Introduction to Combustible Dust Explosions Common to Baghouses

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Guest Post By Bevin Sequeira
BS&B Safety Systems (Asia Pacific) Pte Ltd. 

Introduction to Dust Explosions

A Dust Explosion is the fast combustion of dust particles suspended in the air in an enclosed location. Coal dust explosions are a frequent hazard in underground coal mines, but dust explosions can occur where any powdered combustible material is present in an enclosed atmosphere or, in general, in high enough concentrations of dispersed combustible particles in atmosphere.

Dust Explosion at West Pharmaceutical Services

Dust explosion at West Pharmaceutical Services, North Carolina took the lives of 6 people in 2003

Dust explosions can lead to loss of life, injury, damage property and environmental damage as well as consequential damage such as business interruption losses.

Dust explosions involve most commonly “dust”, i.e. fine material. This can be the product being handled or it can be produced as the result of the processing. However, in many cases fine dust is present in material that is otherwise too coarse to pose a dust explosion hazard, either as part of the product or generated by attrition during handling or transport. Therefore, while replacing a fine material by a granular one (such as pellets or flakes) will reduce the dust explosion hazards, this may not be sufficient to eliminate the hazards. Similarly, a user of a granular material may process it to a particle size that introduces dust explosion hazards.

Many dust explosions that occur in process plants are relatively small, leading to limited damage. However, under the right circumstances, even small explosions can escalate into major incidents. This is most commonly the case when secondary dust explosions happen. The typical scenario is that a small “primary” explosion raises a dust cloud, often from dust deposited over time on plant surfaces, and ignites the resulting dust cloud. This “secondary” explosion takes place where often people are present, placing them in immediate danger. Secondary dust explosions can form a chain reaction that can run through a facility as long as fuel is present, leading to widespread devastation.

 

Conditions for Dust Explosion

Dust Explosion Pentagon

There are five necessary conditions for a dust explosion or deflagration:

1. Presence of Combustible Dust
2. Dust suspended in the air at a high concentration
3. There is an Oxidant (typically atmospheric oxygen)
4. There is an Ignition source ( Either Flames & hot surfaces, Spontaneous Ignition, Friction sparks, Static Electricity, Electrical Equipment’s, etc.)
5. Confinement (enclosed location)

Many materials which are commonly known to oxidize can generate a dust explosion, such as coal, sawdust. The dust can arise from activities such as transporting grain and indeed grain silos do regularly have explosions. Mining of coal leads to coal dust and flour mills likewise have large amounts of flour dust as a result of milling. A gigantic explosion of flour dust destroyed a mill in Minnesota on May 2nd, 1878, killing 18 workers at the Washburn A Mill.

To support combustion, the dust must also consist of very small particles with a high surface area to volume ratio, thereby making the collective or combined surface area of all the particles very large in comparison to a dust of larger particles. Dust is defined as powders with particles less than about 500 microns in diameter, but finer dust will present a much greater hazard than coarse particles by virtue of the larger total surface area of all the particles.

Sources of Ignition

There are many sources of ignition and a naked flame need not be the only one: over one half of the dust explosions were from non-flame sources. Common sources of ignition include electrostatic discharge friction arcing from machinery or other equipment or hot surfaces such as overheated bearings. However it is often difficult to determine the exact source of ignition post-explosion. When a source cannot be found, it will often be cited as static electricity. Static charges can occur by friction at the surfaces of particles as they move against one another, and build up to levels leading to a sudden discharge.

Combustible Dust Concentrations:

As with gases, dust is combustible with certain concentration parameters. These parameters vary widely across the spectrum. Highly combustible dust can form a flammable mixture with less than 15 g/m3.

Mechanism of dust explosions:

Imperial Sugar Explosion- Wentoworth Georgia

Imperial Sugar Explosion: Wentworth, GA
17 February 2008: 14 Fatalities

Dusts have a very large surface area compared to their mass. Since burning can only occur at the surface of a solid or liquid, where it can react with oxygen, this causes dusts to be much more flammable than bulk materials. For example, a 1 kg sphere of a material with a density of 1g/cm3 would be about 27 cm across and have a surface area of 0.3 m2. However, if it was broken up into spherical dust particles 50µm in diameter (about the size of flour particles) it would have a surface area of 60 m² This greatly increased surface area allows the material to burn much faster, and the extremely small mass of each particle allows it to catch on fire with much less energy than the bulk material, as there is no heat loss to conduction within the material. When this mixture of fuel and air is ignited, especially in a confined space such as a warehouse or silo, a significant increase in pressure is created, often more than sufficient to demolish the structure.
Even materials that are traditionally thought of as non-flammable, such as aluminium, or slow burning, such as wood, can produce a powerful explosion when finely divided, and can be ignited by even a small spark.

 

Combustible Dust Explosions Since Imperial Sugar Incident

Terminology:

Dust explosions may be classified as being either primary or secondary in nature.

Primary dust explosions: occur inside process plant or similar enclosures and are generally controlled by pressure relief through purpose-built ducting to atmosphere.

Secondary dust explosions: are the result of dust accumulation inside the factory being disturbed and ignited by the primary explosion, resulting in a much more dangerous uncontrolled explosion inside the workplace.
Historically, fatalities from dust explosions have largely been the result of secondary dust explosions.

Best engineering control measures which can be found in the National Fire Protection Association (NFPA) Combustible Dust Standards include:

• Oxidant Concentration Reduction
• Deflagration venting
• Deflagration pressure containment
• Deflagration suppression
• Deflagration venting through a dust retention and flame-arresting devices
• Spark Detection & Extinguishing Systems

 

 

 

Explosive Materials:Dust Explosions - Bucket Elevator Explosion The following materials are prone to dust explosions.
• Coal
• Fertilizer
• Cosmetics
• Pesticides
• Plastic & plastic resins
• Wood
• Charcoal
• Detergents
• Foodstuffs (sugar, flour, milk powder, etc.)
• Ore dusts
• Metal dusts
• Graphite
• Dry industrial chemicals
• Pigments
• Cellulose

Industrial Equipment:
Typical industrial equipment’s that require explosion protection.
• Dust Collectors
• Dryers
• Cyclones
• Crushers
• Grinders
• Silos
• Pulverisers
• Conveyors
• Conveyor ducts
• Screw conveyors
• Bucket Elevators
• Furnaces
• Hoppers
• Bins

Conclusions

Many reported dust explosions have originated in common powder and bulk solids processing equipment such as dust collectors, dryers, grinders/pulverisers, and blenders. Electrostatic discharges are frequently cited as the ignition source for dust collector explosions, whereas particulate overheating is the most common ignition source in dryer explosions, and friction/impact heating associated with tramp metal or misaligned parts is probably the most frequent ignition source in grinder/pulveriser explosions.

Dust explosions are often exacerbated by propagation through ducting between process equipment, frequently via dust collector pickup and return ducting. Moe widespread use of effective deflagration isolation devices in such ducting would clearly be beneficial in mitigating the damage and injuries from these propagating dust explosions. (See article Dust Collector Fire and Explosion Highlights Need for Combustible Dust Considerations In System Designs)

Secondary dust explosions in processing buildings probably cause the largest numbers of dust explosion fatalities and injuries. One crucial aspect of secondary dust explosion prevention and mitigation is greater awareness of good housekeeping and maintenance practices to prevent particulate leakage from equipment and subsequent accumulations of dust deposits in large areas of the buildings.

