APPENDIX
A - MINIMUM PERFORMANCE STANDARDS FOR AIRCRAFT CARGO COMPARTMENT
BUILT-IN FIRE SUPPRESSION SYSTEMS.
1. INTRODUCTION.
Federal Aviation Regulations (FAR’s) and Joint Aviation
Regulations (JAR’s) require fire suppression systems for
some classifications of cargo compartments. In the past, the
aircraft industry has selected Halon 1301 total flood fire suppression
systems as the most effective systems for complying with the
regulations. Because of the ban on production of Halon 1301,
mandated by the Montreal Protocol and effective January 1994,
new fire suppression systems will need to be certified when the
use of Halon 1301 is no longer viable. The tests described in
this standard are one part of the total FAA/JAA certification
process for cargo compartment fire suppression systems. Compliance
with other applicable regulations, some of which are listed below,
is also required. Applicants attempting to certify replacement
systems are encouraged to discuss the required process with regulatory
agencies prior to conducting testing.
1.1 APPLICABLE REGULATIONS.
The following existing FAR’s/JAR’s pertain to cargo
compartment fire suppression systems:
25.851. "(b) Built-in fire extinguishers. If a built
–in fire extinguisher is provided—
- Each built-in fire extinguishing system must be installed
so that—
(i) No extinguishing agent likely to enter personnel compartments
will be hazardous to the occupants; and
(ii) No discharge of the extinguisher can cause structural
damage.
- The capacity of each required built-in extinguishing system
must be adequate for any fire likely to occur in the compartment
where used, considering the volume of the compartment and the
ventilation rate."
25.855. "(h) Flight tests must be conducted to show compliance
with the provisions of Sec. 25.857 concerning—
- Compartment accessibility,
- The entries of hazardous quantities of smoke or extinguishing
agent into compartments occupied by the crew or passengers, and
- The dissipation of the extinguishing agent in Class C compartments.
(i) During the above tests, it must be shown that no inadvertent
operation of smoke or fire detectors in any compartment would
occur as a result of fire contained in any other compartment,
either during or after extinguishment, unless the extinguishing
system floods each such compartment simultaneously."
25.857. "(c) Class C. A Class C cargo compartment is
one not meeting the requirements for either a Class A or Class
B compartment but in which—
- There is a separate approved smoke detector or fire detector
system to give warning at the pilot or flight engineer station.
- There is an approved built-in fire extinguishing system controllable
from the pilot or flight engineer stations;
- There are means to exclude hazardous quantities of smoke,
flames, or extinguishing agent, from any compartment occupied
by the crew or passengers;
- There are means to control ventilation and drafts within
the compartment so that the extinguishing agent used can control
any fire that may start within the compartment."
In addition to these regulations, the FAA issued Airworthiness
Directive 93-07-15 which required, among other things, that after
November 2, 1996 the Class B cargo compartments on Boeing Models
707, 727, 737, 747, and 757 and McDonnell Douglas Models DC-8,
DC-9, and DC-10 Series airplanes have improved fire protection
features. One of three options available to comply with this
AD is to modify Class B cargo compartments on these airplanes
to comply with the requirements for Class C compartments. This
option would require the installation of a fire suppression system.
One other area of rulemaking activity relating to cargo compartment
suppression system requirements is the "Revised Standards
for Cargo or Baggage Compartments in Transport Category Airplanes,
Final Rule", effective March 19, 1998. This rule eliminates
Class D cargo compartments on newly certified aircraft under
Part 25 and requires existing Class D compartments on Part 121
certified passenger aircraft to comply with the detection and
suppression/extinguishing system aspects of Class C cargo compartment
requirements by March 19, 2001. This rule was issued by the FAA
and at this time applies only to aircraft operated by U.S. based
airlines.
2. SCOPE.
This document establishes the minimum performance standards
(MPS) that a cargo compartment fire suppression system must meet.
