Initial Stage Of Fire Research Articles

Experimental investigation into the effect of transparent fireproof coatings on charring behavior of glued laminated timber exposed to fire

As timber structures evolve towards greater heights and longer spans for buildings, there is a pressing need to enhance the fire resistance of timber structures. Considering the charring behavior of timber is crucial to the fire resistance of timber structures, it is a promising way to retard the charring behavior of timber and further enhance the fire resistance by applying transparent fireproof coatings. In this study, a series of fire tests were conducted to investigate the effect of transparent fireproof coatings on the charring behavior of Douglas fir glued laminated timber (Glulam) under small-scale ISO 834 standard fire conditions. Different coating types, coating quantities, exposed time to fire and member sizes were considered in the experiments. The experimental results including temperature profiles, maximum temperature, and charring rates for uncoated and coated Glulam specimens were carefully recorded and analyzed. Then, the effect of transparent fireproof coatings was quantified by the proposed ratio of delayed charring. The main mechanism of the delayed charring in fire was finally discussed. This study demonstrated that two transparent fireproof coatings can both effectively lower the temperature at different depths and delay the charring behavior of timber. The reduction in charring rates increased with the increase of coating quantity and decreased as the fire exposure time progressed. The ratio of delayed charring for two coatings can be over 30% in the initial stage of fire and over 20% for one-hour standard fire exposure. This study can provide technical support for enhancing the fire resistance of timber structures using transparent coatings.

Влияние высоты помещения на расчётное время обнаружения пожара

Introduction. Within the framework of this article, a quantitative and qualitative assessment of the influence of the height of the room on the estimated time of fire detection was carried out. Purpose. Assessment of the effect of the room height on the estimated fire detection time. Methods. Using the Fire Dynamics Simulator software system used to simulate the fire process, numerical experiments were carried out to study the fire detection time, which is considered in this article as an interval from the moment of fire start to reaching the values of optical density of smoke, at which point smoke fire detectors are triggered. Results and their discussion. As a result of numerical modeling of fire in rooms of different heights, data on the change in the optical density of smoke in the initial stage of fire are established. Based on the information received, the estimated time of fire detection by automatic fire alarm was determined according to the algorithms of triggering A and B at different values of permissible sensitivity for point smoke fire detectors, taking into account the height of the room. The results of numerical experiments can be used for expert assessment of the design time of fire detection as a "technical" component of the evacuation start time taken into account when determining the individual fire risk and conditions for safe evacuation of people. Conclusions. It was found that the height of the room has a slight impact on the estimated fire detection time. However, this effect is manifested in the case of the operation of point smoke detectors at the upper threshold of permissible sensitivity. To take into account the time of fire detection as part of the evacuation start time, further study of this issue is required with comparison of modeling results with the results of field experiments. Keywords: optical density of smoke; fire alarm; evacuation start time; fire detection time.

Assessment of operation of safety channel signal cables at nuclear power plants under fire conditions

Introduction. Signal cables of safety systems, installed at nuclear power plants (NPPs), retain the ability to conduct modulated signals during the time period needed to switch the reactor facility to a safe mode. However, the ability of signal cables to transmit signals correctly in the high temperature gas medium, which is typical for the early stage of a room fi re, has not been exposed to research.Aims and objectives. The co-authors offer a theoretical assessment of the ability of NPP safety system cables to correctly transmit modulated electric signals if exposed to fi re and current loads. The theoretical research into the temperature of the conductor of a signal cable at the initial stage of fi re has been performed towards this end.Theoretical background. The steady state heat conduction equation, describing heat transmission from the cable core to the environment through the cylinder-shaped insulation layer, is used to measure the temperature of the cable strand.Results and discussion. Temperature dependences describing the relation between the temperature of the conductor of a single - strand and single-wire cable KNEPng(А)-HF on the gas medium temperature are obtained. Relations between the temperature of the gas medium in the room on fi re and the current intensity in the electric cable (if the cable is laid vertically) are presented with account taken of the dependence between the specifi c resistance of the wire and the temperature if the maximal permissible operating temperature of cable strands is 70 °С, the maximal permissible operating temperature of cable strands in the overload operation mode is 80 °С, and the maximal cable strand heating temperature is equal to 160 °С when the short-circuit failure occurs. Maximal current intensity values are obtained for various operating modes in the condition of temperatures typical for the initial stage of an indoor fire, they allow to correctly conduct modulated signals within the time period needed to switch the reactor facility to a safe mode.Conclusions. The developed mathematical model and results of numerical experiments allow to assess the infl uence of the temperature in the room of a nuclear power plant in case of fi re on the ability of a signal cable of the safety system to transfer undistorted modulated signals depending on current loads and signal cable laying patterns (whether it is laid vertically or horizontally), and also to expand the range of the room temperature dependence on the current load provided in Electrical Installations Code (EIC).

