Sutherland Shire RFS acting superintendent Andrew Pinfold said people needed to be aware of warnings issued through the media and be prepared to abandon their properties before fires broke out.

"The advice is to leave and leave early,'' Mr Pinfold said. "On days of extreme and catastrophic fire danger ratings the safest option is to leave.''

The service has prepared a bushfire survival plan available online or at the Heathcote control centre. The plan explains how best to prepare homes against bushfire, but warns that residents should leave home before fires broke out during ``catastrophic'' conditions.

Fire danger signs capable of displaying catastrophic fire danger warnings will be installed in Sutherland Shire suburbs in coming weeks.

Mr Pinfold said Sutherland Shire RFS had started to replace old signs.

"There are about 470 of them being installed throughout the state,'' he said. "They will replace existing ones.''

He said the new signs were based on a national standard established after the Victorian bushfire disaster in February.

RFS inspector Martyn Kiellor said bushfires at Como and Jannali in 1994 were the last time Sutherland Shire residents experienced catastrophic bushfire conditions.

"The old signs used to stop at "extreme'', but the fire danger can get considerably worse than extreme,'' Mr Kiellor said.

Mr Kiellor said the signs could be used as an indication of how difficult it would be to contain fires that broke out and that catastrophic fires would be uncontrollable.

"Residents need to leave early. They need to appreciate the extreme fire danger and catastrophic fire danger,'' Mr Kiellor said. "Even if they've done all the precautions it's still not really going to be safe to stay and defend it.''

Details: Rural Fire Service