Just how safe is that printer in the office? Depending on the particular model, not very, according to research from Lidia Morowaska at the Queensland Institute of Technology. Back in 2007, we reported on Dr. Morawaska's findings that laser printers were the biggest determining factor of indoor air pollution in offices, a study that didn't go down well with printer manufacturers.

Now there's a follow-up from the same research group, focusing on the nature of the particulate pollution emitted from laser printers. These submicron-sized particles appear to be formed by complex reactions between volatile organic compounds (VOCs) with the help of both heat and ozone.

The work involved tested two printers, an HP 2200 and an HP 1320n. The latter is known to emit many more particulates than the former, by as much as three orders of magnitude (or 100,000 percent more), and both printers were tested while being put through their paces printing pages with no toner coverage, five percent toner coverage, or 50 percent toner coverage. Some tests were conducted in a flow-through tunnel to measure particle nature, while others were performed in another chamber that allowed the scientists to measure the persistence of the particles, as well as other variables that required a longer assay time.

Various components of each printer, such as the fuser rollers, toner powder, and so on, were also heated in a furnace to determine the nature of their emissions as a result of heating. Below a certain temperature threshold, there were almost no emissions from any of the tested components. Above these thresholds (as low as 100?C in the case of a used roller, and as high as 200?C for the lubricating oil) there were rapid increases in the concentrations of VOCs and particulates, with the particulates being formed at slightly higher temperatures than the VOCs in all cases.

The data gathered from the flow tunnel showed the different printers had quite different profiles of particulate release, tested over the course of printing 150 pages. The HP 2200 shoed a peak of particulate emissions within the first minute, which then began to decrease over the course of the print job, until falling rapidly to zero after the printing was finished. The HP 1320n also had an initial peak in the first minute, although the amount of particles emitted was many times higher. However, unlike the other printer, emissions skyrocketed again after about 2 minutes, and stayed elevated until the end of the print run, with levels around 1000 times greater than the HP 2200.

Switching toner between the different printer models had a modest effect on the particle emission, as did different types of paper, although this was not the primary cause. Instead, it appears that the speed and sophistication of temperature control within the printers is the main determining factor governing particle emission. The HP 1320n actually operated at a lower average temperature than the HP 2200, but temperature spikes are likely causing reactions to take place that result in particle creation. Presumably the identification of the makeup of these particles, along with the knowledge of how to avoid their creation (better temperature control in the printing process) should help manufacturers take steps in future printer design to make their devices a little less toxic to the office worker.

Environ. Sci. Technol, 2009. DOI: 10.1021/es802193n