They were "trapped like rats in a cage" according to one witness, after a fire apparently set by an arsonist swept through a Moscow drug rehabilitation clinic on Saturday morning, killing 45 women.
The blaze, which started in the kitchen of Hospital No 17 in southern Moscow, rapidly spread through the second floor women's ward, filling the entire section with heavy black smoke, Russian TV reported.
Patients trying to flee the smoke and flames found the main fire exit blocked by a locked metal grill, apparently placed there to prevent mentally ill patients from wandering off. Windows on the second floor were also heavily barred.
Caught between the flames and iron bars 45 women died, mostly of smoke inhalation, in the 10-minute interval before fire fighters arrived, according to Russian TV.
Most of the victims were young women undergoing treatment for drug addiction.
"Judging by the position of their bodies, they really tried to escape," deputy emergency minister Alexander Chupriyanov told journalists.
Emergency crews extinguished the fire in 20 minutes, and evacuated 160 people. The old brick building had been repeatedly cited for violations of fire safety rules, but nothing had been done about it, Russian TV reported on Saturday.
Moscow fire chief Yuri Nenashev, said he was "90 per cent certain" that the blaze, which started in a wooden kitchen cabinet, was set deliberately.
It was the worst fire in Moscow since a November 2003 blaze in a university dormitory for foreign students, which killed 36 - including one Indian student - and injured 200.
Almost 20,000 Russians die each year in fires, one of the world's highest rates.
At greatest risk are older buildings such as hospitals, dormitories and schools, where maintenance has been largely ignored since the collapse of the USSR 15 years ago.