The 28-year-old rookie flew sideways into a tyre wall at the Hungaroring after the rear wing of his Jordan sheared off as he powered down the straight out of turn four at an estimated 240 kph.
The car veered off the track, careering out of control backwards across a grassy run-off and pulverised the tyre wall as nearby photographers were showered in dust and debris.
The session, with 14 minutes on the clock, was halted immediately.
The Briton was guided out of his smouldering car but was able to sit up after being helped on to a stretcher. He then removed his own helmet and waved before being taken by ambulance to the circuit medical centre.
He was flown by helicopter to hospital.
"We've just had very good news from the professor (Sid Watkins, the FIA safety delegate) that Ralph is now going just for a scan as a precautionary measure," said team boss Eddie Jordan.
"He has a slight pain in his foot but other than that he is in good condition and is very much aware of what is happening. They've just taken precautionary
There was no immediate word on whether Firman would be cleared to race on Sunday. BAR's British driver Jenson Button missed the Monaco Grand Prix in June after suffering a similar heavy impact in Saturday practice.
Jordan's third driver in Friday's private testing was Hungarian Zsolt Baumgartner.
Firman's team mate, Italian Giancarlo Fisichella, sat out the rest of the first session once it restarted but returned to the track for the second to complete 14 laps.
Germany's Ralf Schumacher, in a Williams, was the fastest driver on track with a lap of one minute 21.939 seconds in hot conditions. Spaniard Fernando Alonso set the pace for Renault in the first session with a lap of 1:22.950.
Ralf's older brother Michael, Ferrari's world champion and overall leader with four races remaining, was second fastest 0.374 of a second slower, with team mate Rubens Barrichello third.
Colombian Juan Pablo Montoya, Schumacher's closest rival six points adrift of the German, was fourth fastest.
McLaren's Kimi Raikkonen, third overall and nine points behind Schumacher, suffered a blown engine in the second session.