This article was originally published in the January/February 1994 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.



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Home Energy Magazine Online January/February 1994




Are Blower Doors Hazardous?

New Department of Energy guidelines encourage state weatherization programs to adopt advanced diagnostics, including blower doors and infrared thermography. These technologies are well known in the weatherization industry, but safety questions arose when blower door use was proposed in Delaware. These safety concerns attracted the attention of two state senators and were reported by a major newspaper. The concerns threatened the adoption of these technologies and delayed the entire state weatherization program.

What started this? A contractor and a community organization claimed that blower door depressurization could draw up and circulate loose asbestos, fiberglass or other harmful materials, exposing weatherization workers and home occupants to health risk, and exposing contractors to lawsuits based on that health risk.

As part of a survey of weatherization issues in Delaware, the Center for Energy and Environmental Policy tried to find out what health risks were known. We began by distinguishing between occupants and weatherization workers. We believe that any possible danger could at most apply only to weatherization workers, not to home occupants. This is because hazards from such exposure are a function of dose and exposure time. The dose would be very low in either case. Workers would be exposed for a maximum of an hour or two daily, whereas occupants of the home being weatherized, if they were home during the procedure, would be exposed for less than an hour of their entire life. (The blower door usually operates for only 10-60 minutes.) Because we saw no plausible argument for danger to occupants, we concentrated on the question of a possible hazard to weatherization workers.

We consulted with two researchers, Max Sherman and Rich Sextro, both with Lawrence Berkeley Laboratory (LBL). Sherman is staff scientist and leads LBL's Energy Performance of Buildings Group. He acknowledged the theoretical possibility of a very small risk to weatherization workers. By comparison, he identified common procedures used in weatherization and construction work, such as exposure to chemicals in caulking and breathing of attic air, as larger risks. Thus, he advised, if the goal was to reduce exposure to risk, one could begin by reducing the risks of exposure to these other substances, and then conduct research to see whether blower doors caused any measurable problem. Even if they did, Sherman suggested that a simple solution would be using blower doors in pressurization mode only. Pressurization mode would blow any hazardous materials out of the house, away from weatherization workers or occupants. (The current practice is to use both depressurization and pressurization modes.)

Sextro, a staff scientist with LBL's Indoor Environment Program, has published extensively on health hazards from indoor air. Although he is familiar with blower doors and has conducted research on more hazards from indoor home air than any of us would like to think about, he had not previously ascertained any reason for concern about blower doors. The physical process that could expose anyone, he said, would require increased air flow through cracks small enough to have high air velocity, combined with a place where asbestos or other hazardous particles accumulated. Most cracks in existing housing would not meet these criteria. Further, the velocity would have to be high enough to re-entrain the dust (raise it from the surface up into the air). Sextro's experience was that re-entrainment required a strong jet of air, and that it would be difficult to demonstrate any building configuration that would re-entrain dust under blower door pressurization.

Sextro said dust in existing furnace ducts would be a larger problem, since ducts have high air flow through them whenever the heating or cooling system is on. However, measurements in ducts have shown that dust does not move much when the furnace is blowing. As another comparison, Sextro noted that whole house fans depressurize houses at pressures up to those of blower doors. Since whole house fans run for long periods of time in summer, if there were such a risk from blower doors, existing whole-house fans would constitute a greater hazard. Like Sherman, Sextro compared the speculative hazard to installers from blower doors with other hazards faced by construction workers. Common operations such as tearing out an old wall during remodeling, he said, would expose a worker to far more hazardous materials than would a blower door.

In short, it may be conceivable that blower doors can raise hazardous materials into the air, but while such risks are theoretically possible, they are quantitatively very small or zero.

We presented this conclusion in administrative hearings of the Delaware Office of Community Services and relayed them to the Delaware General Assembly as part of our broader report on weatherization. The state found the arguments against using blower doors unconvincing. Delaware now uses blower doors and infrared thermography in its weatherization program.

-- Willett Kempton

Willett Kempton is a senior policy scientist with the Center for Energy and Environmental Policy at the University of Delaware in Newark. The report referred to above was written by Craig R. Kuennen, Ashley Miller, and Chongfang Wang, under the supervision of John Byrne and Willett Kempton. Copies can be obtained from the Center for Energy and Environmental Policy, University of Delaware.


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