Dual-Temperature, Sealed-System Critical Temperature Indicator

An inexpensive, disposable apparatus that visually indicates whether an object has been exposed to either one or both of two predetermined critical temperatures such as a critical high T1 or a critical low T2 temperature. The apparatus includes a housing having a reservoir portion, and a capillary tube portion with a first, proximal end in fluid connection with the reservoir portion and an open, second, distal end. A first fluid is contained within the reservoir portion and a portion of the proximal capillary tube portion. A second fluid is contained within the capillary portion intermediate the first fluid and the distal end. A barrier is located intermediate the first fluid and the second fluid. The barrier prevents the first and second fluids from intermixing until the apparatus is exposed to T1 and then allows at least a portion of the second fluid to mix with the first fluid when the apparatus is exposed to T1 and irreversibly changes an observable characteristic of the second fluid. An indicator material is fixed proximate to and in fluid communication with the distal end of the capillary tube portion. The indicator material has an observable characteristic that irreversibly changes at T2 when contacted with the second fluid. An outer sheath encapsulates the indicator and the distal open end of the capillary tube portion to prevent the fluids and barrier from evaporating from the housing.