Volume 7, Number 2
May 1983

Contaminated Aerosol Dusters

A recently recognized problem in the electronics industry may be of interest to conservators. It concerns the widely used duster cans containing fluorocarbon liquids that generate small jets of "clean" gas for blasting dust off surfaces.

Aerosol dusters were first introduced over 1S years ago for photographic darkrooms and general laboratory applications such as cleaning microscope slides. But then stories began to appear in photographic literature cautioning against using them on camera lenses because the gas jet is very cold and can produce small areas of frost that cracks glass. Even so they have become quite ubiquitous. Museum people use them to dust rows of books, silver articles, rocks and minerals, and in general any irregular objects that are difficult to dust by contact.

Recent (unpublished) infrared spectrophotometric analyses by Dr. Richard N. Roberts showed that the gas from duster cans of five manufacturers was contaminated with appreciable amounts of the organic oil dioctylphthalate (2-ethylhexylphthalate). This oil is commonly used as a plasticizer in plastics such as vinyl (PVC); it is sometimes seen as a film on new car windows. This same contaminant was also found in a five-gallon bulk container of fluorocarbon liquid, indicating that the contamination occurred at the liquid manufacturer who supplies the various can vendors. If so, it should eventually be eliminated at the source now that it has been recognized, but this still leaves existing inventories of duster cans of unknown quality.

The amount of oil in the cans is more than a trace and is observable by a simple test. Invert a duster can and insert the long nozzle into a clean test tube or small beaker. In this position the can will discharge liquid instead of gas as it does in the upright position. Run several milliliters of liquid into the test tube to a depth of about an inch and let it evaporate. The oil, if present, will be visible to the eye as a hazy residue on the glass.

The oil is not extremely toxic nor readily flammable. The National Institute of Occupational Safety and Health (NIOSH) has placed an inhalation limit of five milligrams per cubic meter. The usual warnings against excessive inhalation of fluorocarbon vapors should also be observed.

There are two reasons for conservators to be concerned:

1. Dioctylphthalate is fairly stable chemically but its long-term effects on archival documents and artifacts are unknown. Obviously it is capable of spotting.
2. There is a possible reaction between dioctylphthalate and chlorofluorocarbons (propellants in aerosol cans) that under certain conditions can produce hydrochloric and/or hydrofluoric acids. Such a reaction can be catalyzed (accelerated) on metal surfaces.

It is inadvisable to use contaminated dusters on uncovered daguerreotypes, historic photographs, or silver surfaces. Indeed, even uncontaminated dusters are capable of delivering droplets of fluorocarbon liquid in the gas jet if the can is not upright. These droplets can hydrolyze (react with water of condensation), producing minute particles of acid. Metal surfaces usually promote this reaction.

Rubber bulb brushes, if kept clean, are one alternative to dusters and are recommended by at least one major camera manufacturer for dusting lenses and camera interiors.