 

About the Author

Bevin Sequeira holds a B.E. (Mechanical) degree & a MBA (Marketing) specializing in business development & enhancement of virgin markets all over the globe. With over two decades of international working experience in the industry, Bevin’s knowledge of the industry spans various sectors like Iron & Steel, Foundry, Chemicals & Fertilizer, Power, Food, Pharma, etc.  He is currently serving as Regional Sales Manager at BS&B Safety Systems (Asia Pacific) Pte Ltd. specialising in Combustible Dust Explosion Protection Systems & Risk Management. In his spare time, Bevin likes to read, travel, socialise & collaborate with business houses for M&A, Management Consultancy, etc.

Dust Collector Fire and Explosion Highlights Need for Combustible Dust Considerations In System Designs

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New-England-Wood-Pellet-combustible-dust-fire-explosion

A massive fire and explosion in the dust collection system of a New Hampshire wood pellet manufacturer demonstrates the need for adequate system design to prevent combustible dust explosions in general industry.

By Dominick DalSanto
Baghouse Technology Expert and Sales Director
Baghouse.com

May 16 2012 – Baghouse.com Editorial | On October 20 2011, a combustible dust fire began in the wood pellet cooler, most likely caused by a spark or ember from the pellet hammer mill. The fire then spread through the ductwork throughout the plant, eventually reaching the dust collector causing it to explode. When the collector exploded, the explosion vented through the baghouse’s explosion vents into adjacent storage silos setting them ablaze further spread the fire throughout the plant. More than 100 firefighters and emergency personnel from at least 14 towns worked for over 15 hours to put out the blaze.

The OSHA report outlines specific areas where the plant lacked adequate spark detection devices, fire suppression systems, and explosion venting/protection within the dust collection system. The fact that the plant had been cited by OSHA for several of the same issues previously after a 2008 incident, led to OSHA assessing total fines of $147,000.

Examining what went wrong in this incident highlights the need for diligence on the part of plant management and operators regarding the dangers of combustible dust.

What Went Wrong?

The October 20 2011 fire and explosion at the Jaffrey, NH plant was not the first combustible dust related incident at the plant. In 2008 the plant experienced a similar fire and explosion that caused more destruction than the most recent one. After completing its investigation, OSHA at that time fined the plant over $100,000 for safety violations that led to the fire. Subsequently, the plant, in an attempt to prevent another such occurrence, “retained engineers and consultants, and spent over $2 million on various improvements to enhance worker safety at its Jaffrey facility” according to a release from the company. This apparently including the installation of some explosion isolation devices in the ductwork (Rembe explosion isolation device) and installed explosion protection (explosion vents) on the baghouse. However the company’s effort and expense failed to prevent another incident from occurring.

Fire fighters work to put out a massive blaze caused by a destructive combustible dust fire and explosion at the New England Wood Pellet Company's Jaffrey, NH facility.

Fire fighters work to put out a massive blaze caused by a destructive combustible dust fire and explosion at the New England Wood Pellet Company’s Jaffrey, NH facility.

The OSHA report is quite thorough in its description each poorly designed, installed and operated part of the dust collection system either caused or intensified fire and subsequent explosion.

For example the report cites the plant for 2 main offenses. The first one is regarding poor housekeeping throughout the plant that led to large accumulations of combustible wood pellet dust forming on top of machinery (such as the pellet cooler where the fire began) and on elevated surfaces such as overhead rafters, ceiling joists, troughs, etc. Secondly, and more seriously, the plant was cited under the General Duty Clause of the OSHA Charter* for failing to take reasonable steps to prevent a combustible dust fire/explosion from occurring. OSHA cited several industry standards such as the National Fire Protection Association building code that the plant failed to heed in the design and construction of the plant’s dust collection system.

Ductwork Lacked Sufficient Spark Detection, Fire Suppression, or Explosion Isolation Devices

A major oversight in the ductwork system, was the lack of appropriate spark detection, fire suppression or fire isolation devices on all of the ductwork between the various machines throughout the plant. For instance, OSHA reported that the connecting ductwork between the pellet hammer mills, the pellet cooler, the bucket elevators storage silos and most of the dust collectors in the plant had no spark detection system, fire suppression system, or explosion isolation devices installed. The only control device the plant had was an explosion isolation device on the conveying duct between the pellet cooler and the pellet cooler baghouse. However, the device did not function properly and allowed the fire to propagate further downstream into the baghouse.

NFPA 664 (2012) Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities: 8.2.1. and Hazard Determination 8.2.4.1. – Conveying systems with fire hazards should be isolated to prevent propagation of fire both upstream and downstream (OSHA isolation can mean spark detection and suppression). 5.2.5.1 Prevention of Fire Extension: When limitation of fire spread is to be achieved the following criteria shall be demonstrated…(4) Particulate processing systems (dust collection systems) shall be designed, constructed, equipped and maintained to prevent fire or deflagration from propagating from one process system to an adjacent process system.

Additionally, the ductwork was not engineered and/or constructed to sufficient strength to withstand the maximum anticipatable explosive pressure resulting from a conflagration involving its intended payload (combustible wood dust). This led to the duct bursting open, releasing the explosion into the plant near firefighters and may have been a contributing factor in the fire by-passing the isolation device.

NFPA 664 (2012) 8.2.2.2.3, Sets forth alternative safety criteria for ducts with a deflagration hazard, to ensure that the ducts are builds with a sufficient strength and with appropriately sized/located protection devices to handle the maximum expected pressure generated by a dust explosion. 

Baghouse Was Not Adequately Protected Against Explosion Hazards

The plant recently installed explosion vents on the baghouse explosion vents.* However, the design and installation of the explosion protection on this particular baghouse may actually made things worse than if there had been none at all.

When the fire reached the baghouse and caused the finely dispersed dust to ignite, the resulting pressure and fireball should have been vented outside the building. However, the explosion vents on the baghouse faced the direction of adjacent storage silos (containing wood dust). When the explosion was vented out it ignited the storage silos resulting in a major portion of the fire.

Additionally, OSHA’s investigation showed that the baghouse lacked an explosion suppression system, was not designed and/or constructed to withstand the maximum unvented pressure of a combustible dust explosion, and in the absence of proper explosion protection, was located indoors.

As a result of these failures, when the reached the dust collector, the resulting explosion: blew the dust collector’s door off its hinges, creating a missile hazard, blew backwards into the duct, which burst open, and blew out the dust collector’s exhaust muffler and roof stack, causing the pressure/deflagration to be vented inside the building near responding firefighters.

NFPA 664 (2012) 8.2.2.5.1.4. Requires an outdoor location for the dust collectors with fire or deflagration hazards, unless they are equipped with one of the following: (4) listed deflagration suppression system, (5) deflagration relief vents with relief pipes extending to safe areas outside the building and the collector meets the strength requirement of this standard (i.e. built with sufficient strength to withstand the maximum expected explosions pressure). NFPA 664 (2012) 8.2.2.5.3 requires dust collectors with deflagration hazards be equipped with an appropriate-sized explosion suppression system and/or explosion relief venting system designed per NFPA 68 (Explosion Protection by Deflagration Venting) and NFPA 69 (Explosion Prevention Systems), and also that such dust collectors be built to design strength that exceeds the maximum expected explosion pressure of the material being collected. NFPA 69, 12.1.2 requires “Piping, ducts, and enclosures protected by an isolation system shall be designed to withstand estimated pressures as provided by the isolation system manufacturer”. NFPA 69, 12.2.2.3 “System Verification” requires that systems shall be verified by appropriate testing under deflagration conditions to demonstrate performance.”

