The apparent rapid descent of QZ8501 raises the question of pressurization effects at impact. I understand there are overpressurization vents; question is their flow capacity and what if any overpressure would remain after a 4 minute descent from FL29, and what additional effects that would have on how the aft airframe might come apart at impact.
No matter how fast you descend, there will never be positive pressure at impact, if anything, you would run into negative pressure relief issues.