The fact Romain Grosjean survived Sunday's Bahrain Grand Prix was remarkable. The forces, flames and destruction involved in his accident on the opening lap of the race could easily have resulted in a much worse outcome, but somehow he was able to walk away from the incident with relatively minor burns to his wrists.
The last data logged by the car before the impact recorded its speed at 137mph and a 53G impact was reported. Haas team principal Guenther Steiner refused to confirm the G-force number on Sunday night, saying the one he had seen seemed too high to be realistic. He also said "an angel was with us, in my opinion."
The force of the impact was enough to tear the steel barrier in two, leaving the safety cell -- the strongest part of the car, which is designed to cocoon the driver in such accidents -- wedged sideways in the deformed metal. The sudden deceleration of the car was so dramatic that it split the car in half, with the rear, which houses the engine and gearbox, torn off by the inertia of the impact.
The engine itself is a structural part of the car, mounted to the survival cell by six studs. Those studs are incredibly strong, but such were the forces involved that they were ripped from their mountings and the rear of the car continued down the barriers.
Within a fraction of a second a fuel leak enveloped the front half of the car in a fireball, with Grosjean still inside. The fact he remained conscious in an accident that tore his car in two was miraculous, but ultimately proved essential to his survival.
He spent 28 seconds working his way loose from the wreckage before emerging from the inferno with the help of Formula One's travelling doctor, Dr Ian Roberts, who arrived quickly on the scene in the medical car. It's horrifying to imagine what those 28 seconds felt like for Grosjean, but his survival instinct kicked in and his fireproof overalls protected him as he scrambled free. It took just over ten seconds for the medical car, which follows the pack at the start of every race, to arrive on the scene.
Dr Roberts, who sits shotgun in the medical car alongside former race driver Alan van der Merwe, ran directly towards the flames to help Grosjean, instructing a fire marshal to aim his extinguisher at the area around the cockpit opening as he went.
"I just [saw] a massive flame and as we arrived, a very odd scene where you've got half a car pointing in the wrong direction and just across the barrier, a massive heat," Dr Roberts said afterwards.
"I could see Romain trying to get up. We needed some way of getting to him. We've got the marshal there with an extinguisher and the extinguisher was just enough to push the flame away as Romain got high enough to then reach over and pull himself over the barrier.
"I told him to sit down [when we reached the medical car]. He was very shaky and his visor was completely opaque and, in fact, melted. So we got his helmet off just to check everything else was OK.
"He had some pain on his foot and hands [from burns], and at that point we knew it was safe enough to move him around into the [medical] car to give him a bit more protection and get some gel onto his burns and into the ambulance and off to the medical centre."
It was an incredibly lucky escape, but one that would not have been possible without a number of safety features on the car.
Halo saved Grosjean's life
Decades of safety research by Formula One and its governing body, the FIA, provided Grosjean with the lifeline he needed to escape the wreckage on Sunday evening. The strength of the survival cell, his fireproof overalls -- which were uprated for all drivers this year -- and, crucially, the halo device all contributed to saving his life.
"It was horrifying," world champion Lewis Hamilton said after winning the restarted race. "His car, the cockpit... I don't know what G's he pulled, but I'm just so grateful that the halo worked.
"I'm grateful that the barrier didn't slice his head off. It could have been so much worse. It is a reminder to us and hopefully to the people that are watching at home that this is a dangerous sport.
"That is why we are out there pushing to the limit and playing with that limit. But you also have to respect it. It shows the amazing job that Formula 1 has done, the FIA have done over time to able to walk away from that."
The halo is a titanium structure that sits above the driver's head. It is capable of resisting forces equivalent to a 12 tonne weight and was initially developed to deflect large pieces of debris that would otherwise hit the driver's head.
In Grosjean's accident the halo protected his head from the upper part of the barrier as it was split from the bottom section by the force of the accident. Amid the flames, Grosjean was then able to pull himself out through the halo's opening above the cockpit and jump to safety.
In the lead-up to its introduction in 2018, the halo received widespread criticism from a number of drivers and team bosses within the sport. The arguments, which were mainly based on aesthetics and the belief that it was against "the DNA" of open-cockpit racing, seem hard to comprehend now, but it's a credit to the FIA that it was pushed through on safety grounds.
Speaking on Instagram from his hospital room, Grosjean put whatever was left of the halo debate to bed.
"I wasn't for the halo some years ago, but I think it's the greatest thing we brought it to Formula One and without it I wouldn't be able to speak to you today," he said. "Thanks to all the medical staff at the circuit, at the hospital, and hopefully I can soon write you quite some messages and tell you how it's going."
Worrying aspects of the accident
While the halo did its job, serious concerns remain over a number of other factors in the accident.
"We have to do a very deep analysis of what happened because lots of things were worrying," F1's motorsport director Ross Brawn said on Sunday night. "The fire was worrying and the split of the barrier was worrying -- the safety of the car is what got us through today.
"Barriers splitting was a classic problem many years ago and normally resulted in a fatality. No doubt the halo saved Romain, and the team behind it deserve credit for forcing it through.
"I don't think anyone can doubt the validity of the halo. It was a lifesaver today.
"[The accident] was a high G load and we have to look at how things failed. The car came apart and we had a fuel fire, which we have not had for a long time.
"There will be some careful scrutiny between now and the next race and the action will be taken that needs to be done. It is something we have not seen in a long time and something we did not predict."
The barrier and the fireball remain the two biggest concerns.
As well as its failure, the positioning of the barrier has been questioned as it angled inwards relatively to the direction of travel of the cars. Barriers do their job when they deflect the car in its direction of travel, absorbing some of the impact, without taking the brunt of it. But in this instance Grosjean's car went through the barrier in a way that was hauntingly reminiscent of Francois Cevert's fatal accident at the 1973 U.S. Grand Prix.
