevco model 8530C were employed and both were operated at a frequency of

1 kHz. Though manufactured by different companies, both have similar electronics and work on 

the same theory of operation, thus, giving similar readings. In a method similar to Shepherd, et 

al. [7], to protect these transducers from the high temperatures associated with the ignition, it was 

necessary to place them in protective housings with a 3/8-in.-thick, sintered porous metal disc in

front of the diaphragms. These protective housings act as a flame arrestor, protecting the 

transducers from the impinging flame front. 

2.3 VAPOR MEASUREMENT.

Ullage hydrocarbon and oxygen concentrations were measured with dedicated hydrocarbon and 

oxygen analyzers connected to the test article via 1/4-inch sample lines. Among the

considerations taken into account when designing the sampling systems were condensation of the 

fuel vapors, fouling of the sensors, depletion of the sample, and maintaining the necessary 

pressures and flow rates for each of the analyzers. A schematic of the sample trains employed

are shown in figure 5, and detailed descriptions of each are given in sections 2.3.1 and 2.3.2 as 

well as brief summaries of the measurement principles of each analyzer. 

6
B

THC

Analyzer

Pressure Vessel

B

Oxygen 

Analyzer

Heated Sample Line

Unheated Sample Line

B

Ball Valve

T-Fitting 3-Way Valve

F

Pressure Regulator

Diaphragm Pump

Bulkhead Fitting

KEY

Cal. Gas Inlet

Bypass

THC Intake

Oxygen Intake

Oxygen Return

Sample

Overflow

Locations

Ice-Temperature Bath lowmeter Flow Meter 

FIGURE 5. ULLAGE VAPOR SAMPLING SYSTEM 

2.3.1 Hydrocarbon Analysis.

Hydrocarbon concentrations were measured throughout all tests with a total hydrocarbon (THC)

analyzer using flame ionization detector (FID) technology. The full length of the sample line 

was maintained above 300°F with analog temperature controllers. This sample line was routed 

outside the rear of the vessel, into a series of ball valves, and into the hydrocarbon analyzer. The 

ball valves were used to switch the sampling process from inside of the fuel tank to the ambient 

air outside of the pressure vessel. This was done for two reasons. First, it was necessary to

ensure that during ignition, the analyzer was not sampling from the fuel tank because it would

damage the sensor. Second, it was necessary to intermittently draw a vapor sample from the tank 

because continuous sampling would result in a severe depletion of the sample. In addition, for 

tests at altitude, an external diaphragm-type pump was used between the ball valves and the 

analyzer to achieve the necessary flow rate through the detector. A flow meter on the bypass end 

of the analyzer was used to confirm the required sample flow rate. Limitations of the sample 

pump prevented experiments above altitudes of 38 kft. Testing at higher altitudes resulted in 

insufficient flow on the outlet of the pump. This caused a reversal in flow direction at the 

sample overflow location, thus, diluting the vapor sample. 

Calibration of the THC analyzer was performed by flowing mixtures of varying propane 

concentration directly into the calibration ports of the analyzer. This calibration was then 

checked by allowing the calibration gas to flow through the pump into the sample inlet to ensure 

that there was no variance between the sample line and the calibration line. 

The measurement principle of a FID analyzer is based on the ionization of organically bound 

carbon atoms in a hydrogen flame. The vapor sample is mixed with a hydrogen fuel mixture

prior to reaching the burner, where the high temperature of the hydrogen flame causes reaction of

the hydrocarbon compounds. Ions produced by this combustion are detected by the electrodes of 

7
the FID, and the resulting current is amplified and outputted. This output is proportional to the 

number of carbon atoms for all hydrocarbon molecules and provides accurate total hydrocarbon 

measurements in terms of a volumetric concentration relative to the calibration gas. 

2.3.2 Oxygen Analysis.

A Rosemount OM-11 EA oxygen analyzer was used to record the tank oxygen concentrations

throughout the test program. Using a diaphragm-type pump in conjunction with a pressure 

regulator and flow meter to maintain a steady flow and pressure, the sample was drawn from the 

tank through an ice-temperature bath, into the analyzer, and then recirculated back into the tank.

A backpressure regulator on the return side ensured positive flow back into the test article. The

ice-temperature bath was used to condense out the hydrocarbons from the sample prior to 

reaching the oxygen sensor, which was found to be sensitive to these liquids. Calibration was 

performed by inserting mixtures of varying oxygen concentration into the sample line upstream 

of the diaphragm pump. 

