Cryogenic vials are intended for placement only in the vapor phase of liquid nitrogen, and should not be used for storage in the liquid phase of liquid nitrogen. Immersion of the vials in the liquid phase could result in penetration of the liquefied gas into the vial, resulting in rapid vaporization of the liquid upon removal and possible violent explosion or leakage from the vial/closure perimeter. To prevent cryogenic vials from exploding, never overfill liquid nitrogen storage units. Always examine vials before use to ensure no visible defects around the closure rims. Always use full faceshields, heavy safety gloves and laboratory protective apparel when removing vials from cryogenic storage. Always permit vials to warm slowly in a biological safety cabinet. Never reuse cryogenic vials.