Authorities are still trying to determine the cause of the gas leak explosion that destroyed two buildings in Manhattan, killed at least seven people, and injured dozens of others on Wednesday, but a possible culprit is old, hazardous iron pipe that has yet to be replaced by safer plastic. Depending on the state you’re in, you might be sitting over a similar pipe right now.

Gas companies used to lay cast-iron and wrought-iron pipes before switching to plastic in the 1970s. Since then, states have been slowly replacing the old pipes to improve safety. Even so, 32,000 of miles of iron pipe are still operating, especially in New England, as illustrated by the map above. In New York state, 9 percent of the main lines are iron, according to the Department of Transportation. In Rhode Island, it’s 27 percent, the highest of all states.

A 2011 Philadelphia explosion put six people into the hospital and killed a gas company worker who had been sent to investigate the leak, caused by old cast-iron pipe. Three weeks after that, a similar explosion in Allentown, Penn., left five dead and eight homes ruined.

Now, that doesn’t mean New Yorkers should go running screaming out of their buildings. In the last two decades, only 18 deaths per year have been attributable to pipeline incidents, and only some of them were connected to aged gas pipe. Still, at the current rate at which the country is replacing iron pipe, it won’t be clear of them for another few decades.