The OM-11 is, in essence, a partial pressure-sensing device. It uses a polarographic oxygen 

analysis technique, whereby two electrodes, immersed in potassium chloride gel, permit the 

diffusion of oxygen across a Teflon membrane. The rate of this diffusion is proportional to the 

partial pressure of oxygen on the outside of the membrane. The OM-11 converts this partial 

pressure into a reading of volumetric percent oxygen concentration, having an output on a scale 

of 0 to 5 Vdc. 

2.4 IGNITION SOURCES.

Throughout testing, several ignition sources were used. An oil burner transformer connected to 

an analog timer provided a low-power arc of both short (0.1 second) and long durations 

(1 second), a spark igniter taken from a J-57 engine provided a very short duration 

(175 μseconds) high-powered spark, and a heated metal block was used as a hot surface ignition

source. The heated metal block, which measured 1′′ x 3′′ x 6′′ long, was heated by two 

0.75′′ diameter heating rods that passed through the unit and was monitored by a thermocouple 

mounted to the top surface. These varied ignition energy characteristics allowed for the 

verification of any variation in the LOC due to a specific type of ignition source. 

2.5 SPARK/ARC ENERGY CALCULATION METHOD AND RESULTS.

For better characterization of the sparks and arcs used in testing, measurement of both voltage 

and current at the point where the high voltage leads entered the fuel tank were made. A

Tektronix P6015A high-voltage probe was used for voltage measurement and an Ion Physics 

model CM-10-L was used for current measurement. Both probes were connected to a Tektronix 

THS730A oscilloscope which was used to record the two traces and transport them to a PC

where calculations could be performed. With the voltage and current data, the energy deposited 

into the gap could then calculated by

(1) ∫ =

1

0

t

E VIdt

8
These tests and calculations were performed for both the short and long duration oil burner 

transformer arc as well as for the engine igniter spark. The results of these measurements can be

found in table 2, while the voltage and current traces for the engine igniter and portions of the 

traces for the oil burner transformer are shown in figures 6(a) and 6(b). 

TABLE 2. ESTIMATED SPARK/ARC ENERGIES 

Ignition Source 

Time Duration 

(s) 

Estimated Energy

(Joules) 

Oil Burner Transformer 1.0 0.5 

Oil Burner Transformer 0.1 0.08 

J-57 Engine Igniter 0.000175 0.5 

(a) 

(b) 

FIGURE 6. VOLTAGE AND CURRENT TRACES OF (a) J-57 ENGINE IGNITER AND 

(b) OIL BURNER TRANSFORMER IGNITION SOURCES 

In addition, noise tests were conducted to determine if noise levels on either of the probes were 

large enough to effect this energy calculation. These tests clearly indicated that any noise on 

either of the probes was insufficient to have affected energy calculations in any significant way. 

9
3. EXPERIMENTAL PROCEDURES.

3.1 METHANE VALIDATION TESTS. 

Prior to each test, the test article was purged with shop air in order to remove any remaining 

methane vapors. The hydrocarbon analyzer was calibrated with a certified bottle of 5-percent 

methane balanced in nitrogen and was zeroed with 100% nitrogen. The vessel door was closed 

and sealed, and data acquisition was initiated. A solenoid valve was opened to introduce 

methane into the test article. The ullage vapors were monitored with the hydrocarbon analyzer, 

providing time for complete mixing of the methane vapors. Once the desired methane 

concentration stabilized, a 1-second spark initiated the combustion process. This was repeated at 

numerous methane concentrations until ignition, defined in these tests as visual observation of

movement of the blowout plate, was unobtainable. This level was then noted as the LFL and 

was compared to published data [5]. 

3.2 JP-8 LIQUID FUEL TESTS.

Prior to each test, the test article was purged of any remaining vapors with shop air until the 

ullage oxygen content was approximately 20.9% and the hydrocarbon concentration was below 

2000 ppm-C3H8. The hydrocarbon analyzer was calibrated and linearized with certified bottles 

of 2-, 3-, 4-, and 6-percent propane balanced in nitrogen. The oxygen analyzer was subsequently 

calibrated with certified bottles of 12% and 16% oxygen with a nitrogen balance. In addition, 

both analyzers were zeroed with a bottle of 100% nitrogen. 

Following this calibration and a check of all critical devices, 3/8 of a gallon of JP-8 fuel was

carefully measured, poured into the fuel pan, and placed in the center of the fuel tank. The 

pressure vessel was hydraulically sealed and the vacuum pump was used to evacuate the 

chamber to the approximate pressure corresponding to the desired altitude. Data collection was 

initiated. The nitrogen solenoid valve was opened to introduce nitrogen into the tank. The flow 

of nitrogen was introduced in stages, while monitoring the ullage oxygen concentration. When

the desired oxygen concentration was achieved, all nitrogen flow was terminated, and the fuel 

heating process was started. 

