Rosetta stone for DOT hazardous material placards

Bill sez, "Every three years the DOT publishes the generically-named 'Emergency Response Guidebook', which is actually a decoder ring for the four-digit hazardous materials placards that adorn all sorts of transport trucks on our highways and byways. Although I'm not a first responder I have a copy in my glovebox, mostly to satisfy my curiosity (that truck's full of bleach? who knew!). You can buy a dead-tree copy from the GPO for only $7.50 (free shipping) or download a PDF from the DOT's website. . ." Link (Thanks, Bill!)