Federal safety officials investigating a bus accident that claimed 23 lives were told Tuesday that fire extinguishers currently used on motor coaches can't put out tire fires.

This assertion came at a National Transportation Safety Board hearing on the Sept. 23 bus fire in Texas that killed 23 nursing home patients. The fire-suppressant equipment on the bus, a five-pound fire extinguisher, couldn't have put out the fire, which originated in the rear wheel well and then engulfed the vehicle and its passengers in minutes, officials were told.

"The five-pound fire extinguisher is essentially useless," said Robert Crescenzo, who represented Lancer Insurance, which insures buses.

Earlier, two witnesses told investigators of their rescue efforts at the fire that killed the residents of a Houston-area nursing home as they were being evacuated from the path of Hurricane Rita.

Jason Saulsbury and Drew Wood said they were driving to work when they saw a small fire in the back of the bus. When they saw the passengers still on the bus, they stopped to help.

"We started pulling them off," said Wood. "It didn't take long to be engulfed in black, thick smoke."

Wood and Saulsbury tried to break open the bus windows, with little success. Wood said he couldn't manage to get a woman out of the window, so he went around to the front.

"That was when everything started blowing up," he said.

Investigators think the patients' oxygen canisters caused the explosions.

Kitty Higgins, the NTSB member conducting the two-day hearing, said safety officials investigating the tragedy think bus fires might be a bigger problem than previously thought.

"It's a big issue here we're just trying to understand," Higgins said.

Though data is sketchy on the number of bus fires, Mart Ahrens of the National Fire Protection Association estimated that there are an average of six per day for all kinds of buses, including school and inner-city transit buses. Safety investigators noted they are rarely fatal because passengers can evacuate in time.

The driver and some of the 44 passengers escaped the bus ferrying people from Brighton Gardens nursing home in Bellaire, an enclave of Houston, to a site in Dallas owned by the same company, Sunrise Senior Living.

Texas officials ordered the emergency evacuation of the Gulf Coast.

With a new hurricane season now under way, investigators want to know how decisions are made about transporting frail people when they're ordered to evacuate, Higgins said.

NTSB investigators will also be asking:

—Should more safety precautions, such as fire suppression equipment, be taken for frail bus passengers?

—Is there enough state and federal oversight of bus companies?

The bus company, Global Limo Inc. of Pharr, Texas, failed two safety reviews by state and federal authorities. "It was the third review that led to their being put out of service," Higgins said.

Federal regulators shut down the company's bus operations after the fire, saying the conditions of its vehicles and drivers "are likely to result in serious injury or death."

The tragedy gave rise to a host of lawsuits, though a grand jury declined to indict the driver.

Global Limo and its president and director, James H. Maples, are accused in a three-count federal indictment of conspiring to falsify driver time records and failing to inspect buses to ensure their safety.

In May, victims reached an $11 million settlement with the bus owner and a travel broker.

The bus company and BusBank, which hired Global Limo on behalf of the nursing home, agreed to give the money to the 21 survivors and the families of the 23 who died.

Victims are suing the owners of the nursing home as well as the manufacturer of the bus over possible design flaws.