The explosion not only destroyed the phone, but it also resulted in him getting burnt in the process. According to the poster MiYzu, he claims that there wasn’t any external stress to the phone prior to the explosion, suggesting that there could be a hardware defect in the phone. Interestingly enough the OnePlus One handset uses a lithium polymer battery as opposed to the more common lithium ion.
This apparently makes it hardware to damage via external pressure, thus corroborating speculation that it could be due to a hardware defect that caused the explosion. MiYzu has since submitted a support ticket and a OnePlus representative has managed to get in touch with him about the issue.
Assuming that this is indeed a hardware defect, it could prove to be a big blow to OnePlus who not only have had trouble getting their phones into the hands of their customers, but have also come under fire recently for some of their more controversial marketing tactics.