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FIRE TESTING FURNACES
STANDARD 12-7-3

State Fire Marshal Scope

This standard sets forth the general requirements for the design and control of fire testing furnaces intended for fire exposure testing and assignment of fire endurance ratings of building materials, assemblies of building materials, equipment and devices.

Furnace design and dimensions

Furnaces shall consist of a furnace chamber and an insulated specimen frame. The furnace chamber walls and floor shall consist of insulating fire brick or equivalent heat-reflective materials. Furnace dimensions shall be not less than shown in the following:

  1. Vertical large-scale wall furnace. The furnace exposure panel or door shall consist of an insulated steel restraining frame having an available opening for the test sample of not less than 200 square feet in area with neither dimension less than 9 feet.
  2. Vertical half-scale wall furnace. The furnace exposure panel or door shall consist of an insulated steel restraining frame having an available opening of not less than 50 square feet for the test sample. Neither dimension of the furnace opening shall be less than 7 feet.
  3. Horizontal large-scale floor furnace. The furnace exposure panel shall consist of an insulated steel restraining frame having an available opening of not less than 180 square feet for the test sample. Neither dimension of the furnace opening shall be less than 12 feet.
  4. Horizontal small-scale furnace. The furnace exposure panel shall consist of an insulated frame having an available opening of not less than 35 square feet for the test sample. Neither dimension of the furnace opening shall be less than 5 feet.
  5. Horizontal large-scale beam furnace. The furnace exposure panel shall consist of an insulated steel restraining frame having an available opening of not less than 180 square feet for the test sample. Neither dimension of the furnace opening shall be less than 5 feet.
  6. Horizontal small-scale beam furnace. The furnace exposure panel for the "Alternate Test of Protection for Structural Steel Beams, Girders and Trusses" shall consist of an insulated steel frame having an available opening of not less than 35 square feet for the test sample. Neither dimension of the furnace opening shall be less than 5 feet.
  7. Column furnace. The column furnace shall be of such dimensions as to provide an opening for column sections not less than 8 feet in clear length.
  8. Protection of equipment and test specimen. The testing furnaces, equipment and test specimen undergoing the fire test shall be protected from any condition of wind or weather, that might lead to abnormal results. The ambient air temperature of the testing room at the beginning of the test shall be within the range of 50°F to 90°F (10°C to 32°C). Velocity of air across the unexposed face of the test specimen shall not exceed 4.4 feet per second, as determined by an anemometer placed at right angles to the unexposed surface, measured before or during the test. If mechanical ventilation is employed during the test, an airstream shall not be directed across the surface of the specimen.

Burners and Fuel

  1. Burners.

    1. In vertical furnaces, burners shall be placed in the back wall of the furnace. The location of the burners and provisions for combustion air shall be such as to provide an even flame exposure to the entire exposed face of the test specimen. Combustion air openings shall be provided in such a manner as to normally prevent induction of combustion air through any opening in the test specimen.
    2. In horizontal furnaces, burners shall be placed in the floor or side walls. Burrs and the provisions for combustion air shall be so arranged as to provide a uniform exposure to the entire exposed face of the test specimen.
    3. In column furnaces, burners shall be placed in the four walls to provide an even luminous flame exposure to all sides of the test sample.
  2. Fuel. Furnaces shall be supplied with natural, manufactured or bottled gas.

Time-Temperature Curve

The conduct of fire tests of materials, assemblies, methods of construction, equipment and devices shall be controlled to conform to the applicable portion of the standard time-temperature curve shown in Figure 12-7-3-1. The points on the curve that determine its character are:

1000°F (538°C). . . . . . . . . . . . . . at 5 minutes
1300°F (704°C). . . . . . . . . . . . . . at 10 minutes
1500°F (843°C). . . . . . . . . . . . . . at 30 minutes
1700°F (927°C). . . . . . . . . . . . . . at 1 hour
1792°F (978°C). . . . . . . . . . . . . . at 11/2 hours
1850°F (1010°C). . . . . . . . . . . . . at 2 hours
1925°F (1052°C). . . . . . . . . . . . . at 3 hours
2000°F (1093°C). . . . . . . . . . . . . at 4 hours

For a closer definition of the time-temperature curve, see Table 12-7-3A.

