SILVERSTONE, England - Formula 1 and tyre supplier Pirelli faced a crisis as the 2013 British Grand Prix came close to being stopped for safety reasons due to a spate of explosive tyre blow-outs.The spectre of Indianapolis 2005, when only six Bridgestone-equipped cars competed in a farce of a US Grand Prix, since teams equipped by tyre supplier Michelin did not compete due to safety concerns.There were also uneasy flashbacks to the 2009 Hungarian Grand Prix, when Ferrari's Felipe Massa suffered a near-fatal head injury after being struck by debris thrown up from a car in front.‘CLOSE TO BEING RED FLAGGED’With television images broadcast around the world showing bucking cars scraping along on rear left wheel rims stripped of rubber, the drivers wrestling to keep them on the road, the sport breathed a sigh of relief that the race had ended safely.Race director Charlie Whiting said: "It was quite close to being red flagged. It did occur to me to do that. I don't want to put a figure on it but it was close."I don't think we've seen anything like this. I can't remember anything. To have four total catastrophic failures, I believe, is a first."Lewis Hamilton, who had led for Mercedes from pole position, was the first casualty when his rear tyre blew after eight laps.He was followed by Ferrari's Felipe Massa, Toro Rosso's Jean-Eric Vergne and McLaren's Sergio Perez. Sauber's Esteban Gutierrez suffered a front tyre failure.Mercedes' race winner Nico Rosberg had signs of imminent delamination (when the tread peels away from the rest of the tyre) when he made a pitstop and champions Red Bull said cuts were found on the tyres of triple champion Sebastian Vettel, who retired with a gearbox problem.JUST UNACCEPTABLEHamilton said: "The safety is the biggest issue. It's just unacceptable."Someone could've crashed. I was thinking behind the safety car that it's only when someone gets hurt that something will be done about it."With the next race in Germany only a week away (July 07), Pirelli's motorsport director Paul Hembery said the Italian company, which has come under fire all season for the performance of its product, was making the investigation a top priority.Hembery said: "We can exclude that the new bonding process, which we introduced at this race, is a cause for the tyre failures we have seen today. "There might be some aspect to this circuit that impacts specifically on the latest version of our 2013 specification tyres but at this point we do not want to speculate."SAFETY CONCERNSMcLaren team principal Martin Whitmarsh declined to use the word crisis but said safety was the main concern.Whitmarsh said: "We are lucky no one has been hurt. For people like Checo (Perez) it has destroyed his weekend, but first and foremost we are primarily concerned about the safety of our drivers."I think there is an argument that Nuerburgring is a slightly less severe circuit than Silverstone, but we have Spa (Belgium) looming not long after that and we would certainly not want to go there with these tyres."Whitmarsh said the sport could not wait for a scheduled meeting of the governing International Automobile Federation (FIA) working committee on Wednesday to discuss the situation.Whitmarsh said: "You just have to say to Pirelli 'Do whatever you can do by Germany'. They know what stock they have, they know what they can do practically before Germany and they should do whatever they can to enhance the safety and durability of the tyres."Asked whether the German race might be cancelled, Whitmarsh suggested a solution would be to go back to last year's specification of tyres.‘GO BACK TO 2012 TYRES’Whitmarsh said: "In fairness to Pirelli, I don't know how they can respond in such short order but we have to do what we can to support them."We don't want an Indianapolis but cancelling a race is a big step, we don't have all the technical insight Pirelli have. All I would ask is they do everything they can to give us the most durable tyres they can for next weekend."Red Bull principal Christian Horner said: "The most logical thing would be to go back to the tyres that worked well for them previously. The tyres they had in 2012 did not have these failures."Whatever has changed, has changed but you would have thought the most logical thing would be to go back to the tyres that had served them well."