Each of the Elemental Burst special abilities follows a pretty similar template:
"... functions as a (elemental type) weapon that explodes upon striking a successful critical hit. This does not harm the wielder." (emphasis mine)
It goes on to talk about doing 1d10 points of damage (or more on weapons with different critical modifiers, etc).
There seem to be no rules that actually specify a radius burst of a particular size, so why call out that the effect cannot harm the wielder? In what way should I expect this to harm the wielder?
Someone might accidentally believe the weapon doing a flaming burst hurts the wielder? Who knows. The burst is just a small cool burst where you hit them with the blade I thought.
I'm not a fan of such pointless asides in the rules, because they tend to make some people believe that similar abilities without the clause do harm the wielder. I'd prefer it if those wasted words were used to describe what exactly does happen, instead of what doesn't.
The idea is that when you crit, the fire covering your sword blossoms in a miniature fireball, or a firewave maybe, covering about a five foot square. Eletricity throws lighting bolts around, sound does a thunderclap, acid splashes a wave everywhere and cold creates a localized sleet storm, or maybe a hail of ice spikes. This only hurts your enemy but you might be able to use the fluff to create interesting effects if your DM allows.
That line is there so the DM doesn't use that fluff against you.
It says the same thing about normal flaming weapons, doesn't it?