Eleven people were injured yesterday, two seriously, after they were overcome by chlorine fumes that seeped into a pool area at a Fairfax County recreation center, Fairfax fire and hospital officials said.

Four people were taken from Providence Recreation Center, 7525 Marc Dr., to Fairfax Hospital and seven were taken to Northern Virginia Doctors Hospital at 7:30 a.m. after they breathed hazardous fumes, fire officials said. One man had to be rescued from a locker room by firefighters wearing protective gear, a fire department spokesman said.

Robert Edward Woodruff, 29, of Annandale, was admitted to Fairfax Hospital in serious condition, and Joan Shejik, 67, of Annandale, was reported in critical condition last night with undetermined damage to her lungs, according to a hospital official. The others were treated for chlorine gas inhalation and released.

Merni Fitzgerald, a spokeswoman for the county park authority, said she could not comment on what caused the gas leakage.

Pam Weiger, a spokeswoman for the county fire department, said that as of late yesterday, officials did not know exactly what chemicals caused the problem and that the investigation was continuing.

Weiger said several chemicals may have been involved. She said the fumes were contained to the pool area. However, the entire center, which includes racquetball courts, a weight room and a craft center, was closed for about seven hours yesterday. The center was reopened about 3 p.m., but the pool area remains closed.

The victims, some of them elderly, were swimming at the center, one of eight such facilities owned and operated by the Fairfax County Park Authority, when some noticed a hissing sound coming from the area around a closet, according to a witness's account.

"I didn't pay much attention," said Laura Sessions Stepp, a Washington Post reporter who was swimming at the center and was one of the 11 treated for gas inhalation. "About three minutes later, every breath you took was like inhaling gas. It was a pungent gas that made it hard to breathe."

The lifeguard yelled at the swimmers to get out of the pool, Stepp said. "We got into the dressing room, but it had started to seep into the dressing room." Stepp said she was overcome by coughing and a burning sensation in her chest.

Doctors at Fairfax Hospital said yesterday that chlorine gas can burn nasal passages, eyes and bronchial passages. Injuries can range from minor, temporary damage to permanent damage to the eyes, vocal cords or lungs. "The key issue is damage to the lungs," said Barry G. Simon, a respiratory disease specialist. "It can kill you."

Thom Mayer, chairman of the emergency department at Fairfax Hospital, said that when chlorine is inhaled, it can be toxic to lung tissue. The damage depends on the length of exposure and the concentration of the gas, Mayer said.

Fire spokeswoman Weiger said that yesterday's chemical leak was not the first at the Providence pool. On April 30, about 50 people were evacuated from the building after firemen found muriatic acid spewing from the piping system in the pool area. No one was injured during that incident, Weiger said. The rescue team flushed the acid into a pit area to remove it and ventilate the building. Muriatic acid is used in the process of purifying the pool.