FAA Federal Aviation Regulations (FARS, 14 CFR)

(a) Summary of Method.
(1) The specimen to be tested is injected into an environmental chamber through which a constant flow of air passes. The specimen's exposure is determined by a radiant heat source adjusted to produce the desired total heat flux on the specimen of 3.5 W/cm2, using a calibrated calorimeter. The specimen is tested so that the exposed surface is vertical. Combustion is initiated by piloted ignition. The combustion products leaving the chamber are monitored in order to calculate the release rate of heat.

(b) Apparatus. The Ohio State University (OSU) rate of heat release apparatus as described below, is used. This is a modified version of the rate of heat release apparatus standardized by the American Society of Testing and Materials (ASTM), ASTM E-906.
(1) This apparatus is shown in Figures 1A. All exterior surfaces of the apparatus, except the holding chamber, must be insulated with 25 mm thick, low density, high temperature, fiberglass board insulation. A gasketed door through which the sample injection rod slides forms an airtight closure on the specimen hold chamber.
(2) Thermopile. [The temperature difference between the air entering the environmental chamber and that leaving is monitored by a thermopile having five hot and five cold, 24 gauge Chromel-Alumel junctions. The hot junctions are spaced across the top of the exhaust stack, 10mm below the tope of the chimney. One thermocouple is located in the geometric center, with the other four located 30mm from the center along the diagonal toward each of the corners (Figure 5). The cold junctions are located in the pan below the lower air distribution plate (see paragraph (b)(4)). Thermopile hot junctions must be cleared of soot deposits as needed to maintain the calibrated sensitivity.]
(i) Thermal Inertia Compensator. A compensator tab is made from 0.55mm stainless steel sheet, 10 by 20mm. An 800 length of 24 gauge Chromel-Alumel, glass insulated, duplex thermocouple wire is welded or silver soldered to the tab as shown in Figure 2, and the wire bent back so that it is flush against the metal surface.
(ii) The compensator tab must be mounted on the exhaust stack as shown in Figure 3 using a 6-32 round head machine screw, 23mm long. Add small (approximately 4.5mm O.D., 9mm O.D.) washers between the head of the machine screw and the compensator tab to give the best response to a square wave input. (One or two washers should be adequate.) The "sharpness" of the square wave can be increased by changing the ratio of the output from the thermopile and compensator thermocouple which is fed to the recorder. The ratio is changed by adjusting the 1-K ohm variable resistor (R1) of the thermopile bleeder shown in Figure 4. When adjusting compensation, keep R1 as small as possible. Adjustment of the compensator must be made during calibration (see paragraph (c)(1)) at a heat release rate of 7.0 plus or minus 0.5 kW.
(iii) Adjust the washers and the variable resistor (R1) so that 90 percent of full scale response is obtained in 8 to 10 seconds. There must be no overshoot, as shown in Figure 5A. If an insufficient number of washers is added, or R1 is too small, the output with square wave input will look like Figure 5B; if too many washers are added and R1 is too large, the output will look like Figure 5A.
(iv) Subtract the output of the compensator from the thermopile. The junctions enclosed in the dotted circle of Figure 4 are kept at the same constant temperature by electrically insulating the junctions and placing them on the pipe carrying air to the manifold, then covering them and the pipe with thermal insulation.
(v) Thermopile hot junctions must be cleared of soot deposits on a daily basis during periods of testing.
(3) Radiation Source. [A radiant heat source for generating a flux up to 100 kW/m2, using four silicone carbide elements, Type LL, 20 inches (50.8 cm) long by inch (1.54 cm) O.D., nominal resistance 1.4 ohms, is shown in Figures 2A and 2B. The silicone carbide elements are mounted in the stainless steel panel box by inserting them through 15.9mm holes in 0.8mm thick ceramic fiber board. Location of the holes in the pads and stainless steel cover plates are shown in Figure 2B. The diamond shaped mask of 24-gauge stainless steel is added to provide uniform heat flux over the area occupied by the 150 by 150mm vertical sample.]
