1.   Diesel fuel produces more potentially hazardous pollution, known as particulate matter, than natural gas.

2.   He said burning fuel always produces byproducts, but ventless fireplaces are designed to burn their fuels as completely as possible so potentially harmful byproducts are minimized.

3.   In the proposed reactors, the fuel would produce too few neutrons to sustain a chain reaction, and so would normally remain inert.

4.   Such alcohol-based fuels produce far less pollution than do petroleum-based fuels.

5.   Methanol used as a fuel for automobiles produces vapors that humans can tolerate, according to a study released Thursday in the Journal of Occupational and Environmental Medicine.