v 

FUEL SYSTEN F ll<.E HAZARD k.EDUCilm\ 

The 1oa j()r ;>ourcl' of energy in post crash aircraft fires is the •• irvlal1~.: it•, J 

supply . In ra~"t, if there is no airplane fuel fi.re , aJmost i'1vari:'l.hly •1•' fi•· 

of any signifi.ca•Ke devt:lops. Consequently, developing a l!lt!;)ns or mi .,;_~i ··i ~: . 

•Ill C.O'ltribtlti.o'l nf this fue-l to post crash fire~ i~ nf pri"lP imporL.q;•''- · 

do1 :1b L:li .? , how· ve r , the overall aircraft safety on the p,round ancl in fli · t,~ 

mu"~ ut,~ · bL r: 'l'(lrromi:::cd . The application of t!"lis philnb'>phy 'tn c: '~r""'~ : ; 1 

ai :.:r.-:~ft d•.!Si;2n over the.! past three decade~ has res11lterl i•1 :l:1 c.xcPll~·nL .. ~< . '".• 

record . It is incumhcnt upon the industry that this prarlico:: he co'1Li -:tt d "'.• 1 

that it be the paramount conside ration when evaluating Rystem desig ns intend~~ 

to ~educe the fire hazard i, survivable crashes. 

An assessment of curr-=:nr desi:~n practices in this rep,ard is revi e wed in li r,l-} t c-t 

opera tiona 1 experience in the following j)eir,J,grnphs . Al te r no t i ve nppr•):-'!Chef: tn 

reduce the post c rash fire potential are described and ev~luated in term~ nf an 

ov<..rd] 1 airplane safety eftectivenesb. Finally, the adequacy of currt.nr '1-r:ci••: ;l 

AvJ ·lt i.on Reeulat ions and th(~ neen (or ;nor~ (\:!SC-'lrdl and dl.!llclopment in !.pee I I i 

~r as ~re di~cussed . 

~~SC':.~~mcn t of _Curre_nt Design Adequacy 

Current Design Practice 

ThL dc~-; ign rhiloc;o!)hy whi c h has for :;o many years resulted i11 :111 P X(.I. lh~n~ r lr, 

safety record for the aircraft i.ndustry has been to isolate the ;OJi r cratt 'u•: 

fro•n pot~ntial ignition sources . This isolation ic; funcl-'lmcnt:l1 tn [i.re prr.v.·n 

tion. Very specific fire safety design requiremen t,.; are ::>tate<! in thL Fe ~r r_,, 

Avi.l'lti.on kegul.:ttions requiring the ..tircraft industry t o expend a C01l*>idenld··· 

porli()n of it<; development effort to C01<1ply with thes ~ regulati0.,., , l!nw~:.:v• r, 

since an excellent safety record by the industry is mdndMtory tu mai.,t&ininn t~ r 

good~ill of the traveling public , the design rel'juir~mcnls di·~tatl d by Lhc 

rPgulRtions .:tr0 often exceeded . 

The application of these regulations fall into three major c~tcRnri~~: 

powerplant fire protection, fuel system fire protection, and fuel tao~ 

crashworthiness. Powe:-plant fire protection putc; heavy eml'h~};it~ on tilt! 

isolation of ignition sources since the power source ar0as in"•)h·r.· h"t <:11c·i•1C' 

parts and c:ornponents that .:ire convert in~ fuel e nergy Lo us..- tul wori<. 1\t \ i-lt : t 

fires are locRl ized by firewalls which isoL1te them from atij.H:er.t bll'l · <!.,: 

are<1s . Lines and components contAining combustible fluid!:i H~ r~o:'] l•in::! t ·-·-

fire-resistant materials to protect their contents from fire LnvoJ v<.mc•~L . 

Potential l eakage areas are shrouded and drained to ar ea~ which ~re tr~r "f 

ignition sources. Fuel supplied from the fuel tanks •nay hL· isol..ltl.!d fro•:t !"•:•' 

power source areas by means of shutoff valves in the ~vl:!nt o)f enr, jrH.' fire:~. ·- re 

detection and ~xtinguishing systems dre used to control fires whJ..-.11 n•-'~Y sL HL h 

high fire potential areas . All of these cap<Jbilities •nLISt b•' rl cmonl-L rdU··d 

according to Federal Air Reeulations prior to eertificatiOP hy tlte FAA. 
In the multicomponent fuel system, each component receives fire protection 

consideration to achieve a high level of safety for the overall system. Spaces 

adjacent to fuel tanks incorporate drains protected by flame arrestors and are 

air purged to prevent the buildup of combustible mixtures. Component 

temperatures in fuel tanks are maintained at a low level and electrical parts 

are made explosion proof. 

In the event of a wheels-up landing, special design measures are taken to 

protect the fuel system components from damage which may release fuel. 

Components and fuel lines are located where they are protected by the basic 

aircraft structure. Where the relative motion of the aircraft structure in 

survivable crashes could cause fuel lines to part within the fuselage area, fuel 

lines capable of stretching as much as 50% of their installed length , are 

employed to absorb impact and relative motion without leaking . The capability 

of exhibiting a reasonable degree of deformation and stretching without leakage 

must be demonstrated during certification. 

Fuel shutoff valves, which are provided in the fuel lines to each engine and 

auxiliary power unit (APU), are often duplicated for increased reliability in 

the isolation of fuel from potential ignition sources . These valves are located 

at the fuel tank boundaries so that they are not affected by line damage. 

Open flow fuel tank vents are provided for each tank to maintain the tank vapor 

space at or near outside ambient pressure for all conditions of flight. The 

utilization of unpressurized tanks in commercial jet aircraft eliminates the 

potential of pressurization component failures which can subject the tanks to 

excessive burst and collapsing pressures in the event of failu res during ascent 

or descent. Flame arrestors or other means are provided in most transport 

category aircraft to preclude external fires from entering the vent line and 

igniting vapors within the fuel tank. 

In the wing fuel tank areas, such hardware as landing gear, wing flaps, and 

engines are designed to fail in a break- away manner without compromising the 

wing structural integrity to maximize fuel tank crashworthiness. Fuel tanks 

within the fuselage receive special attention in this regard. While they are 

designed to withstand emergency landing loads, standard design practice dictates 

that they have greater than the minimum required strength. A heavy outer shell 

is provided in addition to the basic aircraft structure and an innerbag to 

contain the fuel . Break-away, self-sealing couplings, or stretchable hoses are 

used to minimize fuel spillage in the event the tank is displaced from the 

connecting fuel lines by impact loads in survivable crashes. 

By adhering to these design practices and incorporating new practices only after 

their worth has been proven by extensive testing, the industry has provided the 

traveling public a continuously decreasing rate of accidents involving fuel 

fires over the years. 

47 
Operational Experience 

Before evaluating potential i mprove:ilents to fuel system desi,5n, it is 

appropriate to look at the accident record to define, if possible, the 

effectiveness of proposed design changes in r~ctucing fatalities due to postcrash fuel fires. A summary of the accidenL~ involving post-crash fuel tank 

explosions for the worldwid~ turbine-~owered aircraft i s shown in Figure 3. Note 

that these accidents include foreign carriers os well as two accidents for which 

the re wer~ no fatRlities. Th~ tank explosion accidents listed on Figure 3. are 

divided into two categories, those \vhlch involved Minor damage so that the fuel 

tanks were initially undamaged and those accidents which resulted in massive 

impact damage causi~g tank rupture and subsequent massive ground fires. ln the 

first category of accidents, two involv d ground fires which propagated through 

the v-:nt systen, and two involvF::d failure to stop fuel tlow through a ruptured 

engine feed line. It is believed that the tank explosions could have been 

prevented or substantially d.dayed tor Lhese four c<-1ses by design changes which 

have since been developed . 

Propagation of fire through the fuel vent cRn be d~lay ed to permit passenger 

evacuation by the use of vent flamt! arrestors which have been developed for that 

purpose. Vent flame arrestors and suppressurs are offer~d as standard or 

optional equipmenL on all large U. S. transports in currt:::nt production . 

Design changes in the fuel shutoff systems have been made to provide great e r 

assurance of fuel cut<>ff under l:!rncrgency conditions . In the 707 case , t" ~ fuel 

fire, fed from the ruptured fuel line, continued to burn bec<'iuc.;e of failu r e to 

activate the spar fuel shutoff valve by pulling the fi re shutoff handl~ . The 

throttle had previously been rt!tiirded to the ertgi.n~:: off position . These 

airplanes now incorporate actuation of the spar (u('l shutoff valve by a fuel 

shutoff lever on the throttle quadrant as well AR on the fi.re handle , thus 

providing increased assurance of shuLoff valv ~ actuatlon . 

Returning to Fig . 3, the DC-8 accident at Anchorage involving fuselage breakup 

and ruptured fuel tanks occurred while overrunning the runway during an aborted 

takeoff. The fire started shortly before the airplane came to a stop. Sometim~ 

thereafte r two or mor e large explosions occurr~d . l!ost of the passenge rs and 

crew (182) evacuated the airplane. However, 46 passencers and one stewardess 

were unable to escape . Presumably if the ex~losions (assumed to be fuel tank 

explosions) had not occurred , these 47 people could have also evacuated . It is 

possible that a fuel tank vent fire protection system or inerting system mieht 

have reduced the fatalities from this accident by delaying or preventing the 

explosions. A review of the remaining accident briefs does not indicate that 

any fuel tank anti-explosion system would have effectively reduced the 

fatalities in the remainder of the accidents which involved major airplane 

damage, large quantities of tuel spillage and subsequent fuel tank explosions . 

Design Alternatives 

The various design alternatives which l~ve been considered tor potential 

improvement of the post- crash hazard including fuel tank inerting , quenching, 

suppression, crash-resistant fuel tanks, anti-misting fuels, and alternate fuels 

are discussed in the following paragraphs. lt should be noted that an 

evaluation of these alternatives inherently requires the conside ration of their 

effect on the total airplane design and operation and is not limited to only 

post- crash considerations. 

48 
Ground 

Fire-M inor 

Impact 

Damage 

Massive 

Ground Fire 

Wing T ank 

Breakup 

Severe Body 

Damage 

World-Wide Turbine Powered Fleet 

Fuel Potential Reduced Fatalities 

Hull l oss or Hull Damage 

Survivors 

Fatahtoes ~ Vent Improved Fuel Tank 

Arrester or Fuel Explosion 

(All Causes) Suppressor Cutof f Protection 

Year ~ Systems 

Model ~ 

Rom~ 

oj 

707 1964 48 25 y JP·4D X _X 

lnn<l<>n 707 1968 5 121 y Kero X X X 

Sll'lgapore I CMT 1964 0 68 y ) X X 

Stockton DC 8 1969 0 5 y ) X X X 

AnchOiage DC 8 1970 47 182 y Kero ) ? 

