By now, you should know what SCR and DEF stand for, but if you don't I'll recap: SCR stands for Selective Catalytic Reduction, the technology that most of the major diesel engine manufacturers have chosen to meet the EPA's 2010 diesel engine emissions standards, and DEF stands for Diesel Exhaust Fluid, the urea solution that is injected into the aftertreatment system of a truck with an SCR engine. Last week at the Mid-America Trucking Show in Louisville, KY, you could hardly go five minutes without someone talking about SCR and DEF, and the conflict that has erupted between the OE's that will be using SCR and DEF in 2010 (Daimler, PACCAR, Cummins, Volvo and Mack) and those that will be using "enhanced EGR" (Navistar/International). The conflict over which system is best is not a simple one, and many of the claims and counter-claims made by the manufacturers can't be validated until 2010 trucks and engines are on the road a year from now. But, as I sat through nearly 20 hours of "EPA 2010" presentations in Louisville last week, it occurred to me that there is one issue that we can lay to rest right here and right now. The folks at Navistar/International have been getting a lot of mileage out of their claim that DEF, a solution of urea and water that truck drivers will have to fill regularly on their trucks, is a "possibly volatile" substance. Quite naturally, the other manufacturers take issue with this, insisting that DEF is about as hazardous as Windex... Of course we all know there's one way to find out if a substance is dangerous: you check its Material Safety Data Sheet (MSDS). So today I went online to the website of Terra Industries, a DEF supplier that was represented on one of last week's DEF panels, and I looked up the MSDS for DEF. You can see it for yourself here. Turns out, both sides can make their points: yes, DEF can emit toxic ammonia vapors when and if it degrades, but--realistically--the biggest risk posed by a DEF spill in your shop is that the floor will be slippery. If you are considering purchasing new trucks with 2010 engines, it's worth your while to read the MSDS for DEF. Like all chemicals, DEF should be handled with care, but the MSDS makes it quite clear that DEF is NOT a hazardous substance. Score one for the SCR guys..