Thursday, June 21, 2012

Combustible Dust Hazards 101

Excellent primer, training video on Combustible Dust 101 from our friends at EMSL by IAQMarketer.

Published on Apr 22, 2012 by
Combustible dusts are fine particles that present an explosion hazard when suspended in air in certain conditions. A dust explosion can be catastrophic and cause employee deaths, injuries, and destruction of entire buildings. In many combustible dust accidents, employers and employees were unaware that a hazard even existed.

Monday, June 11, 2012

Safety Pays

Safety 2012: OSHA’s Continuing Mission | EHS Today

Does Safety cost or save money?  Here is the other side of the argument:

Safety 2012: "Safety Pays"

From by Sandy Smith, OSHA Administrator David Michaels says "Safety Pays".

"Safety saves lives, said Michaels, and also, “Safety pays. Safety does not just prevent injuries, it will save you money.”

Safety 2012: OSHA’s Continuing Mission

Bolstered by recent studies that indicate OSHA inspections, and corporations’ subsequent emphasis on safety, actual save companies money, OSHA Administrator David Michaels told a packed room at Safety 2012 in Denver that OSHA “levels the playing field” for responsible employers who are investing in safety and must compete with companies that are cutting costs by compromising worker safety.

“Employers who don’t make the investment look at workers as replaceable cogs,” said Michaels.

While the rate of fatal workplace injuries continues to decrease, Michaels noted that:
  • More than 4,000 Americans die from workplace injuries every year.
  • Perhaps as many as 50,000 workers die from illnesses in which workplace exposures were a contributing factor.
  • There are more than 3 million cases of non-fatal workplace injuries and illnesses annually.
  • The annual cost of occupational injuries and illnesses totals more than $170 billion.
Michaels offered concrete proof that OSHA inspections save lives. He referred to a March 8, 2011 incident in Mercer, Ohio, in which an OSHA inspector ordered workers out of an unshored trench and took a photo of the trench at 10 am. Five minutes later, at 10:05, the trench collapsed. A similar incident occurred in Auburn, Ala., on April 20, 2011.

When employers ignore OSHA standards, workers often are injured or killed. As an example, Michaels cited an incident in Cincinnati in June 2002. An employer, cited for several safety violations, continued to operate as usual. The site of an excavation caved in, entombing a worker. Eight hours later, his body was removed from the trench.

Safety saves lives, said Michaels, and also, “Safety pays. Safety does not just prevent injuries, it will save you money.”

He cited the recent Harvard Business School study that revealed that in the state of California, companies that were the target of random OSHA inspections experienced a 9.4 percent reduction in injuries, a 26 percent reduction in injury costs and saved about $355,000 (14 percent of the average annual payroll of the sample of employers). Two additional studies, of employers in Pennsylvania and Washington, recently came to similar conclusions.

He also cited the case of Alcoa, which under the leadership of Paul O’Neill, embraced safety as part of its culture. A good company producing a good product before O’Neill and his emphasis on safety at board and corporate meetings. Alcoa become an extremely profitable company. Coincidence? No way, said Michaels.

“If you embrace safety, you produce a better product,” he said.

Related Articles

Researchers: OSHA Inspections Saving Employers Billions

It will come as a surprise to many members of Congress that occupational safety and health regulations and inspections are not “job killers.” In fact, say researchers, they reduce injuries for years following the inspections, resulting in greatly reduced workers’ compensation costs for employers....

Cost of Job-Related Illnesses Exceeds Costs of All Cancers, Diabetes and Strokes

A new NIOSH-funded study from J. Paul Leigh, a professor of public health sciences at the University of California – Davis, determined that the cost of job-related injuries and illnesses is $250 billion, which is $31 billion more than the cost of all cancers and $76 billion more than the cost of diabetes. The study results beg the question: Is industry and the federal government doing enough to eliminate occupational injuries and illnesses and their associated costs?...

Study Estimating EHS Regulations Cost Business $65 Billion Annually “Vastly Overstated”

A 2010 study by Nicole V. Crain and W. Mark Crain (Crain and Crain 2010, 29-31) conducted for the Small Business Administration’s Office of Advocacy often is cited by opponents of new federal workplace regulations to support their opinion that OSHA regulations are bad for the economy. However, another group of researchers claim the Crain and Crain study is poorly researched and includes “vastly overstated costs”...

