Last Thursday, about 20 Southwest Philly neighbors and environmental activists gathered in a conference room at Mercy Wellness Center, headquarters of the community group Eastwick Project Area Committee, to hear Sunoco officials explain why the company decided last month to switch to a safer form of the highly toxic chemical hydrogen fluoride (HF) after a two-year campaign by Clean Water Action and the Community Labor/Refinery Tracking Committee (CLRTC), a refinery watchdog headed by Joanne Rossi.

If released into the air, HF can travel up to 25 miles, causing severe respiratory problems, heart attacks and even death along the way, according to CLRTC. Starting in 2008, a modified form of HF will be used that has reduced volatility and risk of being dispersed into the air. But why now?

"Maybe they're tired of me suing them," joked Rossi, who has sued Sunoco several times on behalf of CLRTC during the past 15 years.

But Sunoco has more motivation that just satisfying its neighbors. The $61 million change will allow it to process 7,500 more barrels of crude oil in a day. Now that this battle is won, Rossi will turn to other ways to keep an eye on the 130-year-old refinery she calls the "old grand lady." Soon, she'll start cruising past the refinery with a "Hound," the nickname for a portable monitor that uses ultraviolet light to scan the air for 150 chemicals. The Hound and two stationary models cost $80,000, which came from the settlement of one of the air-pollution lawsuits. Rossi expects the machines will detect unhealthy levels of chemicals, proving that Sunoco and other industrial sites are violating air-quality standards. If that's the case, she'll report them to the city. "The refinery may be the largest player in the city," she says, "but they're not the only player."

Thanks to a settlement from another Sunoco suit a decade ago, CLRTC is also ready to test an emergency notification system; June 3 is the tentative sounding date for 10 sirens that would alert the community in the event of a chemical emergency. Rossi applauds the progress, but remains wary of Sunoco's intentions.

"I think, as a community, we're finally seeing a light at the end of the tunnel," she says. "Hopefully, it's not a train."