Nenana Ridge Experimental Fuel Treatments

Chronology The A-Unit of the Nenana Ridge burn project (Fig.1) was ignited with a test burn at 13:40 on 6/17/09. Winds were light (2 mph, gusting to 6 mph) out of the southwest with a relative humidity of 47% (using Kestrel), and temperature of 69 deg F taken at the overlook. Blacklining began on W and E sides of the unit. Initially, only white smoke (indicating high fuel moistures) could be seen, but by 13:50 the first torching tree crowns were visible from our overlook point approximately 2.2 miles northeast of the burn. Cumulus buildup was providing 100% shading on the project area for the initial firing (and keeping the RH high). Aerial firing began at 14:23 in the lower Aunit, but after 5 minutes a malfunction in the injector required a short break to repair. Wispy smoke trailed to the NE during this period, and only intermittent torching was observed, with no column development. At 14:55, while the firing ship was refueling, we noticed a slight shift in wind to the SSW and twin columns began to develop on the east and west flanks where hand lighting was continuing. Smoke became darker now and began to loft, with a column height of 2000 feet. Flame lengths initially (13:00-14:00) averaged 1.5 feet with the little smoke produced drifting NE and dissipating, but by 15:15 we started to observe convection, black smoke, and active crowning (Fig. 2). Helicopter 3AE was in the area filming the behavior during this period. Fire behavior escalated rapidly and by 15:38, the well-developed column was estimated at 5000’, advancing above a continuous active crownfire and a 3-acre spot fire into the B-unit was reported. At 15:40 the firing ship 15S returned from fueling. At 15:45 (Fig. 3) hand lighting was completed on the west flank, 15S reported fire had spread all the way to A-1 and helicopter bucket drops were being called on the slopover near B-1.