Ventilation and FFFS fire tests for “Calle 30” road tunnels

Between 2003 and 2007 an urban network or road tunnels with a total constructed tubes length of 45 km was built in the city of Madrid. This amazing engineering work, known as "Calle 30 Project" counted with different kinds of tunnel typologies and ventilation systems. Due to the length of the tunnels and the impact of the work itself, the tunnels were endowed with a great variety of installations to provide the maximum levels of safety both for users and the infrastructure includieng, in some parts of the tunnel, fixed fire fighting system based on water mist. Whithin this framework a large-scale programme of fire tests was planned to study different aspects related to fire safety in the tunnels including the phenomena of the interaction between ventilation and extinguishing system. In addition, these large scale fire tests allowed fire brigades of the city of Madrid an opportunity to define operational procedures for specific fire fighting in tunnels and evaluate the possibilities of fixed fire fighting systems. The tests were carried out in the Center of Experimentation "San pedro of Anes" which includes a 600 m tunnel with a removable false ceiling for reproducing different ceiling heights and ventilation conditions (transverse and longitudinal ones). Interesting conclusions on the interaction of ventilation and water mist systems were obtained but also on other aspects including performance of water mist system in terms of reduction of gas temperatures or visibility conditions. This paper presents a description of the test's programme carried out and some previous results obtained.

Large Scale Fire Tests for the “Calle 30 Project"

Between 2003 and 2007 an urban network of road tunnels with a total constructed tubes length of 45 km was built in the city of Madrid. This amazing engineering work, known as “Calle30 Project” counted with different kinds of tunnel typologies and ventilation systems. Due to the length of the tunnels and the impact of the work itself, the tunnels were endowed with a great variety of installations to provide the maximum levels of safety both for users and the infrastructure including,in some parts of the tunnel, fixed fire fighting system based on water mist. Within this framework a large-scale campaign of fire tests were planned to study different aspects related to fire safety in the tunnels including the phenomena of the interaction between ventilation and extinction system. In addition, this large scale fire tests allowed fire brigades of the city of Madrid an opportunity to define operational procedures for specific fire fighting in tunnels and evaluate the possibilities of fixed fire fighting systems. The tests were carried out in the Center of Experimentation "San Pedro of Anes" which counts with a 600 m tunnel with a removable false ceiling for reproducing different ceiling heights and ventilation conditions (transverse and longitudinal ones). Interesting conclusions on the interaction of ventilation and water mist systems were obtained but also on other aspects including performance of water mist system in terms of reduction of gas temperatures or visibility conditions. This paper presents a description of the test’s campaign carried out and some previous results obtained.

An eco-friendly way to fire retardant flexible polyurethane foam: layer-by-layer assembly of fully bio-based substances

The objective of the present study is to develop fully renewable and environmentally benign techniques for improving the fire safety of flexible polyurethane foams (PUFs). A multilayered coating made from cationic chitosan (CS) and anionic alginate (AL) was deposited on PUFs through layer-by-layer assembly. This coating system exhibits a slight influence on the thermal stability of PUF, but significantly improves the char formation during combustion. Cone calorimetry reveals that 10 CS-AL bilayers (only 5.7% of the foams weight) lead to a 66% and 11% reduction in peak heat release rate and total heat release, respectively, compared with those of the uncoated control. The notable decreased fire hazards of PUF are attributed to the CS-AL coatings being beneficial to form an insulating protective layer on the surface of burning materials that inhibits the oxygen and heat permeation and slows down the flammable gases in the vapor phase, and thereby improves the flame resistance. This water-based, environmentally benign natural coating will stimulate further efforts in improving fire safety for a variety of polymer substrates.

La ventilación como elemento fundamental en la seguridad frente a incendios en túneles

La movilidad geográfica es, sin lugar a dudas, uno de los aspectos sociales que más se ha potenciado en los últimos años tanto en el ámbito nacional como mundial. Debido a las grandes dificultades orográficas que se dan en la Unión Europea es preciso desarrollar complejos proyectos donde los túneles son un elemento clave. Paradójicamente, los recientes incendios acaecidos en túneles en todo el mundo han generado dudas acerca de la necesidad de incrementar el número y, sobre todo, la longitud de túneles pero han supuesto un aliciente para profundizar en el estudio de los criterios de seguridad adoptados hasta ese momento. En concreto, dentro del conjunto de instalaciones disponibles en los túneles de carretera el sistema de ventilación juega un papel fundamental por su relación con los criterios de seguridad. En este sentido, el mayor conocimiento de los fenómenos que intervienen en los procesos de producción y evolución de los humos permiten definir criterios de dimensionamiento y funcionamiento de la ventilación más sofisticados. Sin embargo para poder asegurar la calidad del conjunto es preciso, por una parte, partir de una correcta definición a nivel de Proyecto de la solución constructiva la defmición de criterios de actuación precisos a adoptar en caso de incendio y por último el establecimiento de procedimientos de supervisión globales. En el artículo propuesto se abordan desde una perspectiva global las distintas etapas de definición y control que deben realizarse para garantizar el correcto funcionamiento de la instalación, se profundiza en los modelos numéricos empleados para el dimensionamiento y se recogen aspectos de la experiencia resultante de ensayos in-situ realizados. Como ejemplo se presentan resultados para distintos túneles de carreteras en España.

