The church bus that collided with a pickup truck and burst into flames, killing 27 people, was built only months before safety standards were imposed to prevent explosions in crashes, investigators say.

The bus's gas tank was punctured by wreckage as its panels broke apart and its front collapsed in the head-on collision with the truck traveling the wrong way on Interstate 71 near Carrollton, investigators with the National Transportation Safety Board said Tuesday.They said the bus, sold by a school last June 11 to the First Assembly of God Church in Radcliff, Ky., was a 1977 model but built before April 1977 when tougher federal regulations took effect.

Those rules required improvements in the structures of large school buses, including crash resistant steel cages around fuel tanks to prevent explosions in crashes and construction standards to prevent separation of the roof and side panels.

A federal investigator called Tuesday for closer state scrutiny of private buses because of the collision, the worst involving a drunken driver in the nation's history.

The driver of the pickup truck, Larry Mahoney, was charged with 27 counts of murder in Saturday night's crash after a test determined he had nearly 21/2 times the legal limit of alcohol in his blood.

Forty of the 67 teenagers and adults aboard the bus were injured, and Mahoney, 34, of Worthville, Ky., was transferred Tuesday from intensive care to the prison section of Humana Hospital-University in Louisville. His condition was upgraded from serious to fair.