Air Board Delays Vote on Hazards of Diesel Fumes


From truckers to farmers to manufacturers, industry leaders descended Thursday on the California Air Resources Board in an effort to stop the board from declaring diesel exhaust a potent cancer-causing danger to the public.

The board heard six hours of public debate but delayed its long-awaited decision at the request of top-ranking state legislators until late August. A Senate hearing will be held next week on the economic and environmental ramifications of diesel fuel.

The delay comes after an independent panel of scientists and state environmental officials have spent nine years--an inordinate length of time--reviewing the health effects of diesel exhaust to judge whether it should be deemed a toxic air contaminant.


Despite the lobbying, the air board is still expected to declare diesel exhaust toxic. State officials would then need to consider strategies to ensure that Californians are protected from the hazards posed by trucks, buses, trains, farm machines and other equipment that burns diesel fuel. Air board officials say that they would not ban diesels, but they are likely to tighten standards for exhaust and fuel. That would include increased efforts to prompt trucking companies, bus fleets and others to remove their dirtiest diesel vehicles from the roads.

The issue has been one of the most contentious decisions before the Air Resources Board in recent years, largely because diesel plays such a central role in the state’s economy.

On behalf of industry, 66 state legislators--more than half the Legislature--intervened and urged Gov. Pete Wilson’s air quality chief, John Dunlap, to delay the board’s decision. Senate Transportation Committee Chairman Quentin L. Kopp (I-San Francisco) is holding a hearing Tuesday at the urging of the California Trucking Assn., a powerful lobby of trucking companies.

On Thursday, industry representatives, environmentalists and scientists spent the day debating the link between diesel exhaust and lung cancer and the implications for California’s economy and public health.

Trucking companies and engine manufacturers worry that if the air board implicates diesel exhaust as a potent carcinogen, they could be held liable for paying massive damages for causing people’s cancers. Even without an outright ban on diesel, the air board’s decision would make it difficult to operate a wide variety of businesses that depend on the engines, from grocery stores to construction firms, industry officials say.

“Diesel engines are an integral part of our economy in California, so what you do here may have a significant effect,” said Allan Zarember, president of the California Chamber of Commerce. “In some circumstances, the consequences may be worse than the cure.”


Diesel fumes are substantially cleaner than a decade ago. New engines--those produced since 1988--emit 90% fewer of the tiny particles that can lodge in lungs than earlier, unregulated diesel engines.

But environmentalists, backed by state and independent scientists, argue that even the cleaner diesels still endanger public health. In California, the engines emit about 27,000 tons a year of tiny sootlike particles that can lodge in lungs.

“We’re very concerned that people in California who are exposed to diesel may die,” said Paul Knepprath of the American Lung Assn.

Scientists and state officials say there is little doubt that diesel exhaust qualifies as a toxic air contaminant. Under a 1983 California law, the air board must identify a substance as toxic, then consider steps to protect the public, if it “may cause or contribute to an increase in mortality or serious disease” or “may pose a present or potential hazard to human health.”

State environmental officials first recommended that diesel exhaust be listed as toxic in 1994, but under fire from industry, their report was revised twice.

In April, the state’s Scientific Review Panel concluded that diesels could be killing more than 14,000 Californians by causing 450 lung cancers among every 1 million people exposed to average concentrations over a lifetime. Based on that risk estimate, diesel exhaust ranks sixth in potency of 19 air pollutants now identified as hazardous.


More than 30 human health studies from around the world show a link between diesel exhaust and cancer--more so than with any other substance reviewed by the state in 15 years, said John Froines, a leading environmental health specialist at UCLA who heads the Scientific Review Panel. In the studies, railroad crews and other workers regularly exposed to large doses of the fumes suffered 40% more lung cancer than average.

Engine manufacturers and other industry groups argue that the studies are flawed, especially because they involved workers exposed several decades ago, before improved engines and low-sulfur fuel reduced the particles and other toxic ingredients in the exhaust.

The crux of the debate is over the state’s effort to quantify the cancer threat to all Californians.

Most scientists agree that diesel exhaust does increase cancer in many occupational settings in which people breathe high concentrations.

Diesel exhaust contains a mix of thousands of compounds, including more than 40 that have been declared carcinogenic.

But some scientists say that the California scientific panel has gone too far out on a limb by estimating the number of cancers among people in the general population--who are exposed just from breathing ambient air while driving on freeways, walking near intersections, or sitting at bus stops.


Industry representatives say that if the state board adopts the cancer estimate, it makes the science sound conclusive when it remains highly uncertain because of holes in the research.

“Something with this huge of an implication for the economy of the state of California should not be a back-of-the-envelope calculation,” said William Bunn, medical director of Navistar International, the largest diesel engine manufacturer. “Before you say ambient air causes cancer, you should be very certain, and we don’t think that evidence is there.”