FORMATION OF RESIDUAL STRENGTH OF STRUCTURAL FIBER IN CONDITIONS AFTER FIRE

The article presents the results of dynamic mechanical tests of fiberglass specimens under the conditions of the effects of intense heating on them, which corresponded to the development of a slowly developing fire. It is established that with intensive heating at the initial stage of fire, the considered type of fiberglass loses its initial strength, but then, upon cooling, acquires increased rigidity, while maintaining sufficient integrity and relative structural functionality. In our view, this increase is due to the significant increase in the carbon fraction in the polymer binder with the formation of a more densely packed structure due to the formation of sites with associated aromatic fragments. At the same time, the drop in strength occurs due to the formation of a sufficient number of voids (pores and cracks), the occurrence of which is characteristic of materials of organic nature (plastics based on synthetic polymers) in the process of thermal oxidation destruction under intense heating. It is established that the degree of conservation of the load-bearing strength of the fiberglass can be arranged in the following order: bending> stretching> compression. This behavior of the material indicates the use of additional structural measures when using it as the supporting elements of construction and technological structures. The determining factor in the observed modification of the composite is the extent of the passage of the pyrolytic transformations of the polymer bond, which can indirectly be characterized by a change in the dynamic mechanical properties of the material under intense heating. The main role is played by the binder component - the epoxidized naphthalene type oligomer, whose function is reduced to the ability to play a role in the volume of the polymer matrix of coke formation germs. The above composition of components and the method of its production allows to develop polymeric composite materials without the use of additional components - flame retardants (retardants), which complicate the technology of obtaining the composite and in some cases reduce its initial physical and mechanical properties. Keywords: fiberglass, residual strength, fire aftereffect, dynamic mechanical tests, epoxidised dinaftol

Designing Fire Protection of Steel Corrugated Web Beams for Wastewater Treatment Plant

The paper describes effective constructive fire protection of steel corrugated beams by using large sheet and slab cladding. It introduces a scheme of fire-resistant steel beams with contact connection of elements of sheet and slab cladding to a steel bearing core. The study provides analytical equations of thickness of sheet and slab cladding with account of required fire resistance. The technical result of the new design solution includes increase of reliability of cladding elements fastening by means of fastening screws with a countersunk head and a pointed end, weight reduction of large size cladding materials and steel, reducing cross-sectional area of fire-resistant beams, increasing actual fire resistance of steel beams, reducing the risk of steel beam failure in the initial stage of fire and direct losses.

PROBLEM ISSUES OF CREATING A SYSTEM OF FIRE PROTECTION OF A CRITICAL INFRASTRUCTURE OBJECT WITH FIRE LOAD FROM CELLULOSE-CONTAINING MATERIALS

Обґрунтовано актуальність проблеми протипожежного захисту об'єктів критичної інфраструктури держави, до яких віднесено об'єкти, системи, мережі або їх елементи, порушення функціонування або руйнування яких призводить до найсерйозніших наслідків для соціальної та економічної сфери держави, негативно вплине на рівень її обороноздатності та національної безпеки. Аналізуючи статистичні дані, визначено особливу вразливість об'єктів критичної інфраструктури з пожежною навантагою із деревини, паперу, тканини, очерету та інших целюлозовмісних матеріалів. Визначено, що на об'єктах, матеріали пожежної навантаги яких здатні займатись навіть від малокалорійних джерел займання, потрібно створювати системи протипожежного захисту, що забезпечують запобігання та ліквідацію пожежі на початковій стадії її розвитку. Системи протипожежного захисту об'єктів критичної інфраструктури мають об'єднувати заходи і засоби як активного, так і пасивного протипожежного захисту. Активний захист визначається застосуванням речовин, техніки, засобів, що придатні в будь-який час бути мобілізованими для гасіння пожежі, а пасивний захист визначається застосуванням заходів вогнезахисту, що виконані заздалегідь і не потребують додаткової мобілізації під час гасіння пожежі. Обґрунтовано перспективність використання водних вогнебіозахисних і водних вогнегасних речовин для створення систем протипожежного захисту об'єктів критичної інфраструктури. Доведено ефективність реалізації запропонованої системи методом Гретенера.

Критические времена воздействия моноксида углерода на человека при пожаре в помещении

