Over the course of many decades, most cesspools have been abandoned in favor of the more sanitary city systems. Thousands of cesspools have turned into dried holes lined with decayed fecal matter. These old brick cesspools tend to collapse after their brick-and-mortar lining weakens. As they collapse, they produce a suction that can pull people into them. Since 1998, several instances of people being pulled into collapsing cesspools have been documented. More than half of those people died in those collapses. In 2011, two New York teenagers drowned in a cesspool they had fallen into when it collapsed. Abandoned cesspools also produce methane, which can explode.