This is not meant to scare, just to draw attention to the fact that flour, and the vast majority of dusts are combustible, and dust explosions can occur in any enclosed area. Dust explosions are a frequent occurrence in underground coal mines, but they can happen in any location where powdered combustible material is present.
Even an extremely thin dust layer in a closed room is sufficient to trigger an explosion when the dust is swirled up and ignited. Ignition sources for dusts include sparks from electrical or mechanical processes, arcs, open flames, electrostatic discharge (ESD), and electromagnetic waves among others.
A publication by German-based company Stahl explains the mechanisms of a dust explosion: “If a draft of air swirls up a layer of dust in a small area, the dust, along with oxygen, forms a combustible dust/air mix. If this mix is ignited by an ignition source, an explosion is triggered. The force of the resulting explosion swirls up more dust, which is in turn ignited. This process continues, and under some conditions chain reactions such as these sweep through entire buildings or facilities, destroying them.”
The first documented dust explosion is said to have occurred in Turin, Italy, on 14 December 1785, at Mr Giacomelli’s Bakery Warehouse “when flour dust generated during normal handling operations allegedly contacted an ignition source in the form of a lamp mounted to help flour handlers see.”
Since then, numerous dust explosions were recorded in mills, refineries or food processing plants throughout the world. Over time, preventive measures, specific equipment for hazardous areas have helped reduce the number of incidents and better protect those working in explosive environments. But even as recently as 2008, 14 workers died at the Imperial Sugar Savannah in Georgia, USA, when sugar dust accumulated in production areas exploded.
Another tragic example is the “festival of colour” at an amusement park outside Taipei, Taiwan. As part of the entertainment during the event, coloured powder was sprayed over the party-goers, creating a very dense dust cloud over the stage and in the park area nearby. The powder – corn starch – was repeatedly blown into the air for beautiful special effects…until an explosion occurred. It is believed that the powder was ignited either by a cigarette or by the heat emanating from the powerful spotlights and an immense ball of fire very quickly engulfed the stage and ripped through the crowds, injuring more than 500 participants.
Avoiding dust accumulation
The key word here is accumulation. Combustible dust can accumulate inside of, or escape from, equipment and settle on work area surfaces. These accumulations, when dispersed in the air in the presence of an ignition source, can result in an explosion.
Workers, whether they operate in small artisanal bakeries or in industrial-size food processing plants, have specific explosion-proof equipment at their disposal to ensure that storage areas, conveying systems and any piece of machinery used in the production chain meet the strictest safety criteria. The same goes for the vacuum-cleaners and dust collectors that help remove excess dusts and powders from surfaces and crevices to prevent fires and explosions.
The IEC at the forefront
Through its standardization and conformity assessment work, the IEC has a solution for all sectors of industry that are operating in those hazardous environments. The Commission has been at the forefront of Ex standardization for many years, preparing International Standards and establishing a Conformity Assessment (CA) System that provides testing and certification for all types of Ex equipment and related services as well as personnel competence.
Specific requirements for explosive atmospheres
IEC Technical Committee (TC) 31: Equipment for explosive atmospheres, has a complete series of International Standards, IEC 60079, that cover all specific requirements for Ex equipment and systems, from general requirements to protection levels for apparatus used by all sectors that operate in hazardous environments, such as food processing, pharmaceuticals, sugar refineries, flour mills, grain silos as well as the paper and textile sectors.
TC 31 developed the IEC 61241 series of International Standards to focus on electrical equipment in the presence of combustible dust and has recently integrated these requirements into the IEC 60079 series, e.g. IEC 60079-31, Explosive atmospheres - Part 31: Equipment dust ignition protection by enclosure "t".
How to ensure compliance and safety
To make sure that the equipment they purchase meets the very strict requirements specified in the IEC 60079 series, as referenced by national or regional regulations, the Ex industry can rely on IECEx, the IEC System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres for testing and certification.
An IECEx certificate, which is publicly accessible from the official IECEx website, provides clear proof of compliance with International Standards, an important assurance for anyone responsible for the safety of those working in such areas.
Ex areas are a part of almost every industry, from transport, food production and textiles to petroleum and mining. IECEx covers the broad spectrum of devices, systems and services used in explosive environments and verifies their conformance with International Standards. The System also includes the certification of organizations providing services for the inspection (location and other), installation, maintenance and repair of equipment and systems and for the assessment and certification of the competence of personnel working in this highly-specialized area.
More information: www.iecex.com