Monrovl8 DC 8 1967 51 39 y ) 

CII'ICiflnatr 880 1967 70 12 y Kero 

C1nC1nnat• 727 1965 58 4 y Kero 

St Thomas 727 1970 2 53 y Kero 

Pago Pago 707 1974 97 4 y Kero 

Na•obr 747 1974 59 97 y Kero 

TPnArlfP 747 11977 335 61 y Kero 

New Hope DC 9 1977 61 23 y Kero 

Wnghtstown l·382 1970 J 0 y Kero 

New Haven CV-580 1971 28 3 y Kero 

FIGURE 3 

TANK EXPLOSION ACCIDENT ASSESSMENT 

(POST CRASH FIRES) 

49 

l ow 

Probability 

of Any 

System 

Benefit 

7 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 
Fuel Tank Inerting 

Fires within the fuel tank can be prevented if the oxygen concentration in the 

vapor space above the fuel is maintained below combustible limits by displacing 

part of the oxygen with an inert gas. Nitrogen is the most logical inertant. 

Nitrogen extraction from the air requires a complex separation system if the 

nitrogen is extracted in flight , or a costly and complex distribution/ handling 

system if the nitrogen is obtained by a ground operation and then carried 

onboard as a cryogenic liquid. The tank system, which is pressurized above 

outside ambient to preclude air f r ow entering the tank, must accommodate vent 

relief valves and back up relief valves, pressure regulators , distribution 

lines, and a fuel "scrubbing" system. The latter is needed to remove the oxygen 

dissolved in the added fuel which would otherwise outgas oxygen during climb. 

The reliable functioning of these additional components must be assured if a 

decrease in overall system safety is to be avoided. 

In the post-crash situation, a fuel tank inerting system could provide limited 

benefits depending upon the severity of the crash. In a massive wing breakup, 

little or no benefit would be available . In a minor wing breakup or no damage 

situation, the inerting system could provide some benefit . In either case, the 

system benefit would be reduced considerably if the source of agent were lost 

during the c r ash. In the case where little or no damage occurs to a particular 

tank, there has been considerable experimentation conducted to deter111ine whether 

or not inerting will pro tect against an explosion from an under-wing fire. These 

tests by NAFEC (Reference 14) showed that it is possible for a very inte~se 

under-wing fire applied to an intact, unwetted tank surface to initiate an 

explosion and that inerting could prevent such an explosion. Even in this most 

intense underwing fire, the tests showed that no explosion took place until 95 

seconds had lapsed . They also showed that in a less severe fire, 

particularly with modest fuel loads, the tank would self-inert, i.e., a slow 

oxidation would take place and the tank would become inert . It was concluded 

that, except for the case where a small tank penetration had occurr ed, fuel tank 

inerting did not provide any significant additional protection over existing 

vent protection systems in a post-crash rire situation. 

At the 1977 Public Hearing, the Aerospace Industries Association of America 

projected that the cost of inerting, system acquisition and operation of the 

worldwide fleet would cost $19 billion through 1996, and would result in an 

additional 1. 3 billion gallons of fuel usage over that period of time. Reference 

13 presents a recent update of this evaluation which indicates the cost for a 

20-year period has increased to $24 billion even though the system weight was 

decreased significantly from the original study (3460 lb to 1743 lbs for the 747 

airplane, based on inputs from Parker-Hannifin Co r poration) . This lighter 

weight system is problematical in that it eliminates the second LNz storage 

tank system and therefore does not provide a fail safe operational system and 

would not meet the airlines' dispatch criteria. The projected cost increase 

mainly reflects an increase in fuel price (774/gal assumed vs 384) and 

inflation. Current estimates of jet fuel costs are far in excess of $1.00 per 

gallon, further escalating the cost of the inerting system. It should be noted 

that development and installation of certifiable , fail-safe operational systems 

for commercial aircraft requires at least S-6 year time span. 

50 
The concept of onboard inert gas gene ration (IGG) offers potential reduction of 

cost dae to the elimination of the formidable logistic costs associated wit~ 

ground- produced LNz . The self-contained onboard generation of Nz would 

provide an operational inerting system worldwide , thus f r eeing the ~irplane fr0m 

dependence on LNz ground support equi pment . The IGG system would use much 

of the component technology which has been developed for the LNz systems. 

Additional research and development would be needed in the area of onboard 

generation technology and systems application before it could be considered for 

comcercial application (Ref. 15). 

Fire Quenching 

An alternative to fuel tank inertine is the insta llation of r eticulated 

polyurethane foam or expanded metal foil i.n the fuel tanks. This passive 

system, depending on the porosity of the foam or foil, works by either flame 

arrestment and/or an energy absorption mechanism which pr~vents an excessive 

ove r-pressur e or explosion from developine . \.fhile an internal tank firt! is 

possible, the fire does not cause an explosion, and eventually self-exling•tisl~e~ 

from l~ck of oxygen. \fuile some degree of flame propagation is to be inherently 

expected, the reaction is of the low order, flash fi r e variety . Foam by itself 

or in conjunction with flexible bladders has been applied t6 military aircraft 

over the last 13 years for tank pr otection against lightning strikes, gun fir~, 

and resulting explosions. Experience in combat situations is report~d to be 

good . 

However, a translation of this military need to the commercial theater presents 

difficulties. Due t o its susceptability to hydrolysis , earlier foams in some 

cases experienced degradation when exposed to extremes in humidity and high 

temperature environments. Some military aircraft have utilized the same 

original foam for over 13 years. Development has continued and newer foams ~re 

not susceptible to hydrolytic degradation . t.1ater accumulation in the foam at 

the tank bottom provides a perf~ct location for microbacteria! growth and 

subsequent tank corrosion in wet wing configurations. Foam removal for periodic 

structural inspection may prohibitively increase maintenance cost. 

System weight , weight of retained fuel from wetting and loss of fuel capacity 

displaced by the foam would present severe operating penalties on commercial 

aircraft. For a B-747 , the combined weight penalty (foam and fuel wetting) is 

estimated at 14,000 lbs. This penalty assumes a 40% voided volume which is 

probably optimistic for the large size tanks . Lost fuel capacity varies from 

0. 75% to 2. 0% , depending on the type of foam . 

The military services have temporarily removed foam in some of the C-130 

air planes for some of the above reasons although they are currently in the 

process of installing the new improved hydrolytically stable foams in the C- 130 

fleet . Reticulated foam is being utilized in the majority of new combat 

aircraft. 

In an accident situation , foam could provide protection in a "no or minor wing 

damage situation. Little is known about its performance under external fire 

conditions. 

51 
Although tesring has not been performed, it is assumed that in massive wing 

hrr.~~ up, foam would not help since flammable fuel mists would be formed and 

struct11r al damage would permit flame propagation around the foam and negate its 

effectiveness with respect to the damaged tanks. However, explosions in foam 

containing areas would be prevented . 

Foams are categorized as potentially useful only in limited circumstances and 

they would i~pose a performance penalty and maintenance burden on the 

operators. 

Muc h of the preceding discussion applies to an expanded aluminum foil mesh and 

will not be repeated . However, there are some significant differ ences which are 

discussed below. 

Because of the higher melting point (1100° F) of foil, its performance under 

external fire conditions has been proven to be excellent . It is also 

hydrolytically stable , and when installed, does not encourage electrostatic 

discharge during fuel operations. In small transports problems associated with 

installation and removal due to its semi-rigid and non-collapsible 

characteristics can likely be overcome with proper engineering; however in large 

transports, aluminum f oil mesh may be impractical because of the additional 

weighr involved and possible need t o redesign existing fuel systems. 

The hasic concept of this system is one in which the flame of an incipient 

explosio~ js sens d by a detector (IR or UV) which triggers the discharge of a 

fire extingnsing agent to extinguish the fire before a hazardous overpressure 

c..:1 o develop . 

Evpansi.on of the c:•trrently applied surge tank flame suppression system to a 

f••ll-~cPle tAn~ suppression system increases the system complexity by an order 

of magniturle or more . A typical aircraft system will involve two t o eight or 

nine tanks, each of which will have a large number of bays. Since each bay 

ul~ r~q11irP nn ~ nr more flame sensors , a typical system could have 50 or more 

~-' C" "' 0rs, ~nrl se er e~ l discharge bottles and distribution plumbing . This presents 

~ PYtrPmP.ly difficult system to install and maintain. The sensitivity of the 

det ~tors ~akes the probability of inadvertent firing of the system likely 

during routine system maintenance or tank entry. The application of explosion 

S"ppres~ion to co~mercial transport fuel tanks has been studied on numerous 

A~ caslo~~ . In Pll cPses, the complexity of the installation prompted by the 

"""lP.ro11s ctr.tP.ctnr~ and suppressors overrode any potential value except in 

~ilitpry P) r~raft. f.ven recent state of the art improvements which would 

si.2nific<>ntly reduce the number of detectors has not shifted the balance in 

f<>vor of in~tallatio~ . Retrofit of the system to existing aircraft in 

Prlrlitio~ to the maintenance of the system after the one per aircraft per year 

actuatin~ that presently occurs, would be prohibitive from an operator's 

~tPn~point. It iA therefore concluded that explosion suppression applied to 

the fuel ta~~ is not applicable for protection of commercial transports during 

cra~h conditions. 

52 
) 

The above systems were evaluated i~ terus of weight, cost , maintenance, 

reliability, retrofit capability, and effectiveness. The results of this 

evaluation are shown i~ Figure 4 . In every category the incorporation of a v~nt 

line flame arrestor is rated as better than, or equivalent to, the h.Ore complex 

syst~ns currently under discussion . Of tne more complex systems, only the 

inerting system appears to offer some impr ovement in the post- crash fire 

em•ironment. Again referring to Figure 3, of the 15 accidents involving 

post-c rash explosions, 1nerting hcd the po t ential of reducing fatalities or hull 

damage in five cases. In four of these five cases , it is believed that the 

relatively simple approach of vent flame arrestors or suppressors D r improved 

fuel cutoff would have been as effective as the inerting system. These simple 

and reliable systems are presently installed in most commercial transports. 

They are typical of the tried and proven fire protection designs which the 

aircraft industry has ?Ursued throughout its history . Since 1962, this policy 

in jet transport desi~n has resulted i~ a reduction i~ accidents i~volving fuel 

vapor explosi~ns fro1J 1. 4 to B?proxi~ateli 0. 1 per ~illion departures 

(Figure 5) . 

Fro ~ the above survey of existing and proposed methorls to elimi"late fi r es inside 

jet transport fuel ~anks, the follo~ing conclusions ~ere arrived at: 

o An analy&is of uccident hi.Hory i:1dicates that existing fuel ;;yste::~ nrc 

protection oechods are as e ffec tive dS quenchi~g a~d suppression syst~ ms and 

supply most of tne protection offered by i~erti,g in ~urvivable accide~t~ 

where minor win~ tank daod3e occurs. 

o Although quenching, suppress ion , and inert ing ~ys tefTls r:JdY ~duc..: the 

pr vbability of explol>ions ~here intense externdl .5round fir~s i:npact near 

empty but intact ~ing :anks, the incredsed conplexity oi these syste~s can 

comp r omise the i.nflight safety of the airplane in comoer.:ial applications . 

o Quenching, suppressio,. , and i,erting syste~s repr~sent la r6e econo~ic, 

operational, and maintenance penalties. 

