Cellulose insulation consists of shredded recycled paper stock, such as newspaper or cardboard, that is chemically treated to satisfy ASTM combustion and ignition tests. However, these chemical treatments serve as retardants and not preventatives. Numerous fire research sources discuss the ability of cellulose insulation to ignite and smolder. However, an investigator should understand how the data provided by these sources applies and relates to actual applications and installations present at a fire scene.
Testing was conducted to determine the ignition and combustion characteristics of a sample of cellulose insulation gradually heated within an oven cavity. In this testing, specimens of insulation included samples of approximately four year old, previously installed cellulose insulation and samples of new-from-the-package insulation from two different insulation manufacturers. In addition to these tests, samples of shredded, untreated newspaper were also heated to provide a comparison to cellulose insulation and what effects its chemical treatments have on ignition and combustion.
Temperature data during testing was collected via thermocouples mounted in multiple locations throughout the tested sample including one thermocouple mounted in the center of the sample. Once prepared, the sample was placed into the oven cavity and heated utilizing a rate of temperature increase of approximately 3.6 °C (6.4 °F) per minute as measured by the centered thermocouple. The temperature data was monitored until a rate of temperature increase at the centered thermocouple exceeded the input rate of temperature increase and was self-sustaining. Smoldering combustion without visible flame was present in the cellulose insulation samples while the shredded newspaper samples eventually resulted in flaming combustion of the sample.
Following completion of the testing, overlaying the time-temperature curves produced by the data acquired during testing, as shown in the attached image, revealed the temperature, 246 °C (475 °F), at which a self-sustained, increased rate of temperature rise occurred. These time-temperature curves were sufficiently similar regardless of the sample tested including the shredded, untreated newspaper. This self-sustained, increased rate of temperature rise represented ignition of the test sample and resulted in eventual combustion occurring within the sample