It describes the tests that should be performed to demonstrate
that the performance of the replacement agent/systems equals
the performance of the currently approved Halon 1301 systems.
3. AGENT SELECTION GUIDANCE.
3.1 ENVIRONMENTAL.
The replacement agent must be approved under the Environmental
Protection Agency (EPA), Clean Air Act, Significant New Alternatives
Policy (SNAP) program, or other international governmental approving
program. The primary environmental characteristics to be considered
in assessing a new agent are Ozone Depletion Potential (ODP),
Global Warming Potential (GWP) and Atmospheric Lifetime. The
agent selected should have environmental characteristics in harmony
with international laws and agreements, as well as applicable
local laws. This MPS sets out the means of assessing the technical
performance of potential alternatives. In selecting a new agent
it should be noted that an agent which does not have a zero or
near zero ODP and the lowest practical GWP and Atmospheric Lifetime
may have problems of international availability and commercial
longevity.
3.2 TOXICOLOGY.
The toxicological acceptability of an agent is dependent on
its use pattern. As a general rule, the agent must not pose an
unacceptable health hazard for workers during installation and
maintenance of the suppression system. At no time should the
concentration present an unacceptable health hazard in areas
where passengers or workers are present or where leakage could
cause an agent to enter an occupied area. Following the release
of the agent during fire suppression, the cumulative effect of
the agent, its pyrolytic breakdown products, and the byproducts
of combustion must not pose an unacceptable health hazard.
FAR Parts 25.851, 25.855 and 25.857 all address the issue
of hazardous quantities of smoke, gas or extinguishing agent
in occupied compartments. Conducting the fire tests described
in this MPS does not address those issues. The FAA Technical
Center has conducted tests in an aircraft fuselage with inflight
airflow conditions. Data on the level of smoke, gases and extinguishing
agent in the normally occupied sections of the fuselage are available
for some suppression agents and systems.
4. TEST REQUIREMENTS.
4.1 TEST ARTICLE.
The fire tests are to be conducted inside a simulated below
floor cargo compartment of a wide body aircraft. The volume of
the compartment should be 2000 +/- 100 cubic feet (56.6 +/-2.8
m3). See figure
1. The leakage rate from the compartment should be 50 +/-
5 cubic feet per minute (1.4 +/-.14 cubic meter per minute).
The leakage from the compartment should be configured to simulate
the "U" shape of the cargo door seals that would exist
on an actual aircraft. This can be done by installing perforated
ducts inside the compartment in the shape of the perimeter of
a cargo door and then venting those ducts outside the test article.
A variable speed fan installed in the exit of the duct should
be used to draw air out of the compartment. One-inch diameter
holes spaced at one hole every 5 inches (12.7 cm) in a round,
four inch diameter steel duct has been shown to be effective.
The perforated ducts should be installed on the opposite side
of the cargo compartment from where the ignited box for the bulk
load and containerized load fire scenarios are located. The make
up air back into the compartment should be evenly distributed
and not from any one location.
4.2 INSTRUMENTATION.
Temperature measurements should be taken throughout the cargo
compartment. Type K chromel/alumel 22 gauge thermocouples have
been found to be effective at measuring temperatures in the range
these fire scenarios produce. Ceiling thermocouples should be
evenly spaced along the compartment ceiling with a maximum of
five feet between adjacent thermocouples. One of the ceiling
thermocouples should be installed directly above the initial
ignition location for all fire scenarios. The beads of the ceiling
thermocouples shall be 1 inch (2.5 cm) below the compartment
ceiling. At least one thermocouple should be placed on the compartment
sidewall one foot below ceiling level and centered on the fire
ignition location. The sidewall thermocouple should be installed
on the side of the compartment nearest the ignition location.
At least two additional thermocouples should be placed in and
above the box containing the igniter for the bulk and containerized
fire scenarios. The purpose of these two thermocouples is to
monitor and verify the ignition of the boxes. The readings are
not part of the acceptance criteria. Care should be taken to
prevent these thermocouples from contacting the energized coil
of nichrome wire.
