The blast occurred in a two-story educational building on North Kargar Street.
Jalal Maleki, spokesman for the Tehran Fire Department, said the explosion was triggered when a hydrogen cylinder being replaced inside a ground-floor laboratory suddenly blew up.
“The explosion was so powerful that windows, doors, and part of the internal wall were destroyed,” he said.
Maleki confirmed that a man died instantly at the scene, while a man and a woman sustained severe injuries.
Several others suffered lighter wounds from flying glass and debris.
“Fortunately, the incident did not lead to fire or secondary explosions. The situation is fully under control and firefighters are conducting safety operations,” he added.
According to officials, both seriously injured victims remain under medical care, while other minor injuries were treated on-site or at local hospitals.