The new and improved NIST Dragon's LAIR (Lofting and Ignition Research) facility

Abstract

SUMMARY Several studies suggest that the firebrands are a major cause of structural ignition of Wildland–Urban Interface fires in USA and Australia. For 40 years, past firebrand studies have focused on how far firebrands fly and do not assess the vulnerabilities of structures to ignition from firebrand showers. The development of the National Institute of Standards and Technology (NIST) Dragon has allowed the quantification of structure ignition vulnerabilities of full‐scale building assemblies. Full‐scale tests are necessary to highlight vulnerabilities of structures to ignition under firebrand attack, whereas bench‐scale test methods afford the capability to test new firebrand‐resistant technologies and may serve as the basis for new standard testing methodologies. To this end, the present investigation was undertaken to construct a new and improved Dragon's Lofting and Ignition Research facility. This entailed removing the NIST Baby Dragon from the wind tunnel facility and inserting the new and improved NIST continuous feed Baby Dragon. The unique feature of the continuous feed Baby Dragon, over the current NIST Baby Dragon, is the capability to produce a constant firebrand shower in order to expose building materials to continual firebrand bombardment. The efficacy of the new experimental facility to determine ignition regime maps of building materials exposed to wind‐driven firebrand showers is presented. Specifically, ignition regime maps are presented as a function of continuous firebrand generation rate, wind tunnel speed, and cedar moisture content. Copyright © 2011 John Wiley & Sons, Ltd.

Exposing Decking Assemblies to Continuous Wind-Driven Firebrand Showers

“…When comparing the mass required for Cedar crevice ignition of Manzello and Suzuki [42], to the deck results reported here, it was observed that the decking assemblies required significantly more mass of firebrands to produce flaming ignition. This was expected since the firebrands were not allowed to accumulate in such a tight, V-shaped crevice as the bench-scale experiments, resulting in larger heat losses (see Equation 1).…”

“…The net heat flux, q" net to the fuel bed from the accumulated firebrands is given as (see Figure 7): where q" FB is the heat flux from the firebrands, q" conv is the convective heat flux, q" rad is the radiative heat flux, " m  is the mass loss rate per unit area, and L v is the heat of gasification of cedar. The ignition time for thermally thick materials is known to be proportional to the room-temperature density, ρ, of the material and inversely proportional to the square of the net heat flux to the fuel bed, q" net [41][42] Therefore, for wood with similar moisture content, and the same net heat flux, the wood with the highest density is expected to take the longest time to ignite. The densities were measured for the three wood types, and the Douglas-Fir boards (534 kg/m 3 ) were found to have the largest density, followed by Redwood boards (437 kg/m 3 ), and then Cedar boards (361 kg/m 3 ).…”

“…The Dragon's LAIR facility has now been upgraded to include the NIST Continuous Feed Baby Dragon. The interested reader is referred elsewhere for a very detailed description of the new and improved Dragon's LAIR facility [42]; capability is presented briefly below. The success of the new bench-scale Continuous Feed Baby Dragon provided the impetus to construct the full-scale Continuous Feed Firebrand Generator presented in this report; the full-scale Continuous Feed Firebrand Generator was scaled up from this bench scale device.…”

“…The efficacy of the Dragon's LAIR facility to determine ignition regime maps of building materials exposed to continuous wind-driven firebrand showers has been determined [42]. To do this, Cedar crevices were constructed for ignition testing.…”

The Performance of Concrete Tile and Terracotta Tile Roofing Assemblies Exposed to Wind-Driven Firebrand Showers

“…Clearly, full-scale experiments are required to observe vulnerabilities of structural components to wind-driven firebrand showers and, yet bench scale test methods afford the capability to evaluate firebrand resistant technologies such as firebrand resistant sarking. The bench scale Dragon's LAIR (Lofting and Ignition Research) facility, described in detail elsewhere [13], is a unique experimental platform to evaluate sarking material performance to wind-driven firebrand showers. Once promising technologies are identified, full scale tests, similar to those described in this paper, could be conducted to test the performance to provide firebrand resistant tile roofing assemblies.…”