Be ready for B-RISK

This is a part of the Fire feature

By Greg Baker and Dr Colleen Wade - 1 October 2012, Build 132

Research in New Zealand is leading to advances in fire engineering design and protection. We look at some of the work under way at BRANZ and the universities.

Figure 1: Polyurethane foam armchair being tested in the furniture calorimeter.

THE MAJOR RESEARCH EFFORT BY BRANZ and The University of Canterbury to develop a risk-informed design fire tool for fire safety engineering is nearing completion with the B-RISK software entering a beta testing phase.

Experimental results ensure accuracy

A practical issue for the research project team has been getting suitable data to test the tool – experimental results that can be compared against the B-RISK modelling prediction.

Recently approved funding from the Ministry of Business, Innovation and Employment has allowed the team to conduct an experimental programme to generate this data.

The B-RISK tool estimates what size fire could occur in a room by populating the room with combustible objects from a database of typical items in buildings.

From this, it simulates how the fire in the room will grow and develop as it spreads among the objects.

B-RISK requires information about each of the objects, such as how easily the item will ignite and how large the associated fire will be.

The experiments are generating data for the modelling of room-scale configurations. Results will be compared with B-RISK predictions for the identical configuration to ensure the accuracy of the new tool.

The experiments involve three materials:

Polyurethane foam – used in upholstered furniture.
Medium-density fibreboard (MDF) – used for cabinetry.
Acrylonitrile butadiene styrene (ABS) – used for casing electronic goods.

The experimental programme uses reaction-to-fire testing equipment in the BRANZ laboratories to undertake a range of experiments:

A series of bench-scale experiments using the cone calorimeter to determine the ignitability of the three materials.
A series of real-scale tests on items made from the three materials in the furniture calorimeter to determine the fire size of each item (see Figure 1). This information will be used as item property data for the modelling of full-scale multi-item layouts in the standard ISO 9705 room.
The same multi-item fire experiments in the ISO 9705 room, to compare the results to the B-RISK predictions.

Spill plumes widen application

The effects of balcony spill plumes are also being included in B-RISK with the assistance of Dr Roger Harrison. Spill plumes occur when smoke from a fire flows beneath an upper balcony construction and mixes with air, increasing the smoke volume as it spills around the balcony edge and rises to the ceiling in the adjacent space (see Figure 2).

The inclusion of spill plumes in B-RISK extends the applicability of the model to large public spaces such as atriums and shopping malls. Overestimating smoke production volumes in these can result in costly mechanical extraction equipment, while underestimation can lead to unsafe conditions in the event of a fire.

Compatible with Code changes

Along with new capability to include uncertainty estimates and sensitivity analysis, the fire design tool has been developed to be compatible with the new Building Code Verification Method (C/VM2) Framework for fire safety design. This allows modelling and calculation demonstrating Building Code compliance to be carried out more efficiently.

The Verification Method ensures more consistent design assumptions and safety outcomes by engineers undertaking performance-based fire design than before – design fire loadings and quantitative performance criteria weren’t previously published.

Launch in early 2013

Following the beta testing phase in the last quarter of 2012 where feedback and input will be sought from potential end-users, BRANZ plans to launch the B-RISK tool with a series of training seminars and workshops in March 2013.

University of Canterbury

Projects associated with the B-RISK fire engineering tool include developing item-to-item fire spread algorithms, including the ability to generate design fire curves, enhancing the model's capability to simulate active fire protection features and determining relevant active fire protection system performance measures to use in the model. Complementary investigations look at the fire risk of buildings, particularly enclosed car-parking structures.

ENGINEERED WOOD AND CONCRETE

In passive and structural fire engineering, the university is focusing on the performance of engineered wood systems such as LVL. This work is part of a larger study that includes small-scale fire testing, large-scale furnace testing at BRANZ and computational modelling.

Recently, furnace tests were carried out on different timber floor systems and post-tensioned beams. The results will create new guidance for designers.

Investigations into the performance of precast prestressed concrete flooring systems has involved numerical modelling of the behaviour of heated flat slabs, single-tee slabs, hollow-core slabs and multi-bay prestressed hollow-core floors.

MODELLING

Research is on-going into improving the National Institute of Standards and Technology’s (NIST) Fire Dynamics Simulator (FDS) computational fluid dynamics model, providing the developers with feedback and data on the solid phase combustion algorithms, particularly the melting and burning of foam materials.

Real-scale, replicate fire experiments are used to examine the model’s ability to recreate burn patterns on gypsum wallboard. Comparisons of FDS predictions with experiments on spill plumes and flame radiation will form part of the validation guide in the next release.

enabling secondary beams to be solid web or to have multiple closely spaced web openings
amending the detailing requirements for the floor system to remove impractical requirements such as congestion of reinforcement in the slab panel corners
rewriting the 2006 software to make it more user-friendly.

Victoria University of Wellington

A student is researching the fire safety implications of green or sustainable building features. To date, the most negative impacts appear to be atriums and double-skin façades. Atriums have well developed mitigation measures for fire safety, but double-skin façades do not. Features such as low volatile organic compound (VOC) paints have positive fire safety impacts, and many have no or little impact.

Researchers have also been working with GNS modelling post-earthquake fire spread in Wellington.