The danger of honeycomb and collapse is somewhat reduced, therefore the DBT can be raised gradually. The Fourth Stage begins when the core moisture content of the lumber in the charge reaches the fiber saturation point. This occurs when the average moisture content of the wettest half of the kiln samples reaches approximately 15 percent. The danger of defects occurring is minimal at this point in the drying cycle. They are not appropriate for refractory hardwoods.
Steps correspond to each of the partially completed kiln schedules on the following pages.
Repeat the last Wet-Bulb Depression Step if necessary. The wet-bulb depression may now be calculated. This corresponds to the end of the equalizing step. WBD must be determined from a psychrometric table. Conditioning stops when stresses are relieved.