In response to an alarm back in 2007, about alleged health threats from home and office laser printers, researchers conducted controlled experiments to determine just what substances the devices release into indoor environments and how much they release.

A report just published by a team from the International Laboratory for Air Quality and Health at Queensland University of Technology in Australia gives a clearer picture of the problem.

The main issue in the report is fine particulate matter emitted by the printers. Apparently, it’s not the laser toner or paper that’s the problem. Rather, it’s the product of a complex reaction between the paper dust, toner and mechanical lubricants in the presence of ozone and heat generated during the operation of the machines — particularly, by the fusing assemblies which use intense hat to bind the toner to the paper.

The report emphasizes that occasional printing produces only low levels of the potentially toxic particles. But during sustained printing — periods of continuous operation lasting more than a few minutes — the level of toxic emissions skyrockets.

The report also noted that there is a wide variance been makes and models of printed in the amounts of particulate matter they expel and the temperature that must be reached to accelerate emissions to dangerous levels. Some printers, in fact, produced up to 1,000 times more particle emissions than others.

The Ars Technica Web site offers an in-depth look at the report and a complete copy of the report can be ordered from ACS Publications for (US)$30.