The risk assessment of reactive chemicals or energetic materials is an important concern in chemical and petrochemical industries and is a key area of research at the Mary Kay O'Connor Process Safety Center. The paper discusses applications of molecular modeling to obtain thermochemical data for reactive or hazardous materials and to predict calorimetric data based on molecular properties. Hydroxylamine (HA) is an example of a highly reactive and poorly characterized compound with important industrial applications. The heat of formation for gaseous hydroxylamine under standard conditions is calculated, using isodesmic reactions at several levels of theories, including HF, B3P86, B3LYP, MP2, MP3, MP4, CCSD(T), G2, G2MP2B3, G3B3, G3, and CBS-Q, and several basis sets, including Dunning correlation consistent and Pople-style. To gauge the computed HA values, the gaseous hydrogen peroxide heat of formation is calculated by the same methods and compared with experimental data. Based on our calculations, we recommend an average value of -11.4 kcal/mol for the gaseous HA heat of formation at 1 atm and 298.17 K. The oxygen balance method, ASTM CHETAH, and the calculated adiabatic reaction temperature (CART) are a few of the theoretical methods that are commonly employed for reactive hazard evaluation. In an alternate approach, data obtained from calorimetric experiments and published kinetic parameters were correlated using calculated molecular properties. Quantitative structure-property relationships (QSPR) based on quantum calculations were employed to correlate calorimetrically measured onset temperatures and heats of reaction with molecular properties. The primary objective is to extend and complement available experimental data with predictions for the species where no or few experimental data exist. (C) 2004 Elsevier B.V. All rights reserved.