The impact of ambient pressure and tunnel inclination angle on the smoke transport in a subway tunnel

The subway tunnel will be built in the plateau where the pressure is relatively low, and the tunnel will tilt at a certain angle due to topographic factors. In order to investigate the smoke transport characteristics of moving subway trains caught fire under different ambient pressures and different tunnel inclination angles, three-dimensional full-scale calculation models of subway trains, two stations and one tunnel are established, and three different environmental pressures (50kPa, 75kPa, 100kPa) and three different tunnel inclination angles (− 1.5 °, 0 °, + 1.5 °) are simulated. The IDDES turbulence model based on kω-sst RANS combined with the overset grid technology is used to simulate the subway train movement and the detailed flow field. The velocity and temperature distribution characteristics and smoke concentration field are studied in detail. The soot density of smoke and temperature increases with reduced ambient pressure due to the weakening of air entrainment and the decreased air density and the influence of ambient pressure on smoke diffusion decreases with the increase of pressure. The longitudinal airflow induced by the stack effect under the negative inclination angle of the tunnel is helpful to prevent the flowing back of smoke.

Simulación de la eficacia de ignífugos inorgánicos en la extinción de incendios con CFAST. Caso de un laboratorio químico.

Introducción. El uso de ignífugos inorgánicos en sistemas contraincendios tipo rociadores es una alternativa que puede ayudar en la extinción de fuegos no controlados y la protección en laboratorios químicos con alto riesgo. Objetivo. Se estableció las condiciones de extinción según normas NFPA 13 y UNE 12845 y se calculó la eficacia por comparación de las dos condiciones: uso de agua y uso de ignífugo inorgánico, utilizando el software Consolidated Model of Fire and Smoke Transport (CFAST) y Smokview 7. Metodología. Se determinó: el nivel de riesgo de incendio según la norma UNE 12845, luego las condiciones de operación en condiciones críticas de funcionamiento y en carga de trabajo máximo según norma NFPA 13 y UNE 12845 y finalmente se probó la eficacia del desalojo de humo y disminución de la temperatura del recinto probando la solución ignífuga inorgánica con valores conocidos de disminución en la curva de liberación de calor (HRR) con el programa CFAST y Smkeview 7. Resultados. Se determinó: nivel de riesgo de incendio riesgo extra-grupo 2, la superficie máxima por rociador es de 12 m2, la densidad de diseño mínimo es 5mm/min por cada sprinkler, el tiempo de mejora de saturación de humo del emplazamiento considerando el uso de agua y de dilución de ignífugos inorgánicos a base de Hidróxido de Magnesio Mg(OH)2 al 9% (Pozo Álvarez, 2020) como medio de extinción es 37% y se observa un 48,57% de mejora en el tiempo de enfriamiento, con una presión de 101500 Pa, una temperatura promedio de 20 °C en la ciudad de Ambato, un porcentaje de oxígeno del 15% según la norma NFPA 13 y UNE 12845. Conclusión. La aplicación de ignífugos inorgánicos Hidróxido de Magnesio como método de extinción de incendios resulta en un 37% de mejora en el incremento del tiempo en el desalojo de los contaminantes y un 48,57% de mejora en el tiempo de enfriamiento, por los resultados se asume una mejora en la eficiencia del sistema según CFAST.

Wildfire Smoke Transport and Air Quality Impacts in Different Regions of China

The air quality and human health impacts of wildfires depend on fire, meteorology, and demography. These properties vary substantially from one region to another in China. This study compared smoke from more than a dozen wildfires in Northeast, North, and Southwest China to understand the regional differences in smoke transport and the air quality and human health impacts. Smoke was simulated using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) with fire emissions obtained from the Global Fire Emission Database (GFED). Although the simulated PM2.5 concentrations reached unhealthy or more severe levels at regional scale for some largest fires in Northeast China, smoke from only one fire was transported to densely populated areas (population density greater than 100 people/km2). In comparison, the PM2.5 concentrations reached unhealthy level in local densely populated areas for a few fires in North and Southwest China, though they were very low at regional scale. Thus, individual fires with very large sizes in Northeast China had a large amount of emissions but with a small chance to affect air quality in densely populated areas, while those in North and Southwest China had a small amount of emissions but with a certain chance to affect local densely populated areas. The results suggest that the fire and air quality management should focus on the regional air quality and human health impacts of very large fires under southward/southeastward winds toward densely populated areas in Northeast China and local air pollution near fire sites in North and Southwest China.

Observation of Wildfire Smoke Transport and PBL Variation During Summer 2018 Listos Campaign in New York City

Air pollution associated with wildfire smoke transport and heat wave in summer pose serious public health concerns in the populated New York City (NYC) area. In this study, we present a synergistic lidar, ceilometer and in-situ observation for wildfire smoke transport and planetary-boundary-layer (PBL) variation in the NYC urban and coastal area during the summer 2018 Long Island Sound Tropospheric Ozone (O3) Study (LISTOS). A dense smoke plume and mixing into PBL on August 15-17, 2018 was analyzed while the coincident enhancement of PM2.5, CO and O3 exceedance of NAAQS was demonstrated from both the observation and model. In addition, we show the temporal-spatial variation and difference of the PBL-height (PBLH) in the NYC urban and its coastal vicinity. We further evaluate the NAM-CMAQ model forecast of O3, PM2.5 and PBLH with the ground observations.