Sophisticated alarms will be required on all petroleum storage tanks at the Fairfax Tank Farm starting Jan. 1, under an ordinance approved last week by the Fairfax City Council.

Prompted by a 300,000-gallon gasoline spill at the tank farm last May, which forced the evacuation of nearby residents, the council voted to require oil companies to install sirens and flashing lights that would go off 10 minutes before a tank could begin overflowing.

Three oil companies using the storage depot -- Gulf, Citgo and Amoco -- now have alarms, while the fourth, Texaco, needs to install the devices, according to Tom Welle, information director for the city. The gasoline spill last spring was at the Amoco facility, where the alarm was not operating properly, Welle said.

Oil companies using the tank farm opposed the ordinance, arguing that the city has no authority to enact such a measure under its fire prevention code, said Ben Trichilo, a Fairfax City attorney representing the oil suppliers.

"We are not adverse to having these high-level alarms, but we would have preferred voluntary compliance," Trichilo said. He said the companies may challenge the ordinance's legality.

Under the new ordinance, companies failing to install the alarms could be subject to fines of up to $1,000 and a jail term of up to one year for company officials, Welle said.