SPRINGFIELD, Va. - An extensive, scientific study of a representative sample of 12 school buses in the fleet of Fairfax County Public Schools (FCPS) concluded the concentration of diesel exhaust inside the buses is below the limits of detection. The study concluded, "Breathing the air on Fairfax County Public Schools buses poses no health risks to our students and staff."

FCPS operates a fleet of 1,428 school buses of various makes and models to transport, daily, approximately 105,000 students to 234 schools and education centers. Approximately half of the buses are more than ten years old, and all but seven are powered by diesel engines.

FCPS transportation officials were concerned by media reports out of Los Angeles about research findings on the possible negative health effects of diesel exhaust from older school buses.

Twelve buses, representing different makes, models, sizes, ages, and engine types were selected for evaluation. Those selected included diesel fuel general education buses and special education buses with wheelchair lifts, a bus fueled by CNG, and one dual-fuel bus. The buses were monitored without student passengers during a simulated 90-minute bus run over an exact 19.9-mile-route in normal traffic with periods of loading, unloading, and idling. The tests were conducted from mid-February through early March.

The school buses ranged in age from 17 years to brand new. They included one 1984 model, three 1987 buses, one 1988 bus, one 1989 bus, two 1991 buses, one 1993 bus, one 1994 bus, one 1995 bus, and one 2001 model bus. Makes included Ward, Wayne, Bluebird, Thomas, International, AmTran, and Ford. By contrast the Los Angeles study by the Natural Resources Defense Council tested four buses, all manufactured prior to 1988 diesel emission standards.

Air samples were collected by filtration in accordance with standardized methods prescribed by the Occupational Safety and Health Administration for respirable particulates and the National Institute of Occupational Safety and Health [NIOSH] for elemental and organic carbon particulates. Analysis of the filtrates was performed Data Chem Laboratories, Salt Lake City, Utah, using standard methods NIOSH 0600 and NIOSH 5040.

Researchers concluded that there was "no detectable elemental carbon and subsequently no evidence that the bus air is contaminated by diesel/exhaust at a concentration that would be of any concern. ... All of the twelve respirable samples were below the Occupational Safety and Health Administration occupational threshold for respirable particulates for an 8-hour Time Weight Average."

Moreover, researchers said, "The detection of exhaust odor while riding a school bus may suggest to some passengers that exhaust is significantly being contaminating the bus air. The smell of the diesel exhaust is pungent and unpleasant but the intensity of an odor should not be construed to be representative of a health threat.

A complete copy of the report, "A Representative Sample of Fairfax County Public School Buses," can be found in PDF format on the website of Fairfax County Public Schools. Access requires Acrobat Reader.