Kathryn M. Butler

Flame retardant mechanism of silica gel/silica

Various types of silica, silica gel, fumed silicas and fused silica were added to polypropylene and polyethylene oxide to determine their flame retardant effectiveness and mechanisms. Polypropylene was chosen as a non-char-forming thermoplastic and polyethylene oxide was chosen as a polar char-forming (slight) thermoplastic. Flammability properties were measured in the cone calorimeter and the mass loss rate was measured in our radiative gasification device in nitrogen to exclude any gas phase oxidation reactions. The addition of low density, large surface area silicas, such as fumed silicas and silica gel to polypropylene and polyethylene oxide significantly reduced the heat release rate and mass loss rate. However, the addition of fused silica did not reduce the flammability properties as much as other silicas. The mechanism of reduction in flammability properties is based on the physical processes in the condensed phase instead of chemical reactions. The balance between the density and the surface area of the additive and polymer melt viscosity determines whether the additive accumulates near the sample surface or sinks through the polymer melt layer. Fumed silicas and silica gel used in this study accumulated near the surface to act as a thermal insulation layer and also to reduce the polymer concentration near the surface. However, fused silica used in this study mainly sank through the polymer melt layer and did not accumulate near the surface. The heat release and the mass loss rate of polypropylene decreased nearly proportionally with an increase in mass loading level of silica gel up to 20% mass fraction. Polyethylene oxide samples with fumed silicas and silica gel formed physically strong char/silica surface layers. This layer acted not only as thermal insulation to protect virgin polymer but also acted as a barrier against the migration of the thermal degradation products to the surface.

Generation and Transport of Smoke Components

Smoke is a mixture of gases, vapors, and suspended particulate matter, or aerosols. The nature of the aerosol component of smoke can play a significant role in its deposition in the fire environment and in its lethal and sublethal effects on people. This paper presents the current state of knowledge about smoke aerosol phenomena that affects smoke toxicity: soot generation, fractal structure of soot, agglomerate transport via thermophoresis, sedimentation, and diffusion, agglomerate growth through coagulation and condensation, and the potential for the aerosols to transport adsorbed or absorbed toxic gases or vapors into the lungs. Tables are included for measured smoke yields and aerodynamic particle sizes, equations and references are provided for the smoke agglomerate transport properties and wall loss, and key literature references are provided for adsorption of irritant gases on soot particles and water droplets and the toxicity of nanosize particles.

Three Dimensional Modeling of Intumescent Behavior in Fires

A method of studying the swelling and thermal behavior of intumescent materials using understanding of the basic physical and chemical processes is described. The material is treated as a highly viscous fluid with properties dependent on temperature. The growth rate, migration, and thermal effects of a large number of bubbles are individually calculated using approximate analytical solutions to mass, momentum, and energy equations, and the collective behavior is obtained as a summation of the individual velocity and temperature fields. The approach and implementation of this model are described and demonstrated.

A Mixed Layer Pyrolysis Model For Polypropylene

A one-dimensional model describing the melting. degradation, and bubbling behavior of polypropylene exposed to a high heat flux is presented. The region of vigorous bubbling observed in experiment is represented as a mixed layer of uniform temperature. Temperature profiles and thicknesses of solid, melt, and mixed layers are determined by solving conservation equations supplemented by simple models of turbulent mixing. The results of the model with and without a mixed layer are compared with experiment.

Assessment of factors affecting fire performance of mattresses: a review

An in-depth analysis of U.S. residential fire statistics shows that although the total number of fires and deaths due to mattress fires has dropped as a result of several regulatory approaches, the mattress/bedding fires continue to account for one of the largest shares of residential fire deaths and injuries. To address the increasing number of deaths per 1000 mattress/bedding fires, the open flame mattress flammability regulation (16 CFR 1633) was introduced in 2007. The 16 CFR 1633 prescribes performance standards rather than design standards; this allows manufacturers the flexibility to meet the needs of the consumer without sacrificing fire safety. This flammability regulation for residential mattress has generated much interest in understanding the burning behavior of mattresses as well as in developing new materials for mattress construction. To comply with this regulation, it is essential to understand mattress construction, fire performance testing, factors affecting mattress flammability, and compliance solutions.This report reviews the impact of current mattress flammability standards, examines factors affecting mattress flammability, and reviews full-scale and bench-scale test methods that are being developed for mattresses. The construction type, geometry, and size of a mattress are major factors in determining the fire threat of a mattress. The soft materials used in the mattress set, including cushioning materials, fire blocking materials, and tickings, act both individually and collectively to affect the fire performance. The performance of fire barrier materials designed to protect the inner cushioning material from heat and flame is largely dependent on the choice of cushioning material and ticking. When used with an incompatible combination of filling material and ticking, a fire barrier may fail to protect thermal degradation and subsequent burning of filling material. Some of the challenges in designing mattresses have been identified and reported here.

Using 3D Head and Respirator Shapes to Analyze Respirator Fit

A computational approach to analyzing respirator fit is demonstrated using geometries generated by laser scanning, mechanical drawings, and CAD files. Three fit-related problems that can be solved using computational tools are demonstrated: 1) The study of an outward leak of breathing gases into a near-flammable environment. 2) The study of a flow field inside a half-facepiece respirator. 3) The characterization of the relationship of respirator design and head shape to fit and comfort.

Three-Dimensional Kinetic Model for the Swelling of Intumescent Materials (NISTIR 5499)

This paper presents the first measurements of the burning rate of premixed flames inhibited by three fluorinated hydrocarbons who’s chemistry is similar to agents which may he used as replacements for CF3Br. Measurements were made of the reduction in the burning rate of premixed methane-air flames stabilized on a Mache-Hebra nozzle burner. The burning rate was determined with the total area method from Schlieren images of the flame. The inhibitors were tested over a range of concentrations and fuel-air equivalence ratios. The measured burning rate reductions are compared with those predicted by numerical solution of the species and energy conservation equations employing a detailed chemical kinetic mechanism recently developed at the National Institute of Standards and Technology (NIST). This paper presents initial efforts at testing and validation of the mechanism using burning rate data. The mode of inhibition of these chemicals is inferred through interpretation of the numerical results.