Renault forced to write off Heidfeld's chassis after Hungarian GP fire

The German had to rush out of his car after it caught fire following a longer-than-expected pitstop.

Although Heidfeld escaped injury, his team said on Thursday that it will be unable to use the chassis again because of the heavy damage.

"The incident was highly undesirable, as it has caused us to write off a chassis," said technical director James Allison. "We will take steps prior to the next race to reduce the likelihood of a further fire and to ensure that the air bottle cannot overheat.

"We are in touch with the FIA both to provide them with a full report of the incident and also to explain to them the actions we are taking to prevent a re-occurrence."

He said that after an investigation, the team had found that the explosion that followed the fire had been caused by an air bottle inside the car.

"This was caused by the air bottle which supplies the air valves in the engine. It has overheated in the fire and failed."

Allison admitted several circumstances had combined to cause the fire.

"As with most accidents, several incidents combined to cause the fire that Nick suffered in Hungary," Allison explained. "First of all, we ran a slightly different engine mapping strategy in qualifying, which produced hotter than normal exhausts. We believe that this elevated temperature and caused a preliminary crack in the exhaust pipe.

"We presume that the crack then propagated during the laps to the pitstop - this was not evident to us as we believe that the failure occurred upstream of the place where we have a temperature sensor. We believe that Nick then came in with a partially failed exhaust.

"This pitstop took longer than normal, the engine was left at high rpm for 6.3 sec, waiting for the tyre change to be completed.

"Under these conditions, a lot of excess fuel always ends up in the exhausts and their temperature rises at around 100°C/sec. This temperature rise was enough to finish off the partially failed pipe and to start a moderate fire under the bodywork."