Los riesgos de impactos y explosiones

Durante las últimas décadas, científicos e ingenieros han desarrollado un gran esfuerzo en la comprensión por los temas relacionados con el impacto entre cuerpos sólidos. La complejidad del desarrollo teórico y el desconocimiento acerca del comportamiento real de los materiales en problemas de carga rápida ha limitado tradicionalmente los problemas de impacto a geometrías muy concretas de los cuerpos incidentes, sin embargo, la evolución de la velocidad en los ordenadores y las mejoras en los métodos y elementos de instrumentación han aumentado el alcance y la fiabilidad de los datos experimentales y consecuentemente han sido un nuevo impulso en el estudio en este campo. El enfoque actual de las normativas basado en el análisis de riesgos permite la posibilidad de abordar la seguridad estructural a través de modelos explícitos, en los que las variables básicas del problema se definen de forma estadística y la seguridad se fija en función de probabilidades de fallo frente a los estados límite. Los métodos de fiabilidad estructural deben ser capaces de analizar toda la información estadística; es habitual el uso del método de Montecarlo, superficie de respuesta, estimaciones puntuales, nivel 11, etc. y en todos ellos es fundamental el conocimiento de un procedimiento determinista que permita evaluar el grado de cumplimiento de los estados límite. En ésta presentación se entra directamente en los modelos deterministas de cálculo, obviando el estudio estadístico más propio de un capítulo destinado a la fiabilidad estructural. Para ello, se han recogido unas ideas acerca de cómo se aborda el problema del impacto de una forma tradicional, se comienza con los choques elásticos e inelásticos de cuerpos rígidos. Los cuerpos rígidos dan paso a cuerpos elásticos donde la colisión genera una onda que recorre el cuerpo a una velocidad finita que se refleja en los contornos generando una vibración y en consecuencia una pérdida de energía en el choque. Posteriormente se abordará el impacto con materiales plásticos donde parte de la energía se transforma en la deformación permanente. Las explosiones pueden ser tratadas de forma análoga al impacto, ya que poseen la misma característica de cargas rápidas y son consideradas solicitaciones accidentales. La diferencia fundamental se centra en que los impactos requieren la existencia de dos cuerpos mientras que las explosiones sólo requieren un receptor y es el medio transmisor, generalmente el aire, quien transmite la solicitación mediante una onda de presión. En este artículo se comentan diferentes aspectos de la naturaleza de la solicitación y de su efecto sobre las estructuras.

The structure of lean hydrogen-air flame balls

An analysis of the structure of flame balls encountered under microgravity conditions, which are stable due to radiant energy losses from H₂O, is carried out for fuel-lean hydrogen-air mixtures. It is seen that, because of radiation losses, in stable flame balls the maximum flame temperature remains close to the crossover temperature, at which the rate of the branching step H + O₂ -> OH + O equals that of the recombination step H + O₂ + M -> HO₂ + M. Under those conditions, all chemical intermediates have very small concentrations and follow the steady-state approximation, while the main species react according to the overall step 2H₂ + O₂-> 2H₂O; so that a one-step chemical-kinetic description, recently derived by asymptotic analysis for near-limit fuel-lean deflagrations, can be used with excellent accuracy to describe the whole branch of stable flame balls. Besides molecular diffusion in a binary-diffusion approximation, Soret diffusion is included, since this exerts a nonnegligible effect to extend the flammability range. When the large value of the activation energy of the overall reaction is taken into account, the leading-order analysis in the reaction-sheet approximation is seen to determine the flame ball radius as that required for radiant heat losses to remove enough of the heat released by chemical reaction at the flame to keep the flame temperature at a value close to crossover. The results are relevant to burning velocities at lean equivalent ratios and may influence fire-safety issues associated with hydrogen utilization.

Ventilation system design and large scale fire tests

The design, construction and operation of the tunnels of M-30, the major ring road in the city of Madrid (Spain), represent a very interesting project in wich a wide variety of situations -geometrical, topographical, etc.- had to be covered, in variable conditions of traffic. For that reasons, the M-30 project is a remarkable technical challenge, which, after its completion, turned into an international reference. From the "design for safety" perspective, a holistic approach has been used to deal with new technologies, integration of systems and development of the procedures to reach the maximum level. However, one of the primary goals has been to achieve reasonable homogeneity characteristics which can permit operate a netword of tunels as one only infraestructure. In the case of the ventilation system the mentioned goals have implied innovative solutions and coordination efforts of great interest. Consequently, this paper describes the principal ideas underlying the conceptual solution developed focusing on the principal peculiarities of the project.

Experiences on the specification of algorithms for fire and smoke control in road tunnels

The main objective of ventilation systems in case of fire is the reduction of the possible consequences by achieving the best possible conditions for the evacuation of the users and the intervention of the emergency services. The required immediate transition, from normal to emergency functioning of the ventilation equipments, is being strengthened by the use of automatic and semi-automatic control systems, what reduces the response times through the help to the operators, and the use of pre-defined strategies. A further step consists on the use of closed-loop algorithms, which takes into account not only the initial conditions but their development (air velocity, traffic situation, etc.), optimizing smoke control capacity.

Probabilistic approach for longitudinal ventilation system design in fire situations

The main objective of ventilation systems in tunnels is to reach the highest possible safety level both in service and fire situation; being the fire one, the most relevant when designing the system. When designing a longitudinal ventilation system, the methodology to evaluate the capacity of the system is similar both in service and fire situation, with the exception of the chimney effect and the phenomena of thermal transfer which is responsible or the changes in the density of the air. When facing the dimensioning task for longitudinal ventilated tunnels, although similar methodologies are used in different countries, specific hypothesis (aerodynamic, thermal properties, traffic) even if discussed in the literature or current practice, are not usually detailed in the regulations or recommendations. The aim of this paper is to propose a probabilistic approach to the problem which would allow the designer, and the tunnel owner, to understand the uncertainty and sensibility adopted in the results and, eventually, identify possible ways of optimizing the ventilation solution to be adopted.