Gas-leak explosions are devastating enough to destroy entire buildings, as we saw this morning in Harlem—and experts tell Popular Mechanics just how it can happen. It's not uncommon for underground pipes to leak gas that gets trapped under several inches of frost in winter and moves sideways, they say, often into a house or building. Gas travels "to the foundation and to every opening—water lines and sewer lines," said NatGas Consulting President Mark McDonald. "If a foundation is porous or cracked, that is how it gets in."
When trapped, gas only needs a spark to cause an explosion. "Unfortunately explosions are way to common and occur on a regular basis," he said. "It appears to be getting worse." In fact, McDonald spoke while investigating an explosion that killed a woman and destroyed 10 townhouse units last week in Ewing, NJ. A Star-Ledger report on that blast notes that aging US pipes—many laid in the 1950s and 60s—are corroding and often need to be repaired or replaced; gas providers can even run robots through the pipes to search for weak spots. "It’s not always how old the system is," said an engineering instructor. "It could be how well they’re trying to prevent corrosion in the pipes." (Read more explosion stories.)