New Delhi, Jan. 27 -- The Australian Open put its Extreme Heat Protocol into play for the second time this tournament because of searing heat on Tuesday.

The policy uses a 'Heat Stress Scale' ranging from 1 to 5 and taking into account the air temperature, radiant heat, humidity and wind speed.

When the index hits 5, play is suspended on outside courts and the roof is closed on the three arenas at Melbourne Park which have retractable covers.

That happened on Saturday during Jannik Sinner's match on the center court.

The roof was open to start Day 10 but the measures were imposed again after Aryna Sabalenka beat Iva Jovic 6-3, 6-0. The roof was closed for the next match, a men's quarterfinal between No. 3 Alexander Zverev and American...