OK Strips are indicators that monitor all critical sterilization parameters: steam, time and temperature.. In sterilization cycles OK Strips guard against incomplete steam penetration, presence of noncondensing gases or excessive air, as well as from inadequate temperature or insufficient exposure time.. The pre-printed standard reference color permits rapid and certain visualization of the results.. If the sterilization conditions meet requirements, the arrow and the K will change to become at least as dark as the reference color O forming the OK expression.. There are 250 Class 4 sterilization chemical indicator strips in a box..