Some residents of the area received a few minutes warning.  At about 7 A.M. a worker from the gas storage station warned Caroline and Mitchell Hall that there had been a gas leak and urged them to stay inside their home about a quarter of a mile away from the pipeline, said Mrs. Hall's mother, Nancy Althaus, who spoke to her daughter at the hospital where she was treated for bruises and other minor injuries. 

But, for many of those injured and for hundreds of thousands of people across a broad swathe of east central Texas, the explosion made itself known with a shock wave that seemed to rumble eerily through the air. 

Charles Hamby, a Brenham police officer, was just waking up when he heard the explosion. " There was a tremendous loud blast and then the house shook like we were being hit by a tornado and it seemed to go on for 30 seconds or something," he said. 

Liquefied petroleum gas is denser than the kind of natural gas used in urban homes.  If a large amount of it is ignited, it causes "a slower and longer lasting explosion than the kind of chemical detonation you get with an explosive like TNT," said Roy Hahn Jr., a professor of engineering at Texas A&M University. 

A seismograph at Rice University in Houston measured the blast at between 3.5 and 4 on the Richter scale, about the power of a small earthquake.  Pipeline in Question

The leak appears to have occurred at a station where a six-inch pipeline feeds liquefied petroleum gas into an underground storage cavern, but it is unclear whether the leak occurred in the pipeline itself, a secondary line or in a valve, said Gary Garrison, a spokesman for the Texas Railroad Commission, the state agency that regulates the oil and gas industry. 

Although the blast destroyed the above ground pipeline station, the underground storage cavern, operated by the Seminole Pipeline Company of Tulsa, Okla., was not affected.