Comparison of toxic gas data from different tests
BS ISO 29903-1:2020 pdf free.Comparison of toxic gas data from different tests Part 1:Guidance and requirements.
The yields and nature of the fire effluent component from a fire test of any scale are determined by the involved fuels and the prevalent thermal and oxidative conditions in the current stage of the fire. These conditions also determine the burning rate of the products/materials and thus the rate of effluent generation. See ISO 163124.
During a fire test of a finished product, the combustion conditions are likely to change. These changes include the chemistry of the combustible item and the sufficiency of the ventilation.
Whether decomposition is flaming or non-flaming is a dominant factor in the production of toxic gases.
The combustion conditions under which toxic gas data are developed shall be as close to equivalent as possible between the physical fire models or test scales compared (see Clause 6).
NOTE I A large change in the rate of combustion can affect the degree of oxidation of the emitted effluent. Smaller changes in combustion rate can have no significant effect.
NOTE 2 Fire stages and the corresponding combustion conditions are described in 150 19706.
4.2 Thermal environment
The thermal boundary conditions in a test include the external applied heat flux and the heat flux from any flaming combustion. Also of importance is the heat flux distribution among radiation, convection, and conduction.
The thermal environment sensed by the test specimen during combustion includes both gas temperature and the temperature of the sample material, as defined by the thermal boundary conditions.
The oxygen availability (ventilation) in the physical fire models compared determines the combustion conditions. Comparison among different methods requires characterization of the ventilation conditions in order to assess the degree of similarity.
For a given experiment, it is necessary to identify how the ventilation is characterized and whether the characterization is local or global.
For a physical fire model in which the fuel gasification rate and the entering oxygen flow and concentration are each controlled independently, the relative oxygen availability can he characterized by a fuel/oxygen equivalence ratio. For other models and real-scale fire tests, one or both of the terms in the equivalence ratio may not be well-known. In those cases, a broader characterization is used. This could be a global equivalence ratio or a term such as underventilated burning’ or Nwell ventilated burnings.
NOTE 1 Methods br calculating equivalence ratios [or physical lire models are given in ISO 19703.
NOTE 2 The local air speed rate can be a significant factor in some fire tests. This applies especially for a tube furnace, where the air speed can affect the results of the combustion.
4.4 Characteristics ol test specimens
The test specimens used for comparison of gas yields among physical fire models or between a physical fire model and a larger scale test shall be prepared from a single batch of the finished product or a single batch of each of the component materials. Alternatively, it shall be demonstrated that any differences in composition among the test specimens, tested in the different apparatus, do not affect the test outcome significantly.
For finished products that consist of a single, homogeneous material, the test specimen used in a physical fire model shall be prepared to accommodate the constraints of the test apparatus.
For specimens from non-homogeneous products, the test specimen shall also contain the same portions of the different materials present in the finished product in both tests compared.
For layered commercial products, an ideal physical fire model accommodates specimens that preserve the relationship of the layers. When this is not possible within the constraints of the model, the rationale for the configuration of the layers shall be documented.
NOTE The yields of toxic gases can depend on the surface exposed, and the timing and extent of penetration of the layers.
5 Toxic gas data
5.1 Identification of toxic species
The minimum set of gases that shall be considered are listed in ISO 13571.
Additional gases shall be appraised as warranted by the chemical composition of the test specimen and the finished product from which it is sampled.
The data can be in the form of scalar data or vector data. Some types of data are suitable for direct quantitative comparison, but others require a model for quantitative comparison. The most common quantities used in presentation of toxic gas data are given in Table 1 below.
5.2 Different expressions for toxic gas data
5.2.1 General Subclause 5.2 contains a summary of different expressions typically used for toxic gas data obtained from fire tests and whether the data are suitable for comparison with similar data from other tests or as a basis for the prediction of large-scale results based on small scale data or vice versa.
The experimental data on toxic gases from a fire test can be expressed in several ways. From unrefined measurement data, which is often expressed as gas concentrations from a specific physical fire model, to data in higher degrees of refinement, e.g. yields. What is determined depends in part on the physical fire model used. See Annex A for information concerning the characteristics of different fire models.
The concentration measurement shall be converted to a mass of the toxic gas generated during the sampling time interval using the ideal gas law. Corrections for condensation, solution, and deposition of the gas shall be included, as appropriate, in the calculation.
220.127.116.11 Mass of the test specimen consumed
A measurement or approximation of the consumed mass of the specimen is essential to the calculation of toxic gas yields.
The mass consumed shall be calculated in at least one of three ways.
— Mass loss based on continuous measurement of the remaining mass of the test specimen.
— Mass loss based on a final measurement of the remaining specimen mass.
— Estimation of the mass loss, when no gravimetric measurement is possible, using the chemical formulation of the test specimen and a carbon balance of the combustion products.
NOTE The third method can be in significant error if the chemical composition of the specimen residue is not the same as the initial chemical composition. This error can be reduced by determining the chemical composition of the residue.
5.2.3 Concentrations of toxicants
The concentrations measured in a specific physical fire model are a function of the degree of dilution in the sampling point. Concentrations are unique for the specific physical fire model and should not be used for a direct quantitative comparison. The agreement of relative concentrations between different physical fire models, can however be used for comparison.
The CO/CO2 concentration ratio, for example, can be used as a comparison principle (see f2.2). NOTE Concentrations are normally expressed as volume fractions.
5.2.4 The contribution to FED (or FEC) from individual toxicants
The ranking of the different toxicants measured based on the relative contribution to the total toxicity using the FED (or FEC) concept is a semiquantitative comparison principle. The measured concentrations of toxicants are weighted relative to their toxic effects. See ISO 13344 for rodent lethality limits and ISO 13571 for human incapacitation limits,
5.2.5 Lethal toxic potency
Total lethal toxic potency of the fire effluents measured from the physical fire model is a quantitative comparison parameter. The predicted lethal toxic potency (LC5O) has the unit g/m3 and requires data on mass loss or mass charge. The concept of lethal toxic potency referred to here is defined in ISO U44.BS ISO 29903-1 pdf download.Comparison of toxic gas data from different test