The oxygen and hydrocarbon concentrations within the fuel tank were periodically checked 

throughout the test, with the fan being used to ensure a well-mixed ullage vapor space. Upon

achieving the desired ullage vapor concentration, the oxygen analyzer pump was turned off, and 

the hydrocarbon analyzer was switched to sample from ambient air. This was done to prevent 

combustion products from fouling the gas analyzer sensors. 

At this point, video tape recording was initiated and the fuel vapor mixture was subjected to 

several sparks/arcs. In the case of the HSVI tests, the heated block was running and monitored 

throughout the test at between 50%-70% full load and turned to full load as the desired ullage 

vapor concentration was achieved. The hot surface temperature (HST) was monitored

throughout. In all test cases, if ignition, as defined in section 2.1, was not observed the test was 

terminated and the tank was considered inert under these conditions. 

10
In order to obtain worst-case scenario data, it was desired to perform testing at nearstoichiometric mixtures. Calculations of the stoichiometric mixture were performed by 

approximating the fuel vapor as CxHy. Using an existing computer model developed by Ivor

Thomas, the FAA’s Chief Scientific and Technical Advisor for Fuel Systems, a ratio of y:x was 

obtained, as well as the vapor’s molecular weight. These calculations, with the input of a 

stoichiometric fuel-air mass ratio (FAR) of 0.068, resulted in y/x = 1.99 and MWvapor = y + 12x =

126.54. With this information, it was then determined that the approximate fuel vapor was 

C9.05H18.01. This could then be substituted into a stoichiometric chemical equation 

C9.05H18.01 + a[O2 + 3.76N2] → bCO2 + cH2O +dN2 

Solving this equation for the coefficients a, b, c, and d results in 

C9.05H18.01 + 13.55[O2 + 3.76N2] → 9.05CO2 + 9H2O +50.96N2 

From this, the fuel-air mole ratio can be determined as 

( )( ) 1.53%

1 4.76 13.55

1 = + =

air

fuel

mol

mol

Therefore, the stoichiometric mixture in terms of part-per-million of fuel vapor (ppmfuel) is given 

by 15267 ppmfuel. To obtain this value in terms of propane, it is simply multiplied by the carbon

ratio, in this case 3

9.05 . This then results in an approximate stoichiometric mixture of 

46155 ppm-C3H8. Performing this same set of calculations for a 12% O2 environment, one 

could find a stoichiometric 12% O2 air mixture of approximately 24000 ppm-C3H8. As testing

showed and as discussed in section 4.2.2, this stoichiometric mixture at a reduced O2

concentration resulted in the lowest values of the LOC despite initial thoughts that a 

stoichiometric 21% O2 air mixture would be needed. 

4. DISCUSSION OF RESULTS.

4.1 METHANE VALIDATION TESTS. 

As discussed previously, prior to performing any ignition experiments with aviation fuel, a series 

of validation tests were performed with methane in air mixtures. Because pressure was not 

measured in these experiments, ignition was defined by visual observation of the movement of 

the blowout plate, which resulted from a pressure buildup within the tank. 

The experimental data for this series of tests is shown in figure 7, in terms of ignition and 

nonignition criteria. The data shows that the LFL of methane lies somewhere between 5.3% and 

5.35% methane, matching closely the value 5.3% given by Lewis and von Elbe [5]. Therefore, it 

was concluded that the experimental apparatus and methods employed were suitable for ignition 

testing. 

11
FIGURE 7. EXPERIMENTAL METHANE LFL DATA 

4.2 JP-8 LIQUID FUEL TESTS. 

The majority of tests with liquid JP-8 fuel were conducted using the oil burner transformer as the 

ignition source with an arc duration of 1 second. These tests were conducted with both the 

1/4-in. aluminum plate and foil diaphragm pressure relief mechanisms and at altitudes ranging 

from 0 to 38 kft. Subsequent tests used the other various ignition sources in an attempt to verify 

any dependency of the LOC with ignition source. Tests with the short duration oil burner 

transformer, engine igniter, and hot surface focused on sea level conditions because this is the

region which drives the design criteria for an inerting system. 

