Q 2007 ‘Simulation of visibility in smoke laden environments.pdf

SIMULATION OF VISIBILITY IN SMOKE LADEN ENVIRONMENTS P. A. Rubini, Q. Zhang School of Engineering, Cranfield University, Cranfield, Bedfordshire, MK43 OAL, UK ABSTRACT Exposure to the products of combustion, both particulate smoke and gaseous, rather than to the fire itself, is the most significant cause of injury and death in fires. The exposure time of individuals in a smoke environment depends upon their speed of movement and the direction they choose to travel, nominally towards a safe exit. Consequently in the fire safe design of modern buildings, the provision and correct location of emergency exit signs is of paramount importance in minimising such exposure, especially in large spaces, where the occupants are unfamiliar with safe egress routes. A considerable body of research has been accumulated regarding human behaviour in fires and the simulation of the movement of individuals in smoke laden environments. A necessary input to such models is the perceived visibility of the surroundings, whether hazards, obstructions or safe exits. This paper introduces the methodology and presents initial results from the quantitative simulation of visibility through a smoke laden environment. The simulations take account of direct illumination, indirect illumination from surfaces and particulate scattering. The underlying smoke movement is obtained from a prior time dependent CFD simulation and, with appropriate assumptions on soot particle properties, post- processed in a second phase to determine the visibility of, for example, an illuminated exit sign. INTRODUCTION Many different endurance limits have been proposed for movement through smoke, for example a maximum temperature limit of 150 o C, a limit of visibility without a wayfinding system (turn back limit) of 5 m and an accumulated dose of CO of 30 000 ppm. Combinations of these factors further reduces safe evacuation distances. Statistics suggest that 90% of survivors move less than 16m