  Since detonation is the only established theory that allows rapid burning
producing a high pressure that can be sustained in open areas, the generally
accepted opinion was that the mechanism explaining the high rate of combustion
in dust explosions is deflagration-to-detonation transition. We propose a
theoretical substantiation of an alternative mechanism explaining the origin of
the secondary explosion producing high speeds of combustion and high
overpressures in unconfined dust explosions. We show that the clustering of
dust particles in a turbulent flow ahead of the advancing flame gives rise to a
significant increase of the radiation absorption length. This effect ensures
that clusters of dust particles are exposed to and heated by radiation from hot
combustion products of the primary ignited flame for a sufficiently long time
to become multi-point ignition kernels in a large volume ahead of the advancing
flame.