4.2.1 Long Duration Oil Burner Transformer Tests.

The initial oil burner transformer tests were conducted with a spring-loaded, 1/4-in. aluminum 

plate used as the pressure relief mechanism and a 1 second arc duration. As noted previously, 

ignition under these test conditions was characterized by movement of this blowout plate. The 

tests were conducted in the range of 0 to 30 kft, in increments of 10 kft. At each altitude, 

ignition was attempted at an initial ullage concentration of 20.9% O2 followed by reduced 

oxygen concentrations until ignition was no longer observed under the given test conditions. 

The results from this set of tests are shown in figure 8 as oxygen concentration plotted against 

altitude. 

The data in figure 8 clearly indicates that LOC increases with increasing altitude. However, the

precise nature of this trend could not be established due to data scatter and an insufficient 

ignition and nonignition criterion. These results were useful in subsequent tests to determine the 

LOC as a function of altitude. The upward trend in LOC is not observed at 30 kft in figure 8 due 

to an insufficient hydrocarbon sample flow at this low pressure. Prior to continuing with further 

testing, this issue was resolved. 

12
FIGURE 8. LIMITING OXYGEN CONCENTRATION DATA 

RESULTS—ALUMINUM PLATE RELIEF MECHANISM 

To better define the LOC, the aluminum plate pressure-relief mechanism was replaced with a foil 

diaphragm. With this new relief mechanism, ignition was defined simply by rupture of the foil,

allowing for a more definitive measure of ignition and nonignition. These tests were carried out 

in a similar fashion as those depicted in figure 8, with the upper limit of testing being at or 

slightly above the LOC determined from the previous tests. This set of tests was also expanded 

to include a higher altitude of approximately 38 kft, the upper limit at which the instrumentation 

was capable of accurate vapor measurement. The results are presented in figure 9, again as

oxygen concentration plotted against altitude. In addition, figure 10 shows the minimum O2

concentration resulting in ignition along with the maximum O2 concentration resulting in 

nonignition at each altitude. 

FIGURE 9. LIMITING OXYGEN CONCENTRATION DATA RESULTS— 

FOIL DIAPHRAGM RELIEF MECHANISM 

13
FIGURE 10. LIMITING OXYGEN CONCENTRATION DATA RESULTS—

MINIMUM/MAXIMUM VALUES FOR IGNITION AND NONIGNITION 

From these results, there is a clear indication that an increase occurs in the LOC as altitude is 

increased. The LOC rises steadily from a value approximately 12% O2 at sea level and 10 kft to 

approximately 14.5% O2 at 40 kft. 

The sea level LOC data is consistent with previous data, such as Zinn’s work in 1971 [9], in

which he performed an extensive literature search of several inerting level requirement datasets. 

Zinn found that the resulting LOC determined by these experiments varied approximately 1

percent, falling in the 11.5%-12% O2 range. Many aircraft inerting systems, however, have used 

a level approximately of 9% as their design criteria as a result of a Bureau of Mines suggestion 

of using a 20% safety margin [10]. 

While there is not much data available for the LOC at altitude, Stewart and Starkman [11] did 

perform some altitude work with both carbon dioxide and nitrogen inerting. Their data,

however, was generated by using flame propagation as the ignition and nonignition criteria. If 

any visible flame front occurred within the tank, it was considered an ignition. The resulting

pressure rise was not used as a criterion, and it is noted in their report that at times flame

propagation occurred with little or no resulting pressure rise. As a result of this difference in

criterion, Stewart and Starkman’s data set tends to be lower than the data generated here, starting 

at approximately 9.8% O2 at sea level and increasing to approximately 10.8% at 30 kft and 13% 

at 60 kft. While the disparity in criteria does not allow for direct comparison of this data to the

data presented in this report, it does verify the trend of decreasing inerting level requirements 

(higher LOC) as altitude is increased. 

Figures 11-15 depict the data from these tests as approximated fuel-air mass ratio and volumetric 

fuel vapor concentration versus volumetric oxygen concentration for each of the five altitudes 

tested. A large majority of the tests were conducted at sea level, because this is the most 

important region in the design of an inerting system. From the 50 tests conducted at sea level, 18 

14
were conducted in the range of 11%-12.5% O2. Of these 18 tests, only four resulted in ignition, 

and only one of the nine tests at or below 12% O2 ignited. 

