Reality of "electrical explosion" I have often heard people who have been electrocuted refer to the "explosion" and how they were "thrown back" by the "blast". Sometimes the force of the blast is reported to throw people many metres.
There is no explosive involved - how can there be a repulsive force from a discharge of electricity?
 A: CuriousOne's comments basically answered your question.  I will add that if enough current is allowed to suddenly flow it can vaporize materials very rapidly, including metal.  This sudden vaporization can create a rapid expansion and if that expansion is restricted by something then it can explode in the same fashion as a bomb.  You often hear of transformers being "blown" because the high current inside causes it to rapidly expand faster than the pressure can be relieved, thus blowing up the container.
A: The "explosion" is actually a physiological response of the body of the person electrocuted.
Our muscles are basically commanded by electrical signals through the nerves to expand and contract.
When large currents flow in the body from an electric shock (in the form of ion currents), these flows "hijack" the muscles, and the latter "thinks" they are being commanded to contract.
Uninhibited by conscious control, your body's muscles are, for fleeting periods, far more powerful than you would otherwise believe. A violent contraction from an electric shock could easily throw the body a considerable distance. 
The effect may be two way. Just as the brain controls the muscles by electrical impulses, so too do the latter communicate their state to the former by the same. This is how we have sensations. So a large, foreign, current could well induce a preception of havoc or "explosion" in the brain of the shocked person.
EDIT in answer to user Lefty's comment:

I don't buy this answer. Why would a general current through the body cause muscles that conveniently push the victim AWAY from the source of the shock. If the current causes muscle contractions then why wouldn't it cause a form of "rigor mortis" in which all muscles contract together. I know for sure that when I shocked my own hand, I wasn't able to move my hand away from the conductor in either direction but had to use my shoulder to pull the arm away. Also, I don't believe there's a great deal of real evidence in this "superhuman strength" idea. Evolution doesn't give us muscles that are 10 times stronger than they need to be and then never gives us the ability to consciously - or unconsciously - bring it to bear when it's needed.



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*It doesn't happen like this all the time. Indeed, one of the great dangers of electricity is where the shock victim's muscles cause them to involuntarily grasp the high potential conductor, thus causing a huge, sustained, fatal current through the conductor. Gruesome finds of half burnt bodies wrapped around high tension conductors by line workers was commonplace when many citizens tried to steal electricity by attaching unmetered lines to the supply in Tbilisi after the USA power company AES lost their bill payments through corruption in the corporation itself and refused to acknowledge payment as discussed in the 2003 documentary "Power Trip" by Paul Devlin. This uncontrollable grip effect is in keeping with your own observations;

*Evolution does indeed give us the ability to for very high strength over very fleeting time intervals. This is enhanced even further by the fight-or-flight response and results from highly unusual energy source metabolism by the muscles, particularly glycogen or fat. The fight-flight response aside, in a proper bench press setup to measure thrust of your thigh muscles, you may be surprised at the forces that they can exert over short time intervals. It is indeed exactly of the order of 10 times your weight;

*The perception of explosion is probably very important here: the stimulus of the nervous system by foreign currents can lead to who knows what sensory perceptions by the brain. I recall as a child accidentally reading in a news magazine the account of perceptions by someone who survived the electric chair - from memory it was consistent with my point but I can't give you a reference because I categorically DO NOT have the stomach to risk reading this account again if I go seeking it, but it should be readily enough found. I do not have to warn you that this is a thoroughly harrowing thing to read;

*Ohmic losses through an unintended short through living tissue across a very high tension, low source impedance sources does indeed result in an explosion. A tree branch, particularly a green one, yields a neighbourhood-shaking detonation if it falls across the phases of power lines in the street (22kV between phases here in Australia). This arises simply from the swift expansion of water and liquids in the branch as its ionic pathways conduct between the phases. Someone truly exploding off a short like this may very well not be around to give an account.
A: Arc flash is a separate issue from electrocution.  It has only been integrated fully into the electrical codes over the last decade, and is not well recognized by folks not up to date on the latest requirements.
Arc flash is now covered well in the various electrical code documents. A rapidly expanding plasma generated by high voltages and currents rapidly releases very large amounts of energy. Yes, the result can look like a bomb went off, and be fatal to anyone within the arc flash approach boundary.
Think of 100s of volts with 100s of amps initiating an arc between two conductors. The copper starts to vaporize. The currents ionize the air and molten metal, allowing more current to flow. The air rapidly heats up and expands supersonically in a giant glowing plasma ball. As it turns out people die mainly from the blunt force trauma of the event, next by inhalation of superheated air with molten metal. Yes, they are blown backwards by the impact. A very nasty event. 
