Cryogenic materials will remain extremely cold after they have been released. Due to the extremely low temperatures at which they are stored it will take some time before sufficient energy is absorbed from the surroundings to increase the temperature of the released liquid and vapour to a level at which they no longer present a hazard.
The cryogenic material may have harmful or toxic properties if inhaled, and it is likely to displace oxygen to a sufficiently low level that the atmosphere presents an asphyxiation hazard for emergency responders.
Personnel entering the hazard area should wear personal protective equipment (PPE) that is appropriate for the conditions (i.e. extremes of cold and hot, reduced oxygen levels and potentially flammable environments).