Is a bank of cables, with a dust layer evenly distributed on both sides of the cables, more or less dangerous than a bank of cables with the same amount of dust all on one side? This question is answered by explicitly calculating the critical conditions for spontaneous ignition for each case. In the usual situation, with low dust conductivity, the asymmetric situation is more stable. When the conductivity of the ＇＇dust＇＇ becomes comparable to that of the cable, the stability is reversed.