WASHINGTON The National Transportation Safety Board thinks all bus- maintenance manuals should contain a warning that says something like this: "Wheel bearings MUST be kept lubricated at all times. If they are not lubricated they can fail, leading to catastrophic fire and people may die."

Thats what happened on Sept. 23, 2005, on Interstate 45 between Houston and Dallas. A 1998 MCI E-model coach, whose wheel bearings had been allowed to go "bone dry" because of maintenance neglect, burned to the frame because the wheel bearings became super hot, igniting a tire which created flames that swept up the side of the bus and into the interior.

The fire and smoke spread so quickly that 23 old and infirm passengers could not be dragged off the bus fast enough to save their lives.

It was an appalling tragedy caused by human neglect and regulatory bungling.

Staff members from the NTSB were so concerned by what they uncovered as they worked to determine what caused fire that they recommended bus operators across North America be told of the "extraordinary importance" of proper wheel bearing maintenance, particularly the importance of checking the oil level in oil-lubricated bearings, commonly known as oil-bath bearings.

The sight glass used to determine the bearings oil level should be checked daily, as MCI and other manufacturers recommend, and the bearing seals should be inspected regularly for leaks.

Checking wheel bearing lubrication is a simple maintenance item. But NTSB research found it is a procedure that is frequently ignored and there is no federal regulation requiring it. Investigators also discovered that some operators have painted over the sight glass, rendering it useless.

Checking wheel bearing seals can only be done by getting under a coach, meaning those bus companies that do not have a hydraulic lift or pit are at greater risk. That fact was note by NTSB investigators who expressed concern about "store-front operators" who give short shrift to daily maintenance checks.

The NTSB says bus company owners and managers should make sure their drivers and maintenance personnel are trained in proper wheel bearing inspection procedures as recommended by coach manufacturers.

At the conclusion of a hearing the NTSB conducted last month on the Texas bus fire, the board made an "urgent" recommendation to the United Motorcoach and American Bus associations, plus MCI and other bus manufacturers. The board asked the groups to warn operators about the importance of checking wheel bearing lubrication.

UMA immediately responded, issuing an advisory bulletin to its members and coach manufacturers.

According to the NTSB there have been at least 20 wheel bearing-caused bus fires over the past five years, and probably a lot more because of the haphazard reporting of bus fires in the U.S. While no deaths have been attributed to those fires, there have been "close calls," said NTSB investigator Larry Yohe.

What makes wheel bearing-caused fires so insidious is the extraordinary temperatures created when the bearings overheat from friction and lack of lubrication. NTSB tests found that wheel components can reach temperatures of 1,300 degrees.

Tires ignite spontaneously at 800-900 degrees and even when suppressed will reignite over and over again because of the super heat created by the failed wheel-end components.