External fire plumes from mass timber compartment fires—Comparison to test methods for regulatory compliance of façades

Abstract

Post‐flashover fires inherently lead to external fire plumes, constituting a hazard for rapid fire spread over façades. As multi‐storey mass timber buildings with internal visible timber surfaces become more common, there are concerns that such buildings would produce larger external plumes and hazards (assuming all other parameters equal). The literature reveals only indications of this, and how the actual exposure relates to different test methods for assessment is unknown. Here we utilise a series of full‐scale mass timber compartment tests to quantify the exposure to the external façade. An incombustible external façade is instrumented with gauges at positions corresponding to reference data from several different assessment methods. The results show that there is an increase in plume duration, height, and temperatures when increasing the areas of exposed timber, but that this increase is less for normal‐ to large‐opening compartments, than was previously seen in small‐opening compartments. Also, normal variations in external wind speed have a larger influence on plume heights than the effect of doubling exposed timber surfaces. Test methods used for regulatory compliance differ significantly not only in exposure but also in pass/fail criteria. The proposed European large exposure method and the BS8414 method exhibit exposures on par with the severe end of what could be expected from mass timber compartments, whereas methods like SP Fire 105 and Lepir II produce significantly less severe plumes. However, the safety level is always a combination of exposure and assessment criteria. This data can help justify assessment criteria from a performance perspective.

Impact of ventilation on the fire dynamics of an open‐plan compartment with exposed timber ceiling and columns: CodeRed #02

“…With the aim to understand the impact of the observed external flaming in fire safety design of timber buildings, the external temperature data gathered during CodeRed #01 and #02 has also been plotted alongside temperature data collected from the testing of facades (without a combustible façade) to the proposed harmonised European façade test, which is similar to BS 8414. This comparison follows previous work of RISE 20 from other timber framed experiments and is presented graphically in Figure 21. The proposed EU test temperatures were read 50 mm offset from the façade, whereas CodeRed temperatures were 300 mm offset.…”

“…External gas temperature development throughout the first 30 minutes of CodeRed #01 and CodeRed #02 and a comparison to the proposed European harmonised façade test 20 with an inert façade. The grey triangles indicate the position of the working thermocouples.…”

Fire research for timber structures

“…The second article includes a comparison of the thermal exposure from external fire plumes in compartment fire tests with façade test methods used in Europe including the European test methodology under development 2 . In the compartment tests, between 43% and 78% of the surfaces were exposed mass timber.…”

“…The second article includes a comparison of the thermal exposure from external fire plumes in compartment fire tests with façade test methods used in Europe including the European test methodology under development. 2 In the compartment tests, between 43% and 78% of the surfaces were exposed mass timber. The main conclusion was that the thermal exposure from the external fire plumes corresponded best with the British BS8414 façade fire testing method and the European test method under development.…”

A building information modeling‐fire dynamics simulation integrated framework for the simulation of passive fire protection in a mid‐scale cross‐laminated timber compartment: Numerical implementation and benchmarking

“…Several studies conducted experimental fire tests in CLT compartments with different test methods and various scales. For example, Just et al 27 conducted a full-scale compartment test of a two-story CLT building to study delamination behavior of CLT and consequences in compartments with realistic ventilation conditions. Su et al 28 quantified the contribution of CLT building elements to fullscale compartment fires and characterized the effect of gypsum board on delaying or preventing involvement of the CLT elements in the fire under varied ventilation conditions.…”