Hidden Danger of Combustible Dusts|
Article- July 2012 By Larson Electronics.com
Larson Electronics Quadpod Mounted Explosion Proof Metal Halide Light
Most operators within industrial production and processing facilities are familiar with the dangers posed by the presence of flammable gases, vapors and related chemicals or liquids. The presence of these compounds combined with the presence of potential ignition sources such as electric motors and lighting equipment that are common to industrial workspaces creates an extremely hazardous condition that could easily result in serious fires or violent explosions. Most workers are well aware of this danger, and indeed even those not familiar with industrial working conditions often understand the basic dangers of flammable gases and vapors. However, the explosive potential of dusts is often overlooked as many simply do not realize just how flammable almost any material can become when divided into fine particulates.
Combustible dusts pose the same risks of fire and explosion in an industrial setting as any other flammable compound. Everything from iron filings to sugar powders can contain a great deal of explosive potential , and when ignited can produce enough force to destroy entire facilities. For many operators in environments where combustible dusts are commonly present as a result of normal operations, prevention is a major component of any comprehensive program of protection against accidental ignitions. Worker education, frequent cleanup and dust containment, and proper installation and use of equipment approved for use in hazardous locations are some of the main methods of addressing the dangers of combustible dusts. Cleanup and removal of combustible dusts is a critical aspect of preventative safety, however, despite even the best practices can be harder to perform effectively than many realize.
Any industrial process is going to rely on lighting, electrically power processing equipment, and large machinery for the bulk of operations. Such electrically powered equipment is necessary for operations, but also presents a potential source of ignition for flammable materials. As dusts are produced by the industrial process, it is important that dust be constantly removed from the work area, prevented from being suspended in the air, and the accumulation of dusts prevented. Despite the best practices, even with vacuum systems in place, workers frequently performing cleaning, and filtration systems constantly in operation, accumulation of dusts occurs. While an area may appear quite clean and free of any noticeable dust accumulation, it is the accumulation in areas that are not easily accessible which pose the hidden threat.
No matter how clean an operation is, dust is going to find its way into the surrounding atmosphere where it is then suspended and carried along to other locations. This suspended dust eventually settles onto equipment, behind equipment, into openings and spaces within and between machinery, and onto the top of light fixtures. Over time these accumulations can become significant, and eventually they pose a double edged threat that can quickly escalate into a serious incident with the right set of circumstances.
The first problem with such dust accumulation is the difficulty in monitoring and addressing its appearance. Light fixtures for instance are very often mounted at high elevations, far beyond the easy reach or line of sight of workers. Vents and openings within machinery are hard to access or visually inspect. Gaps between machines and ledges, shelves and flat surfaces behind machines are likewise often “out of sight and out of mind”. Within a short period of time it is possible for dust accumulations in the areas to easily exceed an inch in thickness. Once this dust has reached a significant quantity, it then potentially has three features which make it a serious problem.
The first issue with dusts accumulating in hidden areas is that it can become easily suspended in the atmosphere once again, only this time it will be suspended in large and concentrated quantities, presenting a serious risk of explosion should it come into contact with an ignition source. Should an impact occur, the dust can be flung into the air, once again giving it explosive potential. This of particular concern if these accumulations are present and a small primary ignition occurs. While the small primary ignition might be of little consequence, if it dislodges the accumulated dust and sends it into atmospheric suspension, a secondary explosion of extreme proportions can then occur. This has been documented in several serious incidents, and demonstrates just how complex the hazards of combustible dusts can be.
The next issue with dust accumulation concerns the properties of the dusts themselves. Metallic dusts electrically conductive. In addition, they are highly abrasive as well. These dusts can accumulate within machinery and are attracted to magnetically active parts of lighting ballasts, motors, and machinery. They can cause highly increased wear rates, which can lead to excessively worn bearings and moving parts, thus leading to overheating of the equipment and potential ignition. Electrically conductive dusts can also accumulate around or on electrical contact points between circuits or switches, causing a fault or short which in turn can also cause ignitions.
Finally, accumulated dusts act as an excellent thermal insulator. Particularly on light fixtures and equipment which relies on the free flow of air for proper temperature maintenance, the accumulated dust acts as a blanket, trapping heat within the device or fixture, resulting in greatly elevated operating and temperatures and eventually a potential ignition. Although an explosion proof light fixture for instance might carry all the proper approvals for a local environment, an accumulation of dust could potentially raise its operating temperature past its maximum T rating, resulting in an unsafe condition despite the use of compliant equipment.
Although the obvious suspension of dusts and their accumulation around work areas are easily addressed, it is the hidden accumulations that can oftentimes present the greatest danger. Clean practices and utilizing the proper equipment and safeguards offer effective protection against most of the obvious combustible dust hazards. In order to address the less obvious hazards of dust accumulation, however, it is necessary to intensify inspections and perform thorough cleaning procedures targeted specifically at the dangers which are not easily observable. While more time intensive and complex, such intensified efforts pay dividends represented by reduced incidents of ignition and the preservation of workplace safety.