A continuous gas analyzer with a real time display of the
gas concentration is required for the aerosol can scenario when
the suppression system is a gaseous total flood system. A continuous
gas analyzer may be required, depending on the suppression system
design, for the bulk load and containerized load scenarios. Section
4.4 describes the conditions when this may occur. The accuracy
of the analyzer shall be +/- 5% of the reading. The gas analyzer
is used to measure the concentration of the gaseous suppression
agent. The data-sampling rate for all the temperature measurements
and the gas concentrations should be at least one data point
every 5 seconds.
A pressure transducer is also required for the aerosol can
fire scenario. The response time of the transducer should be
.02 seconds or faster. Omegaâ
manufactures several transducers suitable for this application.
The transducer should be mounted on the ceiling in the geometric
center of the compartment. The data-sampling rate for the pressure
transducer should be at least 50 data points per second.
4.3 FIRE SCENARIOS.
The aircraft cargo compartment fire suppression system must
successfully control the following four different fire scenarios.
4.3.1 BULK FIRE LOAD.
The fire load for this scenario shall be single-wall corrugated
cardboard boxes, with nominal dimensions of 18" X 18"
X 18" (45.7cm x 45.7cm x 45.7cm). The weight per unit area
of the cardboard should be 0.11 lbs/ft2 (.5417 kg/m2).
The boxes should be filled with 2.5 pounds (1.1 kg) of shredded
newspaper, loosely packed without compacting. The weight of the
filled box should be 4.5 +/- 0.4 lbs. (2.0 +/-0.2 kg). The flaps
of the boxes should be tucked under each other with no staples
or tape used. The boxes should be stacked in two layers into
the cargo compartment in a quantity representing 30% of the cargo
compartment empty volume. For a 2000 cubic foot (56.6 m3)
compartment, this would require 178 boxes. The boxes shall be
touching each other without any significant air gaps between
boxes. The test fire is ignited by applying 115 VAC to a seven-foot
(2.1 m) length of nichrome wire. The wire is wrapped around several
folded paper towels. The resistance of the nichrome igniter coil
should be approximately 7 Ohms. The igniter should be placed
into the center of a box on the bottom outside row of the stacked
boxes. Several ventilation holes should be placed in the side
of the box to ensure that the fire does not self extinguish.
Ten, 1.0" (2.5 cm) diameter holes have been
shown to be effective. See figure
2 and figure 3.
4.3.2 CONTAINERIZED FIRE LOAD.
The same type of cardboard boxes filled with shredded newspaper
and the same igniter used in the bulk load fire scenario should
be used in this scenario. The boxes should be stacked inside
an LD-3 container as shown in figure
4. The boxes shall be touching each other with no significant
air gaps between them. The container shall be constructed of
an aluminum top and inboard side, a Lexan (polycarbonate) front
and the remainder of steel. Two rectangular slots for ventilation
should be cut into the container in the center of the Lexan front
and in the center of the sloping sidewall. The slots should be
12" by 3" +/-1/4" (30.5 cm x 7.6 cm +/- 0.6 cm).
See figure 5. The
igniter is placed in a box on the bottom row, in the corner nearest
the sloping side of the container and the Lexan. Ventilation
holes should be placed in the sides of the box. Ten, 1.0"
(2.5 cm) diameter holes have been shown to be effective.
Two additional, empty LD-3 containers are placed adjacent to
the first container. See figure
6.