Friday, June 8, 2012

Top 10 Reasons Risk Assessments Are Inadequate

Safety 2012: 10 Reasons Your Risk Assessments Are Inadequate | EHS Today

From, a great article on Risk Assessments, why they may fail to deliver, and why they are important through the life of the process for MOC, etc.  Including hierarchy of controls, and prioritizing risk.

Safety 2012: 10 Reasons Your Risk Assessments Are Inadequate

Two risk control experts who have performed thousands of risk assessments throughout their careers have concluded that "a number of those risk assessments are not performed very well." They shared their expertise with ASSE Safety 2012 attendees in a June 5 session in the Colorado Convention Center.
"Organizations face a wide range of risk every day that has the potential to impact their ability to stay in business," said Bruce Lyon, CSP, PE, ARM, CHMM. "Risk assessment is an important tool to help manage that process."

Lyon and Bruce Hollcroft, CSP, ARM, CHMM, both directors of risk control at Hays Companies, presented the top 10 reasons your risk assessments may be inadequate:
10. Failing to perform a formal risk assessment. Organizations may fail to conduct risk assessments for a variety of reasons: lack of resources, believing that the risk already is managed or doesn't need to be managed, assuming that insurance carriers or consultants are responsible for risk assessments, risk assessments are not mandated or the organization has not experienced significant events. "The key is to identify a strategy when, how and why risk assessments are being performed," Lyon said.

9. Failing to define the purpose and scope of the assessment. "When you fail to have a good purpose and scope, you lack direction, you lack focus," Hollcroft explained. "When you do have a good focus of scope, you get input from people who are going to be using that information."

8. Failing to understand organization's acceptable risk level. "A lot of organizations that I have dealt with have not thought of or defined what they are willing to accept in terms of risk," Lyon said. "Then you see a lot of organizations that promote the zero-injury goal. That's an impossible goal. There is a level where we have to accept the risk based on the fact that it's either impractical to reduce the risk further or the costs outweigh the gains that are achieved."

7. Failing to assemble the best team possible to perform the risk assessment. Without a trained, informed and competent team behind your efforts, the risk assessment will be weak.

6. Failing to use the best risk assessment technique. Organizations that are unaware or unskilled in risk assessment can fall into this trap.

5. Failing to be objective and unemotional during the assessment. Factors that may result in a biased or emotion-based assessment include influence from recent events/trends, personal experiences, personal areas of interest and strong personalities. The assessment team needs to be well balanced, objective and unemotional while assessing risk.

4. Failing to identify hazards and see combined whole-system risk. "Having a diverse team is important to address range of potential risks that exist," Lyon said. "If risk isn't identified, it doesn't get managed." Don't view risks as mutually exclusive; consider how individual risks could impact other risks.

3. Failing to consider the hierarchies of controls or prioritize by risk. "It's just not effective to rely on PPE," Hollcroft said. "If you don't have reliable controls, you might not want to consider them in the assessment."

2. Failing to perform risk assessment during the design/redesign stage. "Unfortunately, many organizations don't even consider doing risk assessments at this stage," Lyon said, but in reality, this is an imperative time for risk assessments. Conduct assessments at new facilities, during installations and when modifications and changes occur.

And the No. 1 reason your risk assessments may be inadequate is…

1. Failing to communicate before, during and after the assessment. Before an assessment, determine who needs to be involved and ensure they understand what's expected of them. During the assessment, make sure everyone understands the process and their responsibilities. And afterward, convey the information to others so they can put it to work for themselves. "Figure out what you can share and share it," Hollcroft said. "Failure to communicate is a huge shortcoming when we conduct risk assessments."
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© 2012 Penton Media Inc.

Thursday, June 7, 2012

Wood Pellet Fire and Explosion Case Study

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

From and Samuel Dal Santo, an excellent case study of what went wrong at a wood pellet operation, creating fires and explosions that in most cases can be prevented.  One key to prevention is proper Safety System design.  And one key to prevention is proper design and application of a listed Spark Detection System.  For more information on Spark Detection and other types of Hazard Monitoring, Fire and Explosion Prevention and Protection systems please contact us in the contact form in the right column of this blog.

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

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

May 16 2012 – Editorial | We recently published a news article on about OSHA’s enforcement actions concerning last year’s combustible dust fire and explosion at the New England Wood Pellet Company’s Jaffrey, New Hampshire wood pellet plant.

