The opening free practice session at the Sochi Autodrom on Friday was delayed because a track sweeper leaked diesel onto the circuit, organisers have confirmed.
The vehicle in question was cleaning the circuit on Thursday evening ahead of practice, but the spillage was not found until ninety minutes before the opening practice session was set to get underway.
An absorbent was used to soak up the diesel, with pressure washers then brought onto the track to remove the spill, with the session delayed by half an hour as a result.
When the session did get underway, turns 7, 8, 9 and 10 were wet, and were still at least damp when the chequered flag fell an hour later, with a number of drivers struggling for grip and running off track in the tricky conditions.
Nico Hulkenberg ended the session with the quickest time for the Sahara Force India team.