WASHINGTON (Reuters) – The U.S. Occupational Safety and Health Administration issued a hazard alert letter to Amazon.com Inc (NASDAQ:) on Tuesday after six contractors were fatally injured and another was severely injured when a tornado struck Amazon’s Edwardsville, Illinois, warehouse in December 2021.

OSHA did not issue any violations or citations after the warehouse collapse, saying that Amazon’s severe weather emergency procedures met minimal federal safety guidelines for storm sheltering. It said that the company should make “improvements to protect workers and drivers during future emergency situations.”