  We construct a hadronic kinetic model for description of excitation functions
of multiplicity ratios K+/pi+, K-/pi-, and Lambda/pi. It is shown that the
model is able to describe data rather well under the assumption that the total
lifespan of the fireball is decreasing function of the collision energy for SPS
energies above 30 AGeV. Thus in order to identify the onset of deconfinement
the proposed model will have to be checked against other kinds of data until
hadronic description can be safely falsified.