FIGURE 11. LIMITING OXYGEN CONCENTRATION DATA RESULTS—FUEL-AIR 

RATIO AND FUEL VAPOR CONCENTRATION VS OXYGEN CONCENTRATION 

(SEA LEVEL) 

FIGURE 12. LIMITING OXYGEN CONCENTRATION DATA RESULTS—FUEL-AIR 

RATIO AND FUEL VAPOR CONCENTRATION VS OXYGEN CONCENTRATION (10 kft) 

15
FIGURE 13. LIMITING OXYGEN CONCENTRATION DATA RESULTS—FUEL-AIR 

RATIO AND FUEL VAPOR CONCENTRATION VS OXYGEN CONCENTRATION (20 kft) 

FIGURE 14. LIMITING OXYGEN CONCENTRATION DATA RESULTS—FUEL-AIR 

RATIO AND FUEL VAPOR CONCENTRATION VS OXYGEN CONCENTRATION (30 kft) 

16
FIGURE 15. LIMITING OXYGEN CONCENTRATION DATA RESULTS—FUEL-AIR 

RATIO AND FUEL VAPOR CONCENTRATION VS OXYGEN CONCENTRATION (38 kft) 

Although excessive amounts of condensation at low altitudes precluded testing at a 

stoichiometric fuel-air mixture, later testing, as discussed in section 4.2.2, showed that the lowest 

values for LOC occurred at a near stoichiometric mixture for a fuel-12% O2 air mixture. 

Upon completion of these LOC tests, it was desired to measure the pressure rises caused by 

ignition, seen at low-oxygen concentrations, and examine the effect of increasing altitude. The

two pressure transducers were used as described in section 2.2 of this report. Tests were

conducted at altitudes from 0 to 30 kft, with the foil diaphragm acting as the pressure relief 

mechanism. Testing was limited to oxygen levels approximately 1% to 1.5% above the LOC 

values previously determined and shown in figure 10. 

Both transducers recorded similar values, and the averaged results are shown in figures 16 and 

17. Figure 16 depicts the peak pressure rise versus altitude. From this plot a decrease in the 

peak pressure is observed as altitude is increased from 0 to 30 kft. Figure 17 depicts the time

duration to reach the peak pressure plotted versus altitude. The time duration increases as

altitude is increased. 

It should be noted, however, that with these particular tests, after the diaphragm ruptured, the 

transducers were reading the pressure of the entire chamber. It is for this reason that the peak

pressures recorded in figure 16 seem relatively small, and similarly that the time durations in

figure 17 are relatively long. Since the vessel volume is approximately 40 times the volume of 

the fuel tank, the peak pressures shown in figure 16 are approximately 1/40 of the potential 

pressure rise occurring in a closed, nonvented environment. This appears to be consistent with 

17
Shepherd, et al.’s [8] work, in which they recorded pressure rises near 50 psig, occurring at 

pressures equivalent to an altitude of approximately 15 kft. 

0

0.5

1

1.5

2

2.5

0 10 20 3

Altitude (kft)

Pressure Rise (psig)

0

FIGURE 16. PEAK PRESSURE RISE VS ALTITUDE AT O2 CONCENTRATIONS 

1%-1.5% ABOVE THE LOC 

0

2

4

6

8

10

12

0 10 20

Altitude (kft)

Time Duration to Reach Peak Pressure (s)

30

FIGURE 17. IGNITION TIME DURATION VS ALTITUDE AT O2 CONCENTRATION 

1%-1.5% ABOVE THE LOC 

18
The pressure rise data was further verified by a brief set of experiments that were conducted 

within the full-pressure vessel with no postignition pressure relief. In these tests, a 3- by 6-foot 

fuel pan was placed inside the vessel with the equivalent fuel loading as in previous tests. 

Heating of the fuel was achieved by three of the identical hot plates used in the 9-ft

3

 tank

attached to the bottom of the pan. Ignition was achieved using the same transformer, connected

to two 1/8-in steel electrodes. Vessel pressure was recorded by a 0-200 psi sealed gauge, 

diaphragm-type transducer. Due to large condensation effects within this chamber, tests were

only able to be conducted at altitudes above 20 kft. The results of these tests can be seen in 

table 3. 

TABLE 3. NONVENTED, FULL VESSEL IGNITION PRESSURE RESULTS 

Altitude

(kft) 

Oxygen 

Concentration 

Initial 

Pressure 

(psia)

Final 

Pressure 

(psia)

Differential 

Pressure 

(psia)

Differential/Initial 

Pressure 

(psia)

20 21.0% 6.9 33.7 26.8 3.88

20 15.0% 6.8 30.5 23.7 3.49

38 21.0% 3.5 16.1 12.6 3.60

38 17.3% 3.8 16.5 12.7 3.34

Extrapolating the results in figure 16 to include a data point of approximately 0.3 psig at 38 kft, it 

can be seen that at both altitudes the nonvented data is approximately 42 times the vented 

pressure results. This data also shows that the ullage oxygen concentration has little or no effect

on the resulting pressure rise from ignition, and that the ratio of differential to initial pressure 

does not vary much with either altitude or oxygen concentration. 

