The planned hazard reductions at Endeavour Nursing Home in Springwood and at Marges/Elizabeth Lookouts in Glenbrook have been postponed until further notice.
RFS Deputy Commissioner Rob Rogers said all Sydney hazard reductions had been cancelled for the weekend as the fire service tried to get the delicate balance between completing important hazard reduction work and minimising the potential health impacts of smoke to the community.
"Conditions have been suitable for burning in recent days and weeks but a large and stable air mass over much of the state has resulted in smoke settling in many areas, and often for several days," he said.
"Forecast winds which would have cleared the smoke away from population centres have not eventuated. This is despite no new burns being undertaken in the past 48 hours."
The decision to postpone hazard reduction was made in consultation with National Parks and Wildlife Service, and Fire and Rescue NSW.
"We understand that this decision may cause some frustration with brigades who are keen to complete this work and improve protection for their local communities," Deputy Commissioner Rogers said.
"However, we also appreciate it is a delicate balance between getting this important protection work complete and minimising the potential health impacts of smoke on the community."
The mid and lower Mountains has been a haze of smoke from hazard reductions over last weekend.
Residents have been warned not to enter any closed area or area with fire and to keep windows shut to avoid the after effects from the smoke.
Crews from the National Parks Service, the NSW Rural Fire Service and Fire and Rescue undertook hazard reduction burns from last Friday. Over last weekend the 22 hectare Marges and Elizabeth Lookouts burn affected Mitchells Pass in Blaxland, as well as Surveyor Abbot Drive, Olivet Street and Barnet Street in Glenbrook.
A larger National Parks hazard reduction started on Sunday May 19 involving a 3300 hectare burn on Lawson Ridge using fire vehicles in Lawson streets and two helicopters.
A Parks spokesman said smoke may be present for some time afterwards and "may affect mid Mountains townships including Lawson, Hazelbrook and Springwood". Smoke has also enveloped the Lower Mountains.
The burn is part of ongoing fire management to protect assets and property in the Mountains.
A second stage of a burn had been planned to continue at Marges/Elizabeth Lookout later this week with eleven hectares scheduled for the burn.
A 10 hectare burn, which was set to start on Thursday May 23, near Endeavour Nursing Home on Hawkesbury Rd, Springwood was postponed until Saturday May 25 but an RFS spokeswoman said they had been "postponed until further notice".