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DUST FLAMMABLE AND EXPLOSIVE RISKS

What is most amazing is how little many of those persons in the chemical process industry, management, health and safety professionals understand about the risks posed by dusts. While most people understood that certain dusts can present an flammable and/or explosion risk — for example, coal dust, wood dust, grain dust and fertilizer dust .Very few of these people including health and safety professionals understood the broad range of powders and dusts that actually posed a fire and/or explosion danger.
Clouds of dust in the air can be flammable and explosive.10g.m3 of dust in the air is regarded as the concentration above which most dust in air is flammable.  

OCCUTECH dust flammable and explosive risks Durban KZN South Africa


How can a powder — a solid, typically non-hazardous material like sugar or plastic — become a fire and explosion (or, more appropriately, a deflagration) risk? .To understand this risk a knowledge of  the nature of finely ground materials, and how fires work, is necessary to understand why this risk exists.
We all know that it takes three components to make a fire: fuel for the fire, a source of oxygen to sustain the fire and an ignition source, such as a spark, flame or heat. But for a dust explosion additional elements are required. These include those listed above and confinement and dispersion.

We should understand that fire is a chemical process — an oxidation reaction. With this knowledge it should be easier to understand how a non-hazardous material can become a great fire or explosion risk. In fact, most materials can oxidize. An example is iron that rusts, or chemically reacts, to form iron oxide. When we place a bar of steel where it is exposed to air, the surface will slowly rust. This process typically takes days, weeks or years.

However, if we grind that iron bar up into very fine particles, there is significantly more surface area that becomes exposed and this surface will react with the available oxygen at a much more rapid rate. The finer the particles are, the quicker the reaction will proceed. This reaction also releases heat, so if the reaction proceeds at a rapid rate, it will generate heat at a quicker rate, and this heat will cause the gas around the particles to expand.

This rapid heat generation and oxidation of the fine particulate creates a flame front. If that flame front moves at less than the speed of sound it generally is considered to be a deflagration.2 When a deflagration occurs in an enclosed space, an increase in pressure results when the expansion of the internal gases caused by the heat generated is restricted by the enclosure walls. This creates an explosion, where the expanding pressure wave can cause damage to the enclosure.
If the flame and pressure wave moves faster than the speed of sound, the “explosion” is classified as a detonation.2 Detonations generally are associated with high explosives and, in general, cannot be controlled with pressure relief vents of any type.

This same mechanism will occur with any material that can oxidize with the release of heat (called an exothermic reaction). Therefore, most organic chemicals, plastics, foods, metals, carbon compounds, pharmaceuticals and chemical intermediates can present a risk when they are in the form of very fine powders. The finer the powder, the greater the risk. In contrast, materials that require the addition of heat to oxidize (endothermic reactions) will not spontaneously ignite or explode.

DUST HAZARD REDUCTION
Once we understand how and why dusts can become fire and explosion risks we can determine how best to dust fires and explosions. While it may not be possible to eliminate all dust, the primary goal must be the elimination of major, or catastrophic, explosions inside the facility.
To accomplish this, the first task is to reduce or eliminate accumulations of combustible dusts from exposed and hidden surfaces inside the plant. It is a fact that most catastrophic explosions — those that create the greatest devastation and loss of life within the plant — are secondary explosions caused when the shock or pressure wave from a smaller, primary explosion causes accumulated dust on horizontal surfaces to become airborne, where it is ignited by the primary ignition source. As this accumulated dust can extend for great distances away from the initial ignition source, the small fire or explosion rapidly can expand and cause millions of rands in damages and the risk of severe injury or death.

The National Fire Protection Association (NFPA) has determined that dust accumulations of as little as 1/32nd inch (approximately the same thickness as an average paper clip) are sufficient to create a dust deflagration when dispersed and exposed to an ignition source.3 The removal of accumulated hazardous materials is the primary preventative measure.

 OCCUTECH dust accumulations are flammable and explosive risks Durban KZN South Africa
 
Dust accumulations are flammable and explosive risks

There are three essential components to the reduction of hazardous dust accumulations.

These are
1 .Identification of problem areas
2. Identification of problem dusts
3. Elimination of dust hazards.

Where powdered materials are processed ,handled or generated some dust will  escape from these processing, activities and conveying equipment. This dust naturally settles on horizontal surfaces in close proximity to the dust source. These surfaces may be on top of the equipment itself, on stairs, railings, support steel, light fixtures, etc.

Over time, the accumulation of dust may become extensive. Those surfaces that are highly visible often are cleaned on a periodic basis and may present a very minimal hazard. However, “hidden” surfaces generally are overlooked.
 

OCCUTECH excessive dust accumulations are flammable and explosive risks Durban KZN South Africa

Over time accumulation of dust may become extensive

These problem areas are the areas that should draw the attention of auditors, inspectors and safety professionals to a potential dust explosive risk and that cleaning is required. The primary control in reducing the risk of dust explosions is housekeeping: cleaning up dust accumulation in all areas, visible or hidden.
The second aspect of reducing the dust explosion risk is to identify the hazardous nature of the accumulated dusts. Not all dusts present a fire or explosion risk. While it is preferred that all accumulated dusts be cleaned up for safety reasons, the emphasis here is to concentrate on those dusts that present a real fire or explosion risk.

Conduct an inventory of all the powdered materials within the facility and review safety data sheets (SDS) to determine if a risk already has been identified. In the event the SDS is incomplete or if no SDS exists for the powder under review, physical hazard testing may need to be conducted. Of course, a hazard may be assumed to exist for all unidentified materials and a cleanup undertaken anyway.

OCCUTECH address the sources of the primary dust and ignition sources accumulations are flammable and explosive risks Durban KZN South Africa

Address the sources of the primary dust and ignition sources

Eliminating the dust problems be good housekeeping chores is the beginning but solving the problem goes beyond just cleaning and must address the sources of the primary dust and ignition sources. This involves a review of the process and process equipment to minimize any openings where dust can escape and to eliminate sources of ignition ( electrostatic discharges ,mechanical friction, heat, sparks, electrical malfunctioning , combustion ) wherever possible. To facilitate this process, management should OCCUTECH who is qualified to identify and evaluate and provide appropriate process safety and occupational safety and health mitigational measures using the latest knowledge and skills .


PRIVACY POLICY II ANTI-SPAM II AUP II SECTION 51




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Designed, Developed & Maintained by Michael Hickman
This page was  created on 15.01.2018
This page was last updated on 15.01.2018