Explosion risks resulting from the industrial handling of aqueous ammonia solutions are often not taken, into account in risk assessments, especially for dilute solutins, although accidental explosions implying ammonia vapors are reported in the literature. In fact, ammonia solutions do not show any flash point, but are able to form an explosive atmosphere. In this study, explosivity characteristics of several ammonia solutions, more or less diluted, were determined in a 20-L sphere device. It appears that the explosion range of ammonia solutions depends on the temperature and on the ammonia concentration. The explosion severity is smaller than for pure ammonia because of the presence of water and it tends to decrease slightly with dilution. However, the maximal explosion, pressure is still above 3 bar with the 10% solution. Hence, such aqueous solutions, even diluted, handled in enclosed spaces can. generate great disasters. (C) 2009 American Institute of Chemical Engineers Process Saf Prog 28: 36-44, 2009