These design oversights directly increased the destructive power of what had until then been only a dust fire in the ductwork.

Lessons Learned From Wood Pellet Company Dust Explosion

Simply put, this disaster was bound to happen due to glaring design and/or construction flaws throughout the entire system.

The fact that multiple similar incidents have occurred at the facility demonstrates that the dust collection system, and perhaps even the entire production process requires modification to ensure this kind of incident does not occur again.

Under OSHA’s National Combustible Dust Emphasis Program, OSHA inspectors are on heightened alert for any combustible dust hazards in facilities in all industries. Indeed OSHA is under a federal mandate and its has as its own goal to issue a comprehensive combustible dust standard for general industry. In the meantime, OSHA has been citing plants under the general duty clause for having combustible dust hazards. In most cases, OSHA is informally requiring general industry to conform to the NFPA’s guidelines for combustible dust hazards. As seen in this case following they suggestions would have prevented this kind of incident from occurring.

Therefore, we can take away from this the need to be conscientious and proactive regarding combustible dust hazards in your facility. As we have seen, being reactive will simply not do.

Footnotes:

* OSHA General Duty Clause (a) Each employer — (1) shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees; (2) shall comply with occupational safety and health standards promulgated under this Act.

*  Baghouse Explosion Vents – Explosion vents are a form of explosion protection used on baghouses. During normal operation the vents are closed and maintain an air-tight seal. However, if an explosion occurs within the baghouse, the vents are designed to “strategically fail” being the weakest part of the baghouse structure, thus allowing the pressure from the explosion to vent out and away from other combustible materials and workers.

 

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in dust collection systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Sales Director at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

CSB Nine Years Later, Still No Dust Regulation – Urges OSHA To Finalize Combustible Dust Safety Standard

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A factory that has been destroyed by a Dust Explosion

Nine years after the first of a series of deadly combustible dust explosions in the U.S., the CSB (Chemical Safety Board) is imploring OSHA to take decisive action and finalize its court-ordered Combustible Dust Standard. Investments in plant dust collection systems will be vital to meeting the new proposed standards.

April 4, 2012 – Baghouse.com News | Fed. 20, 2003, CTA Acoustics plant in Corbin, Ky, 7 dead; Feb. 7, 2008 Imperial Sugar Refinery in Port Wentworth, Ga, 14 dead, 38 injured; various dates in 2011, Hoeganaes powdered iron metal manufacturing plant in Gallatin, Tn, 5 dead in 3 separate incidents in 5 months. These are just a few of the deadly industrial dust explosions to occur in the U.S. over the last decade. In each of these incidents, the lives of these workers were tragically cut short by the seemingly-innocuous dusts present in the facilities.

The Chairperson of the U.S. Chemical Safety Board (CSB) Rafael Moure-Eraso, in a recent article has called attention to the fact that despite several deadly incidents occurring in the nine years since the CTA explosions, OSHA still has yet to follow through with its pledge to issue a comprehensive combustible dust safety standard for general industry.

Chairperson Moure-Eraso  relates the progression of events that lead to the CSB calling for OSHA to implement a comprehensive standard for combustible dust.  “The safety board launched a study into the hazards of combustible dust. Our 2006 report revealed there is no national regulation that adequately addresses combustible dust explosion hazards in general industry. Although many states and localities have adopted fire codes that have provisions related to combustible dust, a CSB survey found that fire code officials rarely inspect industrial facilities to enforce the codes. The board clearly stated that American industry needs a comprehensive federal combustible dust regulation.”

While the explosion at the CTA Acoustics plant in Corbin, Ky did lead the CSB to issue a number of recommendations to both plant management, local and state regulators, it was not until the 2008 Imperial Sugar Refinery explosion in Port Wentworth, Ga, that left 14 dead and 38 injured, that the CSB made its recommendation to OSHA to issue a “comprehensive combustible dust standard for general industry”.

The CSB is an independent governmental agency charged with investigating industrial chemical accidents. And while they do have limited authority to investigate and issue recommendations, they do not have the power to enforce safety regulations.

Despite its repeated recommendations to OSHA for the urgent need for hazardous dust standards, he relents: “ Yet, nine years after the CTA catastrophe, and more than five years after our recommendation to OSHA, there is still no comprehensive OSHA standard to prevent these accidents.”

After the CSB’s recommendations, OSHA in April, 2009 announced that it planned on issuing a comprehensive dust standard for general industry. However, its recent 2012 agenda does not include any specific mention of goals or targets for the development of the standard during the course of this year.

Will There Ever Be a Comprehensive Combustible Dust Safety Standard?

While the U.S. is still struggling to prevent these kinds of incidents from occurring, the rest of the world is not immune from them either. In fact, major manufacturers such as China, which often lack extensive safety regulations, are even more prone to experience these kinds of incidents. According to recent reports, last year saw two electronics manufacturers in China that produce parts for Apple Computer products experienced dust explosions when fine particles of aluminum ignited, killing four workers and injuring dozens of others. Apple’s Supplier Responsibility documents state that the company is now requiring improved ventilation, inspections and cleaning methods for dust deposits.

Without a standard that comprehensively addresses the hazards of combustible dust, American workers will continue to be put at risk for future catastrophic explosions and fires.

“I don’t know what steps China is taking to prevent its dust explosions, but I do know what can be done here in the U.S. It’s time for OSHA to move on a comprehensive regulation to adequately address combustible dust hazards” – stated CSB Chairperson Moure-Eraso.

What Does This Mean For U.S. Manufacturers?

While the current status of combustible dust regulation is not fixed on a federal level, (i.e. OSHA) the dangers of combustible dust still present a clear and present danger to both the financial interests of U.S. manufacturers and the lives of U.S. workers.

As a result of the long history of combustible dust explosions in the U.S. many state and municipal fire codes and other regulatory agencies already have combustible dust regulations for most industries.  In addition, many insurance providers are requiring plants as part of regular safety audits to improve dust hazard protection in their facilities as a condition of maintaining their coverage.

dust collection systems

Maintaining a sufficiently-sized dust collection system is vital to prevent combustible dust explosions.

The first step to preventing these incidents is recognizing the dangers combustible dusts present in an industrial setting. Measures to control or mediate combustible dust hazards include maintaining a adequate dust collection system (i.e. a baghouse), good house-keeping practices and good facility design.

A main contributing factor in all of the above mentioned incidents was an improperly operated or maintained dust collection system. From inefficient collection pickup points, to bucket elevators that were not properly cleaned and sealed, to conveyor systems that were overloaded to baghouses of insufficient size and fire protection. A relatively minor investment in a facility’s dust collection system, such as changing to a sufficiently sized collector (i.e. larger CFM, larger baghouse with more dust collector bags) or additional baghouses will prevent the kind of massive capital loss and loss of life seen in these past incidents.

