A report is given on research work with a model-flame arrester DN 20 without shock wave absorber to identify the limit of safety against flame transmission through a barrier layer of crimped metal ribbon at the different stresses possible with detonativ reactions. It can be shown that the limit pressure of safety against flame transmission is much lower when stressed by a stable or instable detonation at instationary conditions than when stressed by a stable detonation at stationary conditions. This low limit pressure can be raised considerably when the flame arrester is fixed to the pipe by means of a short T-connexion just ahead of the end of the pipe.