Office workers can breathe easily now that German scientists have shown that laser printer emit 'hardly any' particles of black toner, a potential carcinogen.

A previous study by the Queensland University of Technology found that printers emitted clouds of particles that were five times higher than levels outside, which they assumed could include potentially dangerous toner dust.

However, researchers at the Fraunhofer Wilhelm Klauditz Institute in Braunschweig looked into exact composition of the emissions.

"Some printers do emit ultra-fine particles made of volatile organic-chemical substances," says WKI Professor Tunga Salthammer. "But one essential property of these ultra-fine particles is their volatility, which indicates that we are not looking at toner dust."

Toner deaf

The scientists confirmed their conclusions by testing a range of printers without any paper or toner in them - and still detected the ultra-fine particles.

They concluded that the particles were coming from the printers' fixing unit – a component that heats up as high as 220°C during the printing process in order to fix toner particles on the paper.

Ultra-fine particles are produced by many household gadgets that have an electric motor or heating element - such as toasters - but little research has been done into their possible toxicity.

In any case, say Fraunhofer boffins, there's nothing to be done: "Our investigations show that as the ultra-fine particles are not emitted from a specific part of the printer, but also from the paper output, filters can only have a limited effect."