4.3.3 SURFACE BURNING FIRE.
0.5 U.S. gallons (1.9 liters) of Jet A fuel
in a square pan should be used for this scenario. The pan should
be constructed of 1/8" (0.3 cm) steel and measure 2 feet
by 2 feet by 4 inches high (60.9 cm x 60.9 cm x 10.2 cm). Approximately
13 fluid ounces (385 ml.) of gasoline should be added to the
pan to make ignition easier. 2.5 gallons (9.5 liters) of water
placed in the pan has been found to be useful in keeping the
pan cooler and minimizing warping. This quantity of fuel and
pan size is sufficient to burn vigorously for approximately 4
minutes if not suppressed. The position of the pan in the cargo
compartment should be in the most difficult location for the
particular suppression system being tested. The pan should be
located 12 inches below the cargo compartment ceiling if the
suppression system uses a gaseous agent with a density at standard
pressure and temperature (14.7 psia (101.3 kPa), 59.0 oF.
(15 oC)) greater than air. The pan should be 12 inches
(30.5 cm) above the floor of the compartment if the suppression
system uses a gaseous agent with a density less than air at standard
pressure and temperature. The pan should be at the compartment
mid height when the suppression agent has a density equal to
that of air. The pan should be located at the maximum horizontal
distance from any discharge nozzles for all tests, regardless
of the suppression agent used. See figure
7.
4.3.4 EXPLODING AEROSOL CAN
FIRE.
This scenario addresses the overpressure and bursting of an
aerosol can involved in a cargo fire and the potential for the
ignition of the released hydrocarbon propellant used in these
cans. The FAA Technical Center has developed an aerosol can simulator
that releases a mixture of propane and alcohol through a large
area valve and across sparking electrodes.
The aerosol explosion simulator must utilize a cylindrical
pressure vessel for the storage of flammable base product and
propellant. The pressure vessel must be capable of withstanding
a minimum pressure of 300 psi (2068.5 KPa). The pressure vessel
must be mated to a ball valve capable of withstanding a minimum
pressure of 300 psi (2068.5 KPa). The port diameter of the ball
must be 1.5 inches (3.8 cm) (Note: a ball valve is typically
classified according to the diameter of the pipe that it connects
to, but this is not necessarily the size of the ball port). The
ball valve must be capable of rotating from the fully closed
position to the fully open position in less than 0.1 seconds
to allow the formation of a vapor cloud. Longer opening durations
will significantly affect the vapor cloud formation, and hence
the explosive force yielded. The ball valve can be activated
by any suitable means, including pneumatic or hydraulic actuators,
or manually via the appropriate linkage. The pressure vessel
must be mounted vertically above the ball valve to allow for
complete expulsion of the liquid contents. A discharge elbow
located vertically under the ball valve will direct the contents
horizontally. (Figure
8).
Pressure Vessel. A steel 2-inch diameter (5.1 cm), 11 inch
long (27.9 cm) schedule 80 pipe welded or capped at one end has
been found suitable for storage of the pressurized mix.
Ball Valve. The 2-inch (5.1 cm) valve must be constructed
of a material capable of withstanding interaction with ethanol
and propane. A DynaQuipâ stainless
steel valve has been found suitable for this application.
Ball-Valve Actuator. A pneumatic rotary actuator has been
found suitable for quickly and reliably rotating the ball valve
from closed to fully open. A Speedaireâ
ninety-degree actuator with a 2-inch (5.1 cm) bore performs well.
Propellant heater. A system for heating the pressurized propellant
mix after transfer to the pressure vessel must be provided. This
would include a hot-air gun directed toward the pressure vessel,
a hot wire wrap, or other suitable means.
Pressure Gauge. A suitable device for measuring the pressure
of the contents must be installed on the simulator pressure vessel.
The device must be capable of measuring the pressure to within
+ 5 psi (34.5 KPa).
Propellant Mix. The base product/propellant mix should consist
of 20% liquid propane (C3H8, 3.2 ounces
[0.09 kg]), 60 % ethanol (denatured alcohol, 9.6 ounces [0.27
kg]), and 20% water (3.2 ounces [0.09 kg]) The total weight of
the base product/propellant mix should be 16 ounces.
