Diesel School Bus Study Contradicts 'Toxic' Claim

Diesel Fuel News, April 30, 2001 by Jack Peckham

In a scientific study of 12 representative school buses, Fairfax County (VA) Public Schools (FCPA) found "no health risks to our students and staff' from breathing the air inside diesel-powered school buses.

The new study comes on the heels of a Natural Resources Defense Council (NRDC) study that claimed to find cancer risks for students, based on data collected on one old diesel bus (among four total tested) in California.

The Fairfax school district followed the standardized sampling methods by Occupational Safety and Health Administration (respirable particulates) and National Institute of Occupational Safety & Health (elemental and organic carbon particulates).

"Analysis of the filtrates were performed by independent, certified laboratories following standard methods," FCPA said. The school district is in one the most heavily-populated areas of metro Washington, D.C., with 1,428 buses transporting 104,000 students to 234 schools. All but seven buses are diesel.

FCPA tested 10 diesel buses, one compressed natural gas (CNG) bus and one dual-fuel CNG/diesel bus that only burns diesel while idling. The buses were from one to 17 years old.

All the buses were run through the same route, ending with a 15-minute idle, with the average run to tailing 93 minutes.

* No Detectable EC

Using elemental carbon (EC) measurements as the surrogate for diesel exhaust, "in all 12 sample runs 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," the study found.

The highest respirable particulate found was with the CNG/diesel bus, not any diesel bus. Even this bus had 125 times less PM than the OSHA standard of 5 mg/[m.sup.3] This bus "was in excellent hygienic condition and there were no diesel exhaust odors detected during the run," although there was a "hint of CNG mercaptan" at one stop on the route.