While governmental regulation will not ensure that these tragic incidents are the last of their kind, it is hoped that along with increase corporate awareness and ever-improving dust collection technology, these incidents will become rarer and rarer. Saving not only billions of dollars for companies, but safeguarding millions of workers in these industries.

Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

CSB Video Report On Series Of Combustible Dust Explosions At Tennessee Powdered Metals Plant

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The Chemical Safety Board issued a final report on a series of deadly combustible dust explosions in Tennessee. It highlights dust collection systems as the only way to prevent deadly combustible dust explosions. Recommends OSHA issue new comprehensive dust regulations within one year. 

January 6th, 2012 Baghouse.com News | The Chemical Safety Board has issued its final report regarding a series of deadly industrial dust explosions accidents that occurred at the Hoeganaes powdered metals plant in Gallatin, Tennessee in 2011. The main cause of these three deadly explosions and fires that claimed five lives and injured many others was determined to be negligence regarding combustible dust hazards. The CSB further noted that a main factor in these accidents was the constant neglect of the plant’s dust collection system.

All three of the incidents occurred when large amounts of accumulated highly combustible iron dust where dispersed into the air and then ignited. The plant manufactures various metal powders for industrial use, the most produced of which is iron powder.

Hoeganaes Cumbustible Dust Hazard

Picture of combustible dust accumulations near a bucket elevator that killed 2 workers when the dust was ignited by the motor.

The CSB investigation found that iron dust was present in high enough concentrations in the air to be clearly visible, and had accumulated on nearly all surfaces including elevated ledges, rafters, and other overhead spaces in amounts of 4 inches or greater. In addition the CSB clearly documented through photos and videos how dust handling equipment such as bucket elevators, conveyor belts, etc.  were not adequately sealed, regularly leaking large amounts of dust into the air when in operation, and were not connected to the plant’s dust collection system. Additionally, plant workers told investigators that the dust collection system was regularly out of service due to maintenance.

Three Combustible Dust Incidents At One Plant In Six Months

The CSB investigation begin after the first of the three incidents occurred on January 31st, 2011 when fine iron dust particles coming from a broken bucket elevator were ignited while two maintenance personnel were performing repairs. The airborne particles were ignited by a spark from the bucket elevator’s electrical motor when it engaged. The resulting explosion and fire severely burned both workers, and eventually proved fatal for both men.

Just two months later, while the CSB was still conducting an investigation into the first incident, another flash fire occurred on March 29th when a maintenance worker used a hammer while reconnecting a gas line on the side of one of the plant’s furnaces. When he struck the side of the furnace with the hammer it lofted accumulated iron dust into the air, which then ignited, severely burning him, and causing him to fall from elevated working position further injuring him.  According to CSB officials, “the build up of so much iron dust near a furnace with open flames and hot surfaces was a recipe for disaster. A fire was basically inevitable the moment the dust was dispersed into the air.”

Hoeganaes Cumbustible Dust Hazard

March 29, 2011 Combustible dust fire in Gallatin, Te Hoeganaes powdered metals plant. The second of two serious dust fires/explosions in six months at the plant

Even with two such incidents within two months of each other, Hoeganaes management and its parent company still failed to take action to address the combustible dust safety issues at the Gallatin, Tennessee plant.

This failure proved to be catastrophic as just a few months later on May 27th when the an even deadlier third incident took place. Workers were repairing a corroded furnace pipe containing extremely flammable hydrogen gas caught fire when workers used a forklift to raise a metal floorplate to access the pipe. Workers has assumed the leaking gas was non-flammable nitrogen. After the initial explosion, the leaking gas continued to burn as a continues jet fire. The force of the initial explosion shook loose largeamounts of accumulated iron dust from overhead rafters. As the large plumes of iron dust fell they were ignited by the jet fire causing massive explosions further injuring workers and damaging the plant. One worker stated that so much iron dust was lofted into air, that even with a flashlight he was only able to see two to three feet in front of him as he tried to escape.

Hoeganaes Combustible Dust Explosion

The aftermath of the third Hoeganaes combustible dust explosion in 2011. Notice the dislodged metal floor grating.

Evidence of Danger Present Well Before

All of these incidents were easily preventable. However plant management refused to take appropriate action to improve dust collection at the plant.

Even before the series of incidents, the plant had twice tested its dusts for combustibility. They ever were warned of the potential for a dust explosion after an insurance audit, which cited the potential for a such an accident due to the plant’s poor dust collection system policies, and housekeeping.

In addition to these warnings, the plant had firsthand knowledge of the combustibility hazards present in the plant, when on several occasions flash fires had occurred when workers performed maintenance using welding torches on dust covered conveyor belts. In fact the Gallatin Fire Department Hoeganaes facility in the last 12 years. These included one in June of 1999 where an iron dust fire in the baghouse lead to the hospitalization of one worker for smoke inhalation.

The CSB found that part of the core problem was that the plant, which was built over thirty years ago, was not designed according to good practice guidelines for combustible dust hazards, such as those set forth by the NFPA (National Fire Protection Association). “During its decades of operation, [the plant] was never redesigned to address the serious dust hazards” states CSB investigator Johnnie Banks.

Hoeganaes Cumbustible Dust Hazard - Accumulated Dust

Accumulated combustible iron dust on rafters at the Hoeganaes plant lead to several deaths when a series of dust fires and explosions occurred in 2011.

The plant has numerous flat elevated surfaces that easily accumulate large amounts of dust, and are difficult or impossible to clean with regularity. NFPA 484, which covers combustible metals safety, recommends that “floors elevated platforms, and gratings be designed to prevent dust accumulations and facilitate cleaning.” The same standard also requires that any machinery that emits combustible dust be connected to a dust collection system. Both of these recommendations were not followed by the Hoeganaes plant.

Many have asked how is it that these accidents were allowed to happen, even when plant management had all of these warnings and was in clear violation of best industry standards?

The city of Gallatin requires industrial facilities, including the Hoeganaes plant, to comply with the International Fire Code, which includes a brief chapter on combustible dust standards and references the more detailed NFPA standards. However the code does not require compliance with the more stringent NFPA standards. As a result the plant was not directly in violation of the International Fire Code that it was mandated to follow.

CSB Recommendations Based On Its Investigation

As a result of the CSB investigation, the CSB has proposed several actions be taken to reduce the risk of more combustible dust incidents from occurring elsewhere.

First, the CSB recommended that the International Code Counsel “revise the International Fire Code to mandate compliance with the combustible dust safety standards set forth by the NFPA.”

Secondly, in its 2006 report on the dangers of combustible dust hazards in industry, the CSB recommended that OSHA (Occupational Health and Safety Administration) issue a comprehensive combustible dust safety standard for general industry. As a result in 2007 OSHA instituted a national emphasis program for combustible dust, with the stated goal of eventually issuing a comprehensive combustible dust standard in the near future. In 2009 OSHA announced that it would begin the rule making process for combustible dust hazards. However, in 2011 at the time of these accidents, no standard had yet been proposed, or completed.

As a result, in its final report on the incidents, the CSB recommended that OSHA issue its long awaited combustible dust standards “within one year”, and that the standard include combustible iron and steel powders.  In the meantime, the CSB recommended that plants that manufacture steel and iron powders be included in the national emphasis program. for combustible dust.

