Immediate public health concerns and actions in volcanic eruptions: Lessons from the Mount St. Helens eruptions, May 18-October 18, 1980

A comprehensive epidemiological evaluation of mortality and short-term morbidity associated with explosive volcanic activity was carried out by the Centers for Disease Control in collaboration with affected state and local health departments, clinicians, and private institutions. Following the May 18, 1980 eruption of Mount St. Helens, a series of public health actions were rapidly instituted to develop accurate information about volcanic hazards and to recommend methods for prevention or control of adverse affects on safety and health. These public health actions included: establishing a system of active surveillance of cause-specific emergency room (ER) visits and hospital admissions in affected and unaffected communities for comparison; assessing the causes of death and factors associated with survival or death among persons located near the crater; analyzing the mineralogy and toxicology of sedimented ash and the airborne concentration of resuspended dusts; investigating reported excesses of ash-related adverse respiratory effects by epidemiological methods such as cross-sectional and case-control studies; and controlling rumors and disseminating accurate, timely information about volcanic hazards and recommended preventive or control measures by means of press briefings and health bulletins. Surveillance and observational studies indicated that: excesses in morbidity were limited to transient increases in ER visits and hospital admissions for traumatic injuries and respiratory problems (but not for communicable disease or mental health problems) which were associated in time, place, and person with exposures to volcanic ash; excessive mortality due to suffocation (76 per cent), thermal injuries (12 per cent), or trauma (12 per cent) by ash and other volcanic hazards was directly proportional to the degree of environmental damage-that is, it was more pronounced among those persons (48/65, or about 74 per cent) who, at the time of the eruption, were residing, camping, or sightseeing (despite restrictions) or working (with permission) closer to the crater in areas affected by the explosive blast, pyroclastic and mud flows, and heavy ashfall; and de novo appearance of ash-related asthma was not observed, but transient excesses in adverse respiratory effects occurred in two high-risk groups - hypersusceptibles (with preexisting asthma or chronic bronchitis) and heavily exposed workers. Laboratory and field studies indicated that: volcanic ash had mild to moderate fibrogenic potential, consisting of >90 per cent (by count) respirable size particles which contained 4-7 per cent (by weight) crystalline free silica (SiO2); importantly, community exposures to resuspended ash only transiently exceeded health limits normally applied to entire working lifetime exposures to free silica; and there were no excessive exposures to toxic metals, fibrous minerals, organic chemicals, radon, or toxic gases of volcanic origin in community water supplies or air. Recommended preventive measures include: avoidance of areas of predicted hazards during premonitory and ongoing volcanic activity and use of respiratory protection and wetting methods to control unavoidable exposures to ash. In densely populated countries with relatively frequent explosive volcanic activity, resources for epidemiological surveillance and investigation are needed following widespread environmental damage, mass evacuation, refugee resettlement, and disruption of routine public health services.