Crash- Resistant Fuel Tanks 

The term "cr .• sh- resistdnt" fuel tank is ~ener lly associ-ated 1,·ith fuel tanks 

that are capable of remaining reasonably intact during a c rash event , thereby 

eliminating or minimizing fuel spillaee and the corresponding post- crash fire 

threat to surviving passengers . If achieved, this concept can eliminate nost 

destructive external fires and complement the simple measures discussed in the 

previous section. The highly visible success of crash-resistant fuel systems 

installed in Ar~y helicopte rs makes direct application of this technology t o jet 

transport aircraft tenpting. However , the obvi~us differences in aircraft 

characteristics, crash scenarios, and accident experience may dictate another 

course of action. 
Concept Weight 

Liquid N2 Moderate 

Onboard N2 Moderate 

Generation 

Foam High 

Foil High 

Tank 

Suppresion Moderate 

System 

Vent 

Flame Low 

Arrestor 

Summary Evaluation of Concepts 

Cost Maintenance 

Very 

High Moderate 

High Moderate-High 

Not Known High 

Not Known High 

Moderate High 

Low Low 

------

F,igure, 4: Elimination of 54 

Reliability 

Satisfactory in 

Military Service 

Not Evaluated 

Good in Military 

Service 

Not Evaluated 

Not Evaluated 

Good 

Retrofit 

Capability 

Extremely 

Difficult 

Extremely 

Difficult 

Extremely 

Difficult 

Not Possible 

Extremely 

Difficult 

Yes 

I 

s Inside Fuel Tanks 
ACCIDENTS INVOLVING 

FUEL VAPOR 

EXPLOSIONS PER 

MILLION DEPARTURES 

1.4 

1.2 

1.0 

0.8 

0.4 

0.2 

0 

1 0 

I 

1958 60 

• 

0 0 1 

I 

62 

• 

• 

• 

TREND 

• 

• 

NOTES: 

• 

1) APPLIES TO FREE 

WOR LD TURBOJET FLEET 

2)EXCLUDESSABOTAGE 

AND MILITARY ACTION 

3) INCLUDES INFLIGHT 

AND GROUND CASES 

• 

NUMBER OF ACCIDENTS 

2 2 0 3 1 1 3 0 0 0 2 0 1 1 0 

I I I I I 

.I 

64 66 68 70 72 74 76 78 

YEAR 

FIGURE 5. TANK EXPLOSION ACCIDENT RATE 

WORLD WIDE AIR CARRIERS - ALL OPERATORS 

55 
lhe 0bvious 1liff~rence in fuel syst~m and a i r craft design and the crash SCLn~r: 

j ~ f~· t i,.._r r:f'mp ) ic"lted by the definition of "impact survivable . " TlH' \r·~!~i i-2 

its c!· 1 < • .• Ji,,t_i<)n. of whethe r or not an clceident is impact surv"ivablc ?n 111 

dS.>t.:::.:,·:h .. '1L 'Jf" the inerti-'1 fo r ces tr-:J.nsrnitted to the occupant thrnngh hie; r, ,, : 

and rt~l r-::~in.t system and on whet he r or not the cAbi.1 struct•1re t.oll3p&ed ,.,il't· 

the o ... -,11

Jc nt ' s envelope . On the other ha:1d, the FAA considers d c:rds\1 

!:>urvi·,rable if one occupant survives the impact event. 8ecan;;e ,)( tht d:~.: t' T 

t r ansport <~ircrd[t And tht- correspondingly high energy ahsorbine ror~r:t i :.1 , ,, 

is concei'J3ble that <;;oane occupants ~..ill :S11rvive very high cr~sh imrdc t. 

vel<"t.i' i ':!s . On the father hand , because of the r e L'Itively srn-3.1 1 :::i?.• ot ··· \ 

hel i opter~ , all occupants and systems <H.: exposed to approximatr>l y t il' .. 4 

~1.d:c-:1 ~;..n•;i ront" ~l"'t facilit"iting d n:lati.vely clea u definiti•)n ,,f 10 ~ .. ,r~ · • 

s.un·ivat>le crash. 

Tran.;port aircraft fuel t:.tnl<s fall oroacHy into two ca tegories - inte[;r4l ·· 1. • ..., 

tanl-..s and fuselage tanks. The application of crashworthy bladder tnnks tn 

integrol • .,rin~ tanks cannot be accompl i sheri ithout .-t complete r edesign of th~ 

wint; b~caust::: of its multi-cellul.'lr construction . Furthentor~ , it cAnnot :.1- ~~; 1 

with certai.'lty that c r ash-rt!sist.-tnt [uel tanks ~<IUulrl pruviJe fire prntt~ t, '" ·' 

crd~h scen~rios that include wins sepdr~tion . 

feder al rt ·,s ation~ ~q u:re that dar.1a.5e to the nir )lan·~ a:Jclia l;:;w!: , ... ~· tr ··, 

,tnri "..; tc.1keoff inri l3ndlng shall not cauS\:! :;;pillAg.'.! of ~no 11 gh fnel t•• c ,, ~!' it ' 

a fire h'l!'Hd . The fuel tank and landi"lg gea r support stra1ct•Jre i.: rl, :1 n, .. ; : 

hi.;'~· r ~trt_ngth thAn the gea r to prevent fue l t::tnk rupturt2 duP. t•' -111 ·1• .:.: l· v •' 

lAtllii.ng gcil.r OVt!rl~)"id , This desi~n requirement i.s fu r ther t!xt::ended t. · i .• I ,-' 

... tr·•ctur,.l] .'>tt"lchr.H!nt:-. to the \oling fuel t<Jnk which •:tight he nvc:rl•)'l·i '·l .;.,:·!.•• 

whc~ls-uj· or partial wheels- up landing . Flap hi"lges and l~ngint' mttm~L-;, t .r· 

examplo:: , .are desirined to fail without ruptur ing the t::tnk . 

'Befr>r•-;: dic:.r•l&<;i ng the application of crash- resist-lnt fuel tanks i 1 th· t J~··l, • 

Arta, somcthi1g should be said abr>ut current fuselage design pl·.:tr;tir.·o:; . l•t ~! !•:· 

fuel "lnJ he carried in the center wing st r uctnrc or 1.:1 "' pr.:!~<;uri 2 1-•: tr ·~ 1 

as a -:argo co:npartment. Fuel tanks in the c~nter wing struct11re .Jr ~ •k:·it-'1•"' 1 : 

l'lo::t t the "g" loads p r esc r ibed for e10ergency landings. 

In "'irplanes having :uel tanks located 1o1ithin the pressuriz:t::d at -1 , ty~.-i. -1 1 ly 

the ca r go compartment, particular dt t ention is paid t o minimizi.n{ LiH r t ...,k · r 

f uel spillage. An example of one such design is sho"m on Fi,:>,Hr.-; h , 1 ··• L~n~ 

composed of an aluminum honeycomb out er shell with bladder cell~ insi1.;: . LIH 

t"inl<: is supported f r otn the floor beams in such a manner -'iS 1 n prrr I 11i·· f-., ... •:: 

str uctu r e deflections f r om loading t he tank . Clear.-itlces from adjcll't 11 t ·lt•t• L :r. 

~ p r oviJed nround the tank . 

The fuel "'nr! vent lines that connect the tank:> tu the main laa·l ..;y·~te• 

incn rpor.Ht! ~r-dnr1hl~ ::tnd ve n ted shrouds . These line~ .,rl':! either .lc· i ,,.,.. • • 

"hr ... "lk -tw;:Jy" lrOlll t he n••xiliarj tank vr sufficiE-nt ...;tn tch i.; pt••,·i i· ·! l 

.-~cc•u<r,J0dat: tAnk nove1Jent without C"iusi'l£ fuel :::pi ll-'lt;t> . J..J.o~ts th,JI. 11 -. 

requ1red to str·Hch are subjected to whilt is normally ro.:ferrt·.l Ln d~ !l·c 

''!!•Ji.llotine test. " The hose is p r essurized and clamped l:lL nq•_t. cn.h t' ~i ·q ~t ·· 

it~ rnou ntir.;; in the airc raft , then a sharp pointed ln4d is Applitrl in t•n' •.J ~:i! · 

of the hose . The hose must not leak when ~tretcheri to itc; r:..txirn .. ., , 

) 
c 

0 

·:. 

~ .... 

(/) 

Q) 

C) 

~ Q) 

1/) 

;:, 

u. 

0 

~ 

WL208.10 CX) 

Floor beam 

Wing 

Tank 

Wing Center Section 

Designed 

9g per FAR 25.561 

j 

Wing 

Center 

Section 

Tank 

Forward 

Downward 

Upward 

Sideward 

Additional tank protection obtained by keeping 

fuel heads within design limits during 1 radian /sec. 

roll and by using nacelle strut. Landing gear and 

trailing edge flaps attachments for controlled 

breakaway. 

FiguTB 7: Fuel Tank Load FactoTs 

Tank No.2 cargo 

door 

<( 

6 

9.0g 

4.5g 

2.0g 

1.5g 

8.0 min c 6.50 l 

• 

Rear view 15.30--.J 

at Sta. 9500 

FiguTB 6: CaTgo CompaTtmsnt Tank Installation 
During the design of the tank installation, prior accident history is reviewed 

to ensure that likely crash scenarios are considered and that possible leakage 

of fuel is minimized. For example, accidents or incidents where the gear has 

separated are reviewed to insure that the tank will not be hit by a displaced 

gear. Also, incidents or accidents where the fuselage has been crushed are 

reviewed to insure that there is adequate clearance between the fuselage and the 

fuel tank. In addition, incidents or accidents where the fuselage ha~ broken 

fuselage has broken are reviewed to ensure that the auxiliary tank is not 

located where such breaks typically occur . 

In summary, it can be said that the fuselage fuel tank design: 

o Exceeds FAR requirements 

o Is mor·: rugged than center sec tton tanks 

o Provides considerable clear~nce 

o Allows tank displacement without fuel line breakage. 

o Location results in cinimal spillage exposure . 

Crash-resistant fuel tank (CRT) installations in wing and fuselage areas were 

evaluated. A summary of the results of this evaluation is shown in Figure 7. 

As anticipated, the wing installation shows excessively high penalties in almost 

every category evaluated . On the oLher hand, the fuselage installation results 

in only low to moderate penalties. 