 What This Means For Facilities With Combustible Dust Hazards

The continued loss of life due to combustible dust hazards is no longer being ignored by the CSB, OSHA, or other governmental agencies. The only way to prevent the loss of additional lives is for industry to begin following best industry standards as set forth by the NFPA and eventually the comprehensive standard by OSHA.

In the meantime, plant mangers and operators can educate themselves on the dangers of combustible dusts by reviewing educational articles on the subject such as those published here on Baghouse.com (http://www.baghouse.com/2011/01/19/the-potential-for-dust-explosions-in-dust-collection-systems/). They can also seek the assistance of experts in the dust collection industry to identify areas where improvement can be made, and make suggestions of ways to increase dust collection efficiency at their facilities.

For more information about the dangers of combustible dusts, please see the following links:

The CSB video reports on the Hoeganes incidents:

The following LinkedIn groups work specifically to raise awareness of combustible dust hazards, and lobby for comprehensive standards for general industry:

http://www.linkedin.com/groups?gid=1184577&goback=%2Egmp_1184577

http://www.linkedin.com/groupRegistration?gid=2076996&csrfToken=ajax%3A2562522142432018780&goback=%2Eanb_2076996_*2

 

 

About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

 

5 Baghouse Safety Precautions

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Performing any kind of work on a baghouse can be hazardous work. Often set in industrial locations, dealing with baghouse systems can present a number of dangers to personnel. Thankfully, these maintenance tasks can be accomplished safety if proper safety precautions are followed.

A new article authored by Baghouse.com that has been published on a leading environmental and safety magazine EHSToday.com that offers 5 often overlooked baghouse safety proceedures for performing any type of work on dust collection systems. You can read the article here: 5 Essential Baghouse Maintenance Safety Precautions I encourage all of our readers to take a moment and read this article and consider how well are you doing regarding baghouse safety.

Direct URL: http://ehstoday.com/industrial_hygiene/news/baghouse-safety-precautions/

 

About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

Baghouse Malfunction Causes Plant To Tell Workers “Stay Home!”

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A caution sign warning of a danger caused by a malfunctioning Baghouse

Bay Minette, Alabama – A Baghouse fire at a furniture manufacturing plant led to the closure of the entire site for several days. The Bay Minette, Alabama plant operated by Standard Furniture Manufacturing Co. suffered an explosion and ensuing fire in two silos that contain sawdust collected by the plant’s larger dust collection system.

While the exact cause of the explosion, and subsequent fire are not yet known, it is expected that an ignition source (such as a spark or an electric arc) may have been caused during a maintenance procedure.

The 600+ employees of the plant had to remain at home until the Baghouse was repaired and back in operation. This was further delayed when fire inspectors from the local fire department requested that the Baghouse be taken apart to aid them in their investigation of the fire.

This incident, one of many that occur each year, illustrates the importance of a site’s Baghouse, and larger dust collection system to maintaining normal operations. These often overlooked systems can when they malfunction due to maintenance neglect, improper operation, poor design, or other reasons lead to immense immediate costs for plant operators, and even larger long term ones.

Therefore this example highlights the need for constant attention to be given to dust collection systems so as to avoid these expenses, and therefore reduce overall operating costs. Only by maintaining a program of regular Baghouse maintenance, providing operators with sufficient training, ensuring all systems are adequately sized for the facility’s needs and meet all safety standards, can costly incidents like this one be avoided.

 

 
About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

U.S. Congress to Force OSHA to Issue Combustible Dust Safety Standards

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Aftermath of a dust explosion at the Imperial Sugar Plant

Dominick DalSanto
Environmental & Dust Collection Technologies Expert & Author
Baghouse.com

On February 7th 2009 an explosion at the Imperial Sugar Refinery in Port Wentworth, Georgia kill 14 workers, injured dozens more, and resulted in millions of dollars worth of damages. What was the source of this horrifically powerful industrial explosion that took over a dozen lives and completely destroyed an entire factory? Was it some exotic chemical substance that was being used as part of some industrial process?

This devastating explosion was fueled by nothing other than a simple accumulation of otherwise harmless sugar dust.

In an industrial setting otherwise benign substances such as flour, corn, sugar, metals, or wood, can accumulate. When exposed to an ignition source these can lead to immensely powerful explosions.

Bowing to concerns over a lack of standardize federal safety regulations in this area, members of the U.S. Congress have recently taken steps to combat this danger.

Congress Attempts to Force OSHA’s Hand in Setting Combustible Dust Standards

Photo of the U.S. Capital building. Where the U.S. Congress is looking to pass legislation to force OSHA to set a comprehensive combustible dust standards and safety regulations

U.S. Congress is looking to pass legislation to force OSHA to set a comprehensive combustible dust standards and safety regulations

U.S. Congress is looking to pass legislation to force OSHA to set a comprehensive combustible dust standards and safety regulations “]
With such a large amount of deaths, injuries, and property damage being caused each year by combustible dust related fires and explosions, lawmakers are looking to draft legislation to provide safety standards for operations where the danger of combustible dusts exists

Recently three members of the U.S. Congress, Rep. George Miller (D-CA), Rep. John Barrow (D-GA), and Rep. Lynn Woolsey (D-CA), reintroduced legislation  concerning combustible industrial dusts. The Worker Protection Against Combustible Dust Explosions and Fires Act, would force OSHA (Occupational Safety and Health Administration) to set definitive standard

s regarding hazardous levels of combustible dust like coal, sugar, or metals dust in industry. This will accelerate efforts that are already in motion by OSHA. However the forthcoming OSHA standards are expected to take at least 4 years before codification and total implementation takes place.

Rep. Miller, who is a leading member of the House Committee on Education and the Workforce, commented that although he commends OSHA for beginning to take the initial steps to address this hazard, he feels that because of bureaucratic “red tape”, workers that are exposed to these hazards will not be fully protected for years. “While some industries have taken steps to address these hazards, workers are still being killed and injured from preventable combustible dust explosions. Regulatory delays should never be an excuse not to protect workers from a preventable tragedy” stated Miller.

CSB Makes Recommendations, But Finds no Comprehensive OSHA Standards for Combustible Dust

The governmental agency charged with investigating industrial incidents of this kind is the Chemical Safety Board. The CSB while charged with investigating industrial incidents, does not have the authority to issue regulations. Instead the agency merely issues reports details the causes of any particular incident, and then makes recommendations on how to avoid having a repeat incident.

Following a series of dust explosions, in 2006 the CSB undertook a thorough study of combustible dust hazards in industry. The CSB found that despite being a well-known industry hazard, there was no comprehensive set OSHA standards covering combustible dust hazards. In view of the immense danger to live and property that combustible dust hazards pose, the CSB recommended that OSHA begin work immediately to issue a comprehensive set of standards in this area.

In an industrial setting, dust can accumulate on areas such as floors near dust sources, and elevated spaces such as ceiling rafters/trusses, on the tops of machinery and shelving. Even accumulations of less than one inch can pose a great danger. Often times an initial explosion or fire  can take place which is quite small and localized, such as within a dust collector or related ductwork. However the resulting shockwave, even though it might be relatively small can then disperse or aerosolize larger deposits of accumulated dust which then will fuel a much larger secondary explosion, which can then propagate throughout the entire facility, causing massive destruction of property, and loss of life.

