Why do houses explode?

Usually it's a gas leak, but how would you know?

Everything was fine, Donna Bailey said, the last time she and her husband, Gerry, were in their Libertyville home. No trouble with appliances, no gas smell. Nothing out of the ordinary.

Four days later, on July 12, Donna was in Wisconsin checking Facebook about storm news back in Lake County when her phone rang with almost incomprehensible news. Her home had exploded, leaving everything but the family's detached garage flattened and belongings strewed across the wooded acre lot.

Just a month earlier, on June 11, an explosion followed by a fire in Marengo leveled two houses, left 19 uninhabitable and damaged at least 50. Like in Libertyville, the owners of the house at the epicenter were away on vacation and everyone in the neighborhood survived.

The explosions leave neighbors wondering how often houses blow up and why, and what people can do to protect themselves.

While two cases so close together in time and location might be unusual, they're not unique. Homes blew up in February in Dolton, in December in Homer Glen and in October in Romeoville. A 2014 house explosion in Long Grove was felt a mile away.

Natural gas or propane that ignite usually are the culprits, fire officials say.

“There has to be a gas leak somewhere on the dryer, the furnace, oven or hot water heater,” said Tim Turbak, president of the Illinois Fire Prevention Association. Leaks can also come from the pipelines running natural gas to a home.

“If one of those leaks, either through a fitting or a faulty valve, the smallest spark can ignite the gas and cause an explosion,” Turbak said.

The National Fire Protection Association found that about 20,260 fires in homes every year are caused by flammable gas, but most of those don't involve explosions.

The explosions in Marengo and Libertyville remain under investigation.

Investigators who comb through the wreckage of a house explosion look at burn patterns in order to determine the origin of the leak, said Tom Lia, executive director of the Northern Illinois Sprinkler Fire Advisory Board.

Sometimes, it's a malfunctioning appliance, or the improper installation of one, said Phil Zaleski, director of the Illinois Fire Safety Alliance.

Mike Schmitt, fire marshal of the Long Grove Fire Protection District and deputy director of the Illinois Fire Inspectors Association, notes that explosions happen when natural gas mixes with the air at a certain concentration — between 5 and 15 percent — and there is a source of ignition.

For that reason, people who smell natural gas in their home should leave the building and contact the gas company immediately, Nicor Gas recommends.

An empty house allows gas concentrations to build without anyone noticing the telltale odor that's added to natural gas to alert people to leaks. Even when no one is home, electronics or static electricity can spark an explosion.

Schmitt was one of the fire officials who helped with the 2014 explosion in an upscale neighborhood in Long Grove bordering the Royal Melbourne Country Club. More than three years later, he said, the state fire marshal and the federal Bureau of Alcohol, Tobacco Firearms and Explosives are still investigating the blast,which had so much force it damaged an estimated 50 homes.

“You can be in the same situation for 20 years and nothing happens, until just at that right moment, if that gas concentration mixes with (a source of) ignition,” Schmitt says. “These days, we have so many more electronics in our home, there's more chance for ignition if in fact things are in that perfect-storm scenario.”

Some safeguards are in place. Shut-off valves, for instance, automatically cut the gas supply if pilot lights go out on modern appliances.

Utility companies, such as Nicor or Peoples Gas, can check gas lines running to your house, though Zalewski says newer tubes and fittings are far safer than they used to be.

While utility companies are responsible for gas lines, homeowners are responsible for the lines that run from a gas meter to their home, according to the National Association of Pipeline Safety Representatives. Extra caution exercised by homeowners can't hurt, including periodic checks around water heaters, furnaces, clothes dryers and other gas-operated appliances.

Sometimes, Turbak said, homeowners are busy packing for vacation and don't think to stop in the basement to check for the smell of gas coming from any appliance that might be there.

“It's just a matter of going behind the hot water heater and furnace and seeing if you smell gas at all,” Turbak said. “A lot of times, those things are in a basement, and people don't even think.”

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From vacation in Wisconsin, Libertyville woman learned her home had exploded

  This house on Sunnyview Road in Libertyville exploded while the owners were on vacation. Gilbert R. Boucher II/
  An explosion in June in Marengo leveled two houses and damaged more than 50. Mark Welsh/
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