Spark Igniters. A set of direct current (DC) spark igniters
must be used to ignite the propellant/base product mix as it
is discharged from the pressure vessel. An ignition transformer
capable of providing 10,000 Volts output has been found to be
suitable for powering the igniters, which should be placed 36
inches (91.4 cm) from the point of discharge. The spark igniter
gap should be set at 0.25 inches (0.64 cm).
The procedure for conducting the aerosol simulator test is
as follows:
Weight the empty simulator device on a suitable scale. Place
the 9.6 ounces (0.27 kg) of ethanol (denatured alcohol) and 3.2
ounces (0.09 kg) of water into the pressure vessel. Transfer
3.2 ounces (0.09 kg) of liquid propane from a storage tank into
the pressure vessel. Remove all transfer lines and check final
mass. Mount simulator device in either the forward or aft compartment
bulkhead such that discharge is directed into the compartment,
across spark igniters. Simulator discharge port and the spark
igniter must be 2 feet (60.9 cm) above the compartment floor.
Begin heating the pressure vessel to raise the pressure of the
contents to 210 +/- 5 psi (1448 +/- 34.4 KPa). Activate the suppression
agent/system. Activate the spark igniters. Release the charged
contents into the compartment when the concentration of agent
is within +/-0.1% of the minimum design concentration.
4.4 SUPPRESSION SYSTEM DESIGN.
The suppression system design used for these fire tests should
be similar to the design intended for use in aircraft. For a
gaseous total flood system, the quantity of agent used should
be that quantity that will produce the same initial concentration
by volume in an empty 2000 cubic foot (56.6 m3) compartment
as the initial design concentration that will be demonstrated
in the required flight test in the actual aircraft cargo compartment.
Some aircraft total flood system designs consist of single bottle
discharges, multiple bottle discharges at staggered intervals,
and single bottle discharges followed by metered systems that
bleed smaller quantities of agent into the compartment to maintain
the desired concentration. The compartment volume, leakage rate,
and diversion time for the aircraft determines the type of system
necessary. There may be situations when the volume, leakage rate
and 30 minute test duration required by these fire tests would
not allow for the use of the same system design as is intended
for installation in an aircraft. One possible situation could
be when the leakage from the actual aircraft cargo compartment
is much lower than what is required for the fire test and a single
bottle discharge is sufficient to maintain adequate concentration
in the aircraft but not in the fire test article. For this and
other situations that require changing the system design, a metered
system may be used to maintain adequate concentration of agent.
The concentration that should be maintained for the fire test
should be the minimum design concentration that the system will
demonstrate can be maintained by the required flight test. If
a metered system is used in the fire test, the concentration
in the compartment after the metered system is started should
not be allowed to go higher than 10% above the minimum design
concentration. The concentration should be measured at heights
of 16"(40.6 cm), 32.5" (82.5 cm) and 49" (124.4
cm) in the middle of the compartment. The design and initial
concentrations referenced in this paragraph for the fire test
refer to the arithmetic average of the three different probe
heights. The method of measuring the concentration of agent in
the required flight test might not use the arithmetic average
of three probes. The certification authority that requires the
flight test will specify the number and location of the probes
that should be used to determine the concentration of agent in
the compartment.
For a non-gaseous suppression system, parameters such as activation
set points, operating pressures, nozzle spacing and direction,
etc. should be the same as the system intended to be installed
in the actual aircraft. Other factors that are cargo compartment
size dependent such as agent quantity, number of nozzles, zone
sizes, etc. should be scaled up or down as appropriate when the
volume and/or shape of the compartment in the actual aircraft
is different than the 2000 cubic foot (56.6 m3) compartment
required for these tests.
4.5 SUPPRESSION SYSTEM ACTIVATION.
Bulk load, Containerized load and Surface Burning fire scenarios:
The suppression system should be activated 60 seconds after any
one of the ceiling mounted thermocouples exceeds 200oF
(93.3oC).
