PREDICTING PRESSURE IN PACKAGES CONTAINING POLYURETHANE FOAM

Small drum-type Type B shipping radioactive material packages often include materials such as polyurethane foam inside their containment vessels to cushion their contents. During the fire test of hypothetical accident conditions, the gas released from these materials can be a significant contributor to the pressure in the containment vessel. We asked what the major constituents of the gas released from polyurethane foam were and how the pressure rise could be quantified. Our tests involved polyurethane foam samples from two vendors. One vendor provided multiple samples with differing chemistry in order to allow the contribution of different flame retardant additives and processing methods to be studied. Samples were heated in a sealed container and the pressure monitored. At temperatures below 300°F (150°C) the pressure stabilized when the samples were held at constant temperature. Above this temperature the pressure continued to increase. Samples of gas from the test container were analyzed. It was found that fire retardants had a small impact on the quantity of gas released. By far the largest contribution was from water vapor. Samples exposed to 0% humidity released almost no gas below 300°F (150°C) while samples exposed to 100% humidity released much more than samples stored at ambient conditions. Also found were strong dependencies on the relative amount of foam to available air in a container. We found that to best predict the contribution of pressure rise inside a containment vessel, test parameters including sample preparation and the relative foam to test volume ratio must be controlled. Polyurethane foam chemistry and processing methods play a role in the quantity of gas released, but these contributions are small compared to the role of water. No standard test methodology exists for predicting the pressure contributions of materials inside containment vessels. These studies show that the amount of gas released is sensitive to several parameters. Care is needed when using test results to predict pressure in containment vessels. An industry standard for conducting these tests could help ensure repeatability and allow meaningful sharing of test data.