Officials say LP (liquefied petroleum) gas can be safely used as a fuel if properly handled and stored, but several of its unique characteristics may have contributed to three liquid propane explosions in the state since Saturday that killed two people and caused millions of dollars in damage.
"One of the drawbacks of propane is that it's heavier than air," said Scott Lane, a supervisor with the Maryland Energy Office. "Unlike natural gas, it sinks to the lowest point and can accumulate in pockets."
That appears to be what occurred in Perryville early Saturday, when gas from a leaking 250-gallon propane tank behind a sandwich shop settled in the basement and was ignited in a massive explosion by still-unknown causes, said Bob Thomas, deputy chief state fire marshal.
Propane is a potent fuel. One of two types of commonly used LP gas -- the other is butane -- it is an odorless, invisible vapor compressed under 150 pounds of pressure per square inch into a liquid for convenient shipping and storage. One gallon of liquefied propane expands in volume 270 times when released as a gas.
It has caused no "major or continuing fire problems," said Mr. Thomas. In 1990, there were 96 propane fires in Maryland, causing nine injuries and $600,000 in property damage. In 1989, there were 187 fires, with 14 injuries and $1.8 million in damage.
That accounts for less than 1 percent of total property losses from fire in the state and less than 1 percent of total fire incidents, he added.
"Propane is as safe as any other fuel, which means it has to be handled with care by distributors and the people who use it," said Marcel Henry, president of United Propane Inc., a major supplier in the Baltimore area.
The fuel is processed from either crude oil or natural gas, and figures supplied by the National Propane Gas Association show that 18.2 billion gallons were consumed in the United States in 1989, with 8.2 billion gallons going to homes and commercial businesses.
Nearly 9 percent of U.S. households, or 7.7 million people, use propane. About 55 percent of those households are in rural areas.
In 1989, about 100,000 Marylanders used more than 90 million gallons of propane, according to the state energy office. "The primary residential use is probably cooking, followed by hot water heating and house heating," said Mr. Lane.
Baltimore Gas and Electric Co. pipes natural gas -- a natural mixture of methane, ethane and other hydrocarbons -- to some 520,000 customers in a limited area in metropolitan Baltimore, said spokeswoman Peggy Mulloy.
pTC But the industry is largely self-policed once propane systems are installed under the mandated National Fire Protection Association codes, with distributors responsible for maintaining equipment in safe condition.
"We suggest that our members perform a free, yearly gas appliance system check for their customers," said a spokeswoman for the propane association, Amy Potter. "But it is voluntary."
Some industry observers point out two potential problems for consumers in identifying propane leaks, both involving the foul "odorant" added to the gas to alert them to danger. Known as ethyl mercaptan, it also gives the familiar rotten-eggs smell to natural gas.
A 1989 study by the Consumer Product Safety Commission uncovered a phenomenon called "odorant fade:" The bad-smelling mercaptan disappeared from stored propane, apparently after reacting chemically with the insides of the standard steel tanks.
"It occurs largely with new tanks, but was also identified in tanks that were run empty and allowed to remain that way for a while," said Ken Giles, a commission spokesman. "The industry agrees it happens, but only if tanks are not flushed and filled properly." Companies are looking for a less reactive odorant to replace ethyl mercaptan.
Another threat to safe detection of leaking propane concerns humans' sense of smell, which diminishes with age. Researchers are developing a gas detector that would sound an alarm when natural gas or propane leaks into the air.
* All propane containers should be stored and used in the upright position.
* Containers should be placed in a way that protects the regulator valve and piping from physical damage, tampering or excessive temperature.
* Containers should not be stored or used inside buildings, with rare exception.
* Keep open flames or excessive heat away from propane containers or supply lines. Don't store in direct sunlight. High temperatures can cause excessive internal tank pressure.
* Propane containers should only be serviced and maintained by qualified professionals.
* If the odor of gas is detected, call 911 and evacuate the premises immediately.