In light of the recent house explosion in New Milford due to a propane leak, Peter Bernstein, the Georgetown Fire District's deputy fire marshal, reminds residents about the signs of a gas leak, what to do and what precautions to take.

Propane and natural gas do not have an odor of their own. They are odorized with mercaptan so people can be alerted to a gas leak, he said.

"It's a foul odor. It's a 'something is wrong' odor — not pleasant," described Mr. Bernstein.

When people detect the rotten egg smell of mercaptan, "they should call 911," he said. "That pretty much sums it up right there."

Propane has a flammable range of 2% to 10%, he said.

"Anywhere in that range you will have an explosion. Whether it's a small explosion or a big one depends on the area and concentration. If you are under (2%), you won't have ignition; if you're over (10%), you won't have ignition because it's either too lean or too rich," he said.

If entering a house or building where a strong mercaptan odor is present, "get out and away from the structure and call 911," said Mr. Bernstein. "If that odor is strong in the household, it could be pushing 2%."

Any source of electricity can spark an ignition and will cause an explosion, he said.

"Propane is heavier than air, so the gas will settle in low places. If there is a propane leak from a stove on the first floor of a house, it's going to go down to the lowest point, under the door, into the basement, settle on floors and it will build up," said Mr. Bernstein. "When the gas reaches 2% (height of ignition) and there is something there to ignite it, it will ignite."

If gas reaches the height of the oil burner or furnace and the furnace turns on, it will ignite. If it reaches the height of a light switch and it is turned on, it can ignite, he said.

For example, if a person is standing on the lowest level of the house and makes a call using a cell phone, that can cause ignition. "They [cell phones] aren't intrinsically safe — you'll have ignition," Mr. Bernstein said.

Unlike propane, natural gas is lighter than air, said Mr. Bernstein. When comparing two houses that exploded, he said a house with a natural gas explosion will have the roof blown off, but with a propane explosion, the entire house will be missing.

It only takes a spark to ignite propane, unlike gasoline where a match is needed and takes more heat, Mr. Bernstein said.

In some cases, when a faint odor is detected in one general area, a person might just catch a whiff of it, and then it is OK to investigate the source, said Mr. Bernstein.

"If you are unsure, call your propane company," he said. "When it's bad and strong, you need to leave the structure, or not go in. Move away and call 911."

Fire departments have combustible gas meters that can read the percentage of propane.

"They can move in with the reader and take readings at different heights and areas... They'll ventilate the house and put fans on and call the propane company to turn off the propane. You should never turn off your own propane," said Mr. Bernstein.

He said it is hard to say how long it takes for propane to reach the flammable range. It depends on the size of the leak, the size of the area and how long it has gone unnoticed.

"It can be extremely quick or it can be a small leak and you go on vacation — it can take that long. It's hard to say," he said.

The reason propane is a good fuel and used in common household items is because propane is used in the vapor form, he said.

"Propane has a high expansion ratio. In liquid form, propane comes as a cryogenic liquid and we use the vapor emitted from the liquid. A little bit of liquid produces a tremendous amount of vapor," he said.

Common in-house items that use propane are stoves, furnaces, hot water heaters and clothes dryers. Gas grills also use propane.

"If you have propane, you can buy gas detectors, but mount them according to the manufacturer's instructions. Don't put it next to a furnace. They tend to false alarm a lot. There are also portable ones, like battery-operated smoke detectors or ones that tie into the alarm system," said Mr. Bernstein.

Joseph Rose, president of the Propane Gas Association of New England, issued a press release to remind consumers and emphasize the importance of using propane safely.

"Propane is a very popular fuel used by more than three million homes across the Northeast for home heating, cooking, water heating, clothes dryers, fireplaces, pool heaters, and backyard grilling. It is a versatile and safe fuel when handled properly," the release said.

"We cannot emphasize enough that consumers should NEVER tamper with their propane tanks or lines to the appliances in their home. Do not try to repair or modify valves, regulators, connectors, controls, or other appliance and cylinder/tank parts. Propane cylinders incorporate special components which keep them safe for use with grills and other propane appliances. An improperly connected tank or appliance can cause a gas leak. Licensed propane service technicians have the training to install, inspect, service, maintain, and repair your propane system and appliances."

Information: propanesafety.com or pgane.org.