NSF 61 does not set prescriptive requirements for products. The use of flyash is allowed by the standard and NSF International has certified many concrete products to NSF/ANSI Standard 61 that contain flyash as an ingredient. We have not noted any product failures from contaminants specifically associated with flyash, nor have we noted different failure rates between concrete products using flyash and those using Portland cement alone.NSF 61 requires a full formulation disclosure of each ingredient used in a product, and a certificate of analysis for flyash is required as a part of this. Products are tested according to the NSF 61 protocol for the leaching of metals as well as nonmetallic contaminants of concern.Once products are certified, NSF makes annual unannounced inspections of manufacturing facilities to ensure that NSF Certified products continue to use the same authorized ingredients with the corresponding specifications.