The barrier in Bahrain is at that angle to allow an opening further down the straight to remove cars when they stop on track. Such openings are essential to allow the marshals to do their job but require one part of the barrier to be angled slightly in order to create a large enough opening.
Barrier and run-off design around F1 circuits are laid out in meticulous detail so that they maximise protection at parts of the circuit when an accident is likely to happen. Those with a higher risk of being hit are lined with extra protection, usually in the form of Tec-Pro barriers, but those that are less likely to be hit are usually made of either concrete or Armco.
In 16 prior years of F1 racing in Bahrain, no one has come close to hitting that section of barrier and the chances of it happening again are extremely small. Grosjean only hit that barrier because he cut across and made contact with Daniil Kvyat, spearing his car off to the right at a part of the circuit where most accidents would be expected to happen on the left.
Yet at the heart of every accident is a level of unpredictability, and as Grosjean made contact with Kvyat, he had no control over where his car would end up or the angle that it would hit the barrier.
A shallower angle of impact afforded by a barrier parallel with the circuit would likely have seen the car skid down the barrier, as it was supposed to do, but there is also a question of how the nose of the car, which is designed to deform against the barrier and absorb energy, managed to penetrate the barrier. All of these factors will be learned from and could lead to changes in both circuit and car design in the future.
"I think it was a freak accident," Mercedes team principal Toto Wolff said. "The angle at which he crashed into the barrier -- I don't think that the car was flat, I think it was slightly sideways -- the angle must have been so precise like a knife going through the barrier.
"I didn't think modern barriers could split like this, so we need to analyse how this could happen and how we can optimise these barriers in the future."
The other very visible and very worrying aspect of the accident was the fireball that engulfed Grosjean's car almost instantaneously.
F1 has gone to great lengths to avoid such incidents and the fuel tank (or fuel cell to give it its proper name) has been developed with safety in mind to prevent cars going up in flames. It is most easily described as a large deformable bag, although the structure is rigid when fitted in the car and is made of military grade ballistics material.
An investigation will follow, but the feeling among several engineers in the paddock was that the fuel cell itself did not rupture. At the start of the race, the car is carrying just over 100kg of fuel, and Brawn was among the engineers who believed that amount of fuel would have resulted in a much bigger inferno.
That has led to suggestions that the sheer force of the impact may have compressed the fuel cell and spat petrol out of the refueling hatch, resulting in the fire. It's also possible that one of the fuel lines leaked fuel, although they are also designed to withstand massive impacts.
To get definitive answers, the FIA will forensically analyse the remains of the car to see what can be learned and what can be changed on future designs. A lot of the safety features that helped save Grosjean's life on Sunday night were a result of research conducted following other serious accidents and that same scientific approach will be used to further advance the safety of the sport in the future.
"Obviously with every incident, more so with every larger incident, the FIA's Safety Department, the FIA as a whole really, leads the investigation," FIA race director Michael Masi said on Sunday evening. "The single seater department, of which F1 is a part of, from a technical perspective has an involvement, the F1 teams, technical directors, the circuits commission will all be involved. "All of the various parts of the FIA group, the respective subject matter experts, will review their particular area and see what can be learned, what can be improved, be it small, large, in between, there's always something to be learned."
And while there will be a sense of urgency to learn the lessons from Sunday, the sport knows from past experiences that it is best to work together and not make knee-jerk changes.
"A fire like that, regardless of what happens with barriers and everything, is a very scary event," Mercedes chief trackside engineer Andrew Shovlin said. "So rather than us all barreling in and saying what we think should be done differently, the FIA, who have a lot of people dedicated to safety and have no doubt contributed to that kind of incident being survivable, should be allowed to get on with that and the teams will all get involved where they can [to help].
"What has been reassuring about these types of accidents [in the past] is that the teams do share their information. It's a very different environment to the one we work in when we talk about performance and there is a lot of collaboration and sharing out of various bits of analysis.
"The bigger teams are better placed to contribute to those areas of analysis, and hopefully there will be a lot to learn from it so we can make sure that the next time [there is an accident like that] we are not completely reliant on good fortune not to have someone seriously injured.
A stark reminder
Of course, there will always be a limit to how safe motorsport can be. Racing F1 cars around a circuit at speeds of over 200mph will always be dangerous and the laws of physics still apply regardless of how safe the cars become.
"It is a real stark reminder just how dangerous this sport can be -- the speeds that we are travelling, the energy that we are carrying when we are travelling at those speeds," Hamilton said. "The FIA has done an amazing job, but we can't stop where we are, we've got to keep on trying to improve. That's what also makes this sport great. We are constantly evolving.
"But it is still a dangerous sport. I'm sure there are people who tuned in who have never seen something like that and it just shows that those things can happen. I think we are aware of that as racing drivers, the risks we take. Now everyone else is."
That the other 19 drivers got back into their cars is also hard to comprehend. All of them will have known how lucky Grosjean was and how easily a slightly different course of events could have resulted in a very different outcome. Yet all of them strapped themselves back into cars laden with 100kg of fuel and raced into the night.
"For the drivers to get back into the car needs a lot of courage, and this is what these guys do" Wolff said. "Too often we forget that this is a dangerous sport and that these guys race around tracks at more than 350km/h (217mph).
"Today's modern camera technology and wide angles don't really show that speed, but you can see what happens. It has always been dangerous and even with today's safety structures it is still a very dangerous sport and we need to optimise from there.
"It's what makes the sport's best drivers gladiators in the most sophisticated machines, but for everybody who saw the pictures today it was difficult. When we saw Romain getting out of the car it was a big relief -- obviously second-degree burns is still bad enough -- but it could have been terribly worse."