(4) Air Distribution System. The air entering the environmental chamber is distributed by a 6.3 mm thick aluminum plate having eight, No. 4 drill-holes, 51 mm from sides on 102 mm centers, mounted at the base of the environmental chamber. A second plate of 18 gauge steel having 120, evenly spaced, No. 28 drill holes is mounted 150 mm above the aluminum plate. A well-regulated air supply is required. The air supply manifold at the base of the pyramidal section has 48, evenly spaced, No. 26 drill holes located 10 mm from the inner edge of the manifold so that 0.03 m3/second of air flows between the pyramidal sections and 0.01 m3/second flows through the environmental chamber when total air flow to apparatus is controlled at 0.04 m3/second.
(5) Exhaust Stack. An exhaust stack, 133mm by 70mm in cross section, and 254mm long, fabricated from 28 gauge stainless steel, is mounted on the outlet of the pyramidal section. A 25mm by 76mm plate of 31 gauge stainless steel is centered inside the stack, perpendicular to the air flow, 75mm above the base of the stack.
[(6) Specimen Holders. The 150 mm x 150 mm specimen is tested in a vertical orientation. The holder (Figure 3) is provided with a specimen holder frame, which touches the specimen (which is wrapped with aluminum foil as required by paragraph (d)(3) of this part) along only the 6 mm perimeter, and a "V" shaped spring to hold the assembly together. A detachable 12 mm X 12 mm X 150 mm drip pan and two .020-inch stainless steel wires (as shown in Figure 3) should be used for testing of materials prone to melting and dripping. The positioning of the spring and frame may be changed to accommodate different specimen thicknesses by inserting the retaining rod in different holes on the specimen holder.
Since the radiation shield described in ASTM E-906 is not used, a guide pin is added to the injection mechanism. This fits into a slotted metal plate on the injection mechanism outside of the holding chamber and can be used to provide accurate positioning of the specimen face after injection. The front surface of the specimen shall be 100mm from the closed radiation doors after injection.
The specimen holder clips onto the mounted bracket (Figure 3). The mounting bracket is attached to the injection rod by three screws which pass through a wide area washer welded onto a ½ -inch nut. The end of the injection rod is threaded to screw into the nut, and a .020 inch thick wide area washer is held between two ½-inch nuts which are adjusted to tightly cover the hole in the radiation doors through which the injection rod or calibration calorimeter pass.
(7) Calorimeter. A total-flux flush calorimeter must be mounted in the center of a ½-inch Kaowool "M" board inserted in the sample holder to measure the total heat flux. The calorimeter must have a view angle of 180 degrees and be calibrated for incident flux. The calorimeter calibration must be acceptable to the Administrator.
(8) Pilot-Flame Positions. Pilot ignition of the specimen must be accomplished by simultaneously exposing the specimen to a lower pilot burner and an upper pilot burner, as described in paragraph (b)(8)(i) and (b)(8)(ii), respectively. The pilot burner must remain lighted for the entire 5-minute duration of the test.
(i) Lower Pilot Burner. The pilot-flame tubing must be 6.3mm O.D., 0.8mm wall, stainless steel tubing. A mixture of 120 cm3/min. of methane and 850 cm3/min. of air must be fed to the lower pilot flame burner. The normal position of the end of the pilot burner tubing is 10 mm from and perpendicular to the exposed vertical surface of the specimen. The centerline at the outlet of the burner tubing must intersect the vertical centerline of the sample at a point 5mm above the lower exposed edge of the specimen.]
(ii) Upper Pilot Burner. The pilot burner must be a straight length of 6.3mm O.D., 0.8mm wall, stainless steel tubing is 360mm long. One end of the tubing shall be closed, and three No. 40 drill holes shall be drilled into the tubing, 60mm apart, for gas ports, all radiating in the same direction. The first hole must be 5mm from the closed end of the tubing. The tube is inserted into the environmental chamber through a 6.6mm hole drilled 10mm above the upper edge of the window frame. The tube is supported and positioned by an adjustable "Z" shaped support mounted outside the environmental chamber, above the viewing window. The tube is positioned above and 20mm behind the exposed upper edge of the specimen. The middle hole must be in the vertical plane perpendicular to the exposed surface of the specimen which passes through its vertical centerline and must be pointed toward the radiation source. The gas supplied to the burner must be methane adjusted to produce flame lengths of 25mm.