Between 1980 and 2005 combustible dust explosions killed at least 119 people, injured 718 and resulted in millions of dollars in damage in the U.S. alone. In the UK government statistics show that on average one death per week is caused by combustible dust explosions.

Dust Combustible Dust Safety Standards, Why So long in the Making?

With decades of documented cases of violent conflagrations caused by accumulation of combustible dusts, many are asking ask why has OSHA been so slow in issuing safety standards? No doubt a mixture of bureaucratic red tape, preoccupation with other so called “more pressing matters” and a general sense of complacency have all contributed.

However those affected by these terrible accidents want to see that others are not at risk to suffer the same way they have. “We know that standards OSHA has established in other areas have saved thousands of lives,” says Woolsey. “Workers need a standard on combustible dust, and they need it now.” Rep. Barrow added “This legislation will finally provide our nation’s factory workers with the protections they deserve.”

It appears now however that due in part increased activism, combustible dust hazards are being brought to the forefront of industrial safety as well as public attention. * See CBS 60 Minutes Highlights The Dangers of Dust Explosions

Now with new legislation being put forth, and at least partial self-regulating on the part of industry, it seems that progress is being made to give the needed attention to this serious industrial hazard.

 

 

What Can Be Done Now to Avoid Dust Explosions?

Explosions caused by combustible dust, are most often the result of neglecting to recognizing the dangers involved with combustible dust. Being aware of the danger accumulated dust poses is the first step in preventing a violent conflagration from taking place.

In general, there a few keys to safeguarding a plant from these dangers:

Good house-keeping practices throughout the facility – This would including cleaning up any large accumulations of dust, especially accumulations on elevated sites such as ceiling trusses or rafters, on top of storage shelving, and machinery.

Employing a dust collection system – The dust collector or Baghouse, will need to be sufficiently sized to handle the dust loads of the facility. Additionally, the correct type of Baghouse, Baghouse filters, and cleaning mechanism are all vital to ensure adequate collection operation throughout the entire facility. Ductwork design, and installation also play a vital role in ensuring that there are a sufficient amount of collection points throughout the facility in all dust producing areas. Also even the best dust collection system will be worthless if it is operated improperly, or left in a state disrepair due to in adequate maintenance.

Adequate knowledge of dust characteristics – It is vital that each kind of dust present be identified and their individual characteristics be understood. Many companies exist that will perform testing to determine the combustibility and other characteristics of any compound produced at a given site. This information is required to formulate a comprehensive dust control plan for the facility. This information also comes into play when selecting an appropriate dust collector system, filters, and installation and implementation.

Further more extensive information on how to prevent dust explosions can be found here on Baghouse.com in the article: The Potential for Dust Explosions in Dust Collection Systems.

 

 
About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

One Dust Explosion Per Week in UK, and 2000 Per Year in Europe Says New Study

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A new report by leading industry experts states that 2000 dust explosions in factories and industrial facilities across Europe each year. An average of 50 per year are reported in the UK alone, nearly one a week. The report prepared by Dr. Julian Hought of risk management specialists, HFL Risk Services, also highlights that a large percentage of these incedents do not involve what we would normally classify as high-risk manufacturing processes, such as chemical production. In fact nearly 24% of incidents reported occurred in the food industry, with products as benign as flour, coffee, and sugar.

The report however stresses that a large part of the problem is that companies and employees do not realize just how dangerous these dusts can be when found in hazardous amounts within facilities. Proper dust collection equipment, and employee hazardous dust safety training are key to preventing these often deadly accidents from taking place.

To read the full report, please click here: http://www.hazardexonthenet.net/article/40288/Dust-to-Dust.aspx?AreaID=2

 

 
About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

CBS’s 60 Minutes Highlights the Dangers Of Dust Explosions

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Dust Explosion at the Imperial Sugar plant in Georgia

By Dominick DalSanto
Environmental Expert & Author
Baghouse.com

The dangers of combustible dust explosions are among the most overlooked of industrial workplace safety issues. However the price for negligence in this area is often payed not only with millions of dollars, but with workers very lives.

But only recently has the this issue began to attract mainstream attention outside of the industrial world. Recent incidents such as the one that occurred at the Imperial Sugar Plant in Port Wentworth, Georgia on February 8th 2007 that claimed the lives of 14 works, and injured 38 others, have brought this safety issue to the forefront of industrial safety activists.

This segment from the CBS new program “60 Minutes” entitled: The Danger of Combustible Dust – examines the efforts of the victims families and others to force OSHA to create a national combustible dust standard.  Scott Pelley reports on the deaths and property damage caused by dust explosions at American factories, a problem critics say the government needs to do more to prevent.

This report which is of great interest to all in the dust collection industry can be viewed at the link below.

http://www.cbsnews.com/video/watch/?id=4162555n&tag=related;photovideo

 
About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.

The Potential for Dust Explosions in Dust Collection Systems

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At least 281 combustible dust fires and explosions occurred in general industry between 1980 and 2005 in the United States, which caused at least 119 fatalities and 718 injuries; including seven catastrophic dust explosions in the past decade, involving multiple fatalities and significant community economic impact; and occurred in a wide range of industries and involved many types of combustible dusts.

According to a report by the US Chemical Safety Board (CSB) a major factor that lead to the high amount of incidents was the overall lack of education regarding the danger of Dust Explosions. Without this information, plant operators are not able to implement proper safety precautions, and adequately train their personal about the precautions they need to take to minimize the chance of a Dust Explosion occurring in their facility.  This article has been prepared to help bring awareness to the dangers of Dust Explosions, and what precautions can be taken to avoid them.

What Is A Dust Explosion?

A factory that has been destroyed by a Dust Explosion

A Dust Explosion that begins in the Dust Collection System can lead to the destruction of an entire facility.

Most solid organic materials, in addition to many metals and inorganic nonmetallic materials, when reduced to a finely divided size, and sufficiently dispersed into the atmosphere will explode under the right conditions. Many combustible dusts are intentionally manufactured for a wide range of applications such as Metallic Powder Coatings, or certain foodstuffs such as Corn Starch, Flour, and Granulated Sugar. Others are produced during the manufacture and transport of materials such as wood processing, and stone quarrying. Additionally, during the manufacturing process for many materials, actions such as milling, polishing, and transportation may create substantial amounts of dust that can later accumulate on a wide range of surfaces.

Any industry that produces materials of a fine particle size that are combustible, and many that simply though their day-to-day operation create large amounts of secondary dust are at risk for Dust Explosions. Industries such as Metal, Food, Plastic, and Wood Processing are just a few that are at risk for this kind of industrial accident.

The Anatomy of a Dust Explosion

The Beginnings

The basics of combustion deal with the so called “Fire Triangle” that illustrates the importance of the three main factors that need to be present for combustion to take place. These three are Fire, Heat (Ignition Source) and Oxygen. With regards to Dust Explosions, we need to add another two ingredients to create what has been termed the “Dust Explosion Pentagon” Dispersion and Confinement. When all five of these factors are present in the right balance, a dust explosion will occur. The more of these factors that can be controlled or be kept below the combustion threshold, the less likely there will be an incident.

