SPA-FRANCORCHAMPS, Belgium Metal debris from another car caused the alarming punctures suffered by Formula One world champion Sebastian Vettel and Ferrari's Fernando Alonso in Friday's Belgian Grand Prix practice, tire supplier Pirelli said on Saturday.
The Italian company's motorsport head Paul Hembery showed reporters photographs of the tires and a curved metal plate with pointed ends retrieved from the astroturf edge of the track at turn 13 where both punctures occurred.
Alonso's tire showed two penetrations, likened by Hembery to a Vampire bite, of the tread and made by the points of the plate.
He would not say which car the plate came off but other sources pointed the finger at Kimi Raikkonen's Lotus. The Finn is coincidentally Vettel and Alonso's closest championship rival.
Hembery said Alonso's tire was damaged 15 seconds before Vettel's at the same point, but did not deflate immediately. The Red Bull tire also showed clear evidence of being punctured by an external object.
"There are certainly no tire-related issues," he said.
"We've not seen any fatigue issues on any tires whatsoever. In practice three, there were no fatigue issues seen so looking at all the evidence and the timings we conclude that this piece of metal was the problem.
"It's very rare. We've not really seen in three years that size piece of metal. You might see nuts and bolts and things but they tend to embed in the tire. When you get carbon fiber it tends to cut the sidewall. So this was an exceptional circumstance."
Drivers had expressed concern and asked race director Charlie Whiting on Friday for more information about the punctures.
A spate of blowouts at the British Grand Prix in Silverstone in June raised safety concerns that threw the sport into crisis before Pirelli changed the structure of the tires last month to make them stronger.
Hembery said teams had been reassured by the evidence provided.
(Reporting by Alan Baldwin; Editing by John O'Brien and Pritha Sarkar)