Nicotinic acid (C6H5NO2), also known as vitamin 133 or niacin, can be produced from 3-picoline by direct oxidation with air and water vapour at high temperature. For safe handling of combustible or flammable substances, it is imperative to have an understanding of their safety-related flammability characteristic parameters. In this paper, 3-picoline/water mixtures ratios were varied over a wide range (5, 10, 30 and 100 vol%). These were studied in a 20-l-apparatus under initial conditions of 760, 1520 mmHg, 270, together with various oxygen concentrations based on realistic conditions. The water vapour dilution effects on the explosion limits, maximum explosion pressure, vapour deflagration index and minimum oxygen concentration were explored; a triangular flammability diagram was also established. These results will be very helpful for developing a safer design and operation process.