Advantages and challenges with using hypoxic air venting as fire protection

The use of hypoxic air venting system as fire protection is increasing and is sometimes used to replace traditional extinguishing systems. An oxygen level of 15% is generally used because a lower concentration could pose serious health risks. On the request of the Swedish Radiation Safety Authority, a literature review was conducted to determine advantages and challenges with the system and further research needs. The main advantages with a reduced oxygen environment are the reduced probability of ignition and lowered heat release rate. However, at 15% oxygen level, risk for fire still exists, and the system cannot be seen as an alternative to extinguishing systems. Reduced oxygen environment also results in higher production rates of soot and smoke, and there is limited knowledge regarding the effect of fuel configuration and fire behavior of products. In addition, a first evaluation of the test method specified in the hypoxic air venting standards was carried out through testing. The testing showed that the particleboard passed the test criteria at normal atmosphere even though it is commonly known that a particleboard burns in normal air. It is concluded that the test method has deficiencies, and there is clearly a need for development of the test method to guarantee safety levels

PYROLYSIS MODELING OF PVC USING DISTRIBUTED ACTIVATION ENERGY MODEL- MICRO SCALE TESTING

Polyvinyl chloride (PVC) is a common thermoplastic whichfinds widespread applications in the construction industryfor usage inceiling linings, flooring materials, electrical cables and roofing materials.Several fire requirements are put on these types of applications. For fire safety engineering and product development, thermo-chemical decomposition modeling of PVC isrequired. The FIRETOOLS project investigates the possibilities to predict real scale fire behavior of building products, content and barriers by means of using material data on successively increasing scale. This paper focuses on the material modeling and studiesthe thermo-chemical decomposition of PVC using Distributed Activation Energy Model (DAEM).

Simulation of critical evacuation conditions for a fire scenario involving cables and comparison of two different cables

Previous studies on the evaluation of irritant species from burning cables in a modified prEN 50399 fire test produced FEC/FED values based on ISO TS 13571. However, the ISO standard mentions in its scope that these indices can only be used within e.g. modelling. For this reason Europacable (ECBL) initiated a preliminary case-study to asses the possibility of using modern fire safety engineering techniques. The scope of the project was the evaluation of the evacuation conditions for a realistic fire scenario involving two types of cable fires that produce different levels of heat, smoke and gases. Both CFD (Computational Fluid Dynamics) modelling by means of the software package FDS (Fire dynamics simulator) and evacuation modelling by means of the software package Simulex were performed. The results were used to calculate FED (fractional effective doses) and FEC (fractional effective concentration). The results showed that the developed methodology allows evaluation of critical evacuation conditions based on not only temperature and visibility, but also on gas composition. One of the selected cables created critical conditions for some of the occupants during evacuation for the chosen design fire when the production of irritant gases (HCl, acreolein, Formaldehydes) is considered

Kartläggning och kvalitativ analys av möjligheter och risker med reducerad syrehalt i brandceller innehållande elektrisk utrustning

Fires can be an important hazard for the overall safe operation of nuclear power plants. Prevention of fire, fast detection and efficient extinguishment of a fire are some parameters, which are important to consider when designing the fire safety in a nuclear power plant. As an alternative to extinguishment system the use of hypoxic air or hypoxic air venting has been introduced e.g. in storage room of a museum or a historical building. This system is now being proposed for use in fire compartments in nuclear power plants containing electrical equipment such as electrical cabinets, cable trays, etc. This reports is a pre-study to investigate the risk and advantages of this system for use in these types of rooms. This report also stipulates a number of areas where more research or investigations are necessary. The results in this report are based on a literature review of scientific publications and specific technical standards available in the area in combination with the technical expertise of the authors. The report should not be seen as a final evaluation of hypoxic air venting systems

Burning material behaviour in hypoxic environments: An experimental study examining a representative storage arrangement of acrylonitrile butadiene styrene, polyethylene bubble wrap, and cardboard layers as a composite system

Cone calorimeter and controlled atmosphere cone calorimeter experiments were conducted on various samples. The intent of the tests was to examine the behavior of uniform and composite samples in a range of thicknesses, irradiances, and oxygen concentrations. Single, uniform layers of acrylonitrile butadiene styrene (ABS) were compared to a composite mix, comprising of ABS with a surface layer of cardboard and a secondary layer of polyethylene bubble wrap (intended to represent a potential storage arrangement). The horizontal samples have been tested at irradiances of 25 and 50 kW/m2 and oxygen concentrations of 20.95%, 17%, and 15% to examine a range of significant variables. Results for the uniform arrangement indicated various correlations, previously observed in the works of others, such as the relationships typically described between applied heat flux, ignitability, heat release rate and the effect of the introduction of hypoxic conditions. However, results were shown to change significantly when samples were arranged to feature composite layers. A hypothesized cause of the behavioral change, namely the soot and char residual introduced from the incomplete combustion of the cardboard layer, highlights further important variables that require consideration in material testing under hypoxic conditions. Such variables, namely specific material behaviors and sample orientation, must be sufficiently captured in the design methodologies of systems reliant upon the introduction of hypoxic conditions. It is concluded that sufficiently capturing a wider range of variables in burning materials under hypoxic conditions will introduce further design resilience and help optimize fire protection/prevention methods