When a material is finely divided into a dust or power form it in most cases it becomes much more likely to combust than it would in a solid state. The reason for this is because when a material is smaller in size, and is dispersed into the air, it creates a much larger surface area to ignite. For example, a 1 kg sphere of a material with a density of 1g/cm3 would be about 27 cm across and have a surface area of 0.3 m3. However, if it was broken up into spherical dust particles 50µm in diameter (about the size of flour particles) it would have a surface area of 60 m² This greatly increased surface area allows the material to burn much faster, and the extremely small mass of each particle allows it to catch on fire with much less energy than the bulk material, as there is no heat loss to conduction within the material.

The source of ignition in a Dust Explosion is often times very difficult if not impossible to determine with absolute certainty. This is because in an industrial setting there is such a larger amount of possible ignition sources that after an incident, it cannot always be pinpointed with absolute certainty.  Some possible sources include, Open Flames, Electrostatic Discharge, Friction, Chemical Reactions, Arcing (From machinery or other equipment) and Hot Surfaces.

Primary and Secondary Explosions

Primary Dust Explosions, in an industrial setting, usually involve a dust cloud (Dispersed Dust) that is ignited by an ignition source. This explosion while possibly involving a substantial amount of dust is often not the most devastating. That is because this initial explosion can cause a pressure wave that can dislodge settled dust from other areas within a facility (Such as on the top of structural elements like beams and columns, high shelving, and machinery, or other areas that dust and debris may collect) causing it to disperse and then cause a much larger explosion that is termed a Secondary Dust Explosion. The majority of fatalities, and damage caused by dust explosion incidents, are actually caused by Secondary Dust Explosions.

Conditions That Lead To A Dust Explosion

The same CSB report cited earlier, after having discussed several different Industrial Dust Explosion Incidents, concluded that while all had many different factors that contributed to the respective incidents, all had the following circumstances in common:

* Facility management failed to conform to NFPA (National Fire Protection Agency) standards that would have prevented or reduced the effects of the explosions.
* Company personnel, government standards enforcement officials, insurance underwriters, and health and safety professionals inspecting the facilities failed to identify dust explosion hazards or recommend protective measures.
* The facilities contained unsafe accumulations of combustible dust and housekeeping to remove such accumulations was inadequate.
* Workers and managers were often unaware of dust explosion hazards.
* Procedures and training to eliminate or control combustible dust hazards were inadequate.
* Previous fires and other warning events were accepted as normal, and their causes were not identified and resolved.
* Dust collectors were inadequately designed or maintained to minimize explosions.
* Process changes were made without adequately reviewing them for potential hazards.

Listed here are a few of the summery reports published by the CSB. As you will see the above-mentioned factors all played a role in the eventual incidents.

Organic Dust Fire and Explosion: Massachusetts (3 killed, 9 injured)

In February 1999, a deadly fire and explosion occurred in a foundry in Massachusetts. The Occupational Safety Health Administration (OSHA) and state and local officials conducted a joint investigation of this incident. The joint investigation report1 indicated that a fire initiated in a shell molding machine from an unknown source and then extended into the ventilation system ducts by feeding on heavy deposits of phenol formaldehyde resin dust. A small primary deflagration occurred within the ductwork, dislodging dust that had settled on the exterior of the ducts. The ensuing dust cloud provided fuel for a secondary explosion, which was powerful enough to lift the roof and cause wall failures. Causal factors listed in the joint investigation report included inadequacies in the following areas:

* Housekeeping to control dust accumulations;
* Ventilation system design;
* Maintenance of ovens; and,
* Equipment safety devices.

Organic Dust Fire and Explosion: North Carolina (6 killed, 38 injured)

In January 2003, devastating fires and explosions destroyed a North Carolina pharmaceutical plant that manufactured rubber drug-delivery components. Six employees were killed and 38 people, including two firefighters, were injured. The U.S. Chemical Safety and Hazard Investigation Board (CSB), an independent Federal agency charged with investigating chemical incidents, issued a final report2 concluding that an accumulation of a combustible polyethylene dust above the suspended ceilings fueled the explosion. The CSB was unable to determine what ignited the initial fire or how the dust was dispersed to create the explosive cloud in the hidden ceiling space. The explosion severely damaged the plant and caused minor damage to nearby businesses, a home, and a school. The causes of the incident cited by CSB included inadequacies in:

* Hazard assessment;
* Hazard communication; and
* Engineering management.

The CSB recommended the application of provisions in National Fire Protection Association standard NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, as well as the formal adoption of this standard by the State of North Carolina.

Organic Dust Fire and Explosion: Kentucky (7 killed, 37 injured)

In February 2003, a Kentucky acoustics insulation manufacturing plant was the site of another fatal dust explosion. The CSB also investigated this incident. Their report3 cited the likely ignition scenario as a small fire extending from an unattended oven, which ignited a dust cloud created by nearby line cleaning. This was followed by a deadly cascade of dust explosions throughout the plant. The CSB identified several causes of ineffective dust control and explosion prevention/mitigation involving inadequacies in:

* Hazard assessment;
* Hazard communication;
* Maintenance procedures;
* Building design; and,
* Investigation of previous fires.

Metal Dust Fire and Explosion: Indiana (1 killed, 1 injured)

Finely dispersed airborne metallic dust can also be explosive when confined in a vessel or building. In October 2003, an Indiana plant where auto wheels were machined experienced an incident, which was also investigated by the CSB. A report has not yet been issued, however, a CSB news release told a story similar to the previously discussed organic dust incidents: aluminum dust was involved in a primary explosion near a chip melting furnace, followed by a secondary blast in dust collection equipment.

Prevention, Safety and Mitigation

Now that we have discussed many of the contributing factors that can lead to a Dust Explosion, we are going to highlight several areas that if given the proper attention, will lead to a safer working environment, and lessen the potential for property damage bodily harm.

Hazard Analysis

We have discussed the great danger that Dust Explosions can pose to life and property. Now we have listed several areas that if given the proper attention will greatly reduce the probability of a dust explosion occurring, and should one occur, lessen the severity of said explosion, possibly saving lives and lessening the damage to the facility in the process.

Facility Dust Hazard Assessment

Being aware that the possibility of a Dust Explosion exists is the first step to avoiding one. As mentioned previously, most dusts or powders will burn and if dispersed in the air in the right proportions and may explode. The same CSB study quoted earlier found that despite the long history of Dust Explosions in industry, in many cases the hazards involved with explosive dusts were largely ignored by plant operators, as well as by outside insurance auditors and government inspectors. Therefore, recognizing the great potential for this kind of accident during the initial design of the facility and while doing regular hazard analysis, are crucial

Here are some of the items to look for when conducting a facility hazard analysis with regard to the potential for Dust Explosions.

Dust Combustibility

Above all else, it must be determined whether or not that various types of dust produced in the facility are indeed combustible. As stated before, most materials in dust or powder form will burn when dispersed into the air in the right proportions. However, those proportions vary with each material. Therefore, it is vital for those responsible to gather as much data as possible about the particular materials present in the facility. One potential source of said data is the particular material’s MSDS or Material Safety Data Sheet. In some cases, additional information such as combustibility test results will be available from chemical manufacturers. However as noted before, many times a manufacturer MSDS may be lacking sufficient data regarding the combustibility of the material in dust or powder form. Therefore additional testing may be necessary to determine this information.