One other source of potential fuel spillage is a broken engine fuel supply line 

when nacelle damage occurs. An existing regulation, FAR 25 . 1189, requires that, 

"Each tank-to-engine shut- off valve must be located so that the operation of the 

valve not be affected by powerjJlant or engine mount structural failure . " 

However, in one incident where a nacelle separation f rom the wing in flight 

could not be detected by visual means, the crew interpreted the instrument 

indications as an engine flameout . Since normal shutdown procedures only 

required that the engine fuel shutoff valve be closed, the tank-to-engine 

shutoff valve was not actuated. Consequently, excessive fuel spillage occurred 

after the aircraft came to rest resulting in a fire . Subsequently , the fuel 

system design was modified to include closure of this valve during normal 

shutdown. Incorporation of this feature or its equivalent in the fuel system 

design is shown in Figure 7, to have minimal impact on the airplane design and 

operation. The results of this brief evaluation indicate that a careful 

analysis of crash data history to explore modes of failure is essential to 

determine if improvement of fuel retention during transport airport crashes can 

be achieved . A r esearch program involving the 3 domestic widebody airframe 

manufacturers was initiated in January 1980 for the purpose of developing crash 

scenarios and recommending a future test and analysis effort for the development 

of improved crashworthiness. 

58 
Summary Evaluation of Concepts 

Concept Weight Volume Cost Reliability Retrofit Effectiveness 

CRT Feasible Not vs All Moderate Low Low Passive in Fuselage Possibilities 

CRT Difficult Not vs. All High High High Passive in Wing Possibilities 

Emergency Low Low Fuel Shut-off Low Good Yes Good 

Figure 7: Fuel Containment 

59 
From the foregoing , it was concluded: 

o It is feasible to install c rash-resist ant fuel cells in fuselage ca r go 

compartments . 

o lt is not feasible , in most conventional transport aircraft , to install all 

the wing fuel in crash-resistant fuel cells. 

o It may be feasible to install some degr ee of crash-resistance including break 

awa y fittings at criticAl locations in some state of-th~ -ar t air craft wings, 

depending upon specific type d~si gn . 

o The existing Fede ral Aviation Regulations allow the use of crash-resistant 

fuel cells in transport aircraft . 

o Further definition of crite ria should evolve f r om total air c r aft 

crashworthiness considerations . The research cont racts with the three widebody manufacturers should accomplish this objec tive . 

Anti-Misting Fuels 

The fundamental consideration in developi ng a crash-safe fuel is t o produce ~ 

fuel which will not burn in a crash envir onment and which will not compr omise 

engine performance throughout the :tircra f t ope r ating envel ope . Ant"i- misting 

ker osene (A)OC) is the latest development in the search for such a fuel . An 

anti-misting additive pr events the fuel f r om breaking up into a fine, hi5hly 

combustible mist when subjected t o the high shear rate expulsion of fuel from a 

small tank opening or by air shear breakup of the large fuel masses expelled 

from damaged t:tnks during crash decelerations. Eliminating or preventing the 

rapid development of a l arge fire a r ound an air c raft involved in an impact 

survivable accid~n t where fuel t ank rupture occurs will allow mor e time for 

passenger and crew evacuation and result in a higher rate of survivability in 

this type of accident . 

The anti-misting quality is imparted to the fuel by the addition o( low 

concentrations of shea r-sensitive high molecular weight polymers. The additive 

currently being evaluated by the FAA is a British-developed polymer known as 

FM-9 . 

AMK is in the early stages of its development. The current candidate has 

already demonstrated its ability to minimize, and in most cases eliminate 

entire ly , the fireball f requent ly experienced when fuel is released during a 

crash although many factors are yet to be investigated . A}OC offers a tremendous 

potential f or post-crash fi r e hazard reduction. With development, it is 

expected to have a minimum impact on a ircraft operation and maintenance . 

Major questions yet to be answe red include the effects of the additive on static 

charge generation and relaxation , engine sta rting and relight cha racteristics, 

heat transfe r cha racteristics, filterability, materials compatability, fuel 

oxidative stability and storage stability, as well as c.osts. 

The most important property of AHK, its tendency t o form large droplets when 

sheared, is not a desirable cha r acteristic when the fuel reaches the engine 

combustor. Consequently , development of a degrader to r estor e the fuel 

ignitability just prior to entering the engine combustor, is high on the list of 

development priorities. 
Although no specifications for AMK exi sts as yet, the following properties have 

been established as targets: 

o Heat content equivalent to current fuels. 

o Anti-misting quality maintained during handling. 

o Minimum impact on engine start and relight. 

o Acceptable pumpability and flowability . 

o Compatable with existing materials and components. 

o Achievevable at reasonable cost. 

In spite of the many questions yet to be answered, the technical community's 

reaction to AMK is highly favorable at this stage of its development. Its 

fluidity has been improved significantly without compromising its anti-misting 

qualities. The development of a suitable degradation process is encouraging. 

Test programs are continuing 

in the areas of engine and fuel systems compatibility , air shear and 

flammability, and r heology definition. In addition, large scale tests are being 

implement ed. 

If no unacceptable aspects of A}OC develop in the continuing program, it is 

estimated that it could be introduced for commercial aircraft usage as early as 

1984 but at least within 10 years. 

Alternate Fuels 

The current effort to develop new sources of crude oil such as synjet derived 

from coal or shale oil must not overlook their post-crash fuel fire hazard 

potential. Although the type of hydrocarbons may differ among synjet and 

petroleum Jet A fuels, these differences will not influence the probability or 

nature of fire in a crash situation if the fuels are produced to the same 

specification. The effect of broadened fuel properties and alternate fuels with 

completely different properties on fuel safety is discussed briefly in the 

following paragraphs. 

One alternative fuel being studied has a flash point specification 10° F to 

20° F lower than the current commercial Jet A or Jet A-1 specification of 100° F 

minimum. The incentive for considering such a jet fuel is increased potential 

availability and more refinery flexibility in meeting other critical jet fuel 

quality requirements such as freezing point . The Canadian and Russian 

commercial jet fuel specifications (CAN 2-3. 23-77 and GOST 10227, respectively) 

have 33° C (92° F) and 28° C (82° F) minimum flash point requirements. The 

recent reduction in flash point was adopted by the Canadians because trends 

showed a reduced growth rate for gasoline and a healthy growth for distillates 

including jet fuel. Considering ambient temperatures in Canada, laboratory 

data, and other operational factors, it was concluded that the reduced flash 

point would have a minimal effect on fire safety (Reference 16). 

61 
Although it is recognized that fuel types currently being studied will have a 

minor effect on the overall safety of turbine aircraft , it is known that large 

differences in flash point can influence fire safety. Consequently , decreases 

in flash point to increase jet fuel availability must be carefully considered 

before a decision is made. 

On the basis of laboratory data and its r~lationship to the accident record , a 

fuel with a flash point of 80- 90° F would be expected to behave more like Jet A 

(100° F flash point) in crashes and inflight fires according to Reference 3. Any 

difference in fire safety compared to Jet A would be expected to occur when the 

fuel temperature is at or near the flash point. It is recommended that FAA 

sponsor studies to quantify what effect reduced flash point fuels might have on 

aircraft fire safety in the U. S. A. 

Liquid hydrogen and liquid methane are being considered as aircraft fuels . The 

use of cryogenic fu~ls involves the hazards arising from low temperatures as 

well as those of combustibles. Studies of safety problems that might arise from 

airline use of these cryogenic fuels should continue and keep pace with the 

overall aircraft development studies. 

Conclusions 

Any evaluation of systems for reducing the fuel fire hazard in impact survivable 

accidents must consider the effects of the system in all phases of the aircraft 

operation: on the ground, in- flight and at landing and takeoff . The t e ndency 

to consider the merits of the system in the impact survivable environment only 

can lead to erroneous conclusions which, if implemented, could be to the 

detriment of the traveling public . Consequently, the conclusions reached in 

this section may differ in some respects from those expected ror th~ crash 

situation only . 

The primary conclusion reached in evaluating both existing and proposed fire 

hazard reduction systems in that the use of anti-misting fuels has Lhe greatest 

potential for improved safety by essentially eliminating the development of fuel 

fir es in a post- crash environment . While much further development work needs to 

be done to improve the currently promising anti-misting fuels for practical use 

in fuel systems, the research on such fuels sltould be expedited. 

The improvements introduced into existing designs in recent years which meet or 

exceed Federal Aviation Regulations have proven to be effective. The proposed 

mor e complex systems do not appear to offer significant additional protections 

in their present states of development. Furthermore , these more complex systems 

have an appreciable weight , complexity, and maintainability penalty which will 

degrade overall airplane performance and safety. 

Fuel tank inerting may have a potential for future aircraft safety improvements 

only if its weight and complexity can be significantly reduced through further 

development . 

62 
VI 

R & D CONSIDERATIONS 

Summary and Perspective 

Although there have been a recurrent number of in- flight fire incidents, all 

fatalities attributable to fire in . air carriers have occurred in crash 

accidents. Therefore, it is imperative that research and development be 

conducted in the context of a postcrash fire. A postcrash cabin fire scenario 

is described in this chapter. This scenario has been utilized and analyzed in 

the FAA C- 133 full-scale fire test facility . The fire scenario was conceived to 

provide a realistic postcrash fire wherein the ignition and burning of interior 

materials would become a significant factor affecting the survivability of cabin 

occupants. Placement of the scenario within the spectrum of actual postcrash 

accidents will be an important task of the comprehensive FAA/NASA sponsor ed 

study by Boeing, Lockheed, and HcDonnel-Douglas of past transport accidents. 

Aircraft cabin materials fire safety technology has historically been focused on 

polymeric material development. Most of these materials, which are functional , 

comfortable, decorative, and economical , will burn under certain conditions. 

Past research has emphasized modifying these materials or developing alternative 

materials to reduce (but not necessarily eliminate) burning and the evolution of 

smoke and toxic gases. We are able to test these materials in the laboratory 

and provide relative data on burning (e.g., flame spread, heat release rate), 

and smoke evolution. The problem; however, is to relate such data to behavior 

in an aircraft fire and to assess its rel?tionship to survivability in a postcrash fire in the design of aircraft. 

It is simplistic to demand a continual change to materials that burn less 

readily or give off less smoke or toxic gas. Before there is a requirement for such changes, it should be possible to define, even 

approximately , the increase in survivability that would accrue. To do so 

one should be able to predict (analytically or empirically) the course of 

a fire in a real aircraft containing a mix of materials. The goal is to 

predict the additional escape time provided by improved materials. 

The leading organizations engaged in research and testing related to aircraft 

cabin fire safety are the FAA, NASA, and the three major airframe manufacturers 

(Boeing, Lockheed, and McDonnel-Douglas). Areas of responsibility between. FAA 

and NASA are defined in a memorandum of understanding (MOU) Reference 21. 

Industry efforts have been supported by NASA as part of the past FIREMEN program 

or by internal funding as part of the IRAD (Independent Research and 

Development) program. 

