WILMER, Texas The National Transportation Safety Board has launched a major investigation into the charter bus that caught fire and exploded here last month, killing 24 elderly nursing home residents that were being moved away from Hurricane Rita.

The incident was the worst disaster to hit the motorcoach industry in more than six years and is one of the deadliest accidents in Texas history. It occurred on Interstate 45, just a few miles southeast of Dallas, where the coach was heading.

The unusual nature of the tragedy and the unique circumstances surrounding it are likely to result in one of the most difficult investigations the NTSB has ever undertaken of a bus-related catastrophe.

Generally, the NTSB conducts an investigations when there is a major crash, resulting in several passenger deaths. In this case, there was no crash, no driver collapsing at the wheel, no bus flipping over, and no other vehicles directly involved.

Much of the NTSB attention will focus instead on the way in which the coach was being used to transport a number of infirm passengers who were carrying and using medical oxygen; on why the coach burst into flames; on the circumstances under which the bus was pressed into service, and on the owner of the bus.

The last time more than 20 individuals died in a bus crash in the U.S. was Mothers Day 1999, when a coach operated by Custom Bus Charters of New Orleans crashed on Interstate 610, killing 22 of the 43 passengers on board.

The ensuing investigation of that disaster found that the driver suffered from several life-threatening medical conditions that probably incapacitated him. The probe also found the driver had marijuana in his system, had used a sedating antihistamine, and was fatigued.

The upshot of the crash was far reaching. It directly led to passage of the federal Motor Carrier Safety Act of 1999 and to the creation of the Federal Motor Carrier Safety Administration.

Roughly nine hours after the Wilmer bus fire and explosion, the Federal Motor Carrier Safety Administration sent an e-mail to the United Motorcoach Association, the American Bus Association and others containing a copy of the USDOT guidelines for carrying medical oxygen tanks on buses; a copy of suggested bus evacuation procedures developed by a taskforce of the Bus Industry Safety Council, and an offer to provide information about brakes and various research on detecting overheated brakes.

Some motorcoach industry observers were underwhelmed with the FMCSA response, pointing out that the motorcoach industry has petitioned the DOT for years for standards for carrying medical oxygen. "In every instance theyve waffled and stonewalled," said one long-time industry safety expert.

Godfrey Lebron, owner of Paradise Trailways, a New York-based motorcoach company, and chairman of the legislative and regulatory committee of the United Motorcoach Association, said UMA "had been harping about oxygen on buses" since the Americans with Disabilities Act became law 13 years ago.

Unlike the strict rules that govern oxygen canisters on airplanes and trucks, the presence of oxygen on motorcoaches is virtually unregulated. The USDOT guidelines limit the amount of compressed oxygen that a coach can carry to 99 pounds.

"If that amount of oxygen were on a truck, it would be subject to all kinds of federal regulation," said Norman Littler, senior vice president of government and industry relations at UMA. "But if its on a bus, its just wide open."

There were reports that several oxygen bottles had been loaded in the coachs luggage bay.

In the days following the Wilmer bus fire, Texas news organizations turned their focus on the operator of the coach, Global Limo Inc. of Pharr, Texas, which has a history of financial and safety woes, The Dallas Morning News reported.

The newspaper said that the owners of Global Limo filed for bankruptcy protection in February in a bid to block a takeover of the business for nonpayment of debt. The company's operating authority also was revoked for a few days in May by federal regulators -- the second time in the past 12 years.

The FMCSA also had singled out Global Limo for full inspections whenever police stopped its buses, the newspaper said.

The Morning News and the Houston Chronicle both reported that Global Limo had a history of driver violations. In the last 2.5 years, the company
had five drivers put out of service during random inspections in Texas, New Mexico and Missouri, according to the FMCSA. The most common violation by Global Limo drivers was failure to properly maintain log books.

According to state records obtained by the Morning News, Global Limo operated nine buses, and is owned by James H. "Butch" Maples, 64, and his wife, Kathleen, 46.

Efforts to reach the company and Maples for comment were unsuccessful.

The Chronicle also reported that the registration for the bus had lapsed
but that it probably had been pressed into service because of the hurricane.
The Chronicle said the 1991 MCI was not among the buses registered with the state as being used commercially by Global.

Mark Cross, a spokesman for the Texas Department of Transportation, told the Chronicle that because the state issued a waiver in advance of Hurricanes Katrina and Rita, Global Limo didnt have to provide information on every vehicle it used to evacuate people.

The coach was one thousands of vehicles used in the evacuation under a Sept. 20 emergency order issued by Texas Gov. Rick Perry. The order suspended some requirements for motor carriers so every available vehicle could operate during the emergency evacuation.

Cross speculated that the reason the bus did not have proper registration was because it was not in regular use and possibly had been in storage. Its registration expired in July.

Whether the bus was insured is unclear. The other Global Limo buses were listed as having the required $5 million in coverage, Cross said.

Although Global Limo had a clean maintenance record, its driver safety rating is 97. That means it is worse than 97 percent of all companies. The company history is based on violations recorded in the past 30 months, said Jim Lewis, spokesman for FMCSA in Washington. The reason for the high rating was because three of the violations occurred this year: in August, June and March. Two years ago, a Texas inspector discovered a driver for Global who was not licensed to drive a bus.

BusBank, the Chicago-based clearinghouse, arranged the Global Limo charter on behalf of Brighton Gardens nursing home of Houston to take 38 residents and six staff members to sister nursing homes in Dallas.

Bill Maulsby, president of BusBank, said his company has always considered Global Limo "a well-operated company."

"I know the operator is a good operator," Maulsby said. "Unfortunately,
something went terribly wrong when they got south of Dallas."

What witnesses saw
Witnesses interviewed by police and news organizations reported seeing smoke and fire coming from the bus before a series of explosions. The bus was headed north toward Dallas about 6:30-6:45 a.m. when a witness saw it pass his car with smoke pouring out of the rear on the driver's side. About two minutes later, the bus exploded just north of Mars Road in Wilmer.

Sgt. Don Peritz, spokesman for the Dallas County Sheriff's Department said a tire on the bus was changed in Corsicana, Texas, but the problem may have originated with the vehicle's brakes. A fire broke out and apparently spread quickly, igniting one of the oxygen tanks, he said.

Dr. Paul Pepe, chairman of emergency medicine at UT Southwestern Medical Center, said one of the victims told him they stopped at 5:55 a.m. to change a tire. After they got back on the road, people started signaling that smoke was coming from the back of the bus. They pulled over and began trying to put the fire out, he said.

According to David Robertson, a Dallas County deputy sheriff on the scene, the bus left a lengthy skid mark on I-45. A piece of metal was lodged in the right rear wheel of the bus, and crash investigators believe this caused the tires to lock up.