Furnace Control

  1. Thermocouples.

    1. Furnace thermocouples shall be protected by sealed porcelain tubes having 3/4-inch outside diameter and 1/8-inch wall thickness, or, as an alternate, in the case of base-metal thermocouples, shall be protected by 1/2-inch wrought steel or wrought iron pipe of standard weight or equivalent protection of approved type. The exposed length of the pyrometer tube and thermocouple in the furnace chamber shall be not less than 12 inches.
    2. In the large-scale horizontal floor and vertical wall furnaces, the temperature of the fire test exposure shall be deemed to be the average temperature obtained from the readings of not less than nine thermocouples symmetrically disposed and distributed to show the temperature near all parts of the test specimen. In the vertical half scale and horizontal small-scale furnaces, the number of thermocouples shall be proportioned to those of the large-scale furnaces, but shall in no case be less than four thermocouples.
    3. In the column furnace, the temperature of the fire test exposure shall be deemed to be the average temperature obtained from the readings of not less than eight thermocouples symmetrically disposed at two levels to show the temperature near all parts of the test specimen. The two levels shall be located approximately 2 feet from the top and bottom of an 8-foot clear height furnace.
    4. In the vertical wall furnaces, the junction of the thermocouples shall be placed 6 inches from the exposed face of the test specimen at the beginning of the test. The junction of the thermocouples shall, during the fire test and as a result of deflection, be maintained at 6 inches from the exposed face of the test specimen.
    5. In horizontal beam, floor and roof furnaces having a furnace chamber not less than 180 square feet in area, the junction of the thermocouples shall be 12 inches from the exposed face of the test specimen at the beginning of the test, and shall not touch the test specimen during the test as a result of its deflection.
    6. In horizontal beam, floor and roof furnaces having a furnace chamber less than 180 square feet in area, the junction of the thermocouples shall be placed 6 inches from the exposed face of the test specimen at the beginning of the test and, during the test, shall not touch the test specimen as a result of its deflection.
  2. Temperature recording. The furnace temperatures shall be read at intervals not exceeding 5 minutes during the first 2 hours, and thereafter the intervals may be increased to not more than 10 minutes.
  3. Furnace control accuracy. The accuracy of the furnace control shall be such that the area under the time-temperature curve, obtained by averaging the results from the thermocouple readings, is within 10 percent of the corresponding area under the standard time-temperature curve for fire tests of 1 hour or less duration, within 7.5 percent for those over 1 hour and not more than 2 hours, and within 5 percent for tests exceeding 2 hours in duration. Individual thermocouple readings shall not exceed or fall below the standard time-temperature curve by more than 15 percent.
  4. Furnace correction. When the indicated resistance period is 1/2 hour or over, determined by the average or maximum temperature rise on the unexposed surface or within the test sample, or by failure under load, a correction shall be applied for variation of the furnace exposure from that prescribed, where it will affect the classification, by multiplying the indicated period by two-thirds of the difference in area between the curve of average furnace temperature and the standard curve for the first three-fourths of the period and dividing the product by the area between the standard curve and a base line of 60°F (20°C) for the same part of the indicated period, the latter area increased by 54 Fahr-hour or 30 Cent-hour (3240 Fahr-minutes or 1800 Cent-minutes) to compensate for the thermal lag of the furnace thermocouples during the first part of the test. For fire exposure in the test higher than standard, the indicated resistance period shall be increased by the amount of the correction and be similarly decreased for fire exposure below standard.

    Note: The correction can be expressed by the following formula:

    where:

    C = correction in the same units as 1

    1 = indicated fire endurance period

    A = area under the curve of indicated average furnace temperature for the first three-fourths of the indicated period

    AS = area under the standard furnace curve for the same part of the indicated period

    L = lag correction in the same units as A and AS (54 Fahr-hour or 30 Cent-hour (3240 Fahr-minutes or 1800 Cent-minutes)

  5. Furnace pressure. The pressure in the furnace chamber during the fire test shall be maintained as nearly equal to atmospheric pressure as possible. Horizontal furnaces may be operated at a slight negative pressure sufficient to reduce haze permitting visual observation. Furnace stacks shall be equipped with dampers to facilitate maintenance of furnace pressure.

Correlation

Tests of specific assemblies of materials shall be conducted for correlation (or correlation factor) of furnace exposure by comparison with tests of identical assemblies and materials conducted in furnaces of "Approved Listing Agencies" which furnaces are deemed as conforming to the design and operating requirements of this standard.

Correlation tests of wall furnaces shall include tests of two assemblies, one combustible and one noncombustible.

Correlation tests of horizontal furnaces dependent on intended test specimens shall include at least one test for each type of assembly such as combustible ceiling-floor assembly, noncombustible assembly having a high thermal capacity floor for heat dissipation, noncombustible assembly having an insulating concrete floor or other type of design.

Comparison of test results shall provide evidence of equivalent exposure based on transmitted temperatures on the unexposed side, on structural framing members, on the underside of floor or roof decks, and in the plenum space.

