Norfolk Southern Corp. has become the first big American freight railroad to require its customers to give the railroad legal protection against damages from fires, explosions or the release of hazardous materials carried in tank cars that don’t meet the rail industry’s latest standards.

The railroad said the change would take effect July 15, which is nine days after the one-year anniversary of the deadly crude-oil train crash that killed 47 people in Lac-M├ęgantic, Quebec, last year. Norfolk Southern said the required…