BARCELONA, Spain - Pirelli is reviewing the construction of its Formula 1 tyres after a series of debris-related failures and assured drivers they need not worry about track safety.Concern was expressed at the 2013 Spanish GP when the tread came off the still-inflated left rear tyre of Paul di Resta's Force India car during Friday's (May 10) second practice.TYRE FAILUREFerrari's Felipe Massa suffered two failures during the Bahrain GP in April and Lewis Hamilton collected a grid penalty after his Mercedes needed an unscheduled gearbox change caused by damage from flying tread.Pirelli's motorsport director Paul Hembery told Reuters on Saturday that the problem occurred when debris on the track penetrated the tread rather than the sidewall of the tyre. This was because the Italian manufacturer had introduced a high-tensile steel belt under the tread to make tyre penetration difficult.Hembery said: "Now when there is debris or an issue it doesn't cut through the belt pack and deflate the tyre, which is what would have happened in 2012. Instead, it arrives at the belt pack and the tread becomes the weak point."It overheats and comes away, which visually is very dramatic although the structure is still intact."Hembery said Resta's tyre still had pressure when the car came back to the pits."Last year that would have collapsed on to the rim and (the car) probably would have crawled down the pits lane on three wheels. It's the mode of failure that's changed," the Briton explained."Bizarrely, it's probably safer this way. For us, it's worse because it's visually not great. From a safety point of view, it's probably safer because the tyre is still inflated. It's not something due to quality or design."SILVERSTONE SOLUTIONHembery said Pirelli would seek a solution to the problem but it would not be available until at least the 2013 British GP at the end of June because teams would have to agree to changes that could affect cars' performance.That would mean similar failures could occur at the Monaco and Canadian GP's which precede Silverstone."We can't test and if we make too-dramatic changes we influence maybe the aerodynamics and some of the chassis design," said Hembery. "If we make anything significant, we have to convey it to the teams and we have to know if that is going to affect what they are doing."It's a very delicate balance."Is our solution to make the tyre deflate when it has debris? Does that look better from a tyremaker's point of view? Is it worse for the teams or better? It's a strange dilemma."Hembery said Hamilton's issue in Bahrain was slightly different in that there was either a suspension problem or something on the track that broke the suspension but Massa's punctures were clearly caused by debris."There were cuts in the tyres. I found a bit of one car in one (tyre) and I know which one it was because it had the branding on it," he said with a smile."We are frustrated, because we don't like to see the tread coming off but we are not alarmed for any safety issues."