Police have ruled out terrorism, saying the store chain had received menacing letters threatening to disrupt business, reports CBS News' Bill Gasperini. Police are calling it a business dispute.
A spokesman for the Emergency Situations Ministry, Viktor Beltsov, said 78 people sought medical care and 66 of them were hospitalized. None of them were assessed as being in life-threatening condition, he said.
A spokesman for the St. Petersburg police, Vyacheslav Stepchenko, later said 15 people were hospitalized. It was not immediately clear if the discrepancy meant that some people had been released.
Stepchenko said the gas was preliminarily determined to be methyl mercaptan. The U.S. Health and Human Services' Agency for Toxic Substances and Disease Registry says methyl mercaptan is a gas smelling like rotten cabbage that is both naturally occurring and manufactured for use in plastics and pesticides.
The agency's Web site said little is known about the gas's potential health effects. One person exposed to very high concentrations of the gas went into a coma and died, the Web site says.
Stepchenko said that a custodian at a branch of the Maksidom home-supplies chain found a suspicious box before the store's opening and when she opened the box, she found ampoules attached to wires and a timer. The woman inadvertently broke one of the ampoules and noticed a repulsive smell, but apparently was not sickened, he said.
All those who sought medical care were from another branch of the chain, Stepchenko said. Boxes with glass containers attached to timers were found in two other stores by employees, who carried them outside and covered them with buckets; police explosives experts defused them, he said.
Officials of the store chain, which has outlets only in St. Petersburg and sells furnishings, home-repair material and other domestic articles, had told police that they had received threatening letters in recent weeks, Stepchenko said.
The letters threatened to disrupt the company's sales during the holiday gift-buying period, the managers said, according to Stepchenko. New Year's Eve is a traditional gift-giving day in Russia, the equivalent of Western celebrations of Christmas.
Police initially are considering the incidents as "hooliganism."