The company building train cars for the Honolulu rail line must retrofit 24 cars that have already arrived in Hawaii to make them more fire resistant, according to the Honolulu Authority for Rapid Transportation.

A sample from one of the rail cars being produced for the city’s $9.2 billion transit project failed roof and floor fire testing in Texas in February, and was to undergo retesting in Italy this week to determine whether the first results were valid.

Hitachi Rail Italy completed and passed the retesting of a train car roof, Honolulu rail officials said. However, after reviewing the roof test results the company has opted to retrofit the floors of the Honolulu rail cars with a thin layer of stainless steel to ensure they will also pass the fire testing, rail officials said this morning.

That fire testing of the car floor with the stainless steel retrofit in place will be done in about a month, HART officials said.

Hitachi Rail will need to retrofit each of the rail cars that have already been shipped to Hawaii, and also incorporate the extra steel floor plate into the manufacture of the rest of the 80 cars that Honolulu has ordered to make sure they meet federal safety requirements, said Andrew Robbins, executive director of HART.

That work will be done at the contractor’s expense, Robbins said. The extra plates will add about 190 pounds to the weight of each car.