The aim of this work was to create the mathematical model for calculation of the carboxyhemoglobin concentration in the human blood in case of fire. Tests were conducted in conditions of variable CO density, typical for the initial stage of indoor fire, and increased pulmonary ventilation rate. It is offered the criteria for determination of the critical values of fire duration under the terms of safe evacuation and people rescue. The methods of theoretical analysis of the content of carboxyhemoglobin in the human blood and calculation of the carbon monoxide (CO) concentration, in conditions of fire in premises, were used during the experiment. The mathematical model was created taking into account the concentration of CO in the inhaled air, the mass of hemoglobin in the blood, the pulmonary ventilation rate, the volume of respiratory dead space and the CO exposure time. Critical time of safe evacuation for people under the effects of CO is accepted when the content of carboxyhemoglobin in the blood reaches the 20 % by mass (minor poisoning). Critical time from the initial stage of fire and until the moment when people, which stay in premises without protection means against CO (respirators, gas masks, self-rescuers, etc.), and, with high probability, are unable to leave the premises independently, is accepted when the concentration of carboxyhemoglobin in the blood reaches the 50 % by mass (moderate poisoning). The model premises were in the form of parallelepiped with dimensions (m): 4´5´3, 4´5´6 and 24´12´3. As combustible materials there were used the wood building materials, PVC sheath of cables and transformer oil. The results of numerical experiments on determination of the carboxyhemoglobin concentration using the analytical solution of the integral calculation model for the thermal and gas dynamics of fire are presented. The estimated values of CO exposure intervals prior to various degrees of human intoxication are obtained. The comparison of critical durations of fire (considering CO effects), obtained using proposed model and existing approach, is made. The critical duration of fire, obtained using proposed model, was significantly greater than the corresponding value determined by existing methods (for example, in case of burning of the transformer oil in the room with dimensions of 4´5´3 m). The main conclusion is that existing scientific and regulatory literature contains the calculation methods for critical duration of fire, considering CO effects, which may lead to qualitatively and quantitatively wrong results. The proposed criteria for determination of the critical values of CO exposure time and the calculation methods for the content of carboxyhemoglobin allow defining the time of safe evacuation and people rescue more reasonably than existing approach.

A Study on Modeling of Fire in Small Scale Buildings (5) - Investigations into Initial Stage of Fire by Computer Simulation -

A Study on Modeling of Fire in Small Scale Buildings (5) - Investigations into Initial Stage of Fire by Computer Simulation -

BURN-DOWN RISK OF ARCHITECTURAL MONUMENTS SURROUNDED BY GROUP OF WOODEN HOUSES DUE TO POST-EARTHQUAKE FIRE SPREAD

Burn-down risk of seven architectural monuments in Kyoto-Higashiyama area due to post-earthquake fire spread was analyzed. The analysis was conducted by the Monte Carlo simulation using a physics-based urban fire spread model formerly developed by the authors. Factors of uncertainty considered in the present analysis were the conditions on: (1) outbreak of fire; (2) firefighting activity at initial stage of fire; (3) structural damage of individual buildings due to seismic motion; and (4) change of weather in time series. The result shows that burn-down risks of Rokuharamitsuji, Hokanji and Kenninji are rather close to the mean value of all the houses in the target urban area. The result indicates that no fire-stops are maintained between these architectural monuments and densely-built wooden houses in their surroundings. Thus, integrated approach involving entire urban area is required on implementing fire safety measure in order to effectively reduce the burn-down risk of the architectural monuments.

Vapor Convection in Gypsum Plasterboard Exposed to Fire: Numerical Simulation and Validation

This article investigates the contribution of water vapor convection to heat transfer through gypsum plasterboard exposed to fire. The vapor is generated as a product of the endothermic dehydration reaction in gypsum, and it is then expelled from the material through the pore network by its own pressure, thereby taking part in the heat transfer from the fire-exposed to the cold surface of plasterboard. The gas permeability values of plasterboard core and paper liner are obtained experimentally. The results of simulations are validated against the temperature measurement data obtained for two types of commercial plasterboard tested in the standard fire ISO 834. It is shown that vapor convection plays an essential role in heat transfer through plasterboard during the initial stage of fire. The amount of condensate developing in the pores of the material is found to be low, which allows it to be neglected in engineering calculations.

鋼板コンクリート(SC)構造スラブの保有火災耐力

To examine properties and load-carrying capacity of composites slabs of steel plates with steel studs and concrete with top reinforcements in ISO fire, fire tests and analyses of heat transfer and elasto-plastic stress-deformation were carried out. And a simple calculation method to evaluate load-carrying capacity of composites slabs was proposed. This calculation method based on simple plastic theory on the viewpoint of considering in strength degradation zone of concrete by heat transfer during fire. After this study, the following conclusion could be obtained. 1) The composites slabs designed within the limit of ordinary live load have flexural failure mode in fire and the load-carrying capacity of composite slabs can be calculated by using the formula proposed. 2) Composite slabs with steel studs having shear stress more than 0.5N/mm^2 collapse by shear stress on the initial stage of ISO fire. This shear failure is caused by decreasing of shear strength of concrete due to giving rise to tensile stress in concrete. Tensile stress in concrete increase on the initial stage of fire, because of the restraint of elongation of steel plates through steel studs. 3) However, generally, composite slabs have axial restraint more than 30% of full axial restraint in structure, the decreasing of shear strength of concrete doesn't occurred during fire, so shear failure can be avoided.

Some Regularities of Heat and Mass Transfer in the Case of Fire Within a Building

Results of a numerical investigation of heat and mass transfer at the initial stage of fire within a building in combustion of kerosene, carried out with the use of a three-dimensional mathematical field model, are presented. A comparison of the distribution of the averaged temperatures and velocities along the vertical axis of the convective column and of the mass rates of gas flows through an open opening with the experimental data has been made. Substantial three-dimensional inhomogeneities of the velocities and the temperatures in the near-ceiling layer have been revealed. It has been established that near the opening there is a critical separation zone which influences significantly the parameters of natural gas transfer.

Mathematical model for temperature fields at initial stage of fire

Mathematical model for temperature fields at initial stage of fire