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Thunderstorm-associated asthma epidemics have been documented in the literature, but no Canadian experience has been reported. On July 31, 2000, a thunderstorm-associated epidemic of asthma or shortness of breath occurred in Calgary, Alberta. The Calgary Health Region investigated the event using diagnostic data from emergency departments, an urgent care medical clinic and patient interviews, in addition to bioaerosol counts, pollutant data and weather data reflecting atmospheric conditions at that time. On July 31, 2000 and August 1, 2000, 157 people sought care for asthma symptoms. The expected number of people to seek care for such symptoms in a 48 h period in Calgary is 17. Individuals with a personal or family history of asthma, allergies or hay fever who were not taking regular medication for these conditions and who were outdoors before the storm appeared to have been preferentially affected. A stagnant air mass the day before the thunderstorm may have resulted in declining bioaerosol concentrations, and the possible accumulation of spore and pollen reservoirs within mould and plant structures. The elevated bioaerosol concentrations observed on the day of the thunderstorm may be attributed to the sudden onset of high winds during the thunderstorm, which triggered a sudden release of spores and pollens into the atmosphere, which was probably responsible for the epidemic. Several pollutant levels slightly increased on the day of the storm and possibly also played a role in symptom development. It is unclear whether an atmospheric pressure drop contributed to the release of spores and pollens.

This paper discusses the implosion of a large inner-city hospital in Calgary, Alberta, Canada, on October 4, 1998. Stationary and mobile air monitoring conducted after the implosion indicated there were several short-term air quality issues, including significant temporal increases in total suspended particles, particulate matter (PM) with aerodynamic diameter less than or equal to 10 microm (PM10), PM with aerodynamic diameter less than or equal to 2.5 microm (PM2.5), asbestos, and airborne and settled lead. In addition, the implosion created a dust cloud that traveled much further than expected, out to 20 km. The ability of an implosion to effectively aerosolize building materials requires the removal of all friable and nonfriable forms of asbestos and all Pb-containing painted surfaces during pre-implosion preparatory work. Public advisories to mitigate personal exposure and indoor migration of the implosion dust cloud constituents should extend to 10 or 20 km around an implosion site. These findings point to a number of complex and problematic issues regarding implosions and safeguarding human health and suggest that implosions in metropolitan areas should be prohibited. Further work to characterize the public health risks of conventional versus implosion demolition is recommended.

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