Four CNG run buses caught fire in 2023, seven in 2022, taking the total number of Department of Delhi transport corporation (DTC) and cluster buses that have been scorched in the past eight years to 30.

Delhi government data given in response to a question in the state assembly put's short circuits as the most common reason for the fires. Most buses that have caught fire in recent years were around 12 years old.

The different committees inquiring into the fires listed the cause of the blazes as short circuit in the main battery, wires directly connected without fuses, technical snags without the problem being looked into and the engine overheating.

In some cases, the committees constituted by the transport department, also blamed the fires on poor maintenance by the service provider and not replacing the spark plug in due time.

On April 21 2022, a 10-year-old, low-floor AC bus caught fire on the Paharganj flyover. The inquiry panel found that the driver had registered a complaint after eight AC malfunctions in March and April that year.

It's report said that it was "of the opinion that the fire was initiated due to short-circuiting near the AC filter. The intensity of fire was high due to higher current of the AC and the wiring harness".

The committee recommended that to avoid such fires, the wiring harness in all buses that had completed 700,000 - 800,000 km should be thoroughly checked and replaced wherever necessary. "The main wiring harness should be covered with a fire-resistant sleeve, properly fixed and clamped at each and every point to avoid hanging and contact with metallic parts of the chassis and hoses," it added.

The fires have also been attributed to negligence by service providers. Anil Chhikara, former transport department deputy commissioner, said that many of the buses were already more than 10 years old. "The new buses that have come are of better quality and do not heat up as much. We gradually need to phase out the old buses," Chhikara said.

He revealed that the service providers were often summoned and directed to take preventive actions. "The old model wiring harness was no longer available and so the wiring was repaired numerous times. In the old models, the engine chamber heat conduction was not proper and resistance increased with heat. The circuit heating damaged the connectors, causing short circuits," Chhikara said. "The traffic jams, overloading and constant use of air conditioning affected the buses."

A transport department official claimed that the old buses were being phased out at a fast pace. "The goal is to convert the entire DTC and Cluster Scheme fleets to electricity by 2025. By the end of that year, 80% of the 10,480 public transport buses in the capital will be electric buses," he said. "Once the number of e-buses crosses 8,000, Delhi will be among the select cities of the world with the highest number of such buses in operation," the official said.