Health hazards and disaster potential of ground gas emissions at Furnas volcano, Sao Miguel, Azores

A health hazard assessment of exposure to soil gases (carbon dioxide and ra don) was undertaken in the village of Furnas, located in the caldera of an active volcano. A soil survey to map the area of soil gas flow was undertak en, gas emissions were monitored at fumaroles and in eight houses, and a pr eliminary radon survey of 23 houses in the main anomaly area was performed. Potential volcanic sources of toxic contamination of air, food, and water were also investigated, and ambient air quality was evaluated. About one-th ird (41 ha) of the houses were located in areas of elevated carbon dioxide soil degassing. Unventilated, confined spaces in some houses contained leve ls of carbon dioxide which could cause asphyxiation. Mean indoor radon leve ls exceeded UK and US action levels in the winter months. A tenfold increas e in radon levels in one house over 2 h indicated that large and potentiall y lethal surges of carbon dioxide could occur without warning. Toxic exposu res from the gaseous emissions and from contamination of soil and water wer e minimal, but sulphur dioxide levels were mildly elevated close to fumarol es. In contrast, evidence of dental fluorosis was manifested in the populat ion of the nearby fishing village of Ribeira Quente where drinking water in the past had contained elevated levels of fluoride. The disaster potential of volcanic carbon dioxide in the area could also be associated with the h ydrothermal system storing dissolved carbon dioxide beneath the village. Fe lt, or unfelt, seismic activity, or magma unrest, especially with a reawake ning of explosive volcanic activity (30% probability in the next 100 years) could result in an increase in gas flow or even a gas burst from the hydro thermal system. A survey of all houses in Furnas is advised as structural m easures to prevent the ingress of soil gases, including radon, were needed in some of the study houses. Evaluations of the human hazards of volcanic g ases should be undertaken in all settlements in volcanic and hydrothermal a reas associated with soil gas emissions. (C) 1999 Elsevier Science B.V. All rights reserved.