Nelson P. Bryner

Comparison of a fractal smoke optics model with light extinction measurements

Abstract Optical cross-sections of carbonaceous aggregates (smoke) formed by combustion sources have been computed based on fractal concepts. Specific extinction depends upon the primary particle size, the structure of the aggregate as represented by the fractal dimension, the fractal prefactor, and the real and imaginary components of the refractive index of the particle material. While the fractal dimension and primary particle diameter are narrowly defined, the refractive index, to which the results are highly sensitive, are disputed. Specific extinction was measured at λ = 450, 630 and 1000 nm in a smoke-filled chamber with an optical path length of 1.0 m that was equipped to continuously monitor both particle mass and number concentration as the smoke aged during a 90–120 min interval. The smoke was generated by the burning of crude oil in a pool fire. Specific extinction at all three values of λ was found to be constant even though the aggregate number concentration decreases by a factor of 24 owing to cluster-cluster aggregation. The refractive indices at several wavelengths that are Cequired to give agreement with the measured specific extinction are compared with literature values. The inadequacy of Mie theory for spheres in predicting the optical properties of soot aggregates is reiterated.

Use of the electrostatic classification method to size 0.1 micrometer SRM particles - A feasibility study

The use of the electrostatic classification method for sizing monodisperse 0.1 μm polystyrene latex (PSL) spheres has been investigated experimentally. The objective was to determine the feasibility of using electrostatic classification as a standard method of particle sizing in the development of a 0.1 μm particle diameter Standard Reference Material (SRM). The mean particle diameter was calculated from a measurement of the mean electrical mobility of the PSL spheres as an aerosol using an electrostatic classifier. The performance of the classifier was investigated by measuring its transfer function, conducting a sensitivity analysis to verify the governing theoretical relationships, measuring the repeatability of particle sizing, and sizing NIST SRM 1691, 0.269 μm and NIST SRM 1690, 0.895 μm particles. Investigations of the aerosol generator’s performance focused on the effect of impurities in the particle-suspending liquid on the resulting particle diameter. The uncertainty in particle diameter determined by electrical mobility measurements is found to be −3.3% to +3.0%. The major sources of uncertainty include the flow measurement, the slip correction, and a dependence of particle size on the aerosol flow rate. It was found that the classifier could be calibrated to indicate the correct size to within 0.1% for both SRM particle sizes if the defined classification length is decreased by 1.9%.

Measurement of the 100 nm NIST SRM 1963 by differential mobility analysis

ABSTRACT The number mean diameter of 100 nm NIST Standard Reference Material (SRM) 1963 was measured to be 100.7 nm with an expanded uncertainty at the 95% confidence level of 1.0 nm by measurement with the differential mobility analyzer (DMA). The low level of uncertainty resulted from the use of the 1.0 μm SRM 1690 for calibrating the DMA. The largest single component of the Type B (systematic) uncertainty was a 0.29 nm uncertainty in the calibration diameter. Measurements of the 0.3 μm SRM with the calibrated DMA give results within 0.001 μm of the certified diameter. Results obtained by other investigators using transmission electron microscopy (TEM), angle dependent light scattering, electro-gravitational aerosol balance, and atomic force microscopy are consistent with this DMA value. The 100 nm NIST SRM 1963 and the Japanese 100 nm Calibration Standard are shown to differ by 10% based on TEM analysis and DMA measurements. This size difference has a significant effect on the calibration of scanning s...

Radiometric model of the transmission cell-reciprocal nephelometer

Abstract A radiometric model has been developed to assess the effects of angular truncation, finite size of the detector, and angle response characteristics of the cosine sensor on the measurement of the total scattering coefficient by a transmission cell-reciprocal nephelometer. These effects are computed for monodisperse polystyrene spheres over the size range 0.02–8 μm based on Mie theory and for smoke agglomerates ranging from 10 to 10 7 primary units based on the Fisher-Burford approximation. The accuracy of the model calculations is determined by comparison with exact solutions for the case of a detector with an infinitesimal area and for a finite area detector with a diffuse scattering function. The predicted results are compared with measured results for six different sizes of monodisperse polystyrene sphere aerosols with particle diameters in the range 0.1–2.35 μm. The measurements were carried out as a function of the distance between the laser beam and detector for 1.3 and 2.7 cm diameter cosine sensors. A table of design parameters for making accurate total scattering measurements is obtained for both spheres and agglomerates. An accuracy of ±5% was obtained for spherical particles with diameters ⩽1.1 μm with our TCRN, and we estimate that similar performance would be obtained for smoke agglomerates with up to 3 × 10 3 primary spheres per agglomerate.

Carbon monoxide formation in fires by high-temperature anaerobic wood pyrolysis

Building fire fatalities often occur at locations remote from the room where the fire is actually burning. The majority of these fire deaths are the result of smoke inhalation, primarily due to exposure to carbon monoxide (CO). Although causing nearly 2500 deaths per year in the United States, the mechanisms for the formation of CO in building or enclosure fires remain poorly characterized. In order to test the hypothesis that high concentrations of CO can be generated by pyrolysis of wood in a high-temperature, vitiated environment, a series of natural gas fires, ranging from 40 to 600 kW in heat release rate, were burned inside a reduced-scale enclosure (RSE). The ceiling and upper walls of the RSE were lined with 6.4-mm-thick plywood. During each burn, the concentrations of CO, CO2, and O2 were monitored at two locations within the upper layer. Oxygen calorimetry was used to monitor the total heat release rate for each fire. Vertical temperature profiles for two positions within the enclosure were also recorded. Much higher levels of CO were generated with the wood-lined upper layer than with comparable fires fueled only by natural gas. Volume concentrations as high as 14% were observed. The fires with wood in the upper layer had higher heat release rates and depressed upper-layer temperatures. The major conclusions of this work based on the experimental findings are (1) the pyrolysis of wood in a highly vitiated, high-temperature environment can lead to the generation of very high concentrations of CO in enclosure fires; (2) the overall wood pyrolysis is endothermic for the experimental conditions studied; and (3) the maximum mass loss rate of wood under the experimental conditions is on the order of 10 gs−1 m−2 with the majority of released carbon being converted to a roughly 1:1 mixture of CO and CO2.

