Using heats of oxidation to evaluate flammability hazards

Abstract

The heat of oxidation is the net heat of combustion per mole of oxygen consumed. For complete combustion it is given by 'AH/S" (kcal/mol oxygen), where 'AH, " is the net heat of combustion (kcal/mol fuel) and "S" is the stoichiometric ratio of oxygen to fuel as written in the stoichiometric equation. Although previously unrecognized, the heat of oxidation 4fiH,/S" is the single most powerful parameter for evaluating the flammability hazards of fuels. %his article derives and discusses eight simple rules for estimating flammabilityparameters of single or mixed organic fuels in air under atmospheric conditions. %e rules apply to fuels containing combinations of C+H+O+N atoms that burn to carbon dioxide plus water Apart from the trivial First Rule, each rule i~ e.?cpressed in term ofthe heat of oxidation.Two Rules are presented for lowerflammable limit (LFL) estimation. %e First Rule is approximate and requires only the stoichiometric ratio of oxygen to fuel "S. "Although it outperforms Lloyd's Rule, it similarly overestimates the LFLs of energetic. fuels such as acetylene and ethylene oxide.The Second Rule requires both 3" and the net heat of combustion "AH. "It is shown that the LFL is inverselyproportional to theproduct of heat of combustion and beat of oxidation. LFL predictions are typically within experimental error of reported values, including energetic fuels such as acetylene and ethylene oxide.%be Third Rule shows that lower limitflame temperatures decrease linearly with increased heat of oxidation and increase stepwise between hydrocarbons and other organic fuels containing oxygen and nitrogen atoms.The Fourth Rule shows that the Limiting Oxygen Concentrations (LOCs) of non-decomposable fuels decrease with the inverse square of beat of oxidation. It is proposed that the optimum fuel concentration at the LOC is related via diffusivity ratio to the stoichiometric concentration. A fuel-oxygen Cartesian flammability diagram is suggested forpresenting LOC data.The Fijth Rule shows that maximum flame temperatures increase linearly with increased heat of oxidation and decrease stepwise between hydrocarbons and other organic fuels containing oxygen and nitrogen atoms. l;be Sixth and Seventh Rules address fundamental burning velocity "S,." and lowest minimum ignition energy (MIE), second order polynomial expressions being presented for easily calculating these parameters. It is shown how the calculated S can be used to estimate normalized rate of pressure rise 'K." data. It is also demonstrated that many published LMIE and quenching distance values are too high.The Eighth Rule gives a tentative expression for quenching distance, which decreases lineady with increased heat of oxidation. A scheme is presented for ranking fuel hazards in terms of heat of oxidation. Demarcations are made in terms of S,,, LMIE and Class I NEC and Zone Groups. It is shown how the approach might be extended to deflagration and detonation arrester selection.

A novel QSPR model for prediction of lower flammability limits of organic compounds based on support vector machine

“…Moreover, these theoretical descriptors have definite physical meanings, which are useful to probe the physicochemical information that has significant contribution to the LFL property. Regarding the statistical parameters of the models, both the MLR and NN models of work [7] were worse in terms of AAE and RMSE than the presented model. Moreover, the presented model is developed based on larger number of compounds in the dataset (830 versus 144), and also more compounds are employed in the test set for model external validation (208 versus 50).…”

“…Moreover, the presented model is developed based on larger number of compounds in the dataset (830 versus 144), and also more compounds are employed in the test set for model external validation (208 versus 50). Finally, regarding the applicability range of the models, the use of the models of work [7] requires extra data of needed physicochemical properties, and if only one of the needed properties is missing, calculation cannot be performed to predict the LFL. Oppositely, because only theoretical descriptors derived solely from the molecular structure is involved, the presented model would theoretically be used to reliably predict the LFL for any organic compound belonging to its applicability domain.…”

“…There have already been several methods reported in the literatures for predicting the LFL of organic compounds, which can be classified into several categories containing group contribution models [2], empirical correlations [3][4][5][6][7], and the quantitative structureproperties relationship (QSPR) models [8]. These methods have been extensively reviewed by Vidal et al [1] and Albahri [9].…”

Sustained Burning of Water-based Paint Sprays

“…Britton [11] summarizes flammability prediction rules for single and mixed organic fuels in air under atmospheric conditions. The author showed that the maximum flame temperature can be approximately computed as a function of the net heat of complete combustion, c H Δ , and the stoichiometric ratio of oxygen to fuel, S .…”

Experimental flammability limits and associated theoretical flame temperatures as a tool for predicting the temperature dependence of these limits

“…That heat of oxidation ranges from 96 to 106 kcal/mol O 2 , with an average close to 100 kcal/mol O 2 . The combustion of hydrogen (H 2 ), carbon monoxide (CO), acetylene (C 2 H 2 ), formaldehyde (H 2 CO), ethylene oxide (C 2 H 4 O), and hydrazine (N 2 H 4 ) are examples of common exceptions to the above energy ranges (Britton, 2002). More recently, reliable and somewhat conservative estimates of both the lowest flammable concentration and limiting oxygen concentration for many fuels have been made using the heat of oxidation, or a combination of the heat of oxidation and the limit heat of combustion of fuel-air mixtures (Britton, 2002;Britton & Frurip, 2003).…”