Photos | Questions over why Waterfall hazard reduction burn became more like a summer wildfire

The weekend bushfire hazard reduction burn in Royal National Park which escaped containment lines will be reviewed by the agencies involved so that lessons can be learned for the future.

Firefighters were continuing to combat the bushfire on Kangaroo Ridge near Princes Highway, Waterfall, on Monday with assistance from the 737 Large Air Tanker Marie Bashir and other water bombing aircraft.

A Rural Fire Service statement said there was still no threat to properties, but smoke was likely to affect areas to the north including Heathcote and Engadine.

Heathcote East residents David and Michael Oblati captured graphic images of the water bombers at work on Sunday (see gallery above).

Sutherland Shire RFS Inspector Scott Deller said hazard reduction burns were risky and were reviewed when they didn't go to plan.

"Introducing fire into the landscape is inherently risky, particularly as we head towards the warmer part of the year," Inspector Deller said in a Facebook post.

"When implementing such activities, multiple controls are applied both in the planning and implementation stage, to reduce and manage the risk," Inspector Deller said.

"One of the main controls utilised is referred to as a 'prescription'. A prescription is a set of conditions or parameters that provide limits or thresholds on whether an activity should proceed or not, based on expected fire behaviour.

"A burn prescription often includes parameters such as fuel dryness, in addition to diurnal weather conditions peaks and troughs, such as temperature, humidity, wind direction and strength.

"Choosing a prescription is a complex mix of the right ingredients - with flexibility applied by balancing and offsetting various conditions, which are highly variable.

"An example of flexibility is burning when conditions are windy, but only if fuels are moist and the fuel load are light.

"If fuels loads are high and conditions are dry, you need to be more cautious, particularly with lower humidity and changes in wind strength."

Inspector Deller said another important component when introducing fire into the landscape was how the fire was ignited.

"Lighting a line of fire will result in fire reaching its intensity and rate of spread quickly, where if multiple spots are introduced instead, it will spread slower.

"Looking at recent events locally, there will be be community scrutiny surrounding the safe implementation of hazard reduction burning, as there should be!

"In any event when things don't go to plan, it will be subject to review by the various agencies who participated. The aim of which is to understand what occurred and to ensure that reoccurrence is avoided in the future.

"A week ago a hazard reduction burn was implemented at Woronora Heights, where crews worked hard to get it to burn, a week later, a hazard reduction escapes with conditions more akin to a summer wildfire.

"It is a timely reminder, despite being in a La-Nina year, that fires in the landscape can still be problematic."