The new risk on the block
One of the newer organic explosion risks identified in the recycling industry in the last decade is printer toner dust. No one ever really thought that toner dust was a combustible danger. Then in 2008, awareness grew after two significant dust explosions occurred at toner recycling facilities in Japan. In one incident, the initial explosion ignited in a toner cartridge pulveriser. Dust residue in the cartridges ignited during the crushing process, causing a rise in heat pressure in the pulveriser, and resulting in an explosion. The primary explosion further propagated when expelled toner dust reacted with oxygen in the air.
It has become clear that there is an imperative to manage explosion risk in the print cartridge recycling industry because toner comprises various combustible materials such as carbon, iron and other potentially ignitable organic materials. Their combined dust diameter sizes are mostly less than 10 μm. This is not unlike other organic dusts which are well known to cause explosions such as in paper or biofuel recycling plants, or industries that produce wood based by-products like shredding or pelleting.
How does a dust explosion occur?
As toner powder has become much finer for better copy and print performance, the danger of dust explosions has also increased. Therefore, when exposed to an initial spark, toner is an extremely efficient fuel and that makes it very dangerous.
A fire or explosion results from ignition of combustible material (usually dust, gas or even vapour) when mixed with oxygen in the air. When this takes place inside an enclosed space, like a pulveriser, the rapid rise in pressure could cause an explosion in milliseconds, placing personnel and property at risk.
Most materials handling, processing and storage equipment is not designed to resist the pressure of an expanding flame ball, or deflagration. The effects of accidental fires or explosions can be devastating in terms of lives lost, injuries, damage to property and the environment and to business continuity.
Subsequent studies of toner particle hazards in relation to dust explosions showed that toner particles are possibly more dangerous compared with most organic equivalents.
After the devastating explosions in Japan, further studies and applications were undertaken to prevent toner dust explosion risks. The solutions included the use of toner dust collection vessels and cartridge shredders fitted with explosion suppression and venting systems.
The two most effective means of protection when dealing with this kind of risk are flameless vents and chemical isolation. Both methods are established explosion protection solutions; advanced models like those we develop at BS&B are fully compliant with DSEAR 2002 and ATEX 95, giving users full assurance of performance.
In the UK and Europe, there is a requirement to identify any potentially explosive substances in the workplace. In the UK, this requirement is governed by the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). DSEAR classifies dangerous substances as those used or present at work that could, without adequate controls, cause harm because of a fire or explosion.
In Europe, ATEX is the common name given to two European directives that specify the controls employers should use to prevent explosion risks, which are divided into danger ‘zones’.
Both DSEAR and ATEX recognise various dusts as explosive risks.
Flameless venting is a means of passive relief of explosive pressure that may occur in process or dust collection equipment. Should an explosion occur inside a process or storage vessel containing combustible materials, a rapid rise in pressure may occur putting workers, equipment and building structures at risk.
Those flameless vents designed specifically for dust collectors, bins and shredders, intercept, quench and retain all flame and burning materials, preventing them from being released into the immediate surroundings.
Advanced chemical suppression systems pre-empt the smallest indication of a forming explosion in process equipment and delivers a dry chemical extinguishing agent via a Cannon (also known as a bottle or canister) to prevent any growing internal deflagrations. The system isolates a primary explosion from propagating further; in the case of toner dust, to prevent secondary explosions that might be caused from toner dust cloud interaction with oxygen.
Though a relatively new revelation, toner dust explosions remain a potentially destructive spectre in the print cartridge recycling industry. Precautions like flameless venting and explosion suppression could save millions in lost revenue, equipment, buildings and ultimately, human life.
For more information on BS&B Safety Systems' solutions, contact firstname.lastname@example.org