There are thousands of miles of pipes carrying natural gas across Manhattan, and The New York Times reports that more than half of them are made of metals that can corrode and crack. Gas companies serving the city have been replacing these bit by bit every year to improve safety, but the slow speed at which their replacement is happening has come to attention in recent weeks after an explosion in Harlem, caused by an apparent gas leak, killed eight. Gas companies have reportedly been ordered to step up the speed of pipe replacement, but even now, it'll take take almost three decades to replace them all.