(c) Calibration of Equipment.--(1) Heat Release Rate. [A burner as shown in Figure 4 must be placed over the end of the lower pilot flame tubing using a gas tight connection. The flow of gas to the pilot flame must be at least 99 percent methane and must be accurately metered. Prior to usage, the wet test meter is properly leveled and filled with distilled water to the tip of the internal pointer while no gas is flowing. Ambient temperature and pressure of the water are based on the internal wet test meter temperature. A baseline flow rate of approximately 1 liter/min is set and increased to higher preset flows of 4, 6, 8, 6, and 4 liters/min. The rate is determined by using a stopwatch to time a complete revolution of the wet test meter for both the baseline and higher flow, with the flow returned to baseline before changing to the next higher flow. The thermopile baseline voltage is measured. The gas flow to the burner must be increased to the higher preset flow and allowed to burn for 2.0 minutes, and the thermopile voltage must be measured. The sequence is repeated until all five values have been determined. The average of the five values must be used as the calibration factor. The procedure must be repeated if the percent relative standard deviation is greater than 5 percent. Calculations are shown in paragraph (f).]
(2) Flux Uniformity. Uniformity of flux over the specimen must be checked periodically and after each heating element change to determine if it is within acceptable limits of plus or minus 5 percent.

(d) Sample Preparation.
[ (1) The standard size for vertically mounted specimens is 150 X 150 mm with thickness up to 45 mm).]
(2) Conditioning. Specimens must be conditioned as described in Part 1 of this Appendix.
(3) Mounting. Only one surface of a specimen will be exposed during a test. A single layer of 0.025mm aluminum foil is wrapped tightly on all exposed sides.

(e) Procedure.
(1) The power supply to the radiant panel is set to produce a radiant flux of 3.5 W/cm2. The flux is measured at the point which the center of the specimen surface will occupy when positioned for test. The radiant flux is measured after the air flow through the equipment is adjusted to the desired rate. The sample should be tested in its end use thickness.
(2) The pilot flames are lighted and their position, as described in paragraph (b)(8), is checked.
(3) The air flow to the equipment is set at 0.04 plus or minus 0.001 m3/s at atmospheric pressure. Proper air flow may be set and monitored by either: (1) An orifice meter designed to produce a pressure drop of at least 200mm of the manometric fluid, or by (2) a rotometer (variable orifice meter) with a scale capable of being read to plus or minus 0.0004 m3/s. The stop on the vertical specimen holder rod is adjusted so that the exposed surface of the specimen is positioned 100mm from the entrance when injected into environmental chamber.
(4) The specimen is placed in the hold chamber with the radiation doors closed. The airtight outer door must be secured, and the recording devices must be started. The specimen must be retained in the hold chamber for 60 seconds, plus or minus 10 seconds, before injection. The thermopile "zero" value must be determined during the last 20 seconds of the hold period
(5) When the specimen is to be injected, the radiation doors are opened, the specimen is injected into the environmental chamber, and the radiation doors are closed behind the specimen.
(6) [[Reserved.]]
(7) [Injection of the specimen and closure of the inner door marks time zero. A record of the thermopile output with at least one data point per second must be made during the time the specimen is in the environmental chamber.]
(8) The test duration is five minutes.
(9) A minimum of three specimens must be tested.

(f) Calculations. (1) The calibration factor is calculated as follows:



F₀ = flow of methane at baseline (1pm)
F₁ = higher preset flow of methane (1pm)
V₀ = thermopile voltage at baseline (mv)
V₁ = Thermopile voltage at higher flow (mv)
T_a = Ambient temperature (K)
P = Ambient pressure (mm Hg)
P_V = Water vapor pressure (mm Hg)

[(2) Heat release rates may be calculated from the reading of the thermopile output voltage at any instant of time as:



HRR = Heat release Rate kw/m2
V_m = measured thermopile voltage (mv)
K_h = Calibration Factor (Kw/mv)]
(3) The integral of the heat release rate is the total heat release as a function of time and is calculated by multiplying the rate by the data sampling frequency in minutes and summing the time from zero to two minutes.
(g) Criteria. The total positive heat release over the first two minutes of exposure for each of the three or more samples tested must be averaged, and the peak heat release rate for each of the samples must be averaged, and the peak heat release rate for each of the samples tested must be averaged, and the peak heat release rate for each of the samples must be averaged. The average total heat release must not exceed 65 kilowatt-minutes per square meter, and the average peak heat release rate must not exceed 75 kilowatts per square meter.
(h) Report. The test report must include the following for each specimen tested:
(1) Description of the specimen.
(2) Radiant heat flux to the specimen, expressed in W/cm2.
(3) Data giving release rates of heat (in kW/m2 ) as a function of time, either graphically or tabulated at intervals no greater than 10 seconds. The calibration factor (kn) must be recorded.
(4) If melting, sagging, delaminating, or other behavior that affects the exposed surface area or the mode of burning occurs, these behaviors must be reported, together with the time at which such behaviors were observed.
(5) The peak heat release and the 2-minute integrated heat release rate must be reported.


[Figure 1. Release Rate Apparatus]




[Figure 2A. "Globar" Radiant Panel]




[Figure 2B. "Globar" Radiant Panel]




[Figure 3]




[Figure 4]




[Figure 5. Thermocouple Position]




[Amdt. 25-66, Eff. 9/26/88]