What led to Delhi's tragic fire accident leaving 43 killed?

A total of 43 people were killed and dozens seriously injured early on Sunday when a massive fire broke out in a factory in a crowded market in West Delhi's Rani Jhansi Road area. The casualty figure is feared to increase.The people who died in the fire are labourers and they were sleeping in the factory when the fire broke out between 4.30 a.m. and 5 a.m. on Sunday morning.