Re: Emergency exits capacity

From:         don@rata.vuw.ac.nz (Don Stokes)
Organization: Victoria University of Wellington
Date:         18 Sep 95 12:06:48 
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In article <airliners.1995.1437@ohare.chicago.com>,
Jean-Francois Mezei <mezei_jf@eisner.decus.org> wrote:
>I have a few question on emergency exits for airplanes :
>
>Is the "must be able to empty plane in 90 seconds" a real requirement or just
>urban legend ?

It's real.  Federal Aviation Regulations, Part 25 (aka FAR 25):

Sec. 25.803 Emergency evacuation.

   (a) Each crew and passenger area must have emergency means to allow
   rapid evacuation in crash landings, with the landing gear extended as
   well as with the landing gear retracted, considering the possibility
   of the airplane being on fire.
   (b) [Reserved]
   (c) For airplanes having a seating capacity of more than 44
   passengers, it must be shown that the maximum seating capacity,
   including the number of crewmembers required by the operating rules
   for which certification is requested, can be evacuated from the
   airplane to the ground under simulated emergency conditions within 90
   seconds. Compliance with this requirement must be shown by actual
   demonstration using the test criteria outlined in appendix J of this
   part unless the Administrator finds that a combination of analysis and
   testing will provide data equivalent to that which would be obtained
   by actual demonstration.
   (d) [Reserved]

>Are there specific and widely accepted ways to measure each exit's capacity in
>an emergency ? If so, what are the criteria used ? (door size, chute length,
>cabin/aisle design ?) Or do aircraft manufacturers actually load up a plane
>with people and make the test ?

Yes and yes.  The relevant sections are:
                              - Sec. 25.801 Ditching.
                              - Sec. 25.803 Emergency evacuation.
                              - Sec. 25.807 Emergency exits.
                              - Sec. 25.809 Emergency exit arrangement.
                              - Sec. 25.810 Emergency egress assist means
                                and escape routes.
                              - Sec. 25.811 Emergency exit marking.
                              - Sec. 25.812 Emergency lighting.
                              - Sec. 25.813 Emergency exit access.
                              - Sec. 25.815 Width of aisle.
                              - Sec. 25.817 Maximum number of seats
                                abreast.
                              - Sec. 25.819 Lower deck service
                                compartments (including galleys).
                                Ventilation and Heating
                              - Sec. 25.831 Ventilation.
                              - Sec. 25.832 Cabin ozone concentration.
                              - Sec. 25.833 Combustion heating systems.

And the way that you test this is to put a plane in a darkened hanger, stuff
it full of ordinary people (a representative sample of volunteers), fire up
some big fans to blow the slides around, turn out the lights, tell everyone
to evacuate, and carry the wounded away in ambulances.  Yes, people get hurt
doing this, sometimes seriously.  Most tests on large airliners will break
a few bones.

>Does anyone have specific numbers on how many passengers a full fledged door
>(with chute) can process (per minute ?) and how over-wing exits fair in that
>regard ?

Casual reading of the FARs doesn't give a number -- the number is going to
be a function of the other numbers sepcified in FAR 25.

>If the "90 seconds" requirement is true, does it apply to a plane with all of
>its doors usable, or does it assume that a certain percentage of its doors will
>be unusable ?

The test does use all doors.  The problem is that a parked aircraft in a
hangar with volunteers doing what they're told is a very different animal
to a damaged and burning airliner leaning on some of its gear and with
several exits reading straight into the middle of a fire.  FAR 25 simply
specifies that in the best case, ie aircraft intact and all doors working,
the plane can be evacuated in 90 seconds -- in real life it may well be
much longer than that.  The Aloha "737 convertible" took 25 minutes to
evacuate, despite being basically intact and firmly on the runway with
no fire.  Note that the forward doors were forward of the pert of the
fuselage that tore off (although the picture I have here shows the right
hand door doesn't have the slide deployed -- they're deployed on both rear
exits).

FARs can be browsed on the Web at:

		 http://acro.harvard.edu/GA/fars.html

--
Don Stokes, Network Manager, Victoria University of Wellington, New Zealand.
don@vuw.ac.nz(work) don@zl2tnm.gen.nz(home) +64 4 495-5052 Fax+64 4 471-5386