  This paper deals with the triggering mechanism of the boiling crisis, a
transition from nucleate to film boiling. We observe the boiling crisis in pool
saturated boiling experimentally at nearly critical pressure to take advantage
of the slowness of the bubble growth and of the smallness of the Critical Heat
Flux (CHF) that defines the transition point. Such experiments require the
reduced gravity conditions. Close to the CHF, the slow growth of the individual
dry spots and their subsequent fusion on the transparent heater are observed
through the latter. As discussed in the paper, these observations are
consistent with numerical results obtained with the vapor recoil model of the
boiling crisis.
