Steam sterilization process monitor

A sterility indicator device for use in a steam autoclave to determine the degree of completion of a steam sterilization process at or about a predetermined control temperature, the process being intended to result in 100% spore kill of any pathogenic spores, the control temperature being about 250.degree. F. to about 270.degree. F., comprising:

• (a) a backing strip consisting essentially of an aluminum foil having adhesively laminated thereto a polymeric film, said backing strip having a pocket or depression embossed therein;
• (b) an organic compound having a normal melting point which is about 5.degree. to about 50.degree. F. above the predetermined control temperature, said normal melting point being depressed below said control temperature by the absorption of water into the organic compound when said organic compound is exposed to saturated steam at about the control temperature, said normal melting point of the organic compound being above the control temperature, said organic compound containing at least one functional group selected from the group consisting of ether, amide and hydroxy, the organic compound being mounted on the backing strip in the pocket or depression at a first end of said backing strip;
• (c) a wicking means having a first end of said wicking means in intimate contact with said compound, said wicking means extending away from said compound to a second distal end of said backing strip;
• said organic compound and wicking means defining a land area comprising the portion of the backing strip not covered by the organic compound and wicking means;
• and
• (d) a water vapor transmission rate controlling cover strip covering said compound and wicking means, said cover strip being permeable to water vapor and having a water permeability coefficient at the control temperature such that sufficient water vapor will permeate the cover strip to reduce the melting point of the organic compound from its normal melting point to at least the control temperature, the cover strip comprising polypropylene film of about 0.75 to about 3 mils in thickness;
• said device being unresponsive to heat at the control temperature in the absence of steam, and displaying a visual response of the integrated time/temperature exposure of an article to be sterilized to moist heat;
• the cover strip covering the backing strip, wicking means and organic compound, and being bonded only to the land area of the backing strip by heat sealing.