There is currently, on average, one dust explosion a week in manufacturing factories in the UK. A large proportion of these incidents involve low risk manufacturing processes. Why is this figure so high? Industry experts believe that there is a lack of understanding of how dangerous dusts can be. In this article, we will help you understand the issues associated with dust systems so that you can reduce the likelihood of a dust explosion in your factory.
What Type of Dusts Are Explosive?
Most people would not believe that the majority of dusts are explosive. Combustible dusts include:
- Most solid organic materials (wood, flour, grass, paper, cereals, etc.)
- Many powdered metals (such as aluminium, magnesium and titanium)
- Certain non-metallic inorganic materials (although less common)
These materials may not be combustible in large solid formats, but can suddenly become explosive when fine and sufficiently concentrated in oxygen.
How Do Dust Explosions Occur?
Many production processes by their nature produce dusts which are either allowed to dissipate into the workplace or are controlled using dust extraction systems.
For dust explosions to occur, there is a need for five components to come together:
- The fuel (the dust itself)
- The ignition source (heat, spark or flame)
- Dispersion (allowing the dust to become airborne and in the correct concentration)
- Containment (vessel or environment to allow pressure to build)
What are the Legislative Requirements for Explosive Environments?
The following European Directives incorporated into existing UK legislation impose obligations on manufacturers regarding the prevention of explosions in the workplace.
ATEX 137, incorporated into The Dangerous Substances and Explosive Atmosphere Regulations (DSEAR), covers the risk of explosions in the workplace. It is the responsibility of the manufacturing company to ensure compliance.
ATEX 95 has been integrated into the Equipment and Protective Systems Regulations 1996 (EPS). This directive covers the design of equipment to prevent ignition sources when used in explosive atmospheres. It is the responsibility of the equipment manufacturer/supplier to ensure compliance.
Why is there a risk of an explosion in dust extraction systems?
Dust extraction systems are installed to prevent dusts from entering the workplace and subsequently being inhaled by staff. The likelihood of an explosion in these systems will increase as the dust becomes concentrated in the airstream and filtration equipment.
A large number of dust systems rely on large baghouse filter units to abate the dust. These units are in effect large metal containers in which concentrated dust clouds are created when the units clean down, through either shaking or through a pulse of compressed air. During the clean down process, four of the explosion components are present, with only the ignition source missing.
In many cases the ignition source is an easily identifiable risk such as a flame, spark or heat from a process. However, in some instances this source is an unexpected part of the process or environment – the process could produce static electricity, or human intervention may be such that a spark or flame is created due to deviation from approved procedures or incorrect use of machinery.
With all five components now in place, the likelihood of an explosion is very high resulting in potentially devastating consequences to people and surroundings.
So what can be done to either prevent or reduce the impact of an explosion?
It is not normally practical to build a dust filter strong enough to fully withstand the maximum pressure of a dust explosion. Other methods of protection usually taken are:
- Process isolation: isolation of the process from any potential ignition sources.
- Explosion relief or venting: designing filtration plant to allow safe venting of an explosion to the outside of a building.
- Spark detection and extinguishing: installing detection equipment in the ductwork system and extinguishing the spark before it enters the filter unit.
- Explosion suppression: a technique in which the initial stages of combustion in a dust collector are detected and extinguished (using a suppressant), thus preventing the development of pressures that could result in an explosion.
- Explosion isolation valves: these valves prevent the damaging effect of pressure waves and flames from the dust collector travelling back down the ductwork system and causing further damage to people and the work place. These are usually used in conjunction with explosion venting or suppression.
- Wet filtration: the use of wet dust scrubbers or precipitators to avoid the creation of dust clouds and also dousing any sparks.
MECHON are proven experts in the design and installation of explosion protection systems for operations where dust is produced as part of the manufacturing process. We are able to offer free initial consultations to ensure that your processes and people are fully protected from the devastating effects of an explosion.