"More than a dozen years ago, the fire sprinkler industry and code officials recognized a problem in the production of various fire sprinklers that were outfitted with O-ring seals. Corrosion and other contaminants could prevent the sprinklers from operating when subjected to heat. A nationwide recall program was launched to remove and replace more than 35 million faulty sprinklers. […] As seen in this photograph, the recall program did not reach all of its intended customers, and many of the recalled sprinklers remain in their original installations. Meanwhile, the voluntary recall and replacement program has ended, and lives and property continue to be at risk where these sprinklers are installed."
Coffee Break Training - Fire Protection Series No. FP-2014-40
United States Fire Administration: http://www.usfa.fema.gov/