RICHMOND -- Chevron's Bay Area refinery opened its gates to the public on Saturday for the first time since an August 2012 fire that resulted in criminal charges and record fines.

In its third annual Community Tour Day -- which was not held last year because of the accident -- the company sought to assure residents that it had stepped up safety since corroded piping in its crude oil unit leaked, causing a fire that sent 15,000 people to local hospitals, many with respiratory complaints.

"We hope they understand that this is a complex business that we can do very well," said the refinery's new general manager, Kory Judd, who took over in June. "We're going to continue to be here and continue to be a positive influence."

The century-old refinery has long been a source of tension in the city that grew up around it, drawing protests and lawsuits from environmental groups and support from residents who see it as an economic engine and critical tax revenue source.

While the 2012 fire caused no serious reported injuries, it drew far more scrutiny than previous incidents and has cost the company millions of dollars in claims, fines and restitution. A full-scale investigation by the federal Chemical Safety Board blamed the accident on systemic failures to heed warnings and do preventive maintenance, galvanizing local and state authorities and environmentalists.

The state Division of Occupational Safety and Health issued 25 citations and fined Chevron $963,000 early this year. And in August -- two days after the Richmond City Council took the oil giant to court, claiming negligence -- Chevron pleaded no contest to six criminal charges brought by county and state prosecutors.

Now, the company is working to repair its image along with the safety problems that have come to light since the blaze. It also aims to restart a hydrogen plant replacement project that screeched to a halt four years ago. In 2009, a judge sided with activists who argued the project's environmental impact report was inadequate. A new environmental review is expected soon, followed by a public comment period.

A bus tour through Chevron's industrial city within a city, down "Main Street," "Petrolite Street" and "Channel Street," past its vast systems of pipes, furnaces, stacks and tanks, revealed the refinery's complexity and scale.

A recent inventory found that if placed end to end, the pipes on the 2,900-acre property would stretch for 12,000 miles, said Mary Colombo, a fixed equipment integrity manager.

Standing under a tent by the "maintenance & reliability" station, Colombo and other employees in white polo shirts answered questions and let visitors test the thickness of a sample carbon-steel pipe with a hand-held sensor. Colombo said about 16,000 additional components of pipelines -- small segments between welds -- were checked for corrosion after the fire and that 70 were replaced.

Chevron added piping inspectors, bringing the total to 106, she said.

Richmond resident Carol Schauer said many aboard her bus wanted to know where last year's accident happened. "They pointed that out," she said, of Chevron's tour guides. "They're not hiding anything."

Schauer and her husband, Malcolm Bury, said they were satisfied with the level of oversight described to them and were confident that the management -- like the community -- wanted the operations to be safe.

Chevron has its critics, Bury said, but it's the city's largest taxpayer and employs more than 2,000 people. "Richmond would have a hard time surviving if it didn't have the refinery," he said.

Robert Rogers contributed to this report. Follow Katy Murphy at Twitter.com/katymurphy.