The FAA program is described in detail in a recently published program plan 

document Reference 21. A 3-year time f ramework is described for the 

comprehensive development of test methods and criteria for cabin materials. A 

longer range 6-year program has been prepar ed by NASA at JPL which focuses on 
the development of a mathematical cabin fi r e model. Of a shorter time period 

than either the FAA or NASA programs is an 18-month program prepared by Boeing 

to correlate full- scale and laboratory testing, culminating in an interim test 

methodology fo r cabin materials. The FAA program plan was endorsed by the SAFER 

Committee after the program was presented to the committee on ~larch. However, 

the NASA modeling plan and Boeing inte rim proposal must be integrated into the 

FAA progra1n plan. 

Prediction of Cabin Naterials and Human Response to Fire Hodeling 

The ability to analytically or empirically describe a fire and its progress is 

desirable for designing interior systetns and selecting materials, and relating 

small and full scale test data to mat e rials performance in an accident . Fire 

modeling in government and industry is currently in the early stages of 

development and offers many advant~ges in cost and time savings. A concerted 

effort should be made to accelerate the empirical correlation of laboratory and 

full scale tests and to advance analytical modeling development . 

Analytical modeling i s seen as a long-term eftort in cabin fire safety 

technology . The SAFER R&D Subgroup expended extensive effort in 

developing both short term and long term descriptions of modeling needs 

which are attached in Volume II. Modeling would intelligently predict 

cabin materials behavior for given fire scenarios and the resulting human 

survivability envelope, given the establishment of standards for l1uman 

tolerance limits. Each of these elements is now discussed. 

Aircraft Cabin Fire Scenario 

General 

In response to a SAFE!{ Recomme ndation, the FAA developed the following typical 

scenario. A wide body jet transport with a 57 percent passenger load factor 

crashed on the runway of a major airpor t following an abnormally high descent 

rate . The accident occurred on a sunny afternoon. This scenario will be 

refined, and perhaps other scenarios added , following analysis of NTSB accident 

reports and data relating to actual 

crash conditions. This activity is currently underway by the three 1.1ajor 

airframe manufacturers under ten.1s of NASA and FAA contract studies for 

improving structural integrity . 

Fire Description 

During the crash decele ration an integral tank in the right wing was penetrated 

by debris, spilling fuel which was immediately ignited by frictional sparking. 

A train of burning fuel was observed behind the decelerating airplane . As the 

air plane came to r est a large external fue l fire erupted immediately in the 

vicinity of a fuselage rupture . Except for this opening in the fuse lage on the 

right side , t he fuselage was otherwise intact. The size of the opening 

approximates a rectangle 76 inches high and 42 inches wide . The two forward 

doors on each side of the fuselage were jammed and passengers and crewmembers -

none of whom were immobilized or traumatized - utilized the remaining six doors 

to evacuate the airplane . During the crash deceleration, the main and nose 

landing gears were sheared off and the air plane eventually came to rest on its 
belly in a level orientation. All emergency lighting systems operated properly. 

(Note: Based on past a ccident analyses , other plausible openings for the entry 

of fire a re inadvertently opened doors or small ruptures beneath the cabin floor 

line.) Other door openings were not subjected to the pool fire, which involved 

several thousand gallons of fuel. The pool fire reached heights of 

approximately 75 feet, extended beneath the belly of the fuselage and completely 

covered the rupture . The pool fire flames were attached to the fuselage. Only 

those cabin materials very close to the rupture opening were subjectd to the 

intense heat and flames generated by the fuel fire . A relatively steady 3 mph 

wind was blowing in a direction perpendicular to and toward the fuselage. The 

pool fire was upwind of the fuselage. The radiative heat flux in ~he fire may 

have reached 14 BTU/ft2-sec and at the center of the cabin opposite the 

rupture the flux would have been at least 1.8 BTU/ft2- sec. There was 

moderate penetration of f lames from the fuel fire primarily in the vicinity of 

the ceiling next to the opening. 

Evacuation Description 

At the first indication of fire at the ruptured fuselage location, those 

passengers nearby immdiately began moving away from the fire. 

Surviving passengers and crew utilized one-half of all the exits to evacuate the 

airplane . Estimates for the evacuation time ranged from 90 seconds to 3 

minutes. The shell of the fuselage remained primarily intact during the 

evacuation although the cabin was eventually gutted. 

Design Fire Considerations 

An important feature of an aircraft postcrash cabin fire is the possibility of 

intense thermal radiation from a large external fuel fire through a fuselage 

opening. 

In order to be representative of the large fuel fires characteristic of many 

aircraft accidents, a design fire should be "optically thick" to produce this 

intense radiation. 

The severity of the fire exposure to interior materials increases with the 

degree of flame penetration. 

Cabin hazards arising from the fuel fire are dependent on the amount of 

flame penetration into the cabin. The degree of flame penetration for the 

design fire must be selected to provide cabin hazard levels well within 

human survival limits over a prescribed time interval. 

Human Tolerance Limits 

Limited information is now available on the limits of human tolerance to heat, 

smoke, and some toxic gases; however, more work is needed in defining the 

effects of irritant gases and a definition of human tolerance from a systems 

point of view. The combined effects of heat, visual disorientation, and the 

presence of irritating or toxic gases on the behavior of passengers need to be 

evaluated relative to cabin egress design. Efforts along the line of the FAA 

Combined Hazard Index (CHI) program are needed. (CHI would account for the 

combined affects of heat, smoke and toxicity. ) 

65 
Egress, Lighting, Emergency Communications 

These items do not fall under the scope of SAFER; however, the design and 

development of technology must be done within an overall systems approach for 

evaluating survivability . Volume 11-B contains so~e commentary on Egress 

lighting and emergency communication factors , even though the Committee did not 

discuss them in any detail, nor formulate any related recommendations . 

Fuselage Fire Resistance 

Whether the fuselage is a wide body type or a standard body type will have a 

crucial bearing on the development of the fire and its hazards . For example, 

compared to a standard body jet , a wide body jet is more resistant to burn 

through by an external fuel fire , furnished with more flame retardant cabin 

materials, and encompasses a large cabin volume with possibly gr eater dilution 

of combustion products. 

Node ling 

In order to intelligently pred let human survivability, then~ is a need to relate 

material laboratory test results with aircraft cabin geometry , a fi re scenario, 

and human tolerance limits. It is necessary to have analytical or empirical 

tools to model the fire . There are two aspects to this issue which are 

complementary and integrated activities. They are: 

1. Short term analy tical and empirical methods to correlate full 

scale , model , and laboratory testing . 

2. Long term development of mathematical tools to predict the progress 

of burning , temperature , and gas species distributions in a defined geometry . 

These two aspects should not be considered as competitive activities; but 

rather both part of a continuum of activities f r om which increasingly 

valuable modeling tools emerge . 

Short- Term Plan 

The base for the development of such a methodology has been laid down with 

several programs including the FAA contract with McDonnell-Douglas for the 

"Combined Hazard Index" (CHr), Boeing fire test methodology program 

started in 1974 and the NASA-JSC contract on fi re test methods which 

Boeing completed in October 1978 . There are probably others, but these 

are notable because they developed within two of the three major airframe 

companies exceptional knowledge pertaining to the problems of material 

evaluation and fire threat definition. This background combined with the 

knowledge of airplane construction and parts fabrica tion provides 

a currently unique capability to develop a methodology to evaluate the 

fire performance of materials in a fashion both effective in materials 

control and practical in application. 

66 
At the request of the SAFER R&D Subgroup, the program outlined on Figure 8 was 

proposed by Boeing to develop this capability in the shortest time possible. The 

correlation study in the proposal is similar in many r espects to the 

FAA-sponsored CHI contract scheduled for completion in December 1980. Major 

similarities include the utilization of the OSU chamber for the measurement of 

rates of emissions of heat , smoke, and toxic gases, and large-scale tests on 

single mate r ials as part of the test methodology development . The refore , many 

of the pr ovisions of the correlation study are contained in t he CHI study. It 

i s recommended that the CHI contr actor, McDonnel- Douglas, be requested to make a 

detailed p resentation to a select group of FAA, NASA, and industry on the 

design, development, validation, and limitations of the CHI test methodology. In 

light of the degree of success of the CHI methouology , the FAA should request 

Boeing t o r edefine and describe in detail the elements of t heir empirical 

correlation study . At that point in time, the FAA should be in a better 

position, t aking into consideration suitable inputs and r ecommendations by NASA 

and industry, t o consider the r evised Boeing proposal. 

Much of the work r equired in Phases II-V of the pr oposed plan has already been 

started during the previously noted programs . The main ingredients for the 

success of such a short term program are : (1) a sense of urgency to resolve the 

material evaluation pr oblem within the state-of-the-art , (2 ) recognition that in 

this case only the airframe companies have the test correlation, airplane 

design, material selection and laboratory test application background to develop 

the practical solution in a timely fashion , (3) a means of formally requesting 

and obtaining the participation of the industr y in the effort, and (4) timely 

testing and analysis support by the NASA and FAA-CMli, and effective testing and 

program administration support by the FAA-TC. 

Long Term Modeling Plan 

General 

The SAFER R&D Subgroup requested that NASA' s Jet Propulsion Laboratory (JPL) 

develop a comprehensive long-term a ircraft fire modeling technology plan. It is 

included in Vo lume II. The plan was designed t o provide analytical modele which 

possess well- defined predictive capabilities with particular emphasis on user 

needs. Furthermore, since analytical methods should be developed in conjuncti on 

with related experiments , the long-term plan also includes test programs which 

are necessary to establish an effective and valid predictive technique. 

Preparation of the plan began in October 1979 and inputs were made by the 

air f r ame manufacturers, Federal Aviation Administration, National Bureau 

of Standards and the National Aeronautics and Space Administration. Phase 

I, Definition of Fire Modeling Technology Requir ements, of the 6-phase 

plan has been substantially completed by NASA JPL and the phase 1 re~~lts 

are also included in Volume II. 

The overall objective of this Fire Modeling Technology Plan is to develop 

analytical and experimental methods for use in air c raft design and testing t o 

r educe the post-crash fire hazard. Specific objectives developed in response to 

previously discussed needs are: 

67 
FIGURE 8 

PROJECT WORK TIME <DOES NOT INCLUDE CONTRACT NEGOTIATIO

NS, ETC .> 

l.lp:.S.. ~:.S.a ~:.s.. l2..MQ.:,S, JS.J1Q:~ l8..

PHASE I J PHASE II L PHASE Ill I PHASE IV I PHASE V 

I 

i 

I DEFINE POSTCRASH lARGE SOLE TESTS OF FIRE SCENARIO SINGLE MATERIALS J i 

! _, 

I 

: l I I DEVELOP 01"RICAL CORRELATION h BETWEEN OSU AND LARGE SCALE DATA 

~ 

t 

II 

PLAN OSU OSU DEVELOPMENT FOR I l DEVELOP METHODOLOGY FOR 

O[V ELOPHENT AIRCRAFT MATERIALS MATERIAL EVALUATION 

ll PLAN TOXIC THREAT DEVELOP POSITION FOR DEFINE 

HETHOO TO ANALYTICALLY 

ASSESSMENT TOXICITY SIGNIFICANCE MEASURE TOXICANT RELEASE Jil PLAN FOR FLASH DEVELOP POSITION ON NATURE AND POTENTIAL HEAS. SIG

NIFICANCE OF FlASH POTENTIAL 

DEFINE 

"FLASH" 

METHOD 

POTENT

TO 

IAL 

MEASURE 

~ 

. 