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 – 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). 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), 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) 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) 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, “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.

About the Author: Samuel Dal Santo serves as Chairman of Samuel’s focus is on bringing about a reconciliation between often distant front office strategy, and field realities. Samuels unique background and field experience provides him with the needed experience, and real world skills that are often lacking in executive ranks today. 


* 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.

Wednesday, June 6, 2012

Wed, 03/21/2012 - 1:43pm
Vahid Ebadat, Ph.D., CEO, Chilworth North America 

From, an article by Dr. Vahid Ebadat, CEO Chilworth.

This feature originally ran in the March 2012 issue of Food Manufacturing, a sister publication.

A food processor's guide to understanding how dust explosions happen and what can be done to prevent them.

The vast majority of powders in the food industry can form explosible dust clouds if the particle size is small and moisture content is low. Although explosible dust cloud concentrations are not normally expected to be present within processing buildings, explosible dust clouds are regularly formed inside material handling or processing equipment when bins are being filled, powders are being transferred or dust is being collected in a dust collector.

The particle size of the dust is a property which influences the explosibility of the dust cloud. The finer the particles the greater the surface area per unit of mass and thus the more explosible a given dust is likely to be. When the cloud is composed of a series of particle sizes ranging from fine to coarse, the fine particles play a prominent part in the ignition and the explosion propagation. The presence of dusts should therefore be anticipated in the process stream, regardless of the starting particle size of the material.

The moisture content of a product will also affect the explosion risk. A dry dust contains less than five percent moisture. Dry dusts of small particle size will be more easily ignited and produce more violent explosions. It must be noted that particles with moisture contents in the range of 12 to 18 percent, as found naturally in many agricultural products, can still be explosible.

Assessing Dust Explosion Hazards
A systematic approach to identifying dust cloud explosion hazards and taking measures to ensure safety involves:
  • Determining the dust cloud’s ignition sensitivity and explosion severity characteristics through appropriate laboratory tests on representative dust samples
  • Identifying areas of the facility where combustible dust cloud atmospheres could exist under both normal and abnormal conditions
  • Identifying potential ignition sources that could exist under both normal and abnormal conditions
  • Preventing the formation of explosible dust clouds in the plant and reducing the extent and duration of any clouds that may form
  • Taking measures to eliminate and control ignition sources
  • Taking measures to protect against the consequences of dust cloud explosions. Explosion protection measures include explosion relief venting, explosion suppression, explosion containment and explosion isolation. Where practical, one could consider the application of inert gas purging or padding to prevent the combustion process.
Laboratory Testing
To assess the possibility of an explosion in a facility and to select the most appropriate basis of safety, explosion characteristics of the dusts that are being handled and processed in the facility should be determined.

The explosion characteristics of powders normally fall within one of two groups, “likelihood of an explosion” and “consequences of an explosion.” Taken together, these two characteristics determine the dust explosion risk of a material.

