The danger of dust

Author: Ed Cohen

With all due respect to the ’70s rock band Kansas, it may be time to retire “Dust in the Wind” as a metaphor for things transitory and inconsequential.

Dust particles, in their many organic and inorganic forms, are attracting serious and increasing attention from researchers, especially in the health and legal fields.

Earlier this year a New York Times Magazine article described the case of a family in Dripping Springs, Texas, west of Austin, who had to abandon their mansion of a home after discovering it was infested with toxic mold. The homeowners believed invisible mold spores had caused them to suffer symptoms ranging from dizziness to, in the husband’s case, brain damage involving memory loss. The family is suing their homeowner’s insurance company for not addressing the problem when it paid for repair of a water leak. The leak apparently fed the growth of the mold on the backside of their walls. Publicity from the case was said to be nourishing an epidemic of toxic-mold liability litigation.

Spores, pollen and tiny bits of everything from the metal incinerated in welding operations to tobacco from smoked cigarettes hang around in the air at the scale of micro-particles. Larger than individual molecules — which are what strike the sensors in our nasal passages and allow us to distinguish between cookies baking or a cat’s litter box that needs changing — micro-particles are still plenty small enough to be inhaled.

About the only time we become aware of the swarm of micro-particles sharing our breathing space is when we look sideways at a shaft of sunlight casting a bright rectangle on carpet. Most of these micro-particles will catch in our nose hairs or mucous and pass harmlessly through our digestive tract. But some particles, especially those too small to see, will travel deeper. And if they contain pathogens our body isn’t strong enough to fight off, they will make us sick.

“More people die from air pollution each year than from traffic accidents, which in this country alone is over 40,000 people per year,” says Patrick F. Dunn, professor of aerospace and mechanical engineering at Notre Dame.

Since the late 1980s, Dunn and fellow engineering professor Raymond M. Brach have been investigating the physics of how micro-particles adhere to and release from surfaces. In the beginning the pair looked at an idealized situation: tiny, manufactured spheres of glass, plastic and other materials dropped through a vacuum onto a “molecularly smooth” surface like the silicon wafers used in the manufacture of microcircuits. These circumstances bore scant resemblance to the real world of dust movement, but it helped them develop a model of micro-particle surface adhesion and release.

The faculty members and their graduate assistants have since gone on to study how plant spores adhere to such common household surfaces as Formica table tops and wallboard. Among other results, their findings point to an optimum angle at which air filters can be positioned to do the most good.

Soon they hope to investigate how the complex particles that constitute cigarette smoke stick to and release from surfaces. This information could have implications in the area of second-hand smoke, and here’s how: A person could breathe in cigarette smoke particles years after a building went smoke-free if the particles were to become re-suspended in the air as a result of, say, cleaning out the building’s air ducts.


ND aerospace and mechanical engineering