Aerosol can scenario: For a gaseous total flood suppression
system, the aerosol can simulator should be activated when the
agent concentration 2 feet (60.9 cm) above the compartment floor
is at the minimum volumetric design concentration +/- 0.1%. The
agent concentration must be actually measured during this test.
Calculation of agent concentration based on the leakage rate
is not permitted. The sampling probe for measuring agent concentration
should be 36 inches (91.4 cm) from the exit of the aerosol simulator,
and less than 18 inches (45.7 cm) from the spark igniters. For
a suppression system that is not a total flood gaseous system,
the aerosol simulator should be positioned at the most difficult
location for that particular system.
4.6 TEST DURATION.
The duration of the bulk load and containerized load fire
scenario tests shall be for 30 minutes after the activation of
the suppression system. If a non-gaseous agent is used, a sixth
test must be conducted for as long as the duration of the intended
flight and maximum diversion time. The surface burning fire test
shall be conducted for five minutes from the time the suppression
system is activated or until the fire is extinguished, whichever
occurs first. The exploding aerosol test scenario is complete
fifteen seconds after the release of the aerosol simulator contents.
5. ACCEPTANCE CRITERIA
The acceptance criterion for the bulk load fire scenario is
that none of the ceiling or sidewall thermocouples exceed 730
oF (387.8 oC) starting 30 seconds after
the suppression system is initially activated until the end of
the test. In addition, the area under the time-temperature curve
for the ceiling thermocouple that recorded the highest temperature
starting 30 seconds after the suppression system was activated
cannot exceed 11600 oF - minutes (6426.7 oC
- minutes). The area should be computed from the time of initial
suppression system activation until the end of the 30-minute
test duration. In the case of the sixth test (longer than 30
minutes), the worst 30-minutes interval shall be used for the
acceptance criteria.
The criteria for the containerized load fire scenario is that
none of the ceiling or sidewall thermocouples exceed 670 oF
(354.4 oC) starting 30 seconds after the suppression
system is initially activated. The area under the time-temperature
curve cannot exceed 15700 oF- minutes (8704.4 oC
- minutes). These values for the bulk and containerized fires
are based on an approximate 10% increase over the maximum values
obtained in a series of tests conducted under the requirements
of this MPS using Halon 1301 as the suppression agent. Figure 9 shows the critical times during
a test for computing the acceptance criteria for the bulk and
containerized fire scenarios.
The acceptance criteria for the surface burning fire scenario
is that none of the ceiling or sidewall temperatures exceed 1200
oF (648.9 oC) starting 30 seconds after
the suppression system is initially activated until the end of
the test. In addition, the area under the time-temperature curve
cannot exceed 2800 oF- minutes (1537.8 oC
- minutes).
The criteria for the aerosol can scenario is that none of
the ceiling or sidewall temperatures exceed 110 oF
(43.3 oC) at any time and that no overpressure should
be present in the compartment at the time the simulator is activated.
Five tests must be conducted for each scenario. The suppression
system must successfully meet the acceptance criteria for all
five tests. Table 1 summarizes the acceptance criteria for the
four fire tests.
TABLE 1. ACCEPTANCE CRITERIA
 |
| Fire Scenario |
Maximum Temp. - °
F (oC) |
Maximum Pressure - psi (KPa) |
Maximum Temp-Time Area ° F-min. (°
C-min) |
Comments |
| Bulk Load |
|
|
|
Temperature limit starting 30 seconds
after suppression system activation. Temp.-Time area for 30 minutes
starting with suppression system activation. |
| Containerized Load |
|
|
|
Temperature limit
starting 30 seconds after suppression system activation. Temp.-Time
area for 30 minutes starting with suppression system activation. |
| Surface Fire |
|
|
|
Temperature limit starting 30 seconds
after suppression system activation. Temp.-Time area for 4 minutes
starting with suppression system activation. |
| Aerosol Can |
|
|
|
There shall be
no explosion |
|
LAST UPDATED
ON 7/26/99
|