Wildfires that spread into wildland–urban interface (WUI) communities present significant challenges on several fronts. In the United States, the WUI accounts for a significant portion of wildland fire suppression and wildland fuel treatment costs. Methods to reduce structure losses are focussed on fuel treatments in either wildland fuels or residential fuels. There is a need for a well-characterised, systematic testing of these approaches across a range of community and structure types and fire conditions. Laboratory experiments, field measurements and fire behaviour models can be used to better determine the exposure conditions faced by communities and structures. The outcome of such an effort would be proven fuel treatment techniques for wildland and residential fuels, risk assessment strategies, economic cost analysis models, and test methods with representative exposure conditions for fire-resistant building designs and materials.

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A series of real-scale fire experiments were performed to determine the size and mass distribution of firebrands generated from Douglas-fir (Pseudotsuga menziesii) trees. The experiments were performed in the Large Fire Laboratory at the National Institute of Standards and Technology. The Douglas-fir trees used for the experiments ranged in total height from 2.6 to 5.2 m and the tree moisture content was varied. An array of pans filled with water was used to collect the firebrands that were generated from the burning trees. This ensured that firebrands would be quenched as soon as they made contact with the pans. The firebrands were subsequently dried and the sizes were measured using callipers and the dry mass was determined using a precision balance. For all experiments performed, the firebrands were cylindrical in shape. The average firebrand size measured from the 2.6-m Douglas-fir trees was 3 mm in diameter, 40 mm in length. The average firebrand size measured for the 5.2-m Douglas-fir trees was 4 mm in diameter with a length of 53 mm. The mass distribution of firebrands produced from two different tree sizes under similar tree moisture levels was similar. The only noticeable difference occurred in the largest mass class. Firebrands with masses up to 3.5 g to 3.7 g were observed for the larger tree height used (5.2 m). The surface area of the firebrands scaled with firebrand weight.

EXECUTIVE SUMMARYThe 3 Megawatt Heat Release Rate Facility (3MWHRRF) was developed at the National Institute of Standards and Technology (NIST) as a first step toward having broad capabilities for making quantitative large scale fire measurements. Such capabilities will be used at NIST to validate fire models and to develop sub-grid models. It will also serve to provide a data base for studying a broader range of fire phenomena, and to address issues related to material acceptance and fire codes. An equally important objective is to provide templates for use by other laboratories including commercial testing facilities to improve the quality of their data.Heat release is the result of the combustion of a fuel with the oxygen in air. The fuels of primary interest are those found in constructed facilities and include wood, plastics, foam materials used in furnishings (such as polyurethane), wire insulation (such as polyvinyl chloride), and carpet materials (such as nylon).The rate at which heat is released is the single most important quantity in terms of fire safety. Thus it is important that this measurement be made in a quantitative manner. It is a key predictor of the hazard of a fire, directly related to the rate at which heat and toxic gases build up in a compartment or the rate at which they are driven into more remote spaces. Heat release rates on the order of 1 MW to 3 MW are typical in a room that is flashed over or from a single large object such as a bed or sofa.It is important that heat release rate measurements be made accurately because fire regulations are frequently based on peak rates of heat release. Testing laboratories must be confident that the objects tested pass the required regulation and manufacturers need accurate information in defining the fire safety characteristics of their products. A second need for accurate heat release rate data is for the development of quantitative models for predicting heat release rate. In comparing a fire experiment and a model prediction, it is essential that the heat release rate measurement have an estimated uncertainty.The 3MWHRRF developed at NIST meets the needs described above for objects that can be placed under the 6 m × 6 m hood, which is approximately 4 m above the floor, or for enclosures whose effluent can all be directed into the hood. It is capable of measuring heat release rates in the range of 0.10 MW to 3.0 MW including brief peaks as high as 5 MW. As documented in this publication, the expanded uncertainty (95 % confidence interval) is 11 % of the heat release rate for fire sizes larger than 400 kW. The response time of the system is such that it can accurately resolve dynamic heat release rate events of 15 seconds or more.This document is intended to serve as a description of the NIST 3 Megawatt Heat Release Rate Facility and as an operations manual. It is also intended to serve as a general guide for implementing, operating and maintaining quality control of similar quantitative large scale heat release rate measurement facilities. The m...

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