This sterilizer test identifies air leaks in a pre-vacuum steam sterilizer at 270° -276° at a minimum 3.5 minute exposure. Distinctive color change from purple to green that is easy to read and is not reversible. Free of lead or any toxic heavy metals.The unique test card design does not require packing material for accurate readings. Reusable holder saves space on your shelf and reduces waste. Load record log on the back of each test card provides room for all necessary information.