Electrical Considerations

Areas that require a special electrical equipment classification due to the presence (or potential presence) of dubitable dust need to be identified during a facility hazard analysis. There are several published sources of guidelines and/or regulations regarding special electrical equipment classification. These include: The OSHA Electrical standard (29 CFR Part 1910
Subpart S), NFPA 70, the National Electrical Code®, and NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (classified) Locations for Electrical Installations in Chemical Process Areas.

Several of these guidelines identify three different groups of combustible dusts, (Metal, Carbonaceous and Other) and the different safety considerations that are needed for each. For example Metal dusts are considered electrically conductive; therefore special care needs to be taken to ensure that no electrical current can pass through layers of the dusts causing short circuits and arcs, which could then lead to an ignition. Additionally, in certain industrial settings, other high-energy ignition sources such as welding arcs may be present and need to be accounted for.

Potential For Dust Accumulation

The exact amount of dust accumulation necessary for an explosion to occur can vary greatly. As discussed earlier variables such as particle size, methods of dispersion, ventilation system models, air currents, physical barriers and volume of the area where the airborne dust exists can all vary in each different type of dust. With the site-specific data at hand, potential areas of concern can be identified. And the hazard analysis can then be tailored to the specific circumstances in each area and the full range of variables affecting the hazard.

Even seemingly small amounts of accumulated dust can cause catastrophic damage. The CSB estimated, for example, that the explosion that devastated a pharmaceutical plant in 2003 and killed six employees was caused by dust accumulations mainly under 0.25 inches deep. The NFPA warns that more than 1/32 of an inch of dust over 5 percent of a room’s surface area presents a significant explosion hazard.

Many different locations throughout a facility can be a potential starting point for a conflagration. An area where dust is concentrated is an obvious place to start. In Dust Collectors for example, a combustible mixture of diffused dust and air can be found whenever the Collector is operating. Additionally, locations where dust can settle whether occupied, or concealed spaces (such as in ceiling rafters, the tops of shelving, etc). When conducting the Hazard Analysis, careful consideration needs to be given to all possible scenarios in which any previously identified settle dust can be dispersed into the air, either though normal operations, or potential failure modes.

Precautionary Measures

After hazards have been assessed and hazardous locations are identified, one or more of the following prevention, protection and/or mitigation methods may be applied.

Dust Control

Controlling the amount of dust generated, where it is generated, and the dispersion of it throughout the facility, is key to reducing the likelihood of an explosion from occurring. The following steps should be taken in this regard:

* Minimize the amount of dust that escapes from processing equipment and ventilation systems.
* Install a Dust Collection System and monitor it closely to ensure it is operating properly.
* Where possible, install materials (Surfaces) that collect dust poorly and facilitate easy cleaning.
* Inspect and note all hidden or concealed spaces where dust accumulation might occur.
* Maintain a set schedule for cleaning all dust prone areas, and follow it closely.
* Use cleaning methods that do not themselves generate dust clouds when ignition sources are present.
* Locate Relief Valves away from dust hazard zones.
* Maintain a comprehensive dust control program, with hazard dust inspections, testing, housekeeping, and control initiatives.

In several of the cases highlighted earlier, the initial explosion spread by means of ductwork that connected various equipment (usually the Dust Collection System, and/or different parts of the ventilation system) throughout the plant. It is therefore vital that these ductwork systems be fitted with isolation values and inspected regularly to remove excess sitting dust accumulations.

Additionally, certain dust generating operations (such as the use of abrasives, blasting, grinding, or buffing) fall under OSHA  (or similar governmental agencies) ventilation requirements.

Ignition Control

Along with Dust Control, controlling all possible ignition sources also plays a major role in any comprehensive Dust Control Program. Along with Electrical Considerations, there are many other areas that merit attention with regard to ignition potential. Here are several key recommendations for controlling possible Dust Ignition sources.

* Proper Installation, Classification, Operation, and Maintenance of all Electrical Equipment and Wiring (Class II wiring methods and equipment such as “dust ignition-proof” and “dust-tight” should be employed)
* Employ adequate Static Electricity control methods such as Grounding Wires/Rods, etc.
* Limit Smoking, Open Flames, and Sparks in work area.
* Limit or isolate sources of mechanical sparks and friction
* Separate foreign materials that may ignite combustibles from process materials.
* Limit contact between heated surfaces and heating system from combustible dusts.
* Install spark arrestors/spark traps in all dust collector ductwork.

Further resources including US regulation, guidelines, and recommendations can be found in the following sources:

* NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
* OSHA’s Powered Industrial Trucks standard (29 CFR 1910.178).

Damage Control

Despite the best efforts of all parties involved, incidents may still occur. It is therefore, the wise course of action is to prepare for the worst, and implement a strategy that will reduce the severity of such an incident should it occur. The following is a list of recommended steps to take to minimize the impact of a Dust Explosion:

* Separate, and Segregate the Hazard to the extent possible. Place distance between the hazard and the work area, and isolate the hazard with barriers where possible.
* Install deflagration venting.
* Install pressure relief valves on applicable equipment.
* Employ Spark/Ember detection systems, and extinguishing equipment.
* To the extent possible, install explosion protection system, including sprinkler systems, and other assorted specialized suppression techniques.

Proper Employee & Management Training

Even with all of the aforementioned precautions, without a workforce, both employees and management, that have been properly educated about the dangers of Dust Explosions, and safety procedures to reduce the likelihood of their occurrence, and control, and limit the damage should they occur, there still remains high degree of probability for a Dust Explosion occurring.

Employees

Workers that are trained in preventing, and proper incident response techniques are integral to the safe operation of any facility. They are the people closest to the hazard, if these ones are trained to recognize and prevent these types of occurrences from taking place, they can accomplish much in this regard. These ones should also be encouraged to feel free to report unsafe working conditions, or areas where there could be an improvement in safety standards. Therefore all employees, whether they are working directly in hazard areas or not, should be adequately trained in safe work practices applicable to their job tasks, as well as on the overall plant programs for dust control and ignition source control. Periodic refresher courses should also be arranged to keep these safety issues fresh in their minds, and up to date with any possible changes to the hazard conditions themselves.

Management

A qualified team of managers should be responsible for conducting a facility analysis (or for having one done by qualified outside persons) prior to the introduction of a hazard and for developing a prevention and protection scheme tailored to their operation. Supervisors and managers should be aware of and support the plant dust and ignition control programs. Their training should include identifying how they can encourage the reporting of unsafe practices and facilitate abatement actions.

Conclusion

The dangers of Dust Explosion are quite real; they have caused great amounts of damage to property, and have cost many lives. The importance of implementing a comprehensive dust control program, including hazard analysis, implementation of proven dust control and ignition control techniques, damage mitigation, and employee and management training cannot be overstated.

View this video report by the CSB

 
About the Author

| Dominick DalSanto is an Author & Environmental Technologies Expert, specializing in Dust Collection Systems. With nearly a decade of hands-on working experience in the industry, Dominick’s knowledge of the industry goes beyond a mere classroom education. He is currently serving as Online Marketing Director & Content Manager at Baghouse.com. His articles have been published not only on Baghouse.com , but also on other industry related blogs and sites. In his spare time, Dominick writes about travel and life abroad for various travel sites and blogs.