Under contract to Sycon Teknikkonsult AB the Swedish Defence Research Agency - FOI has made tests where a cooling system of a protected structure was exposed to different blast loads. One conclusion from the tests was that most of the tested components in the cooling system received no visible reduction of function for different blast loads. Another conclusion was that area-reduction of a duct system and hatches have reducing effect on the blast wave. At last proposals are made for further work, whose important part is the work out of a manual for design of cooling system for protected structures.