3-3.1 The total area, AT, under the flame-spread distance–
time curve shall be determined by ignoring any flame front
recession. For example, in Figure 3-3.1, the flame spread
shown is 10 ft (3.05 m) in 21/2 minutes and then recedes. The
area is calculated as though the flame had spread to 10 ft (3.05
m) in 21/2 minutes and then remained at 10 ft (3.05 m) for the
remainder of the test or until the flame front again passed 10
ft (3.05 m) as indicated by the broken line in Figure 3-3.1. The
area, AT, used for calculating the flame-spread classification is
the sum of areas A1 and A2 as shown.