One man was killed and three others were sickened by a mixture of pungent and toxic gases this afternoon while working in a deep, narrow shaft at the Sewickley sewage treatment plant.

Borough Manager Kevin Flannery identified the man who died as Jack Hogan, 31, of Baden.

He fell about 20 feet and the co-workers who went in to see about him were overcome by sewer fumes.

One of those sickened was plant superintendent Dennis Mike. An inspector and a contract worker were the other two taken to the hospital. The surviving workers were being treated at Allegheny General Hospital for injuries officials said were minor to moderate. They were taken by ambulance to the North Side hospital because it has a hyperbaric chamber, which provides intensive oxygen treatment, although it has not been determined that they will need it.

A hospital spokeswoman said two of the workers are in good condition and the other worker is in fair condition.

Investigators are probing what happened just before 12:40 p.m., when 911 dispatchers first received reports that four people were trapped in a shaft 30 feet below the ground.

Firefighters, paramedics and a hazmat team responded and began pumping the shaft with fresh air as firefighters entered the shaft to rescue the workers, Fire Chief Jeff Neff said.

The firefighters wore breathing apparatuses and brought extras for those trapped. Within 30 minutes, by about 1:18 p.m., rescuers had pulled the men from the shaft using a system of ropes and harnesses.

The shaft is about 30 feet deep and 10 foot wide -- "a very tight situation to work in," the fire chief said.

Initial rescuers reported him unconscious while inside the shaft, said Valley Ambulance Chief J.R. Henry.

"He never regained consciousness," he said.

Mr. Hogan is the father of an 8-week-old daughter, said Borough Manager Flannery.

He personally went to inform Mr. Hogan's wife and mother.

"The employees in Sewickley are a close group," Mr. Flannery said. "We're all taking it pretty hard."

The men were performing routine maintenance on the shaft, work that has halted while investigators examine the scene.

Officials weren't sure what gases were inside the shaft but they likely included methane and hydrogen sulfide.

Guillermo Cole, spokesman for the Allegheny County Health Department, which inspects all sewage treatment plants in the county, said the department has dispatched an employee to the plant to help evaluate what happened and offer any assistance needed.

"We don't think this will have any effect on their operation," he said of the incident.

Personnel from the federal Occupational Safety and Health Administration also were headed to the scene.

This past winter, the Sewickley Water Authority, which is owned by Sewickley Borough, began working on two projects at its treatment plant that are expected to cost $6 million and take two years to complete.

One of the projects is designed to improve its headworks, which grinds up the solids that come into the plant. The other is construction of a dewatering facility, to remove water from wastewater sludge, in an effort to reduce the odor that comes from the plant.

The water authority serves not only customers in Sewickley but in Aleppo, Bell Acres, Edgeworth, Glen Osborne, Haysville and Sewickley Heights.

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