! 

-··················· 

--········; ......... i i --

I'IIJI.Stt r PHAStt 11 -;;;;;; ;;~··-

1 P

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I CONSID£RIH

•• PLAtt 1'0 ASSt:SS tilTH STAR-<Jr•AIIT J , INDUSTRY AND P'AA POSITION (S} AJID t.OCA~

1WCHHOWGY ~Hit SIGHiriCANCtt Or ON TOXICI~Y -··············-·· 

~If 

A " D

COHBUS~ION 

TOXICITY IN POS~-cRASM PHAStt CY 

WC~HOIJT 

H

I 

PII!t:S 

.. CNOCIS~RY AND P'AA 

POSITION(S) ON •rLASH" 

s. DttriNI~lON OT f'Htt rLASN PIIOBtt.lf 

POTttN~IAt. 

r'AA AND INDIJSf'RY CONCIJRRI!IfCtt OW 

AND PLAN roll lfi!ASUI!ING tilTH I N 

TOXICANT AND "PLASH" POTttNTIIIt. 

' CURRI!IfT STIITtt-Dr·AI!T f'ttCHNOWGY Hl:ASIJRI!IfttNf' 

I 
1. Determine the capabilities of existing modeling methodologies relative 

to user needs; and accelerate activities to improve these methodologies with 

regard to the stated needs. 

2. Develop a detailed , analytical fire dynamics model that will describe the 

post-crash scenario; and develop other new modeling methodologies as 

required. 

3. Determine the capabilities of existing small- and large- scale test methods 

for model application. 

4. Develop and refine appropriate test methodologies which can be used with 

models to give well defined predictive capabilities. 

5. Develop hazard evaluation modeling methodologies. 

For a number of years, the FAA has sponsored the development of a mathematical 

cabin fire model at the University of Dayton Research Institute (UDRI). Of 

necessity , development of the UDRI model must fit within the 3- year time 

framework of the FAA program plan. The FAA has identified "weak" portions of 

the UDRI model which require improvement. While SAFER has endorsed a long- range 

mathematical modeling endeavor , it is recommended that the long-range program be 

structured to provide "early'' products (subroutines) to upgrade the UDRI model. 

These "early" products include theoretical modeling of burning processes of 

aircraft mmaterials and of flame spread under superimposed radiation and 

ventilation, including scale and ventilation effects. 

During the entire Fire Modeling Technology program there should be close 

coupling and interactions between the activities associated with modeling , 

hazard evaluation, experimental/testing and existing aircraft design and design 

methods. The establishment of a government-industry Technical Working Group is 

intended to assist in furthering these interactions. 

Finally, the long-term plan would be complimentary to the short-range plan 

for the development of empirical correlation methods . 

Testing 

General 

Testing methodology was singled out as a technology requirement because of the 

lack of reliable predictive methods which are demonstrated to be correlated with 

performance in an accident. Near term focus should be on well instrumented full 

scale tests (e.g. , FAA's C-133 tests and NASA' s B-737 tests) to provide 

quantitative design requirements , contribu- tion of cabin interior materials to 

the post-crash fire hazard, and to realistically evaluate current and new 

materials systems. Mockup tests, similar to the concepts used in the 

McDonnell-Douglas Cabin Fire Simulator, should be employed to provide similar 

evaluations in t he future at lower cost. Also, further development is needed to 

develop correlation between lab tests and full scale/accident performance . The 

SAFER R&D subgroup made the following findings and recommendations. 
Findings. 

1. Full- scale and mockup testing are required because there is a lack of 

reliable predictive method$ . 

2. Laboratory and full- scale test corr~lation with accident 

performance needs extensive development. 

3 . Correlation of laboratory tests with full-scale tests requires further 

effort. 

4 . The Ohio State University (OSU) Heat Release calorimeter methodology 

appears to provide the most promise for long-term laboratory test application. 

The OSU shows promise of providing correlation with additional work. Laboratory 

methods for weasuring toxic gases do not currently correlate with full-scale 

test results and require further work . Part of this effor should be conducted 

as an ASTM activity after the tests are proven to be valid indicators for at 

least ranking the various materials regarding their relative hazards. 

Recommendations. 

1. Continue full- scale tests with the C-133 at the FAA Technical Center 

and B-737 at NASA, Houston test articles. These tests should utilize an agreed 

upon fire scenario and be completed in approximately 2 years. Additionally, the 

test program should include advanced material tests after testing of 

contempor ary materials is completed . (Note: It is recommended that for 

technology development purposes, a 5-minute evacuation time be considered t o 

represent the majority of cases.) 

2. Mockup test configurations should be defined and the validity verified. 

This type of test is less expensive to conduct and provides more rapid 

turn- around times. 

3. Further effort should be expended to correlate laboratory tests with 

full-scale and mockup tests. 

4 . Expedite the development of the OSU Chamber Calorimeter and 

evaluate its use as a regulatory tool (within 3 years) . Establishment of 

an industry/government test develo~ment advisory committee is essential . 

Coordination of R&D Between Domestic and International Groups 

An important lesson learned during the SAFER proceedings is the strong desire by 

industry to establish a government-industry forum for exchanging technical 

information, coordinating research and technology planning and the development 

of materials and safety fuel standards. The R&D subgroup after exploring 

several alternatives, recommended that such activities be pursued by the ASTM 

Committee F- 7, Aerospace Industry Methods (Cabin Interior Materials) and ASTH 

Committee D-2, Petroleum Products and Lubricants (Modified Fuels) . 

70 
The FAA in its response to the interim SAFER Recommendations briefed SAFER on 

April 5 on two dra ft parallel research and development plans designed to improve 

human survivability and reduce hull losses resulting from fires in otherwise 

crash survivable accidents. Both plans will develop the technical data base by 

1984 which when coupled with other rationale , i.e ., economic analyses, will 

support FAA regulatory proposals. The Cabin Fire Safety Plan will evaluate 

current and improved cabin interior materials , determine means to r etard the 

progress of cabin fires, improve evacuation systems, and improve 

crash-fire-rescue effectiven~ss . 

The Anti-Misting Kerosene (AMK) Plan will determine AMK feasibility, develop 

promising AMK additives, de1nonstrate ~~ effectiveness in large and full scale 

tests, and develop recommendations for the use of AMK in civil aviation 

operations. 

The draft program plans have subsequently been developed to a final form. 

The SAFER Committee has reviewed the Cabin Fire Safety, FAA-ED-18-7, and AntiMisting Kerosene, FAA-ED-18-4, Program Plans and recommends that the FAA 

vigorously pursue them in parallel until such data are available to determine if 

continued parallel research is required. 

Complementary to the SAFER activity, the FAA , NTSB, and the aviation community 

are expanding the scope of accident investigations to fully develop the 

performance of cabin interior materials , fuels, and aircraft seats and airframe 

structures. In ce rtain of these investigations experts from NASA will oe 

involved. 

At the time this report was prepared, NASA was developing long-term plans for · 

fireworthiness materials, modeling and safety fuels research. The planning 

includes specific research at each NASA Center (Ames, JPL, Johnson , and Lewis) 

based on technical expertise and facilities and uses draft FAA- TC Engineering 

and Development Program Plans fo r Cabin Fire Safety and Anti-Misting Kerosene in 

the 1981-1984 time frame as inputs for short-term requirements. The joint 

research is conducted under terms of a formal NASA-FAA agreement established 

during the Firemen Program. NASA and FAA are also establishing the details of 

coordinated research for improving transport aircraft structural integrity that 

would enhance crash survivability. 

International r esearch coordination and cooperation is also required because of 

the potential for implementing more stringent airworthiness requirements for 

existing and future U.S. manufactured aircraft and the extent of the 

international accident statistics. The current trend in Europe is for adopting 

common airworthiness requirements in the form of Joint Airworthness Requirements 

(JARs) which are heavily influenced by the FAA airworthiness regulations. The 

FAA and UK-CAA meet annually to review operations and research activities and 

perhaps this mechanism would serve as a means to enhance international 

coordination of research and a more extensive, unified approach to fire 

safety improvement world-wide . 

71 
Anti- Misting Kerosene (A}~) Research 

A}OC has been previously discussed under Fuel System Fire Hazards and at this 

point, A}OC R&D and economics analysis requirements are discussed . NASA and FAA 

have been conducting AMK research using a British industry developed proprietary 

additive. Cooperative research between the FAA , NASA and the UK-CAA is 

conducted under terms of a government- to- government agreement. The AHK additive 

in jet fuel reduces the possibility of fuel pool fires in crash survival 

accidents because of the inhibition of the fine fuel mist which typically allows 

fire-propagation from an ignition source to the fuel pool. SAFER was briefed on 

the status of US/UK AMK research and the FAA ' s Program Plan for continued 

research assuming sufficient rationale will be developed by October- November 

1980 for further research . SAFER concurs with the need for further research to 

include alternate fuel additives to jet fuel and expansion to other fuels that 

could appear in the market place and where warranted for othe r air craft classes, 

e . g., commuters, corporate, general aviation. Sufficient concurr ent research in 

both research a r eas , i.e . , fireworthy materials and~~ will be required to 

determine their r elative effectiveness anci the costs and benefits to the various 

potential users. 

The FAA is faced with multiple research tasks , limited available research funds 

and pressures to resolve other high priority safety issues. Therefore, it 

would be reasonable t o expect more sophisticated and timely FAA management 

techniques to determine the extent to which multiple solutions to safety 

pr oblems should be pursued . 

72 
VII 

CREW PROTECTION AND ?ASSENGER EVACUATION 

The scope and expertise of the SAFER Advisory Committee was limited to 

transport category aircraft and t he de sign aspects of such aircraft as they 

relate to fire and explosion r eduction. Be cause of the relatively short time 

involved for the Committee's effo rts , attention was focused primarily on impact 

survivable accidents where control of fire and explosions would enhance 

occupant survival. Certa in o f t he discussi ons of the Committee were beyond 

this scope; howeve r, since they did aff ect occupant survivability they are 

reflected here so they can be kept in view for regulatory activities outside 

SAFER. (See Volume Il-B for additiona l items in this category.) Protection and 

evacuation of airc raft oc cupants are the critical elements of safety in a 

postcrash fire environment. The FAA should work to attain these goals by (1) 

ensuring that effective escape me chanisms a re built into the airframe and are 

present in the cabin i nt e rio r, (2) en~u ri ng that the flight and cabin 

crewmembers are properly trained, protected, and able to direct and assist 

evacuation, and (3) improving passenger education efforts. In addition, the 

Committee suggests ~alu io n of seve ral measure s to reduce the hazards present 

during an inflight fire. It should be noted that these issues, since they were 

beyond the s cope and expe rtise of SAFER, we re no t discussed or evaluated by 

SAFER or its technical gr oups. 

