Acute Events and Fatal Outcomes Following Exposure to Volcanic Gases (SO2, CO2, H2S): A Systematic Review

Background: Volcanic gas emissions represent an important but frequently underestimated non-eruptive natural hazard capable of causing severe acute intoxication and sudden death, even in the absence of volcanic eruptions. Although numerous reviews have investigated the chronic health effects of volcanic emissions, evidence regarding acute exposure events remains fragmented. This systematic review aimed to synthesize the available evidence on acute intoxication events and fatalities associated with exposure to sulfur dioxide (SO2), carbon dioxide (CO2), and hydrogen sulfide (H2S) of volcanic origin. Materials and Methods: A systematic literature search was conducted according to the PRISMA 2020 guidelines across six electronic databases (PubMed/MEDLINE, Scopus, Web of Science, Embase, Google Scholar, and WHO IRIS). Results: Six eligible studies describing fatal and non-fatal acute exposure events from five countries (Italy, France, the United States, Cameroon, and the Democratic Republic of Congo) were included. Carbon dioxide and hydrogen sulfide were the gases most frequently associated with fatal outcomes, predominantly occurring in confined spaces, geothermal areas, fumaroles, topographic depressions, or environments where adverse meteorological conditions promoted gas accumulation. The most common clinical manifestations included sudden loss of consciousness, pulmonary edema, respiratory failure, and asphyxial death. The largest documented event, the 1986 Lake Nyos disaster, resulted in more than 1700 fatalities following a massive limnic release of carbon dioxide. Conclusions: Across the included studies, recurring environmental determinants, exposure pathways, and toxicological mechanisms highlighted the critical role of environmental accumulation in shaping exposure risk. Despite the limited number of published cases, the available evidence demonstrates that acute volcanic gas exposure constitutes a significant yet underrecognized public health hazard. Strengthening environmental monitoring, risk communication, visitor safety measures, and interdisciplinary surveillance systems may substantially reduce preventable morbidity and mortality in volcanically active regions.