ISO 19700:2007 download.Controlled equivalence ratio method for the determination of hazardous components of fire effluents.
The framework for the long-term standardization of fire safety in support of performance-based design (ISOITC 92 SC 4) requires general engineering methods for specific performance aspects of fire safety, but is applicable to all types of structural systems, products and processes. These are referred to in the document as Level 2, Group B standards. One such aspect of fire safety is the yields of toxic products evolved in fires. This Technical Specification has been developed to measure toxic product yields from materials and products over a range of decomposition conditions in fires. The decomposition conditions are defined in terms of fuel/air equivalence ratio, temperature and flaming behaviour.
The toxic potency of a fire effluent represents the combination of a number of factors, including the concentrations of toxic products, gases, and smoke particles. The concentrations of toxic products in turn depend upon a number of factors, one of which is the yield of each toxic product from the burning fuel. In order to make a performance-based assessment of the toxic hazard in a fire, one required input is the yield of toxic products under specified fire conditions.
For any specific material or product, the effluent yields in fires depend upon the thermal decomposition conditions. The most important variables are whether the decomposition is non-flaming or flaming, and for flaming decomposition the fuel/oxygen ratio. Based upon these variables, it is possible to classify fires into a number of types, as detailed in ISO/TS 19706:2004, Table 1
The use of this Technical Specification provides data on the range of toxic product yields likely to occur in different types and stages of full-scale fires. More comprehensive data on the relationships between decomposition conditions and product yields can be obtained by using a wider range of apparatus settings. Guidance on the choice of additional decomposition conditions, the application of test data to ISO 13344 and ISO 13571, to health and safety and environmental situations and the use of the tube-furnace method for bioassay purposes is provided in the annexes.
This Technical Specification makes use of the same apparatus and a similar basic methodology as specified in IEC 60695-7-50. The test method has been developed to fulfil the requirements of ISO 16312-1 and ISOITS 19706, for data on the yields of toxic products in fire effluents evolved under different fire conditions as part of the data required for input to the toxic-hazard-assessment calculation methods described in ISO 13571. The data may also be used as input for the toxic-potency calculation methods described In ISO 13344 and
ISO 13571.
This Technical Specification descnbes a tube-furnace method for the generation of fire effluent for the identification and measurement of its constituent combustion products, in particular, the yields of toxic products under a range of fire decomposition conditions.
It uses a moving test specimen and a tube furnace at different temperatures and air flow rates as the fire model. The use of this apparatus is generally applicable to individual materials, to products that are layered such that the layering will not result in a significant change in product yields with time in real fires, i.e. to products where the upper surface does not provide major protection to the sub-layers.
This method has been designed as a TC 92 Level Group B performance-based engineering method to provide data for input to hazard assessments and fire-safety engineering design calculations. The method can be used to model a wide range of fire conditions by using different combinations of temperature, non-flaming and flaming decomposition conditions and different fueL/oxygen ratios in the tube furnace. These include the following types of fires, as detailed in ISOITS 19706:2004, Table 1:
– Stage 1: Non-flaming:
— Stage ib) Oxidative pyrolysis from externally applied radiation, Stage 2: Well-ventilated flaming (representing a flaming developing fire) (see Note 1); Stage 3: Less well-ventilated flaming (see Note 2):
Stage 3a) Small vitiated fires in closed or poorly ventilated compartments;
— Stage 3b) Post-fiashover fires in large or open compartments.
NOTE 1 Where the fire size is small in relation to the size of the compartment, the flames are below the base of the hot layer and the fire size is fuel-controlled.
NOTE 2 Where the fire size may be large in relation to the size of the compartment, the flames are partly above the base of the hot layer and the fire size is ventilation-controlled.
3.14
smoke production
integral of the smoke production rate over the steady-state burn period being considered
3.15
volume yield
volume of an effluent component at 20 °C and 101,325 kPa divided by the mass loss of the test specimen associated with the production of that volume of the effluent component
3.16
yield
mass of an effluent component divided by the mass loss of the test specimen associated with the production of that mass of the effluent component
4 Principle
Since the yields of products in fires depend upon the decomposition conditions (references (1) to L5J), it is possible to examine the relationships between product yield and a range of variables affecting the decomposition conditions using this apparatus and the methodology described. The specified test conditions represent a minimum set designed to obtain data for oxidative pyrolysis under non—flaming conditions, for wellventiLated flaming conditions at an equivalence ratio of less than 0,75, and for vitiated flaming conditions at an equivalence ratio of more than 2. The test is designed to replicate real fire conditions, and it is essential that proper observations are made to ensure that those conditions are being met.
Samples of a material or product are combusted under steady-state conditions in one or more of four environments whose temperature and equivalence ratio are representative of a particular stage of a fire. The four types of fire to be represented are: oxidative pyrolysis. well-ventilated flaming developing fires, small flaming vitiated fires, and post-flashover vitiated fires, as defined in ISOITS 19706.