Countermeasures f or lnf light Fire I njury 

A. Lower Lobe Galley and Lava t or y fire De tectors 

Continuing attention t o smoke/tire de t e ctors in critical areas such as lower 

lobe galleys and lavatori es is needed . 

Consideration should be given t o be ing independently powered with a "press to 

test" feature for operability and activation indicated by an aural alarm and 

lights visible to flight attendants. In similar systems now used, very few 

false alarms have been r e port ed, whil e seve ral fires have been detected at an 

early stage. 

The lavatories are particularly vulnerable to fires because of: 

1. the inability of cabin crew to monitor all passenger uses of the 

lavatory; 

2. the design of the lavatory t o provide forced air ventilation for odor 

prevention which could promote fire propagation; 

3. the private nature of the lavatory even when unoccupied. With 

the door closed, there is little indication of fire to outside 

observers. In recent tests, two minutes had passed before even wisps 

of smoke we re visible . By then a fire is hard to contain with 

onboard portable exti nguishe rs. 
After a warning, a means to combat an existing fire in a lavatory without 

opening the door should be developed (NTSB Recommendation) . 

Lower lobe galleys should have detectors with warning systems that activate in 

the lower galley as well as the main deck se rvice center since there are times 

on the ground and in flight when the lower galley is not occupied by a 

crewmember. An alternative is designing for fire containment, as discussed 

earlier in this report. 

Countermeasures for Postcrash Fire Injury 

A. Aircraft Structure 

Based upon presentations made to the SAFER Committee and its technical groups, 

but not discussed or evaluated in detail, the following areas relating to the 

structure of the transport aircraft may be worthwhile for research, evaluation 

outside the SAFER Committee: 

1. Emergency Exits 

The design of aircraft exits should consider outside visibility as 

well as the ability to close off an exit inadvertently opened. 

a . Design aircraft door windows to provide flight attendants with 

sufficient visibility downward and outward to assess conditions 

on the ground. ("Assessment of evacuation condition," is the 

flight Rttendants first step in an evacuation.) 

b. Examples of alternate aids which should be considered are heat 

sensors or fiberoptic viewing devices which could be placed at 

exits. 

c. Once a door has been opened inadvertently due to lack of 

vision of the gr ound or a noncrew member opening an exit , there 

should be a means of closing the exit/opening to preclude venting 

of fire, heat and fumes into the cabin. 

Narrow-bodied aircraft doors have closing capability since they 

are manually operated. Howeve r, on wide-bodied aircraft the 

emergency door opening mode is pneumatic (DC- 10, 747) or springpowered (1011). Once the door handle is actuated in the 

emergency mode the door is opened and may not be closed in all 

cases. This is a factor which must be considered in protecting 

occupants from intrusion of flames from exterior fires. 

B. Aircraft Interiors 

Based upon presentations to the SAFER Committee and review by some members of 

design proposals being discussed in the industry , (but not discussed or 

evaluated in detail by SAFER or its Technical Groups) the following 

modifications or studies involving aircraft interiors should be evaluated 

beyond the SAFER Committee considerations: 

7b 
1. Distribution of Emergency Lights 

Accident experience has shown that overhead emergency lights 

currently installed in cabin ceilings and over exits often become 

obsecured by smoke from burning fuel and aircraft components. This 

not only prevents rapid visual location of exits by passengers but 

also eliminates the light source necessary for illuminating an 

aircraft interior. In view of the potential for obscutation, 

additional emergency lighting placed at or below armrest level should 

be considered to provide emergency evacuation guidance and 

illumination in the relatively clear air found at lower cabin 

levels. 

2. Firehardening of the upper cabin 

In addition to the hazard of smoke obscuration heated air also 

collects in the upper cabin. This stratification of smoke and heat 

means that the upper cabin can be rapidly subjected to high heat . 

While passengers and crewmembers have avoided the hazards of smoke 

and excessive heat by bending low or crawling when exiting the cabin, 

their egress and survival may be impeded by the effect of the heat on 

upper cabin materials and equipment. Tests and accident experience 

have demonstrated that ceiling panels sometims begin to deterioriate 

structurally while the lower level of the cabin may still be livable. 

Should deterioration of overhead panels occur, it can represent an 

impediment to successful evacuation and a source of injury. Further, 

equipment which is used to aid egress, such as lighting and public 

address systems, can be disabled by excessive heat . Electrical 

wiring in overhead areas may be equally vulnerable . For this reason, 

the upper area of the cabin should be protected to an appropriate 

level. Relocation of emergency equipment from upper areas may be 

appropriate, and regulatory attention should consider to the 

differing fire hazards of upper and lower cabin areas. 

3. Tactile Placarding (signs read by feel or touch) 

Armrests and overhead compartments at rows associated with emergency 

exits should have a tactile system of identifying markings to 

facilitate location by crew and passengers whose vision has been 

debilitated by smoke and combustion. Such markings would be of 

critical importance to blind passengers. 

C. Crewmembers 

The effective intervention of crewmembers during a postcrash fire or any other 

emergency is necessary for the ultimate survival of the aircraft occupants. 

For this reason, certain protective measures should be taken on behalf of the 

highly trained crew to ensure their ability to provide leadership during the 

emergency . 

75 
1. Training 

The subsequent discussion , also beyond the scope of the SAFER 

Committee is offered for consideration outside the SAFER Committee. 

All crewmember training should incorporate Qaterial derived from the 

latest industry and FAA testing which demonstrates the hazards of 

aircraft fires and suggests actions and procedures appropriate for 

the fire situation. Education regarding stratification of heat and 

gases , fire patterns, fiber fabric flammability, necessity for 

crawling or stooping during cabin egress, and the effects of smoke 

and gases on mental acuity and judgment should be incorporated in 

required crew training . 

3. Protective Equipment 

Any special protective equipment provided for crewmembers must be 

located at their stations and be immediately accessible. Crew 

ability to aid passengers ln evacuating an aircraft during a fire may 

be enhanced by protective breathing devices and gloves; however, 

tests should be conducted which address the specific problems of time 

required to don the equipment, ability to direct passengers and be 

understood, and freedom of move~aent . 

76 
VIII 

ASSESS~~NT OF ADeQUACY OF CURKENT ~TANDARDS AND EXISTING TECHNICAL BASIS FOR 

NEAR TE.ID\ UPGMDING OF RULES 

Interior l1aterials: 

An assessment of the adequacy of current standards begins with the issuance 

o f ~PRM 69-33 on August 12, 1969. This notice considered amending many 

~P.~tions covering emergency evacuation and operating procedures in addition 

to materials fire safety. It was the result of much study and testing by the 

FAA, materials producers , suppliers and the airframe industry. The pertinent 

sections of 69-33 dealt with compartment interiors, cargo and baggage 

compartments and electrical system fire and smoke protection. Those 

sections, with relatively minor changes are current in todays FAR Part 25 

Amendment 25-32 . 

The 69-33 rules "-'ere prepared to be used in procurement specifications as 

acceptance criteria for materials as well as minimum standa r ds for assemblies 

as installed in aircraft. ASU1 tests, nonstandard tests and other special 

t ests were devised such as for ceiling panels in an effort to simulate real 

f ire situations. In addition to test method development, all candidate 

aircraft materials that could be made available from a country- wide search 

were tested to determine the then current state- of-the- art flammability 

level . With this background some tests were found more suit~ble for specific 

shapes or generic classes. All had various degrees of severity but were not 

correlatable with each other and none could measure how a material would burn 

in actual fire scenarios. With no technology available to relate lab test$ 

to actual tires the Bunsen burner test was selected as the most suitable 

materials test for industry needs. A significant improvement was made, 

however, from a horizontal burn rate requirement in prior rules to a 

self- extinguishing requirement for large area materials in a vertical 

position. This Bunsen burner test, was and still is, a very good measure of 

the materials flammability, as well as a good rating method for 

self- extinguishing material. }~terial improvements have been made to reduce 

flammability . This was usually done by adding self-extinguishing agents to 

existing materials which may increase both smoke and toxic . decomposition 

products. In an effort to continue improvement in aircraft fire safety the 

FAA requested comment s on two new proposed rules, one for smoke and another 

to measure toxicity. It was then recognized that fire , smoke and toxicity 

could not be considered individually , but must be combined so the proposed 

rules were properly withdrawn . The wide-body jets were then just being 

designed and FAA required that smoke data be submitted on interior materials 

to assure that smoke was considered in the normal material selection 

compromise . 

During this 10 year time period efforts were not lacking to increase safety 

by improving materials, laboratory and full size fire test methods and 

analytical modeling of fire . In retrospect , one of the largest programs 

relating to a single subject (i. e., fire safety) was undertaken in this 

country by involving representative groups from all organizations involved in 

77 
fires. Specifically related to aircraft was the NASA FIREMAN program, the 

many FAA programs including construction of the new burn test facility at 

NAFEC, the many programs by trade organizations representing the material 

producers and their in- house and supplier work, the new courses and programs 

at universities as well as the aircra ft industry itself. Concern was 

expressed by many persons and organizations that a test for a 

"self-extinguishing" or "fireproof" material by its title was misleading in 

the way it might react in an actual fire. In addition, a method urgently 

needs to be developed to r.te.lsur~ how "good" a material really needs to be 

since it was recognized that material improvement beyond 3ome point would do 

little to improve personnel survival but would be very costly. 

Design Goals and Mandated Standards: 

Industry design goals are to meet or exceed eve ry FAk mandated requirement. 

Improvements in safety are a never-endin~ design goal of government and 

industry. This is evidenced by periodic upgrading of FAR standards and 

incorporation of advances in aircraft design by industry . When considering 

advanced technology , Federal Air Regulations normally lag behind industry 

because of finite times r equired to revise existing regulations. Industry 

often incorporates newly developed technology during these periods . It would 

be difficult for government to eliminate this time lag since most new 

technology is the result of industry research and development programs. If 

new technology is produced by government, it is then necessary for industry 

to evaluate its full impact prior to FAK incorporation. 

When considering state-of- the- art improvements , federal r egulations can, and 

often do, lead industry . This normally occurs when government decides to 

upgrade standards by incorpor ation of proven existing hardware or techno~ogy . 

Sometimes , this is a result of current aircraft accident investigations which 

may reveal facts not previously known or understood . In addition a review or 

accident data has shown that the major survival fire threat is not the 

in- flight fire but rather the survivable impact post-crash fire . Comments 

relative to the airc raft fuel ' s part in this accident scenario are contained 

in later paragraphs. 

Existing technology consists of many tests for flammability , smoke and 

toxicity. It is r ecognized that these three types of hazards cannot be rated 

individually to determine whether a material has been "impr oved" . For this 

reason a number of tests have been attempted in a series of "screens" to rank 

a material in the same sequence as a selected fire scena rio in a fuselage 

test section. After considerable effort, this has been found largely 

unsuccessful because a material in the usual standard laboratory test does 

not "see" the same heat flux and oxygen flow present in a large fire . 

