SAN FRANCISCO (AP) — Chevron Corp. was bracing Friday for an onslaught of legal claims after one of its Northern California refineries caught fire and sent thousands of people to area hospitals with complaints about respiratory problems and other ailments.

The San Ramon-based oil giant opened a claim center Friday in Richmond, and says it has received more than 2,000 calls to a claims hotline.

"We are going to pay all appropriate and reasonable expenses," Chevron spokesman Sean Comery said. That includes "out-of-pocket" medical costs and other documented losses, he said.

Richmond lawyer Nick Haney, who had long lines form outside his office earlier in the week, said he expects to represent about 3,000 residents with legal claims. Haney says he hopes to negotiate a settlement with the company before filing lawsuits.

Officials said more than 4,000 people sought medical attention immediately after the Monday evening fire at Chevron's Richmond refinery, about 10 miles northeast of San Francisco. Nearly all were treated and released after spending a few hours at the hospital. Consequently, lawyers and others predict the amount of damages each legitimate claim receives will be minor.

Mike Meadows, a Walnut Creek lawyer who has helped settle lawsuits for tens of millions of dollars against Chevron and other refineries because of previous mishaps, said he isn't participating in this incident because of the expected low payouts.

"The liability is pretty clear," Meadows said. "And I'm sure the victims showed up to the doctors with legitimate complaints." But he said most of the health problems caused by the fire likely were minor irritants rather than significant injuries.

The Bay Area Air Quality Management District said it continues to investigate the effects of the fire, which shrouded the area in black smoke, on the region's air quality.

"While air samples taken near the facility detected normal background levels of toxic air contaminants, there was the potential for significant smoke in the area that impacted residents in the downwind neighborhoods," the district said in a statement Thursday. "The likely source of health impacts from the fire is particulate matter from smoke."

The district said it found one dangerous chemical, acrolein, above safe levels in the air, although safe levels of the chemical often are exceeded in the Bay Area. Acrolein can cause runny noses and irritate eyes.

In all, five separate investigations will be done to determine the cause and effects of the Richmond refinery fire.

The same U.S. Chemical Safety Board team that investigated the oil spill in the Gulf Of Mexico, for one, was standing by with state and company inspectors waiting for structural and environmental tests to see if it was safe to enter the unit.