The second free practice session for the Malaysia Grand Prix was brought to an abrupt premature end following a big crash for Haas driver Romain Grosjean.
Grosjean's right rear tyre exploded after being sliced open by a raised drain cover in turn 12 at the Sepang International Circuit. Grosjean was sent spinning off into the barrier, but fortunately was unharmed by the impact.
"I have just seen the footage and apparently a drain came out," Grosjean said. "It was on the racing line and I had a big hit and impact on rear right.
"I was spinning and heading to the wall, so not ideal.
"I see the tyre is not there any more," he noted. "I’m feeling sorry for the boys, as they’ve got to work hard to repair the car. But I know they will do it and in a good way.
"I am good, I am fine," he confirmed after a visit to the medical centre. "That is the most important thing."
Replays suggested that the drain cover had been prised open by the ground effect from cars running ahead of Grosjean on track. It's not something that should ever happen at a permanent race track such as Sepang.
"They need to sort things out," said Grosjean. "It is a shame. Hopefully we find a good set-up for tomorrow and the drains stay in place."
Haas F1 team principal Guenther Steiner agreed that the drain cover failure was unacceptable in modern motorsport.
"Things like this in 2017 shouldn't happen on a permanent circuit. They shouldn't happen on any circuit," he complained.
"This is in my opinion not acceptable, it is not up to the standards," he continued.
"What we need to make sure is how to improve that doesn't happen again in the race, because in the race this would have been a bigger disaster."
Williams driver Felipe Massa was running behind Grosjean at the time of the accident.
"As I was starting my long run the session was red flagged," he said. "I’m glad that Grosjean wasn’t harmed in the incident; I was right behind him so saw it happen.
"The first thing I thought was I had already a spring on my head," he said, recalling his accident in the 2009 Hungarian Grand Prix. "Maybe a drain is a little bit too much!
"Fortunately this time, nothing flew over my car," he said. "I think the FIA need to control everything in the right way, so we don't have these things anymore."
With the session not restarting after Grosjean's accident, FIA officials were quickly on the scene to examine the track. The drainage cover was ground down and welded shut again as they watched.
"One drain grate has come up. It just seems that it has broken away," said race director Charlie Whiting. "We have to get it fixed for tomorrow, of course.
"It’s an inspection hatch. They’re normally bolted and welded but that one has broken away," he explained. "They’ve probably been welded for a long time I expect and have got a bit fatigued.
"We will re-weld those, and then tonight the guys will have to check everything."
"I'm pretty confident we won't see a repeat issue," added Red Bull boss Christian Horner.