Toxicity and flash fire have not been included in this approach either and 

particularly toxicity has been considered necessary for rule making . 

Technology is only now being developed which can analytically relate 

laboratory data to cabin environments and eventually some form of this 

approach may be the basis of a new rule. 

Existing test facilities range trom those required for materials 

qualification to those useful in design evaluation and fire research. t~st 

78 
concerns in the airplane material business have a capability to perform the 

standard Bunsen burner test for material qualification, some are able to 

perform the smoke test using the NBS chamber and a range of capability in 

toxic gas analysis. Most airrrame manufacturers have additional test and 

analysis capabilities including the Ohio State University Release Rate 

Calorimeter and various scales of Fire Simulation Facilities. A large Cabin 

Fire Simulator is available at McDonnell Douglas and a full scale C-133 

fuselage simulator is at NAFEC. Other specialized aerospace facilities are 

located at NASA Ames , Johnson Space Center and Boeing . Standard tests have 

been established for flammability and smoke and are accepted by the testing 

community . No standards have yet been established for the Ohio State 

Calorimeter nor products of combustion . 

A major technical deficiency at the present time is the lack of a good 

modeling technique. Fire modeling for aircraft is different from general 

fire modeling such as for buildings. Building fire models includes more 

detailed physics principles than is needed for aircraft and these should be 

properly eliminated. Two fire models are needed for aircraft and both 

terminate at flashover rather than full destr uctive involvement of a 

structure. The first, for material rating, must predict the cabin 

environment from laboratory data . The second predicts flame propagation in a 

cabin and can be used in design and for evaluating safety. 

A second major deficiency is our lack of understanding of toxicity. 

Technology is lacking in the definition of the maximum time an occupant 

can breathe a given gas concentration in a cabin environment . This is 

further complicated by combining gases at elevated temperature. 

Psychological factors involve a level of understanding technology which is 

apparently beyond our current capability. · This understanding is needed for 

ultimate accuracy which may never be achieved, but a total understanding not 

needed for rulemaking. In the case of toxicity, panic or fear would increase 

breathing rate and therefore decrease escape time. 

It is believed that after approximately 10 years of attempting to develop 

coherent and useful rules, programs are now underway that will develop the 

technology, facilities, test methods and costs from which one or more of 

several approaches for rules may be selected and direct future research 

needs. 

Existing rules which employ the current FAR Part 25.853 , 25 .855 , and 25.1359 

bunsen burner flammability tests, coupled with nonregulatory smoke testing 

and a knowledge of thermal decomposition products , provides the designer with 

reasonable input for the usual compromises in selection of materials. Fullsize component tests in simulated fire tests prove the suitability of new 

aircraft designs. As there is no data or technique available to correlate th 

increase in cabin survivability with each improvement, experience is used to 

decide on the importance of employing newer materials and designs. Recent 

accident statistics indicate this procedure is reasonable even though it may 

not be the theoretical optimum. 

The Committee has identified an area where an improved test method should be 

quickly incorporated. The vertical Bunsen burner test (FAR Part 25, Annex F) 
should be modified to provide a better test for materials which drip and burn 

away f rom the burner flame. This change may evolve into a separate approach 

for materials required to be tested, e . g . , 1" thick (foam) and others , but is 

within the state-of- the-art and could be the subject of a near-term 

regulation change. ASTN Subcommittee F- 7 is already charged with 

responsibility to recommend a revised test for regulatory purposes. 

Laboratory tests indicate that the radiant heat resistance of emergency 

escape slide material can be substantially improved . Materials have been 

developed which reflect radiant heat and extend the useful exposure life of 

the slide, and are now being evaluated by the FAA. 

For the long term, as discussed above, the OSU calorimeter device modified 

for smoke and toxic gas measurement, probably coupled with an analytical 

model to relate OSU test data to cabin environment , show promise for 

providing the basis for regulatory action. Standardizing tests to run in the 

unit and agreeing on personnel hazard limits is yet required to achieve a 

meaningful measure/correlation of human survivability in a postcrash fire 

situation. 

Full-scale cabin-fire testing in facilities such as the FAA and other 

government industry facilities provides for baseline data for cabin fires. 

It is not intended that regulations would be written around these tests; 

rather, the data provides guidance for more detailed design improvements. 

It is expected that full- size component testing (e . g., waste containers) 

in realistic fires will cont inue to provide rationale for improving both 

materials and designs, regardless of future rules for materials. 

RECO~lENDED GOALS FOR FAA RULEMAKING 

Cabin Materials and Evacuation Slides 

The Committee perceives that the existi ng FAR 25 Bunsen burner test is adequate 

for separating burning from self-extinguishing materials and for measuring the 

flammabili t y of self- extinguishing materials except those which drip and melt 

away from the flame. For the materials that drip and melt away like 

polyurethane foam, a revised FAR test method should be developed . 

Development of a radiant panel test method and an improvement in the heat 

r esistance of evacuation slides will be completed in the near future . These 

improvements should be evaluated and implemented as soon as they are 

available . 

Fuel System 

The SAFER Committee believes that technology exists to support rulemaking to 

minimize the hazard of fuel tank explosions during post-crash fires. It is 

considered that fuel tank vent flame arrestors or explosion suppression systems 

used in some commercial production aircraft to protect against 

lightning-induced ignition at fuel vent outlets might also be able to delay 

propagation of ground fires through the vent system and the subsequent 

explosions in intact fuel systems to provide additional time for safe 

evacuation. 

so 
• 

A flame arrestor consists of a web of quenching channels. When a flame front 

enters a relatively cold quenching channel, heat from the flame flows into the 

channel wall at a rate exceeding the rate of heat generation so that the 

temperature decreases and the combustion reaction ceases. If the total heat 

capacity of the arrestor is small, then the temperature of the arrestor will 

increase rapidly to a value where the arrestor fails. A flame stabilized on 

the flame arrestor surface could heat a normally quenching 

channel to a temperature where the flame can penetrate unless the cooling 

effect of the unburned gases approaching the flame arr estor maintain the 

quenching surfaces below the fuel ignition temperature. However, it is 

believed possible to design an arrestor to prevent flame penetration and 

propagation through the vent system for a period of time equal to the time 

required for an external fire to penetrate the undersurface of an empty wing 

tank . Testing of flame arrestors in a simulated crash fire environment has 

not yet been conducted and would be necessary to obtain basic data on their 

effectiveness in this environment. 

An explosion suppression system includes a flame radiation sensor in the vent 

outlet tube to detect the presence of an oncoming flame front and a fire 

extinguishant discharge system in a fuel tank for automatic early and rapid 

suppression of the combustion process when it reaches the tank. This system 

can provide fuel tank vent explosion protection similar to a properl y 

designed flame arrestor if provision is made for adequate extinguishant 

dispersion. This requires continued availability of electrical power to 

enable sensing of any internal combustion process induced by external fire 

effects and triggering of timely extinguishant dispersal. In addition the 

system must be capable of effective operation at elevated temperatures due to 

external heating effects. Data on explosi9n suppression system tests in a 

simulated crash fire environment are needed to substantiate their 

effectiveness in this environment . 

The SAFER Committee also believes that technology exists to minimize the 

post- crash fire hazard by providing means to shut off engine fuel supplies to 

further reduce fuel fire possibilities. 
REFERENCES AND BIBLIOGRAPHY 

l. Lucha, G. V. , Robertson, H.A., and Schooley, F. A. , "An Analysis of 

Aircraft Accidents Involving Fires, " National Ae ronautics and Space 

Administration , Report NASA CR 137690 

2. CRC Report No. 482, "Aviation Fuel Safety - 1975." Novembe r 1975 

3. Report No . FAA-RD-75-156, "A Crashworthiness Analysis with Emphasis 

on the Fire Hazard: U. S. and Selected For eign Tur bine Air craft Accid~nts 

1964-1974 , " July 1976 

4 . Paper Pr epared by A. F. Taylor , "An Evaluation of Worldwide Transport 

Aircraft Fire Experiences," September 1976 

5 . Report No . NTSB- AAS-77-1, "Special Study -- U.S . Air Carrier Accidents 

Involving Fire 1965 through 1974 and Factors Affecting the Statistics, " 

February 1977 

6 . Paper prepared by H. C. Black, "Transport Categor y Airplane Post- Crash 

Fuel Systems Fire and Explosion Hazard Reduction," June 1977 

7. AGARD Report No. 132 , "Aircraft Fire Safety," November 1979 

8 . Na tiona! Transportation Safety Board, "Aircraft Accident Reports," 

Periodic 

9 . SAFER Interior ~Ia terials Short-Term Action Sub- Group , "The Contribution 

of Cabin Supplies and Carry- On Items to a Post- Crash Fuel Fed Fire," 

September 1979 

10. NBS-GCR-7~-168 , "Human Fatalities rrom Unwanted Fires," December 1978 

11. "Special Study : U. S. Air Carrier Accidents Involving Fire 1965 through 

1974 and Factors Affecting the Statistics," National Transportation Safety 

Board, keport NTSB- AAS-77-1 , February 17 , 1977 . 

12. "Investigation of Aircraft Fuel Tank Explosion in Nitrogen Inerting 

Requirements During Ground Fire , " Richard Hill and George R. Johnson, 

October 1975, FAA- RD-75- 119 

13. Boeing Commercial Airplane Company Hemo, B-9200- 3- 371 , "Cost Update of 

LN2 Fuel Tank lnerting Economic Study," da t ed Sept embe r 14 , 1979 

14. " Factors in Using Kerosene Jet Fuel of Reduced Flash Point , " Dukek, Strauss 

Editors; American Society for Testing and Materials Report , STP 688, 1979 

82 
15. Hill , R. G., Johnson, G. R. , and Sarkos, C. P., "Postcr ash Fuel Fire 

Hazard Measurements in a Wide Body Aircraft Cabin," Federal Aviation 

Administration, NAFEC, Report FAA-NA-79-42, December 1979 

16. Eklund, T. I., "Pool Fire Radiation through a Door in a Simulated Aircraft 

Fuselage," Federal Aviation Administration, NAFEC, Report FAA-RD- 78-135 , 

December 1978 

17. "Aviation Safety (Aircraft Passenger Education-- The Missing Link in 

Air Safety)," Hearings before the Subcommittee on Investigations and 

Review, House Committee on Public Works and Transportation, 95th Cong. , 

1st Sess. (1977) 

18. See Federal Aviation Regulations, Parts FAR 121 . 571 , 121. 573 

19. U. S. Civil Aeronautics Board, "Fly-Rights: A Guide to Air Travel in the 

United States," (5th Rev. Ed., July 1979) 

20 . "Special Study : Safety Aspects or Emergency Evacuations From Air Carrier 

Aircraft," National Transportation Safety Board; Report NTSB-AAS- 74-3, 

November 13, 1974. 

21. Engineering and Development Program Plan Antimisting Fuel, FAA-ED-18-4, 

June 1980.