30 July 1998

The Engine Manufacturers Association (EMA) applauded the action of the California Air Resources Board (CARB) in deferring action on the proposed identification of diesel exhaust as a Toxic Air Contaminant (TAC).

In response to a written request from California State Senator Quentin Kopp today, the ARB deferred this action until after a California Senate Transportation Committee hearing that is scheduled for August 4.

“We commend the decision of the ARB and its chairman, John Dunlap, in deferring action until the Senate has conducted a fuller investigation of the fundamental issues that are at stake,” said Glenn Keller, executive director, EMA. “One of the key issues is the quality of the scientific evidence on which such a decision would be made.

“We strongly believe that the data that have been reviewed so far are inadequate to support the designation of diesel emissions as a TAC,” Keller continued. “Under those circumstances, deferral is the only prudent and responsible course of action.”

As one key example, Keller cited a 1988 study previously reviewed by staffs of the ARB and the Office of Environmental Health and Hazard Assessment (OEHHA). This study, which was based on railroad workers’ exposure to diesel engine technology from the 1950s and 1960s, was never intended by its author to be the basis for quantitative risk assessment. Further, it was rejected by the United States Environmental Protection Agency and the World Health Organization as adequate for this type of use. The principal scientists whose studies have been reviewed by ARB and OEHHA so far have all gone on record stating that the underlying data are insufficient to justify such a far-reaching interpretation.

“EMA continues to support the ongoing research efforts of academic, government and independent researchers to evaluate the potential health impact of diesel exhaust using the best scientific information,” Keller said. “We urge both ARB and the California Legislature to carefully review this information, along with other important factors.”

EMA members continue to work with the USEPA and ARB to develop emissions reduction strategies for cleaner diesel engines. Through these efforts, today’s truck engines emit nearly 70% less NOx and 90% less particulates than in 1987. By the year 2004, thanks to an agreement between engine manufacturers, CARB and federal EPA, diesel truck NOx emissions will also be reduced an additional 50% from current levels.

Source: Engine Manufacturers Association