Chemical accidents involving explosions, large fires and leakages of hazardous substances occurring during transport, storage and industrial production of chemicals constitute a real challenge to health, environmental and industrial safety professionals. The aim of this article is to discuss the main questions that this kind of accident provokes, in terms of public health, particularly in developing countries such as Brazil. The paper defines and characterises these accidents and the various health risk they involve excluding the leakages of hazardous substances during "normal" production in industry--through the combination of quantitative and qualitative information drawn from the international literature on the subject. From some examples of chemical accidents such as occurred in Bhopal (India), Vila Socó (Brazil), São Paulo (México) and data of the World Health Organization (WHO), the authors seek to show that these events present a worsening, in terms of immediate deaths and injuries, in developing countries. The statistics of chemical accidents which occurred during the last ten years (1984 to 1993) in the State of Rio de Janeiro are used taken as a frame reference for the purpose of bringing to light the great number of occurrences made with no registration of basic information regarding assessment or surveillance. The complexity of causes and consequences, together with the structural problems of developing countries, present public health professionals and institutions, with some important tasks especially those of health risk assessment and the formulation of strategies to prevent and control future major chemical accidents.