Images of the 2017 Grenfell Tower fire in London remain stark and sobering in the minds of many: flames tearing up and across the exterior façade of the residential high-rise from their source on the fourth floor, engulfing the 24-storey building at devastating and deadly speed.

Closer to home, the 2023 fire at Loafers Lodge in Wellington – while very different in nature from Grenfell – reinforced how the composition and behaviour of smoke in multi-storey buildings with complex interior compartments can cause tragedy.

‘Unfortunately, fire doesn’t normally confine itself to the individual materials, components or fittings that make up a building. Both Grenfell and Loafers showed how the spread and behaviour of fire and smoke in buildings are governed by multiple interactions happening at a building-wide scale,’ says Peter Whiting, Senior Fire Engineer at BRANZ.

‘However, fire testing in the laboratory has centred mainly on small components and sub-assemblies, primarily because constraints on space haven’t allowed full-scale testing to happen.’ Earlier this year, that changed.

Fire science at scale

In June, BRANZ opened a state-of-the-art fire laboratory at its Judgeford campus near Wellington. The lab is one of the few facilities in the southern hemisphere capable of fire-testing buildings up to three storeys high – enabling the assessment of fire risk and behaviour at a real-world scale.

Key to this capability is a large open burn area and height-adjustable burn hood designed for a sustained fire output of 10 MW.

‘The open burn facility enables us to conduct reaction-to-fire tests on complete multi-storey, multi-compartment assemblies – including all components, linings, fittings and ventilation systems,’ explains Peter. ‘We can test whole buildings and other complete specimens such as passenger transport vehicles.’

Specimens for testing can be built in situ or brought in from off site. Cranes can be manoeuvred underneath the hood to position specimens. The height of the burn hood can be adjusted to ensure accurate calorimetry (measurement of a fire’s size and growth rate).

‘This flexibility – in particular, adjusting the orientation of the specimen – is critical for comprehensive reaction-to-fire testing,’ adds Peter.

Once a burn is under way, multiple instruments and sensors continually feed data to two data-logging cabinets. This gives researchers and clients a wealth of data for analysis and extrapolation.

Testing the outside inside

Complementing the open burn hood are two new façade rigs. At 10 metres high, they allow BRANZ fire engineers to test at full scale how fire spreads up the outside of multi-storey buildings.

‘That’s the Grenfell scenario. We test to the British standard BS 8414, which is the standard test method used for determining the fire safety of complete cladding systems. We use the rigs to check that the composition of a cladding system won’t cause fire to spread up the façade,’ says Peter.

The two side-by-side rigs comprise a main face and a shorter return wall. The junction between the walls exaggerates combustion (as heat radiates back towards each wall) and is an important feature of the test method.

Sensors measure the temperature across and within the specimen being tested, providing a comprehensive evaluation of its fire response from top to bottom.

The rigs are located inside the laboratory, so tests aren’t weather-dependent.

‘However, façade testing provides only part of the answer,’ Peter adds.

‘It doesn’t address how fire spreads within a building and possibly leads to a façade fire – or how a fire starting on the outside might spread inside.’

Buying critical time

Understanding the fire resistance properties of materials and structures such as floors and walls is key to fire-safe design. Materials that effectively resist the spread of fire can buy occupants valuable time to make themselves safe.

The new BRANZ fire lab features three gas-fired furnaces for fire resistance testing.

A standard-sized main furnace tests vertical specimens of up to 3 metres wide and 3 metres high and horizontal structures of up to 3 metres wide and 4 metres deep. It allows BRANZ to conduct regular fire tests or tests on much more severe hydrocarbon-fuelled fires.

An oversized furnace tests specimens up to 4 metres wide and 3 metres high when positioned vertically and 4 metres wide and 5 metres deep when positioned horizontally. As well as accommodating larger specimens, the oversized furnace enables engineers to gather data that can be extrapolated to predict the likely fire performance of even larger specimens – analysis known as fire assessment.

‘If required, we can extend the oversized furnace even further – up to 4 metres high for vertical samples and 6 metres wide for horizontal samples. This is useful for testing extra-large or awkwardly shaped structures such as roller shutters or oversized doors,’ Peter says.

A smaller pilot furnace is used to test specimens of up to 2 metres by 2 metres, horizontally or vertically, and for testing variations in components such as different types of fire door hardware.

Future-proofed

‘Combined, these facilities allow us to observe fire behaviour and gather comprehensive data to inform fire safety standards based on full-scale real-world scenarios. Grenfell and Loafers have reinforced how critical that need is,’ Peter says.

‘We’re now positioned to serve the industry decades into the future, as manufacturers, architects and designers innovate with building materials and systems in the interests of sustainability and other market drivers.

‘We have the space and facilities to build, store and test full-scale specimens – and ensure client confidentiality throughout.’

The BRANZ fire lab is designed as a collaborative space where researchers and product innovators from Aotearoa New Zealand and overseas can work alongside BRANZ’s specialists to advance fire science.