A Rayleigh light scattering facility for the investigation of free jets and plumes

A Rayleigh light scattering facility (RLSF) has been developed and successfully used to examine mixing in free jets and buoyant plumes. The RLSF couples laser diagnostics with a cylindrical clean room, test section diameter of 2.4 m and a height of 2.4 m, to monitor the real‐time concentration behavior within turbulent flows. The facility has been carefully designed to minimize interferences of glare and Mie scattering by suppressing background light and removing dust particles. The relatively large working section of the RLSF allows quantitative concentration measurements via Rayleigh light scattering (RLS) in free shear flows entering quiescent surroundings. As a result, RLS measurements are now possible in momentum‐driven flows for conditions which were impossible in the past and in buoyancy‐driven flows for which no previous RLS investigations have been made. Initial measurements of concentration in momentum‐driven jet flows of helium and Freon‐13 and a transitional (momentum‐ to buoyancy‐driven) jet ...

Short-Duration Autoignition Temperature Measurements For Hydrocarbon Fuels Near Heated Metal Surfaces

Abstract An apparatus has been designed, built, and extensively tested for making short-duration autoignition temperature measurements of hydrocarbon fuels under atmospheric pressure conditions where the fuel/air stoichiometry, the nature of the hot metal surface, and the contact time between the fuel/air mixture and the heated surface are well controlled. This approach provides a much more reliable database to establish the importance of fuel structure and surface effects on measured autoignition temperatures than the current ASTM E659 procedure, which involves variable ignition delay times and unspecified stoichiometries for ignition in a heated glass flask. Two series of tests have been conducted: (1) over 1100 individual autoignition temperature determinations for the ignition of 15 hydrocarbon fuels containing 1 to 8 carbon atoms on heated nickel, stainless steel, and titanium surfaces for three different stoichiometries (φ = 0.7, 1.0 and 1.3); and (2)∽ 190 determinations for 10 linear and branched a...

Evaluation of thermal imaging cameras used in fire fighting applications

Thermal imaging cameras are rapidly becoming integral equipment for first responders for use in structure fires. Currently there are no standardized test methods or performance metrics available to the users or manufacturers of these instruments. The Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology (NIST) is developing a testing facility and methods to evaluate the performance of thermal imagers used by fire fighters to search for victims and hot spots in burning structures. The facility will test the performance of currently available imagers and advanced fire detection systems, as well as serve as a test bed for new technology. An evaluation of the performance of different thermal imaging detector technologies under field conditions is also underway. Results of this project will provide a quantifiable physical and scientific basis upon which industry standards for imaging performance, testing protocols and reporting practices related to the performance of thermal imaging cameras can be developed. The background and approach that shape the evaluation procedure for the thermal imagers are the primary focus of this paper.

Realizing the Vision of Smart Fire Fighting

Fires in the wildland urban interface are but one of the common challenges faced by todays emergency first responders. For the Yarnell Hill Fire, and any challenging emergency response event today, the following question is inevitably asked: “Was there information that could have made a difference?” What knowledge-delivered in real time to the people who need it, when they need it, the way they need it-can be made available to the incident commanders and the “boots on the ground” that will make a difference? Enter smart fire fighting. As stated by the English philosopher Francis Bacon, “Knowledge is power,” and smart fire fighting has the potential to provide fire fighters and other emergency responders with the knowledge needed to inform their decision making and their activities. Our changing world today is one of increasingly sensor-rich data; and, smart fire fighting has significant potential to use that data to make the tasks of fire fighters more effective and efficient, with direct improvement to their safety and health.

Measurement of effective temperature range of fire service thermal imaging cameras

The use of thermal imaging cameras (TIC) by the fire service is increasing as fire fighters become more aware of the value of these tools. The National Fire Protection Association (NFPA) is currently developing a consensus standard for design and performance requirements of TIC as used by the fire service. The National Institute of Standards and Technology facilitates this process by providing recommendations for science-based performance metrics and test methods to the NFPA technical committee charged with the development of this standard. A suite of imaging performance metrics and test methods, based on the harsh operating environment and limitations of use particular to the fire service, has been proposed for inclusion in the standard. The Effective Temperature Range (ETR) measures the range of temperatures that a TIC can view while still providing useful information to the user. Specifically, extreme heat in the field of view tends to inhibit a TICs ability to discern surfaces having intermediate temperatures, such as victims and fire fighters. The ETR measures the contrast of a target having alternating 25 °C and 30 °C bars while an increasing temperature range is imposed on other surfaces in the field of view. The ETR also indicates the thermal conditions that trigger a shift in integration time common to TIC employing microbolometer sensors. The reported values for this imaging performance metric are the hot surface temperature range within which the TIC provides adequate bar contrast, and the hot surface temperature at which the TIC shifts integration time.