Juan A. Vílchez

Hazard and operability (HAZOP) analysis. A literature review

Hazard and operability (HAZOP) methodology is a Process Hazard Analysis (PHA) technique used worldwide for studying not only the hazards of a system, but also its operability problems, by exploring the effects of any deviations from design conditions. Our paper is the first HAZOP review intended to gather HAZOP-related literature from books, guidelines, standards, major journals, and conference proceedings, with the purpose of classifying the research conducted over the years and define the HAZOP state-of-the-art.

Historical analysis of accidents in chemical plants and in the transportation of hazardous materials

Abstract A survey of accidents involving hazardous materials has been performed. A total of 5325 accidents taken from the database MHIDAS, covering from the beginning of this century up to July 1992, were used to study the contribution of different situations, activities, equipment, etc to the risks associated with hazardous materials. The data show the percentages of accidents involving transport (39%), process plants (24.5%) and storage (17.4%), as well as the frequency of occurrence of accidents in highly populated areas (66%), low-populated areas (12%) and rural areas (22%). The different types of accidents were also analysed, as well as their origin and causes. The consequences of the accidents, both with regard to people and economic losses, were assessed. The accumulated frequency-fatality curve has been plotted: the line follows approximately a straight line, with a slope of −0.84. Finally, several conclusions were derived about the effort which should be devoted to decreasing the risk in the future.

Historical analysis of accidents in the transportation of natural gas

The purpose of the present analysis is to determine the main features of accidents occurring in the transportation and distribution of natural gas (in a gaseous state). A survey of 185 accidents taken mainly from the database MHIDAS has been performed. Of these, 131 (70.8%) occurred in transport systems, 32 (17.3%) in process plants, 13 (7.0%) in storage plants and nine (4.9%) in domestic/commercial activities. The 131 accidents occurring in gas pipes were selected for further analysis. The data show that the most frequent accident was explosion (86 cases, 65.6%) followed by loss of containment (63 entries, 48.1%) and fire (56 entries, 42.7%). The cause of the accident was identified for 90 cases (68.7%). Of these, the most frequent causes were mechanical failure (39 entries, 43.3%), impact failure (37 entries, 41.1%) and human error (32 entries, 35.6%); of the specific causes, impact failures due to excavating machinery were especially numerous (21 cases, 23.2% of known causes). The consequences of the accidents, in terms of both human and economic losses, are assessed. Finally, some conclusions are given about the risks involved in natural gas transportation.

Fire and explosion hazards during filling/emptying of tanks

Abstract Loading and unloading operations produce 8% of all accidents which occur in process plants and in the transportation of hazardous materials. A survey of 738 accidents was performed, allowing the identification of the accident type distribution and of their cause. Some considerations on flammable mixtures are also presented, and the procedures to avoid these mixtures occurring when filling or emptying a tank are briefly discussed.

Information on the risks of chemical accidents to the civil population. The experience of Baix Llobregat

The population has the right to know the risk to which they are exposed due to the existence of certain industrial plants. Furthermore, the knowledge of this risk and of several simple rules to be applied during an emergency will increase considerably the safety of the population. However, giving the adequate information is not easy, as there is the possibility of creating anxiety and fear instead of calming the population down. This communication describes the experience developed in the strongly industrialized zone of Baix Llobregat (Catalonia), where an acoustic alarm system was set up: a set of informative sessions (55) were carried out to different collectives of nine villages. The public were of very different education profiles (from engineers to people with a low cultural level). Supplementary illustrative material was distributed. As a whole, the results were satisfactory, although several difficulties were found.

A dispersion safety factor for LNG vapor clouds

The growing importance of liquefied natural gas (LNG) to global energy demand has increased interest in the possible hazards associated with its storage and transportation. Concerning the event of an LNG spill, a study was performed on the relationship between the distance at which the lower flammability limit (LFL) concentration occurs and that corresponding to the visible contour of LNG vapor clouds. A parameter called the dispersion safety factor (DSF) has been defined as the ratio between these two lengths, and two expressions are proposed to estimate it. During an emergency, the DSF can be a helpful parameter to indicate the danger of cloud ignition and flash fire.