Office workers may be breathing in dangerous dust emitted from laser printers, finds a disturbing new study from Australian researchers.

The researchers found that certain printers release tiny particles into the air that could pose "a significant health threat" when inhaled into their lungs.

The researchers didn't analyze the chemical makeup of the particles but think that they come from the toner, the ultrafine powder used in laser printers instead of ink. They found that the printers emitted more dust when the toner cartridge was new, and when the printers were used for printing graphics, which require greater amounts of toner.

Lidia Morawska, a professor in the School of Physical & Chemical Sciences at the Queensland University of Technology and colleagues looked at 62 brands of printers. They classified 17 of them as "high particle emitters" because they released such elevated quantities of particles.

One of the printers released so many particles, it was at a rate comparable to the particle emissions from cigarette smoking.

On the other hand, 37 of the 62 printers didn't release enough dust to diminish air quality; six released low levels, and two, medium levels.

The study, to be published in the American Chemical Society's journal Environmental Science & Technology (ES&T), included popular models sold under the names of Canon, HP Color Laserjet, Ricoh and Toshiba.

Morawska said her findings were made by accident. Her team had been testing a large, open-plan office in the Brisbane central business district to gauge the efficiency of ventilation in protecting office workers from outdoor air pollution.

What they found instead was that indoor particle levels in the office air increased five-fold during work hours due. They then realized the particles were coming from the printers.

"We really didn't expect to find anything from indoor sources (but) we soon discovered that the indoor sources of pollution were far higher than the outdoor sources," Morawska said. "We soon realized that we were seeing air pollution originating indoors, from laser printers."

Since the researchers don't know what chemicals lie in the printer dust, the health effects of breathing it in are unclear. But they could range from respiratory irritation to more severe illnesses, such as cancer, Morawska says.

As a result of the study, her team is calling on governments to consider regulating emission levels from laser printers.

"By all means, this is an important indoor source of pollution," she says. "There should be regulations."

• Here is a full list of the results, based on the ratio of submicrometre particles emitted by various printers to the "normal" or base background particle concentration:

*Possible high emitter