Flashpoint models

In the minds of all authors who favour the estimation of flashpoints based on a theoretical model rather than experimental results this approach was temporary and only supposed to be used during the period used by commissions of experts to lay down a standard technique for the determination of flashpoints. As has already been seen, it is less likely that this method will be used in the near future. This is the reason why we think estimation techniques have to be part of the priority tools of risk analysis in work on chemical risk prevention. Why is such work on estimation important We will see later that flashpoint is the cruciai parameter in order to establish the ievel of fire hazard of a substance. 

Two comments can be made on the second point. For a simple mathematical reason mistakes made with the LEL value are of little consequence to the calculated value of flashpoint cc . Indeed, this mistake is not that significant since there Is a logarithm involved. Secondly, in theory no mistake is made with the stoichiometric concentration (except for nitrogenous compounds where there is an ambiguous aspect with regard to the nitrogen reaction). This second approach (with Cg) can thus provide preliminary control of the model parameters (S or the group) and there... 

Are the hypotheses regarding the choice of group and flashpoint oc coherent Calculating flashpoint oc with Cs = 1.716% the oc estimated, Pfla = 54.47°C is obtained, which is perfectly consistent. This approach shows that confidence based on a satisfactory coherence of two values of Pfla oc separated by only 2°C that confirm each other, and on a coherence between the estimated and experimental values of Pf a oc. The result is not inconsistent with the experimental LEL at 100°C given the inaccuracy of LEL and the empirical model linking the LELs at different temperatures. 

It is not crucial in regard to safety to devise an estimation model for mixture flashpoints given the complexity of the issue. Generaliy speaking, in most cases it wiil be sufficient to know the inflammability parameters of the pure compounds, at least for mixtures of inflammable substances. 

The study is based on four iinear hydrocarbons (in Ci, Ce to Ca) and the model uses Antoine and Clapeyron s equations. The flashpoints used by the author do not take into account all experimental values that are currently available the correlation coefficients obtained during multiple linear regression adjustments between experimental and estimated values are very bad (0.90 to 0.98 see the huge errors obtained from a correlation study concerning flashpoints for which the present writer still has a coefficient of 0.9966). The modei can be used if differences between pure cmpounds are still low regarding boiling and flashpoints. 

Thanks to this model it is possible to calculate the quantity of 1-butanol by percentage and weight from which the flashpoint of cyclohexanol decreases significantly. It is found to be 0.14% of butanol (molar fraction 0.002). TNs calculation was made supposing there is no pentanol in the mixture and a flashpoint target at 56.64 C, the lower limit of the confidence interval was at 95% of pure cyclohexanol. 

Finally, mention should be made of the two effects of interaction of the mathematical model whose negative coefficients show minima of flashpoints for the binary butanol/cyclohexanol and butanol/pentanol combinations. Can they be explained by the presence of azeotropes in these substances The tables examined did not list these mixtures and there was no time to do an experimental check with the students. 

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