A nitrous system will backfire if it is activated at too low an RPM (usually under 2500 rpms) because there isnt enough intake velocity to pull all the mixture into the cylinder. Remember your trying to pack more than you normally would into that cylinder when the nitrous is activated, take a look at the first video... he was barely off the line when the explosion happened.. NOw this isnt the only reason/way it can backfire, jetting to high of a fuel jet in hopes of creating a more fuel to nitrous ratio in hopes of preventing detonation. Take a look at the TA in the second vid. Highly doubtful he was jetted for anything less than a 125 shot, with the amount of fuel and nitrous being sprayed in the odds of a backfire increase the higher you go.
Simply put, dont be stupid when playing with nitrous, dont go cheap, buy all the safeguards you can. Get tuned and youll be safer than most.
After something that traumatic, I would pull the heads and inspect the valves, retainers, valve seats, and everything upstream from the valve. Most definitely would need a new MAF if so equiped as it would have destroyed the filiments. Since the heads are off for inspection, I would obviously peer into the cylinder for signs of piston damage.
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