Abstract: An indicator system and device for visually monitoring ethylene oxide sterilization by color changes of the indicating composition of the system upon sufficient and properly conditioned exposure of the composition to ethylene oxide provides a controlled method for indicating the effective sterilization of articles by ethylene oxide. The indicating composition of this invention undergoes color changes that are progressive with the conditions and periods of sterilization, such that a final and complete color change indicates the completion of an effective ethylene oxide sterilization. The indicating composition comprises a leuco precursor of an aryl methane dye selected from the groups herein defined; and an acidic constituent. Acidic organic compounds such as diphenolic acid (4,4-bis [4-hydroxyphenyl] pentanoic acid) are effective acid constituents because they enhance hue, develop color and stabilize the final color change.

Abstract: A sterility indicator device comprising a base of steam permeable, absorbent material, e.g. paperboard, having mounted thereon at least one, though preferably three separate indicator ink spots of chromium chloride that change color in response to predetermined combinations of time, temperature and saturated steam, impermeable transparent cover films bonded to the top surface of the base overlaying the indicator ink spots and to the bottom surface of the base thereby preventing the escape of corrosive reactants there through, and an adhesive substance, to be used to bond the impermeable cover films to the base.