A test specimen in granular or rod form, or a product, is placed in a quartz boat, and introduced at a constant rate into a furnace tube through the hot zone of a fixed tubular furnace. A stream of primary air is passed through the furnace tube and over the test specimen at constant flow rate, to support combustion. The fire effluent is expelled from the quartz furnace tube into a mixing and measuring chamber, where it is diluted with secondary air to a nominal total air flow rate of (50± 1) lmin’ through the chamber and then exhausted to waste.
In the oxidative pyrolysis mode, the furnace temperature is set below the auto-ignition temperature. The three flaming modes are accomplished by using vapour temperatures above typical auto-ignition temperatures. For flaming decomposition conditions, different fuel-to-oxygen ratios, arid hence different equivalence ratios, are obtained when different, constant primary air flows are used in relation to the constant rate of introduction of the fuel. To achieve the required gasification rates, materials may be combusted under different conditions from each other.
The secondary, dilution air is added to generate a greater sample flow and cooler effluent which permits a large number of gas and smoke sampling procedures to be used without the need for a large number of replicate tests.
The requirement in each test run is to obtain stable, steady-state decomposition conditions for at least 5 mm during which the concentrations of effluent gases and particles can be measured. The time taken for steady- state conditions to be established varies, depending upon the nature of the test specimen and the test conditions.
The concentrations of carbon dioxide and oxygen are recorded to establish the steady-state period and samples of the effluent mixture are taken from the chamber during the steady-state period for analysis. Smoke obscuration and smoke yield are calculated from measurement of the attenuation of a light beam by the combustion effluent stream ri the mixing chamber. A sample of smoke is drawn through a filter, and the mass of particles is determined.
5 Apparatus
5.1 General apparatus
The apparatus consists of a tube furnace and a quartz tube which passes through the furnace and into a mixing and measurement chamber. A drive mechanism pushes the specimen boat into the furnace tube at a preset, controlled rate. A constant, predetermined stream of primary air is provided at the furnace-tube entry and a preset, secondary supply into the mixing and measurement chamber. Gas samples are taken from the mixing and measurement chamber. A lightiphoto cell system is used to determine smoke density across the
10.1.6 Start the experimental run by switching on the specimen-boat drive mechanism to introduce the sample boat containing the test specimen into the furnace at a rate of 40 mmmirr1 (see Note).
NOTE For some fast-burning and low-density materials, It has been found necessary to use advance rates of up to 60 mm.min 1 In this case, it may be necessary to change the specimen mass and air flow rates to maintain a constant fuel-mass/air-flow ratio. Depending upon the nature of the specimen, or where high pnmary air flow rates present other diffioulties, It is permissible to use different primary air flow rates, provided the fuel-mass/air-flow ratio is maintained constant (e.g. 25 mgmm 1 specimen loading at an air flow rate of 10 l•min’ corresponds to 12.5 mg.mm specimen loading at an air flow rate of 5 l.min 1)
10.1.7 Look inside the furnace tube to determine the presence or absence of flaming, to determine when ignition occurs and that flaming is continuous during flaming decomposition experiments, also to confirm that flaming does not occur during non-flaming decomposition experiments, see Note. The fire condition can also be verified from the gas analysis where flaming will be indicated by relatively high CO2 values.
NOTE A convex mirror at the primary air inlet end of the furnace tube has been found useful for this.
10.1.8 Observe the recordings from the gas analysers and the smoke density monitor during the early stages of the run. When these have reached approximately constant levels, then dynamic steady-state conditions have been achieved. Record the time and begin chamber sampling at this point.
10.1.9 Continue to observe the test specimen and recordings from the gas monitors. The decomposition conditions need to remain approximately steady for a minimum of 5 mm to enable the specimen decomposition behaviour and toxic product yields to be characterized because data for concentrations of all measured parameters are averaged over this steady-state period.
10.1 .10 When the up-stream end of the sample boat enters the furnace tube, the run is completed. Switch off the sample boat drive and gas sampling systems, pumps, bubblers, etc. Immediately withdraw the sample boat to its starting location in the furnace tube and extinguish any flame by temporarily interrupting the primary air flow.
10.1.11 When the test specimen and boat have cooled, remove from the furnace tube and weigh according to
10.2.3. Store in a desiccator and reweigh when the boat and contents have reached constant mass.
10.1.12 The steady-state period shall be used as the basis for calculating results. If flaming combustion cannot be obtained, or where only intermittent flaming occurs, these should be reported, The results of the
13.2 Reproducibility
The reproducibility of test data has not yet been fully quantified. A statement is in preparation and will be
incorporated Into this Technical Specification after the compilation of suitable test data.
13.3 Accuracy
Accuracy is the relationship between tube furnace and real-scale fire tests,
The tube furnace has been shown to be capable of obtaining both stable non-flaming and flaming decomposition conditions. For flaming decomposition conditions, it has been shown to perform over a wide range of fuel/air ratios typical of different types of fires (references [1] to [3]). A more specific form of validation is to compare the yields of key toxic products, such as CO. obtained in the tube furnace with those obtained in large-scale and full-scale compartment fire tests. Comparison of the yields of CO and other products has shown a good agreement with those obtained in large-scale compartment fire tests (reference [1]).