The Cretex Chimney Seals have an expected design life of 50 years. The first five Cretex Internal Manhole Chimney Seals were installed in sanitary sewer manholes in the suburb of Milwaukee Wisconsin in February of 1981. Recent inspections and third party materials testing conducted on some of the oldest seals have concluded that the high quality rubber seal and stainless steel bands that make up the Cretex Chimney Seal are in excellent condition and show little, if any signs of deterioration. Based on these observations and independent test results, it is reasonable to expect 50 or more years of service from this easy to install, reusable, mechanical seal. Proven results and hundreds of thousands of installations to date make the Cretex Manhole Chimney Seal the longest term, cost effective method of sealing the frame-chimney area in manholes.