Tomorrow, Philadelphia will be one ring of a three-ring circus. In addition to Chicago and Atlanta, our town will be the site for a public hearing on a new EPA rule designed to drastically cut the amount of toxic mercurcy emitted into our air by coal plants.

The EPA is inviting public comment, and many organizations are going to make sure voices for clean air and water are heard, but the SIerra Club is taking the lead. Outside the Westin Hotel (99 South 17th Street at Liberty Place) where the hearings are to be held the venerable eco group promises a parade of dozens of moms and children in strollers ("Pregnant women and children are at greatest risk from mercury exposure, especially if they consume large amounts of fish and seafood" says the Sierra Club), some wearing breathing masks, chanting, etc. as well as fishermen testifying to the dangers in eating fish contaminated with mercury; all of which will be "waving colorful signs calling for EPA clean air protections."

So yeah, kind of a circus. The organizers want to get the public's attention in the first place, and also get more members of the public to weigh in on the proposed anti-mercurcy regulations, especially here, considering that Pennsylvania is one of the states with the highest concentration of old coal plants, the main source of mercury in air and water.

So-called "Mercury and Air Toxics" standards would have a big health effect. Currently, the Sierra Club reminds us, "there are no national limits on the amount of air toxics that power plants can spew into the air. In Pennsylvania, dirty coal-fired power plants emit more than 15,500 lbs of toxic mercury every year, and citizens of the Commonwealth are warned against eating certain fish from 6 different river basins because of mercury contamination."

I spoke with Sierra Club President Robin Mann, who knows Philadelphia pretty well, living as she does in Rosemont.

"This is a terribly important rule," Mann stressed. "At long last the EPA is moving on regulating these sources of toxic air pollutants." It's vital, she said, "for the public to turn out in large numbers, to continue expressing support for the EPA." Already 300,000 comments have been generated.

Mann explained that "This is a project to eliminate 120,000 cases of childhood asthma a year," which will have direct effects on the health of everyone in the Delaware Valley (and beyond). The Club's literature states that these protections would also "prevent 17,000 premature deaths per year."

And even if you only care about the bottom line, she said, it's still a win-win: "For adults suffering from asthma, workdays missed is a very considerable economic impact." With new regulations, "for every one dollar spent on cleaning up power plants, thirteen dollars in economic and health benefits will occur."

Obviously this is not a popular change in the coal industry - though it's not the draconian, business-torpedoing move you might expect to hear some of the rhetoric against - what the Sierra Club prez called "coal-industry attempts to cloud the issue."

"Coal plants need to start now clean up their plant to be able to meet the standard within four years," Mann said, adding that the proposed change "could eliminate ninety percent of emissions in that time."

In fact, more than half the plants have already started on this process. Only 44% have not taken appreciable action in this area. The hope of the Sierra Club and other proponents of the EPA regulations is that an overwhelming public outcry tomorrow will help put it over the top.

If you want to learn more, there's a page here with additional info about the health liabilities of mercury and other toxins in the air, plust what you can do. The Sierra Club also has a zip-code search where you can see how close you are to a coal plant.

"When you add it all up it's amazing it's taken so long and been such a fight," says Mann, who has been a long-term advocate for clean water in our area. But she is gratified that now, "the public is starting to get it."

UPDATE 5/25: Here's the day-after coverage from the Daily News: Residents, experts call for stricter air-pollutant limits