Explosive demolition of buildings can produce significant increases in harmful airborne dust particles, but the consequences are short-lived, according to a study released yesterday by researchers at the Johns Hopkins Bloomberg School of Public Health.
The study - one of the first to examine the effects of explosive demolitions on air quality - concluded that spectators should be discouraged from standing near the site, and that neighbors should stay indoors or try to be upwind from the area.
"There was a huge spike in air particles associated with the implosion, which I think was very intuitive," said Timothy J. Buckley, the study's lead author and an associate professor in the school's environmental health sciences department. "What came as a surprise is that I would have expected that the concentrations would have remained elevated for some time - on the order of hours - beyond the implosion. That didn't happen."
Published in this month's Journal of the Air and Waste Management Association, the report focused on the demolition of the 22-story Broadway Homes at Broadway and Fayette Street in East Baltimore on Aug. 19, 2000. The wreckers used dynamite to collapse the building on itself, a process known as implosion.
In 1999, Baltimore chose that technique to tear down all of its high-rise public housing complexes for families. The last, Flag House Courts, was demolished in February 2001.
For the study, monitors were placed at four indoor and seven outdoor locations around the Broadway Homes site. They measured the implosion's effect on air quality in buildings at nearby Johns Hopkins Hospital and on people in the neighborhood.
Research has shown that airborne dust particles can increase the risk of a variety of health problems. They are particularly irritating to the lungs of children, the elderly and people with respiratory disease, Buckley said.
Scientists found that the concentration of airborne dust particles in the immediate area jumped substantially in the minutes after the implosion - as much as 3,000 times higher than just before the charges went off. About 7 1/2 blocks away, the concentration increased about 20 times when the plume of dust reached the area.
But within 15 to 20 minutes, the concentration of airborne dust had returned to pre-implosion levels, according to the report. Indoor monitors detected no significant change in dust particles.
"There was little to no wind that day, so I was very surprised that the plume dissipated at the rate that it did," said Christopher M. Beck, who worked on the project for his master's thesis and is a doctoral student and senior research technician at the school.
Tests showed that the airborne dust particles did not ex- ceed the Environmental Protection Agency's standards - because the EPA has only a 24-hour standard, not one for short-term events, Buckley said.
"I think it [the report] highlights the need for considering some sort of health-based guidelines," he said.
The preliminary results of the study were used to develop neighborhood warnings before the Flag House Courts implosion to discourage onlookers from standing too close to the dust plume.
"We hoped the spectator aspect of it would be avoided," Beck said. "There were literally families and children lining the perimeter of the fence that was there to keep people safe from debris. They would be coated with a layer of dust."
He added that "the bigger health threat is the dust that doesn't settle out, that's small enough to collect in the lungs."
Johns Hopkins researchers have published at least one other study on the Broadway Homes implosion. That report, released last year, found that there was no increase in the count of Aspergillus fungi or other airborne particles inside the nearby hospital buildings after the demolition.