A cooling system (1), especially for cryopreserving biological samples (2), comprises a cooling chamber (100) and a cooling device (200) for cooling the cooling chamber (100) using liquid nitrogen (220). At least one of the side walls (120) includes at least one predetermined wall element (125) which is essentially designed like the surrounding load-bearing wall and can be moved relative to said load-bearing wall in such a way that a wall opening can be formed in the side wall (120). The cooling system can also comprise a protective device, in particular a dome, to create a local protective atmosphere for an operator (3). A lifting device, e.g. to provide protection against floods, and/or an envelope device to create a protective atmosphere for the entire cooling system, can be additionally provided. Methods for operating the cooling system (1) in case of an emergency are also described.