4.2.2 Engine Spark Igniter Tests.

Results of tests conducted with the J-57 engine igniter can be seen in figure 18. In an attempt to 

verify that testing was being performed at the optimum hydrocarbon concentration, these tests 

were conducted within several fuel vapor concentration ranges. These consisted of those at 

levels near that of a stoichiometric 12% O2 air mixture (i.e., 0.035 < FAR < 0.04), those at levels

near that of a stoichiometric 21% O2 air mixture (i.e., 0.065 < FAR < 0.07), and several that fell

between these two ranges. 

Due to the high amount of condensation occurring in the test tank, it was necessary to slightly 

modify the test fuel so as to be able to achieve those higher fuel vapor concentrations. Being that

hexane has flammability properties that closely mimic that of jet fuel and has a rather low boiling 

point, it was decided to spike the test fuel with varying amounts of hexane as noted in the figure. 

To verify that this modification did not drastically affect the fuel, distillation curves and flash 

points were taken of the JP-8 and JP-8/Hexane mixtures. The results of these tests can be found 

in figure 19. From this figure, it is observed that the addition of hexane has affected the fuel 

only in increasing the quantity of low-boiling point components, thereby reducing the fuel’s 

flashpoint. Above 20% distillation, however, little effect is seen. 

19
FIGURE 18. ENGINE IGNITER TEST RESULTS (SEA LEVEL) 

0

100

200

300

400

500

600

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

% Distilled

Temperature (°F)

JP-8 (No Hexane Added), FP = 114.8°F

JP-8 (20 cc Hexane Added), FP = 91.8°F

JP-8 (30 cc Hexane Added), FP = 81.7°F

JP-8 (40 Hexane Added), FP = 78.3°F

JP-8 (100 cc Hexane Added), Flash Ppoioinntt Unk U nowwn n 

FIGURE 19. ASTM D 86 DISTILLATION CURVES AND FLASH POINT (FP) DATA OF 

JP-8 AND HEXANE MIXTURES

There were 15 tests conducted at the stoichiometric 21% O2 mixture, consisting of ullage O2

concentrations from 11.9% to 13.7%. Of these 15 tests, not one resulted in ignition. Of the 18 

tests conducted at FARs below this, the lowest ullage O2 concentration resulting in ignition was

12.3%. Interestingly, this value of the LOC occurred at a near stoichiometric mixture for a fuel12% O2 air mixture as opposed to the initial thought that a stoichiometric mixture for 21% air 

20
would need to be used to obtain the lowest LOC value. It is believed that the inerting agent has 

effectively lowered the UFL, thereby resulting in a mixture that is too rich. 

4.2.3 Short Duration Oil Burner Transformer Tests.

Table 4 summarizes results of six tests conducted using the oil burner transformer with a 0.1 

second arc duration. The tests were performed near stoichiometric for a fuel-12% O2 air mixture 

and at ullage O2 concentrations ranging from 12.5%–14.3% at sea level conditions. Of these 

tests, three resulted in ignition, all at O2 concentrations greater than 12.8%. Below this value, no 

ignition was achieved. 

TABLE 4. SHORT DURATION OIL BURNER TRANSFORMER TEST RESULTS 

O2

Concentration 

Total 

Hydrocarbons 

(ppm-C3H8) 

% Volume

of Jet-A 

Fuel-Air 

Mass Ratio Ignition?

12.5% 23000 0.7667 0.033 No

12.8% 22000 0.7333 0.032 No

12.8% 23500 0.7833 0.034 No

14.3% 24500 0.8167 0.035 Yes

13.2% 23000 0.7667 0.033 Yes

12.9% 24000 0.8000 0.034 Yes

4.2.4 Hot Surface Vapor Ignition Tests.

To ensure that the heated surface was a capable ignition source, the initial HSVI test was 

conducted in a noninerted atmosphere. The results of these tests are summarized in table 5. A

violent ignition was observed during this test as the HST approached approximately 1350°F. Six

subsequent tests were performed with ullage O2 concentrations ranging from 11.3% to 14.0%, 

again with near stoichiometric concentrations for a fuel-12% O2 air mixture. During these tests,

as the HST approached approximately 1200°F, some slight puffs of smoke could be seen 

emanating from the vent of the fuel tank, however no ignition events were observed in any of the 

tests even as the surface was heated above 1400°F. 

