New U.S. Forest Service data reveals positive gains. Prince (7) demonstrated clearly that what he termed the “ignition temperature”for wood does not have a fixed value but is greatly influenced by the duration of exposure.In that work, oven-dry wood specimens 1-1/4 by 1-1/4 by 4 inches were exposed continuously to different temperatures maintained constant in an electrically heated apparatus. This compares favorably to predictions made using classical self-heating theory. When the temperature of dry wood is raised above 212° F (100° C) a slow exothermic decomposition takes place. The minimum temperature needed to ignite wood is 180 degrees Celsius or 356 degrees Fahrenheit. From an appearance standpoint, unprotected plywood should not be used when temperatures exceed 200° F (93° C). Note that these values would be accurate only if all veneers in each panel were of the group listed. The thermal expansion of wood, however, is quite small and requires exacting techniques for its measurement. This degradation involves the loss of carbon dioxide and volatile materials such as extractives, in the form of gases or vapors. One example of plywood use in extreme conditions involves plywood pallets used in an annealing oven. Using plywood in applications involving periodic exposure to temperatures from 200° F to 302° F (93° to 150° C) should be based on the amount of exposure and the amount of decomposition that can be tolerated without impairing the serviceability of the panel. https://doi.org/10.1016/j.firesaf.2006.03.006. Exposure to sustained temperatures higher than 200° F (93° C) will result in charring and weight loss. The role of self … Because of this, thermal expansion can be neglected in cases where wood is subject to considerable swelling and shrinking. 2a and mostly from 240 to 400 oC in Fig. The leading resource for information about engineered wood products. Copyright © 2020 Elsevier B.V. or its licensors or contributors. A previous investigation by R.E. Thermal expansion may be of importance only in assemblies with other materials where the moisture content is maintained at a relatively constant level. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. Although the temperatures reach 350° F, the plywood performs well, despite the slight charring and discoloration. 1 and 2. The plywood is used in conjunction with insulating foam, and it reaches a service temperature of approximately -150° F (-101° C). Plywood has been successfully used as part of an insulation jacket for ship hulls transporting liquid natural gas (LNG). ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Estimates range from 510° to 932° F (270° to 500° C), but no value should be accepted as an absolute. This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m2 in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m2. The thermal expansion of wood is much smaller than expansion due to absorption of water. When the temperature of dry wood is raised above 212° F (100° C) a slow exothermic decomposition takes place. ICC Evaluation Service ICC-ES Evaluation Report ESR-2586, APA Performance-Rated Wood Structural Panels as Thermal Barriers, APA Performance-Rated Wood Structural Panels as Thermal Barriers, Form TT-060. 230° to 302° F (110° C to 150° C): The wood will char over time with the formation of charcoal. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. On the basis of available test information, published stresses for plywood are considered applicable at temperatures down to -300° F (-184° C). The table below lists representative values for thermal conductivity, k, for plywood species groups as defined in PS 1. The higher the k value, the greater the ability of the material to conduct heat; the lower the k, the higher the insulation value. Plywood and wood expand upon heating as do practically all known solids. Design engineers are well satisfied with the plywood performance for this purpose. This paper investigates the role of self-heating in the smoldering ignition of 18 mm (three-quarter inch) thick maple plywood exposed to radiant heat fluxes between 6 and 15 kW/m2 in the cone calorimeter for up to 8 h. The minimum heat flux for smoldering ignition was experimentally determined to be 7.5 kW/m2. In practice, plywood either carries no group designation at all, or is described by the species group of the face plies, with species of other groups allowed in inner plies. We use cookies to help provide and enhance our service and tailor content and ads. Life Cycle Assessment shows wood is the greenest building product. The role of self-heating was explored via temperature measurements distributed within the specimens. https://doi.org/10.1016/j.firesaf.2006.03.006. If drying occurs, the increase in strength due to drying may offset the loss in strength due to elevated temperature. The rate depends upon temperature and air circulation. A specific temperature is hard to define because there are so many contributing factors, such as size and shape of the material, air circulation, rate of heating, moisture content of the wood and so on. The role of self-heating was explored via temperature measurements distributed within the specimens. Examples of k are 2,700 for copper (a heat conductor), 427 for window glass and 0.27 for glass wool (a heat insulator). This degradation involves the loss of carbon dioxide and volatile materials such as extractives, in the form of gases or vapors. At oven temperatures of 450°-500°F., the wood gradually chars … As a result, the published ignition temperatures of wood will vary widely. All Rights Reserved. At temperatures above 200° F, plywood undergoes slow thermal decomposition that permanently reduces its strength. This increase is consistent with other materials that exhibit increased resistance to changes in form as the temperature drops. In tests, after 165 days at 302° F (150° C) maple blocks showed a 60 percent weight loss, and the samples had the appearance of charcoal. We use cookies to help provide and enhance our service and tailor content and ads. Thermal resistance represents the ability of the material to retard heat flow and is the reciprocal of k, adjusted for actual material thickness. Elevated subsurface temperature profiles indicated self-heating was an important ignition factor resulting in ignition at depth with smolder propagation to the surface and into the material. The thermal degradation and ignition point of wood and plywood may be generalized by the following: A number of attempts have been made to measure a definite ignition temperature of wood, with little success. In the range of 0° F to 200° F, the strength of the panel at 12 percent moisture content or more will increase or decrease approximately 1/2 percent for each one degree increase or decrease in temperature from 70° F. However, such panels exposed to temperatures up to 200° F for a year or more may not experience any significant or permanent loss in strength. Between 70° F and 200° F strength loss is recovered when temperature is reduced. If the heat is n… Cycling of freezing and thawing do not seem to affect the properties of the wood itself, but may reduce the strength of some fastenings by as much as 10 percent. The thermal degradation and ignition point of wood and plywood may be generalized by the following: 1. The ignition temperature rises rapidly as the heat flux is increased. The ignition depth was shown to be a function of the heat flux with the depth moving towards the surface as the heat flux increased. This compares favorably to predictions made using classical self-heating theory.

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