By Abhishek and Takle
SPA-FRANCORCHAMPS, Belgium, Aug 26 (Reuters) - The 'halo' cockpit protection device received a cautious thumbs-up from the drivers who experimented with it in Friday's opening practice session ahead of the Belgian Formula One Grand Prix.
Four drivers, including title hopeful Nico Rosberg, briefly ran with the device fitted to their cars in the opening 90-minute session at the Spa circuit, evaluating it for a possible introduction in 2018.
The German set the fastest time of the morning while running the device on his Mercedes but Red Bull's Daniel Ricciardo, Toro Rosso's Carlos Sainz and Force India's Nico Hulkenberg only completed sole installation laps.
"It doesn't disturb me when driving," Rosberg told reporters. "I could go fast straight away and even set the best time of the session with it this morning so I think that was a success."
The halo is fixed to the cockpit at three points including a central pillar in front of the driver that supports a protective loop above his head.
It is designed to deflect large debris and objects such as bouncing wheels, with the sport's governing body estimating it boosts the chance of driver survival by 17 percent.
The push for increased head protection has gathered urgency following the deaths last year of Briton Justin Wilson, hit by debris in an IndyCar crash, and Frenchman Jules Bianchi who had suffered ultimately fatal injuries at the 2014 Japanese Grand Prix.
But Formula One's strategy group voted last month to postpone its introduction by a year to 2018 as teams felt drivers did not have enough experience with the device fitted to their cars.
They are also continuing to evaluate other options that could be introduced if they prove more effective.
One of the concerns about the halo was visibility at undulating tracks with extreme elevation changes like the daunting 7km-long Spa layout but drivers reported no problems on Friday.
"Through Eau Rouge ... you can see perfectly how the corner goes," said Sainz.
For Hulkenberg, who had opposed the halo, it took some getting used to. "It felt weird," he said.
Teams will continue to test the device later in the season.
(Editing by Tony Jimenez)