TABLE 5. HOT SURFACE VAPOR IGNITION TEST RESULTS 

O2

Concentration 

Total 

Hydrocarbons 

(ppm-C3H8) 

% Volume

of Jet-A 

Fuel-Air 

Mass Ratio 

Maximum 

HST Ignition?

21% 25500 0.8500 0.037 1300 Yes

14% 26000 0.8667 0.037 1430 No

13.1% 23000 0.7667 0.033 1420 No

12.7% 24000 0.8000 0.035 1440 No

11.5% 26000 0.8667 0.037 1430 No

11.3% 21500 0.7167 0.031 1420 No

21
5. CONCLUSIONS.

From these tests, it was determined that the limiting oxygen concentration (LOC) at sea level 

through 10 kft is approximately 12% O2, with a linear increase from 12% at 10 kft to 

approximately 14.5% at 40 kft. Tests with various sparks and arcs as ignition sources under sea 

level conditions showed little variation in results, with the LOC ranging from 12.0% to 12.8%. 

Meanwhile, a heated surface capable of igniting a fuel-air mixture proved insufficient for

ignition in a tank inerted to just 14% O2. Pressure data showed that peak pressures resulting

from ignition at oxygen concentrations 1% to 1.5% above LOC values decreased as the altitude 

was increased to 30 kft, while the time duration to reach the peak pressure increased. 

6. REFERENCES.

1. “Accident Report: In-Flight Breakup Over the Atlantic Ocean Trans World Airlines 

Flight 800 Boeing 747-131, N93119, near East Moriches, New York, July 17, 1996,” 

National Transportation Safety Board, NTSB/AAR-00/03, August 23, 2000. 

2. Aviation Rulemaking Advisory Committee, “Fuel Tank Harmonization Working Group, 

Final Report,” ARAC, 1998. 

3. Fuel Flammability Task Group, “A Review of the Flammability Hazard of Jet A Fuel 

Vapor in Civil Transport Aircraft Fuel Tanks,” FAA Report DOT/FAA/AR-98/26, June 

1998. 

4. “Handbook of Aviation Fuel Properties,” Coordinating Research Council Report No. 

530, 1983. 

5. Lewis, B. and von Elbe, G., Combustion, Flames and Explosions of Gases, 3rd edition, 

Academic Press, 1987. 

6. Esseghir, M. and Polymeropolous, C. E., “Spark Ignition of Near the Lean Limit CH4-Air 

Mixtures at Low Pressures,” Combustion and Flame, Vol. 73, 1988. 

7. Shepherd, Krok, Lee, Brown, Lynch, Samaras, and Birky, “Results of 1/4 Scale 

Experiments, Vapor Simulant and Liquid Jet A Tests,” NTSB Docket No. SA-516, 

Exhibit, No. 20O, 2000. 

8. Shepherd, J.E., Krok, J.C., and Lee, J.J., “Jet A Explosion Experiments: Laboratory 

Testing,” NTSB Docket No. SA-516, Exhibit No. 20D, 1997. 

9. Zinn Jr., S.V., “Inerted Fuel Tank Oxygen Concentration Requirements,” FAA Report 

FAA-RD-71-42, August 1971. 

10. Kuchta, J.M., “Oxygen Dilution Requirements for Inerting Aircraft Fuel Tanks,” Bureau 

of Mines Safety Research Center, in: Second Conference on Fuel System Fire Safety, 

Washington, D.C., FAA, pp. 85-115, May 1970. 

11. Stewart, P.B. and Starkman, E.S., “Inerting Conditions for Aircraft Fuel Tanks,” WADC 

Technical Report No. 55-418, September 1955. 

22
APPENDIX A—COMMERCIAL AND MILITARY AVIATION FUEL SPECIFICATIONS

ASTM D 1655 Detailed Specifications of Commercial Aviation Turbine Fuels 

Property Jet A or Jet A-1 Jet B 

COMPOSITION 

Acidity, total mg KOH/g

Aromatics, vol % 

Sulfur, mercaptan, weight % 

Sulfur, total weight % 

Max 

Max 

Max 

Max 

0.10 

25 

0.003 

0.30 

... 

25 

0.003 

0.3 

VOLATILITY 

Distillation temperature °C: 

10% recovered, temperature 

20% recovered, temperature 

50% recovered, temperature 

90% recovered, temperature 

Final boiling point, temperature 

Distillation residue, % 

Distillation loss, % 

Flash point, °C 

Density at 15°C, kg/m3

Vapor pressure, 38°C, kPa 

Max 

Max 

Max 

Max 

Max 

Max 

Max 

Min 

Max 

205 

... 

