  The NA61/SHINE experiment at the CERN SPS is pursuing a rich programme on
strong interactions, covering the study of onset of deconfinement and aims to
discover the critical point of strongly interacting matter by performing an
energy and system-size scan at the full CERN SPS momentum range. These scans of
p+p, p+Pb, Be+Be, Ar+Sc and Pb+Pb have been mostly completed with Xe+La last
year (more Pb+Pb to to taken this year).
  Results from the different reactions are now emerging. As a surprise, some
measurements did not scale smoothly. In particular, for the $\rm K^+/\piup^+$
ratio, Be+Be collisions behaved similarly to p+p (as superposition of nucleon
collisions), while Ar+Sc was closer to Pb+Pb collisions. This step can not be
explained by onset of deconfinement, and may indicate that there is also a
onset of fireball in relativistic heavy ion collisions. A review of the results
as well as possible interpretation will be presented. The theoretical models
(SMES, PHSD) describe onset of deconfinement at the heaviest system relatively
well. However, no model describes the behaviour of data at previously
unmeasured collisions of light and intermediate size ions. The onset of
fireball is not described by any model.
