FLUKA simulations of the loss of the stored electron beam at BESSY

The synchrotron light source BESSY consists of a 50 MeV microtron, a full energy synchrotron and a 1.9 GeV storage ring. At synchrotron light sources the accidental loss of the stored beam can occur several times a year. This could mean a considerable risk for the users because of the bremsstrahlung flash coming through the open beamshutters. This is to our knowledge the first time, that this occurrences are discussed in detail for synchrotron light sources. We used the particle interaction and transport code FLUKA for the calculations in different scenarios. We present here additional radiation safety measures based on the FLUKA results that decrease the possible personal dose from those beam losses below 1 mSv/year. Comparisons of the FLUKA results with semi-empiric formulas for radiation through lateral shielding are presented too.