TABLE 12-7-3A

STANDARD TIME-TEMPERATURE CURVE FOR CONTROL OF FIRE TESTS

TIME AREA ABOVE 68°F BASE AREA ABOVE 20°C BASE
TEMPERATURE
hr.: min. °Fahr. °Fahr.
min.
°Fahr.
hr.
°Cent. °Cent.
min.
°Cent.
hr.
0;00 68 00 0 20 00 0
0;05 1 000 2 330 39 538 1 290 22
0:10 1 300 7 740 129 704 4 300 72
0:15 1 399 14 150 236 760 7 860 131
0:20 1 462 20 970 350 795 11 650 194
0:25 1 510 28 050 468 821 15 590 260
0:30 1 550 35 360 589 843 19 650 328
0:35 1 584 42 860 714 862 23 810 397
0:40 1 613 50 510 842 878 28 060 468
0:45 1 638 58 300 971 892 32 390 540
0:50 1 661 66 200 1 103 905 36 780 613
0:55 1 681 74 220 1 237 916 41 230 687
1:00 1 700 82 330 1 372 927 45 740 762
1:05 1 718 90 540 1 509 937 50 300 838
1:10 1 735 98 830 1 647 946 54 910 915
1:15 1 750 107 200 1 787 955 59 560 993
1:20 1 765 115 650 1 928 963 64 250 071
1:25 1 779 124 180 2 070 971 68 990 1 150
1:30 1 792 132 760 2 213 978 73 760 1 229
1:35 1 804 141 420 2 357 985 78 560 1 309
1:40 1 815 150 120 2 502 991 83 400 1 390
1:45 1 826 158 890 2 648 996 88 280 1 471
1:50 1 835 167 700 2 795 1 001 93 170 1 553
1:55 1 843 176 550 2 942 1 006 98 080 1 635
2:00 1 850 185 440 2 091 1 010 103 020 1 717
2:10 1 862 203 330 3 389 1 017 112 960 1 882
2:20 1 875 221 330 3 689 1 024 122 960 2 049
2:30 1 888 239 400 3 991 1 031 133 040 2 217
2:40 1 900 257 720 4 295 1 038 143 180 2 386
2:50 1 912 276 110 4 602 1 045 153 390 2 556
3:00 1 925 294 610 4 910 1 052 163 670 2 728
3:10 1 938 313 250 5 221 1 059 174 030 2 900
3:20 1 950 332 000 5 533 1 066 184 450 3 074
3:30 1 962 350 890 5 848 1 072 194 940 3 249
3:40 1 975 369 890 6 165 1 079 205 500 3 425
3:50 1 988 389 030 6 484 1 086 216 130 3 602
4:00 2 000 408 280 6 805 1 093 226 820 3 780
4:10 2 012 427 670 7 128 1 100 237 590 3 960
4:20 2 025 447 180 7 453 1 107 248 430 4 140
4:30 2 038 466 810 7 780 1 114 259 340 4 322
4:40 2 050 486 560 8 110 1 121 270 310 4 505
4:50 2 062 506 450 8 441 1 128 281 360 4 689
5:00 2 075 526 450 8 774 1 135 292 470 4 874
5:10 2 088 546 580 9 110 1 142 303 660 5 061
5:20 2 100 566 840 9 447 1 149 315 910 5 248
5:30 2 112 587 220 9 787 1 156 326 240 5 437
5:40 2 125 607 730 10 129 1 163 337 630 5 627
5:50 2 138 628 360 10 473 1 170 349 930 5 818
6:00 2 150 649 120 10 819 1 177 360 620 6 010
6:10 2 162 670 000 11 167 1 184 372 230 6 204
6:20 2 175 691 010 11 517 1 191 383 900 6 398
6:30 2 188 712 140 11 869 1 198 395 640 6 594
6:40 2 200 733 400 12 223 1 204 407 450 6 791
6:50 2 212 754 780 12 580 1 211 419 330 6 989
7:00 2 225 776 290 12 938 1 218 431 270 7 188
7:10 2 238 797 920 13 299 1 225 443 290 7 388
7:20 2 250 819 680 13 661 1 232 455 380 7 590
7:30 2 262 841 560 14 026 1 239 467 540 7 792
7:40 2 275 863 570 14 393 1 246 479 760 7 996
7:50 2 288 885 700 14 762 1 253 492 060 8 201
8:00 2 300 907 960 15 133 1 260 504 420 8 407

FIGURE 12-7-3-1

TIME-TEMPERATURE CURVE

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