Most of the 43 labourers who died in the fire that broke out early this morning in a factory in a congested central Delhi neighbourhood died of asphyxiation, emergency services personnel have said. A National Disaster Response Force (NDRF) team, dispatched to aid the Delhi fire department with rescue operations, swept the structure with gas detectors and found large amounts of toxic smoke and hazardous carbon monoxide. The NDRF team also found that some windows at the rear of the building were sealed shut, thereby trapping poisonous gases inside the already cramped and dimly-lit interiors.