Discussion of Surface Flash Mechanism for Large Nap Density

Abstract

When a product of napped fabric catches a fire, the flame may propagate over the surface of the fabric at a high speed. This phenomenon is called surface flash, which is a potential hazard to cause a fire disaster. To prevent surface flash, it is important to understand its spread mechanism.Previously, the effects of nap density and nap thickness were mainly studied. According to these previous studies, surface flash occurs when the following conditions are satisfied: the nap thickness is more than a certain critical value and the nap density is less than a certain critical value. Furthermore, it was found that when surface flush occurs, fire spreading rate is highly dependent on the nap density but little dependent on nap thickness. It was concluded that surface flash mechanism is close to premixed flame rather than diffusion flame. In this paper, the surface flash mechanism is revisited, especially the effects of nap density and nap thickness, by conducting new experiments using a similar experimental setup to the previous studies. Napped cotton sheets of a wide variety of nap densities and nap thicknesses are prepared, a sample is held in the normal direction and ignited from the top, and the spread behavior is recorded using a video camera. A new combustion model of surface flash is proposed based on the experimental results.