Private bushfire shelter certification

Is a shelter a safe alternative to leaving?

No. The NSW RFS says leaving early, well before a fire threatens, is always the safest option. On the worst fire days, staying is not an option at all.

The ABCB is clear that a shelter cannot serve as a solution on its own. The Victorian Bushfires Royal Commission warned that misplaced reliance on a bunker can be life threatening. A shelter is a backup for when your Bush Fire Survival Plan cannot be carried out safely.

What does the NCC require?

The NCC classes a private bushfire shelter as a Class 10c building. It must stand apart from the house it serves. It must give occupants a tenable environment during a bushfire. Tenable means conditions people can survive in, such as safe air temperature and breathable air.

There is no Deemed-to-Satisfy route. Deemed-to-Satisfy provisions are the standard rules most building work follows. So every shelter needs a performance solution: a design that is proven to achieve the NCC's goals. The ABCB Performance Standard for Private Bushfire Shelters gives the design guidance. It covers siting, the design fire, temperature and toxic gas limits, doors, signage and maintenance.

Who is a shelter suitable for?

The ABCB standard is written for able-bodied adults. It strongly recommends early evacuation for children, older people and people with disabilities. The same goes for people with heart or lung conditions. Even fit adults may find a hot, dark, sealed space hard to cope with.

Siting matters too. The standard sets minimum distances from the house, boundaries, other buildings and fuel such as trees. It also limits how far people must travel from the house to reach the shelter. A shelter built in the wrong place, or one that people cannot reach in time, may fail them.

What approvals are needed in NSW?

NSW Planning advice says a shelter needs a development application and a construction certificate. Council may consult the RFS, because the RFS planning guidelines do not cover private shelters. After that, the shelter is inspected during construction and needs an occupation certificate before use. A prefabricated product still needs a design and evidence that suit your site. A brochure alone is not enough.

What happens after it is built?

A shelter only protects people if it is maintained. The ABCB standard expects a maintenance manual kept inside the shelter. It also recommends practice runs so likely occupants know how to use it. Do not use the shelter for storage or anything else.

Where the standard lets a shelter go

The ABCB Performance Standard puts hard numbers on siting. The shelter must stand at least 6 m from the house, or 1.5 times the height of the house if that figure is larger. It also needs at least 6 m to the lot boundary.

Sheds, carports and similar structures need the same kind of gap: 6 m, or 1.5 times their own height, whichever is more. Other fuel, such as woodpiles, fences, parked cars and gas bottles, has to be kept 6 m away, and the shelter should sit clear of trees and shrubs.

Getting there counts just as much. The standard caps the trip from the house at 20 m, along a path with a non-combustible surface and a clear width of at least 1 m. On a small or narrow lot, these distances can rule a shelter out before a designer is even briefed.

How many people, and for how long?

The minimum design stay is 60 minutes. Designing for a longer stay calls for a specific study of the air supply. The typical event behind that figure covers the period before the fire front arrives, the front itself, burning close by and a safety margin.

Space is set per person: at least 0.75 m² of floor and 1.2 m³ of air volume, under a ceiling no lower than 1.9 m. The inside air must stay at or below 45°C, and any surface people can touch without a guard must not pass 70°C. Carbon monoxide and other toxic gases have their own limits.

The designed headcount is a real ceiling. Each extra person uses up breathable air and shortens the safe stay. Boxes and stored gear take up air as well, which is one reason the standard says a shelter should not double as a storeroom.

Doors, vents and in-ground shelters

The entry must give a clear opening at least 600 mm wide and at least 0.36 m² in area. The door has to latch both open and shut, and people inside must be able to unlock it even when it has been locked from outside. Handles and latches must stay at or below 55°C after fire testing.

Natural ventilation openings must add up to at least 5% of the floor area. A sealed design can use a ventilation system that stays closed until the outside air is safe. On heavily vegetated sites, the standard prefers a second exit, set apart from the main one.

Shelters built above ground and those set into the ground are both covered. An in-ground shelter must also be designed for possible vehicle loads, and it needs a sign at its entrance.

Signs inside and out

A durable sign must stand beside the main access road. Its heading, PRIVATE BUSHFIRE SHELTER, is red on white in letters at least 100 mm tall, and it gives the distance and general direction to the shelter so crews and visitors can find it.

A second sign goes inside, next to the main door or hatch. It lists the designed number of occupants and the designed stay, how to get in and out, how to run any installed equipment and who to call in an emergency. It must also warn that extra people shorten the safe time, and explain when the vents may be opened.

What the certifier needs from your designer

Because shelters have no deemed-to-satisfy route, a construction certificate cannot be issued without a performance solution report. The certifier has to be satisfied that the report follows the NCC process and that the plans show the physical parts of the solution wherever possible.

That NCC process has three parts. First comes a performance-based design brief worked out with the key people involved in the design. Next is analysis and evaluation of the proposal. Last is a final report confirming the performance requirements are met. Under the standard, the designer can work from first principles of fire engineering, or pair that engineering with exposure testing, such as testing the door to AS 1530.8.2.