I have read through this post and as I sit here and just shake my head, I ma forced to point out several problems with many of the attempts to make this magical trap an offensive weapon.
1. For those of you planning your marauding goblin horde with explosive runes on the front side of tower shield, please note the following from the spell itself:
"Target: one touched object weighing no more than 10 lbs."
A tower shield weighs 45 lbs so a small sized one for a goblin would weigh 22.5 lbs. Too big to put explosive runes on.
2. For those talking about them on a piece of paper, if that is the only thing on the paper it would take a Perception check of 28 to notice them as they are a magical trap (which is what the spell was designed as).
3. For all others, the spell states that there are only three ways to make the runes explode: reading the information they protect, failed erase, or failed dispel magic. So... even if you were crazy enough to sit down and put explosive runes on every page of a book, the first page that is read would cause 6d6 points of damage to the reader and to the book thus destroying all the pages but not triggering them.
4. For the spell to trigger, and this is the irony of it all, you have to read the information. This is ironic because I get the sense that many of the people posting here had not actually read the spell. The information that it protects must be read. The definition of reading, as listed by Merriam-Webster is " to look at and understand the meaning of letters, words, symbols, etc." Please note it says "UNDERSTAND," not just look at.If the information that is being protected is written in Draconic and the person inspecting the book does not know Draconic, they cannot read the book, therefore they cannot trigger the runes. The same with maps; if I created a map and used my own short hand that only I understood, and then cast explosive runes on it, no one else could set it off because they don't understand the meaning of the symbols that the runes are protecting therefore they cannot read it.
In summary, the explosive runes spell is a magical trap spell designed to protect information from getting into the wrong hands. Please stop tying to make it an offensive spell, because it is not.