Analysis of Fire Scenarios in Order to Ascertain an Acceptable Safety Level in Multi-Functional Buildings

The construction of multifunctional buildings has increased over the last years as well as the threat level considering antagonistic events. This presents challenges for the fire safety in these types of buildings since the protection objectives needs to be more focused on the functions the buildings are providing. Further the antagonistic exposures might present more challenging fire scenarios. A structured method how to determine fire scenarios in order to ascertain an acceptable safety level in multifunctional buildings has been developed and is based on the SFPE Engineering guides Fire Risk Assessment and Performance-Based Fire Protection. The method provides guidance on how to determine assets worth to preserve, protection objectives, exposures and finally the fire scenarios for multifunctional buildings. Previous accidents and events are discussed and serve as a background to the additional considerations needed for multifunctional buildings (compared to general buildings) and related to antagonistic exposures when determining fire scenarios. This article is a part of the project SAFE Multibygg that focuses on a methodology to identify fire risks with respect to antagonistic attacks in multifunctional buildings and to define fire safety solutions

Behaviour of an Intumescing System Subjected to Different Heating Conditions

Previous studies have indicated that the expansion of fire seals and fire stoppers will be dependent on the heat exposure. Standardized methods for classification includes exposure to a rapid heat exposure of the product that is tested, but this might not always be the worst case scenario for the product. In this paper a series of tests are presented in order to study how a graphite based intumescing system, intended for cavities, reacts when subjected to fire conditions different form that in the standardised method EN 1366-4. Two different experimental setups, a cone calorimeter at Lund University and a small-scale furnace at SP Fire Technology, were used in the tests. The start of expansion reaction in the tested fire stopper was around 180°C. The start of reaction temperature is rather independent of the incident heat flux, while expansion rate is clearly dependent on the incident heat flux. Furthermore, the studied fire stopper performed well in the small-scale furnace because the graphite expanded enough to give the same protection, although it is preheated or wet, as when subjected to a heat exposure similar to ISO 834. These results are good but they are only considered valid for the studied system and for the given situation. Future research is needed in order to study how other types of intumescing fire protection systems work when subjected to realistic fire environments

Slutrapport: Varför blir vissa små bränder stora?

This project aims to develop knowledge about factors that lead to that some fires develop into large fires and investigate whether there are specific characteristics of large fires in different types of objects. The project has resulted in three reports dealing with three different types of objects (buildings). The first report deals with fires in school buildings, the second deals with attic fires in apartment buildings and the third deals with fires at nuclear power plants. These three reports are summarized in this final report. In addition to the findings related to the three studied objects, the project has resulted in a methodology on how statistics and case studies can be combined in a systematic way to present, analyse and draw common conclusions of different but similar events. The methodology can be used to find factors that contribute or lead to a specific injury or event

En metodik för att utvärdera brandskadescenario på kärnkraftverk

There are a large number of fire scenarios at nuclear power plants that must be analysed to obtain a picture of the fire risk. This report presents a schematic method that can be useful when identifying areas where deeper analysis is necessary. The methodology is based on four possible scenarios. Accepted and generally used calculations methods are available for three of these scenarios. As for the fourth scenario, smoke layer temperature in an adjacent room, there are no general and useful correlations available. For this reason is a large part of this report devoted to describing how such a correlation has been developed. The smaller validation study of the correlation made in the report is promising, but further validation are considered necessary The presented methodology presented provides a rough idea of the fire risks and can be used as a support for decisions on further analysis

A Cost-Benefit Analysis of Fire Protection Systems Designed to Protect Against Exterior Arson Fires in Schools

Fires in school buildings caused by arson are a major problem in Sweden. The costs of these fires are disproportionately high compared to the costs of fires in buildings in general, and it has been shown that fires that start outside of the building in connection with an exterior wall, so called exterior fires are especially problematic. However, technical systems can be used to mitigate the consequences of arson fires in school buildings. In this paper a cost-benefit analysis is used to calculate cost-benefit ratios for four technical systems used to detect these types of fires