Sellal praised the quick wits of a guard who tripped an alarm that stopped the flow of gas and warned workers of an imminent attack.
"It was thanks to him that the factory was protected," he said.
Floria, the former hostage from Romania, remembered the moment when the power was cut.
"I ran together with other expats and hid under the desks in my office, locking the door. Attackers went scanning the office facility kicking the doors in. Luckily our door did not break and they went on to other offices," he said. "Locals were freed, the attackers made clear from the beginning that only foreigners were a target. Expats were detained."
Ultimately, Floria escaped. But not before he heard the two gunshots that silenced a pair of wounded hostages he said he tried to save.
"The perception of time changes. Seconds become hours. You feel you are losing your mind. I went through this for almost 40 hours," he said.
The prime minister said the heavily armed militants had prepared the attack for two months. He said the attackers arrived from northern Mali and had planned to return there with the foreign hostages. Seven French citizens taken hostage in recent years are thought to be held by al-Qaida linked groups in northern Mali.
Sellal justified the helicopter attack Thursday on vehicles filled with hostages out of the fear the kidnappers were attempting to escape.
In a statement, the Masked Brigade, the group that claimed to have masterminded the takeover, has warned of more such attacks against any country backing military intervention in neighboring Mali, where the French are trying to stop an advance by Islamic extremists. Algeria, despite its government's reservations about the French decision, is allowing French jets to overfly.
Col. Thierry Burkhard, the French military spokesman, said he did not know if militants in Mali were aware of the events in Algeria.
"However, I'm convinced the terrorist groups in the field have radios, so there's a strong chance that they're not only up to date with what's happening in Algeria but they're listening to everything that Western journalists are saying about the deployment of different forces in the field," he said.
The militants' operation was led by an Algerian, Amine Benchenab, who was known to security services and was killed during the assault, Burkhard added.
Moktar Belmoktar, who is believed to have orchestrated the attack, said in a statement over the weekend that the Algerian site was chosen after the country opened its airspace.
Sellal said negotiating was essentially impossible.
"Their goal was to kidnap foreigners," he said. "They wanted to flee to Mali with the foreigners, but once they were surrounded they started killing the first hostages."
He said the assault by Algerian special forces on the plant on Saturday that killed the last group of militants and hostages came after the kidnappers attempted to destroy the complex: "They led us into a real labyrinth, in negotiations that became unreasonable."
Associated Press reporters Paul Schemm in Rabat, Morocco, Lori Hinnant and Sarah DiLorenzo in Paris, Bradley Klapper in Washington, Rob Gillies in Toronto, and Nicolae Dumitrache and Vadim Ghirda in Pitesti, Romania, contributed to this report.