LONDON (Reuters) - Formula One cars will continue to use titanium skid blocks for the rest of the season after testing stainless steel alternatives to reduce the risk of trackside grass fires.

Second practice at Suzuka in April was stopped four times by red flags, twice because of trackside fires set by sparks from cars.

Practice at last year's Chinese Grand Prix in Shanghai was also interrupted by a red flag when a small grass fire broke out at trackside.

The governing FIA said on Wednesday that the titanium skid blocks beneath the car, which spark on contact with the asphalt or kerbs, would remain the mandated material but teams would also be required to have stainless steel ones available.

It said this was because "they may become mandatory if similar grass fire incidents occur as seen in Suzuka early this year.

"Additional testing of stainless steel skid blocks will be conducted at selected events throughout the season to support further evaluation."

The decision followed analysis of stainless steel blocks tested at last weekend's Spanish Grand Prix.

(Reporting by Alan Baldwin, editing by Christian Radnedge)