  Data collected by the H.E.S.S. array between 2004 and 2012 have been used to
search for photon bursts from primordial black hole explosions. Bursts were
searched for in a 30 second time-window. The duration of the search window has
been optimized to increase the burst signal while keeping the statistical
background low. No evidence for a burst signal was found. Preliminary upper
limits on the local rate of PBH explosions of $1.4\times 10^{4} {pc}^{-3}
{yr}^{-1}$ have been obtained, which improve previously published limits by
almost an order of magnitude
