I am an electrical engineer by profession for over 30 years, and the description of the explosion sounds just like a faulty battery on a personal electronic device (PED).  If the plane was just starting it's descent, it could be he was stowing his device at the time of the explosion (turning it on/off, cabin pressure fluctuations, etc.), a more likely time for the battery to explode if it were faulty. These PED battery explosions are typically  "small" and limited in area, consistent with the reported events.  Contradictory to this from some experts, if you want to create the most devastation and minimal evidence, you want to blow up a plane over the ocean, not on descent to Detroit.  Others state to generate maximum media impact, you do want to explode over land to expose the results to the media and provide an additional  scare factor.     Additionally, If he really wanted to blow up the plane, why would he detonate a bomb with the explosive power  to only hurt himself ? A pretty dumb terrorist , I would say.   Also, the suspect could have been surprised and stunned himself at the explosion, and coupled with people not helping him, but rather, tackling him, could have put him in a state  of shock, hence, he did not respond to his injuries or questions from others.  It could be possible that the reason why airport security may not have caught his "explosive device of  terror" is because it really wasn't an overt one , and was maybe just a battery? I am a patriotic American, born and bred here and not a terrorist, and, I am not trying to support this person, in fact, I would condemn it if this in fact, was an act of terrorism.  Besides the level of security checks, faulty batteries recalled have been a common issue over the past few years.  I think the government and media regardless of the real answer, needs to hold off on making  conclusions here and scaring us all until forensics gives us the real answer.  I think it would be possible, however, if the reports are true that he was an engineering student in London, that he could have had the knowledge of battery design in order to modify it and to make it explode under certain conditions.  Or, he may have affiliate ties to terrorist groups, and was fitted without his knowledge (or with) a modified battery.  If the TSA does not change their security rules, this only reinforces my beliefs that it could be an accident, or negligence.   If the US decides to increase security efforts and spend more money and in effect, to further limit our economic recovery due to this incident, then we are losing the battle anyway because the terrorist organizations realize that the way to our heart is Capitalism, the more money we spend, the less secure we seem to be.  If I am right,  then eventually say goodbye to bringing your laptop or DVD player onto an aircraft ever again...Either way, do we lose?  I pray not.

It now looks like (at least the reports are) that in fact, he was carrying PETN explosive and tried to ignite it.  If true, then we still need to think...what will they try to use as an "undetectable" explosive device next time...a battery???

Either way, Dutch citizen Jasper Schuringa is a hero in no uncertain terms, flying over seats and burning himself on the suspect's explosive device, he described a "pop", then a 30 second delay , and  then flames.  extremely consistent with a battery explosion.

Techy Explanation:

Batteries have a negatively charged terminal and a positively charged terminal. In a battery, energy from electrochemical reactions causes electrons(negatively charged particles) to collect at the battery's negatively charged pole. Charged particles are attracted to opposite charge, so if you connect a battery to a circuit, the electrons will flow from the negative pole, through the circuit and to the battery's positively charged pole. In other words, the battery generates a moving charge, or electricity.The exact reaction that generates the electrons varies, depending on the type of battery. In alithium-ion battery, you'll find pressurized containers that house a coil of metal and a flammable, lithium-containing liquid. The manufacturing process creates tiny pieces of metal that float in the liquid. Manufacturers can't completely prevent these metal fragments, but good manufacturing techniques limit their size and number. The cells of a lithium-ion battery also contain separators that keep the anodes andcathodes, or positive and negative poles, from touching each other.

If the battery gets hot through use or recharging, the pieces of metal can move around, much like grains of rice in a pot of water. If a piece of metal gets too close to the separator, it can puncture the separator and cause a short circuit. There are a few possible scenarios for what can go wrong in the case of a short circuit:

• If it creates a spark, the flammable liquid can ignite, causing a fire.
• If it causes the temperature inside the battery to rise rapidly, the battery can explode due to the increased pressure.
• If it causes the temperature to rise slowly, the battery can melt, and the liquid inside can leak out.

There are several reasons why  multiple laptop battery models have been recalled in the past few years. People want small, lightweight laptops that they can use for long periods. They also want their laptops to have bright screens and lots of processing power. For these reasons, laptop batteries have to be relatively small, but they also have to hold a lot of energy and last a long time.

All I can say is that the current CNN reports does not dispute my hypothesis.