Report 

Report 

300 

1.5 

1.5 

38 

775 to 840 

... 

... 

145 

190 

245 

... 

1.5 

1.5 

... 

751 to 802 

21 

FLUIDITY 

Frezing point, °C 

Viscosity -20°C, mm2

/s 

Max 

Max 

-40 Jet A 

-47 Jet A-1 

8.0 

-50 

COMBUSTION 

Net heat of combustion, MJ/kg 

One of the following requirements shall be met: 

Luminometer number, or 

(2) Smoke point, or 

(3) Smoke point, mm, and 

_________Naphthaleness, vol % 

Min 

Min 

Min 

Min 

Max 

42.8 

45 

25 

18 

3.0 

42.8 

45 

25 

18 

3.0 

CORROSION 

Copper strip, 2 h at 100°C Max No. 1 No. 1 

THERMAL STABILITY 

JFTOT (2.5 h at control temperature of 260°C min) 

Filter pressure drop, mm Hg 

Tube deposits less than Max 25 

3 

25 

3 

CONTAMINANTS 

Existent gum, mg/100 mL 

Water reaction: 

 Interface rating 

Max 

Max 

7 

1b 

7 

1b 

A-1
Detailed U.S. Military Requirements of Aviation Turbine Fuels as Taken From Reference 4 

Property JP-4 JP-5 JP-8

COMPOSITION 

Acidity, total mg KOH/g

Aromatics, vol % 

Sulfur, mercaptan, weight % 

Sulfur, total weight % 

Color, Saybolt 

Max 

Max 

Max 

Max 

Max 

0.015 

25.0 

5.0 

0.001 

0.4 

Report 

0.015 

25.0 

5.0 

0.001 

0.4 

Report 

0.015 

25.0 

5.0 

0.001 

0.3 

Report 

VOLATILITY 

Distillation temperature °C: 

Initial boiling point, temperature 

10% recovered, temperature 

20% recovered, temperature 

50% recovered, temperature 

90% recovered, temperature 

Final boiling point, temperature 

Distillation residue, % 

Distillation loss, % 

Explosiveness, % 

Flash point, °C 

Gravity, °API (15°C) 

Density at 15°C, kg/m3

Vapor pressure, 37.8°C, kPa (psi) 

Max 

Max 

Max 

Max 

Max 

Max 

Max 

Max 

Max 

Min 

Max 

Max 

Report 

Report 

145 

190 

245 

270 

1.5 

1.5 

... 

... 

45-57 

751-802 

14-21 

Report 

205 

Report 

Report 

Report 

290 

... 

... 

50 

60 

36-48 

788-845 

... 

Report 

205 

Report 

Report 

Report 

300 

1.5 

1.5 

38 

37-51 

775-840 

FLUIDITY 

Frezing point, °C 

Viscosity -20°C, mm2

/s 

Max 

Max 

-58 

... 

-46 

8.5 

-50 

8.0 

COMBUSTION 

Aniline-Gravity product, or 

Net heat of combustion, MJ/kg 

Smoke Point, or 

Hydrogen Content (wt %) 

Min 

Min 

Min 

Min 

5250 

42.8 

20.0 

13.6 

4500 

42.6 

19.0 

13.5 

42.8 

19.0 

13.5 

CORROSION 

Copper strip, 2 h at 100°C Max 1b 1b 1b 

THERMAL STABILITY 

JFTOT ∆P (mm Hg) 

JFTOT Tube Color Code 

Max 

Max 

25 

<3 

25 

<3 

25 

<3 

CONTAMINANTS 

Existent gum, mg/100 mL 

Particulates (mg/liter)

Water reaction interface

Water Separation Index Modified 

Filtration Time (minutes) 

Max 

Max 

Max 

Min 

Max 

7 

1 

1b 

70 

15 

7 

1 

1b 

85 

... 

7 

1 

1b 

70 

... 

A-2
Detailed U.S. Military Requirements of Aviation Turbine Fuels as Taken From Reference 4 

Property JP-4 JP-5 JP-8

ADDITIVES 

Anti-icing (vol %) 

Antioxidant 

Corrosion Inhibitor 

Metal Deactivator

Antistatic 

0.10-0.15 

Required 

Required 

Option 

Required 

0.10-0.15 

Required 

Required 

Option 

... 

0.10-0.15 

Option 

Required 

Option 

Required 

OTHER 

Conductivity (pS/m

Service 

NATO Code No. 

200-600 

All 

F-40 

... 

Navy 

F-44 

200-600 

USAF 

F-34; F-35 

A-3/A-4