General Technical Report FPL–GTR– 190of thermocouples are used to accurately measure the tem-
perature conditions of the chamber and the wood to ensure
that time and temperature requirements for heat treating are
met. Any equipment variance of more than ±5 °F (±2.8 °C)
requires recalibration or replacement.
Heat treatment facilities are also required to monitor tem-
peratures throughout the heat treatment cycle by any of the
following options:
- Wet- and dry-bulb temperature
- Dry-bulb only—unless the specific schedule has been
verified, required heating times shall be equal to or
greater than the time specified for the applicable sched-
ule assuming the maximum wet-bulb depression as pro-
vided in either of the following:
a. FPL–RP–607, Heat sterilization time of ponderosa
pine and Douglas-fir boards and square timbers
(Simpson and others 2003); or
b. FPL–RP–604, Effect of wet-bulb depression on
heat sterilization time of slash pine lumber (Simp-
son 2002); or
c. CFIA PI–07, The technical heat treatment guide-
lines and operating conditions manual, Option C
(CFIA 2006).- Direct measurement of wood core temperature of the
thickest piece(s) by use of thermocouple(s) properly
sealed with non-conductive material
Heat treatment facilities are currently required to annually
calibrate the temperature-monitoring and recording equip-
ment for each facility heat-treating chamber and requalify
a heat-treating chamber any time there is a major change
in equipment or remodeling of the chamber. Except in the
case of wood core temperature of the thickest piece(s) be-
ing directly measured by using thermocouples, when wood
moisture content is not determined at the beginning of the
heat treatment cycle, facilities are required to select and use
Table 20–7. Summary of heating times (at 160 °F (71 °C)) to
133 °F (56 °C) for ponderosa pine boards estimated by multiple
regression modelsaWet-bulb
depression
(°F)Initial
temperature
(°F)Heating time (min)b
1.00 in.
thick1.25 in.
thick1.50 in.
thick1.75 in.
thick2.00 in.
thick
2 40 18 (39) 26 (53) 34 (67) 43 (82) 53 (98)
4 40 22 (45) 31 (60) 41 (76) 52 (93) 64 (112)
6 40 24 (48) 34 (65) 45 (83) 58 (101) 71 (121)
8 40 26 (51) 37 (69) 49 (87) 62 (107) 76 (128)
10 40 28 (54) 39 (72) 52 (92) 66 (112) 81 (134)
12 40 29 (56) 41 (75) 54 (95) 69 (117) 85 (139)
2 50 16 (28) 22 (37) 30 (47) 38 (58) 46 (70)
4 50 19 (31) 27 (42) 36 (54) 45 (66) 55 (80)
6 50 21 (34) 30 (46) 39 (59) 50 (72) 62 (87)
8 50 23 (36) 32 (49) 42 (62) 54 (77) 66 (92)
10 50 24 (38) 34 (51) 45 (65) 57 (80) 70 (97)
12 50 25 (39) 36 (53) 47 (68) 60 (84) 74 (101)
2 60 14 (21) 20 (28) 27 (36) 34 (45) 41 (55)
4 60 17 (24) 24 (33) 32 (42) 40 (52) 49 (63)
6 60 19 (26) 27 (35) 35 (46) 45 (57) 55 (70)
8 60 20 (28) 29 (38) 38 (49) 48 (61) 59 (75)
10 60 21 (29) 30 (40) 40 (52) 51 (65) 63 (79)
12 60 22 (30) 32 (42) 42 (54) 53 (68) 66 (83)
2 70 13 (17) 18 (24) 24 (31) 31 (39) 38 (48)
4 70 15 (20) 22 (27) 29 (36) 37 (46) 45 (57)
6 70 17 (22) 24 (30) 32 (40) 41 (51) 50 (64)
8 70 18 (23) 26 (33) 34 (43) 44 (56) 54 (70)
10 70 19 (25) 27 (35) 36 (46) 46 (59) 57 (74)
12 70 20 (26) 29 (36) 38 (45) 48 (63) 60 (78)
2 80 12 (15) 17 (21) 22 (29) 28 (37) 35 (46)
4 80 14 (18) 20 (26) 26 (35) 34 (45) 41 (56)
6 80 16 (20) 22 (29) 29 (39) 37 (51) 46 (64)
8 80 17 (22) 24 (31) 32 (42) 40 (55) 49 (70)
10 80 18 (23) 25 (33) 33 (45) 43 (59) 52 (75)
12 80 19 (24) 26 (35) 35 (48) 45 (63) 55 (79)
aT°C = (T°F – 32)/1.8; °C = °F/1.8; 1 in. = 25.4 mm.
bValues in parentheses are 99% upper confidence bounds of heating times.