Deemed To Satisfy (DtS) Versus Performance Solutions

Deemed to satisfy solutions 

A deemed to satisfy solution or DtS is a solution designed to satisfy the build’s performance requirements by satisfying the relevant prescriptive BCA provisions.  

Let’s say you were to create a DtS solution for a new, 7-storey building that ensures a safe travel distance and distance between exits. Your DtS solution would include ensuring 20 metres to a single exit and 20 metres to a point of choice where multiple exits are available. With DtS, there is no prescribed angle that the exits need to be from each other. This can lead to an acute angle between exits for a certain distance. As a result, a single fire event can knock out the point of choice. You should consider possibilities like this when designing and assessing a DtS solution. 

Additionally, DtS does not consider subsequent fit-out works extending those distances in open-plan layouts. As a result, you must think ahead to future proof the solution. For example, design to 2/3 of the travel distance where you anticipate a subsequent fit-out. 

Performance solutions 

A performance solution provides a tailored solution that meets the performance requirements of the building.  

Overall, performance solutions consider more scenarios than DtS and do not take the same shortcuts. For example, performance solutions may consider corridor dimensions and their bearing on safe travel distances. In contrast, a DtS solution gives little regard to the path of travel dimensions and the effects of smoke logging. Performance solutions also encourage us to question appropriate levels of safety for all people. For example, an able-bodied person typically moves quicker than someone in a wheelchair. A performance solution may factor this into design calculations to achieve a suitable travel distance for all. 

However, the BCA allows performance to combine with DtS. This combination can lead to a reduced level of safety, as a performance solution for travel distances may be combined with DtS provisions. And a DtS solution would not consider the difference in movement speed between an able-bodied person and a wheelchair user. We must ask: What can we do to ensure a wheelchair user has the same chance of survival in a fire as someone who can use their legs? 

Additionally, real fire events show it is inaccurate to assume people on the fire affected floor will evacuate safely before other floors start to evacuate. A performance solution considers such research in determining how long it takes before people start to evacuate. It also considers the effects of queuing at exits, while DtS does neither. 

Furthermore, performance solutions consider fire load. In contrast, DtS would consider fire load solely under the class of the building. However, performance solutions allow for a more detailed assessment. 

Let’s say you were to create a performance solution for a new, 8-storey building. As in the previous example, the objective is to ensure a safe travel distance and distance between exits. Your performance solution must directly examine the building’s performance against the performance requirements.  

When should you use a DtS solution? 

Typically, you should apply a DtS solution when taking a more traditional approach. In instances where there is no ambiguity or contention relating to the interpretation of the DtS provisions.  

The DtS provisions’ condensed format and aim to be a catch-all for every building design can lead to misappropriation. As a result, a building design can fit like a square peg in a DtS round hole. To ensure that doesn’t happen, consider the building design’s satisfaction of the relevant DtS provisions and performance requirements.  

When should you use a performance solution? 

Where seeking innovation, a performance solution is the best option. Even if the design is complex, the performance solution is easy to understand. The performance solution must be testable and operational. It should be manageable and the best solution throughout the building’s lifecycle.  

Performance solutions often raise the issue of risk, but when performed correctly, they can produce a safer, less risky outcome.  

The middle ground solution 

The UK offers an additional approach to demonstrate compliance. Prescriptive provisions similar to DtS and fire engineered performance solutions are still an option. However, a “middle ground” solution is offered under BS 9999 / BS 9991. This middle ground solution builds on the DtS provisions by incorporating accepted engineering principles, research and risk assessment.  

In recent years, these principles have been limitedly utilised in Australia. For example, concessions are given to sprinkler-protected low-rise residential buildings for fire resistance levels and travel distances. However, there is an opportunity to see wider use of such principles to reduce approval time and cost and achieve safer outcomes. 

In Australia, we currently cannot apply universally accepted engineering principles to demonstrate compliance without the aid of a fire engineer. This compliance burden results in easy money for fire engineers. However, it is an inefficient use of their talent and expertise. 

Lifecycle assessment 

Domestically, there is a tendency for fire engineering to reduce upfront costs and load these costs 10-fold or more onto the operator through additional management requirements. This is a key example of systematic failure in how Australia administers performance solutions. 

For example, a fire engineer may specify fire curtains with monthly or weekly maintenance requirements to validate the FER. These may reduce upfront costs but increase costs when measured throughout the building’s lifecycle. Therefore, both DtS and performance solutions must accurately consider available resources. Additionally, we should design solutions to be easily digested and effectively managed, with any unreasonable assumptions treated as such.  

A DtS or performance solution must be fit for purpose. It must ensure fire safety. In practice and not solely in theory. Not only at approval time but throughout the building’s lifecycle.