The following tests provide information on the likelihood of a dust explosion:
  • Explosion Classification (Screening) Test (ASTM E1226, Standard Test Method for Explosibility of Dust Clouds): This test answers the question “Can this dust explode?”
  • Minimum Ignition Energy (ASTM E2019, Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air): The test is used primarily to assess the susceptibility of dust clouds to ignition by electrostatic discharges (sparks).
  • Minimum Ignition Temperature (MIT) of a Dust Cloud (ASTM E1491, Standard Test Method for Minimum Auto-ignition Temperature of Dust Clouds): The MIT Cloud is an important factor in evaluating the ignition sensitivity of dusts to such ignition sources as heated environments, hot surfaces, electrical devices and friction sparks.
  • Minimum Ignition Temperature (MIT) of a Dust Layer (ASTM E2021, Standard Test Method for Hot Surface Ignition Temperature of Dust Layers): The MIT Layer is used in evaluating the ignition sensitivity of powders to ignition by hot surfaces.
  • Self-Heating (JA Abbott (ed.) “Prevention of Fires and Explosions in Dryers,” Institute of Chemical Engineers, 1990): The minimum onset temperature for self-ignition of a powder depends mainly on the nature of the powder and on its dimensions. If these variables are predictable, a reliable assessment of the onset temperature for self-ignition and also the induction time to self-ignition can be made by appropriate small-scale laboratory tests.
  • Electrostatic Volume Resistivity (General Accordance with ASTM D257, Standard Test Methods for DC Resistance or Conductance of Insulating Materials): Volume Resistivity is the primary criterion for classifying powders as low, moderately or highly insulating. Insulating powders have a propensity to retain electrostatic charge and can produce hazardous electrostatic discharges.
  • Electrostatic Chargeability (General Accordance with ASTM D257, Standard Test Methods for DC Resistance or Conductance of Insulating Materials): This test provides data that can be used to develop appropriate material handling guidelines from an electrostatic hazards point of view.
  • Minimum Explosible Concentration (MEC) (ASTM E1515, Standard Test Method for Minimum Explosible Concentration of Combustible Dusts): This test answers the question “How easily can an explosible dust cloud be formed?”
  • Limiting Oxidant Concentration (LOC) (EN 14034-4, Determination of the Limiting Oxygen Concentration of Dust Clouds): The LOC test is used to study explosion prevention or severity reduction involving the use of inert gases and to set oxygen concentration alarms or interlocks in inerted vessels.
This test determines the consequences of an explosion and explosion severity:
  • Maximum Explosion Pressure, Maximum Rate of Pressure Rise, Deflagration Index (Kst Value) (ASTM E1226, Standard Test Method for Explosibility of Dust Clouds): The maximum explosion pressure and maximum rate of pressure rise are measured and the latter is used to calculate the Deflagration Index (Kst) value of the dust cloud. These data can be used for the purpose of designing dust explosion protection measures such as explosion relief venting, suppression and containment and to classify a material’s explosion severity. This test answers the question, “How bad is it if it happens?”
Approaches To Process Safety Testing
The table below specifies the type of data that might be required to assess dust explosion hazards associated with some common unit operations in the food industry.

Explosion Prevention and Protection Measures
Safety from dust cloud explosions includes taking measures to avoid an explosion (explosion prevention) or designing facilities and equipment so that in the event of an explosion people and processes are protected (explosion protection).
The risk of an explosion is minimized when one of the following measures is ensured:
  • An explosible dust cloud is never allowed to form
  • The atmosphere is sufficiently depleted of oxidant (normally the oxygen in air) that it cannot support combustion
  • All ignition sources capable of igniting the dust cloud are removed
  • People and facilities are protected against the consequences of an explosion by “protection measures” such as explosion containment, explosion suppression or explosion relief venting
  • Housekeeping activities must ensure that secondary fuel sources are not available. Of key importance is the evaluation of dust release points and exhaust ventilation needs. It is much easier to replace a gasket, refit a manway, install local dust aspiration systems, etc., than to spend the time cleaning up the dust that has escaped.
Dr. Vahid Ebadat has worked extensively as a process and operational hazards consultant for the chemical, pharmaceutical and food industries. Dr. Ebadat is a regular speaker at training courses on gas and vapor flammability, dust explosions and controlling electrostatic hazards. He can be reached at (609) 799-4449 or

Combustible Dust: Identifying, Addressing Explosion Risks Can Save Lives

From Plant Engineering

Combustible Dust: Identifying, Addressing Explosion Risks Can Save Lives

A great article by Tony Supine and Mike Walters, Camfil Farr APC, reviews the current status of the OSHA National Emphasis Program for combustible dust, the NFPA standards that address how to prevent or limit explosion hazards, how to identify these hazards, and the types of equipment used to eliminate or control explosion hazards.

Review of the current status of the OSHA National Emphasis Program for combustible dust, the NFPA standards that address how to prevent or limit explosion hazards, how to identify these hazards, and the types of equipment used to eliminate or control explosion hazards.

Tony Supine and Mike Walters, Camfil Farr APC


The National Fire Protection Association (NFPA) sets standards and codes to protect buildings against fire and explosion risks, and OSHA is enforcing these standards with increasing vigilance. When it comes to combustible dust, several standards must be considered. Combustible dust explosions are a risk in many areas of a plant, but one of the most common locations is the dust collection system. How do you know if your dust collection system complies? What do you do if it doesn’t? Are your employees at risk? What are the hazards and how do you identify them?

This article reviews the current status of the OSHA National Emphasis Program for combustible dust, the NFPA standards that address how to prevent or limit explosion hazards, how to identify these hazards, and the types of equipment used to eliminate or control explosion hazards. We will also examine the most common shortfalls to compliance and how to avoid them.

At a the start of a dust explosion and a passive system of protection, explosive dust is injected into the dust collector to create a flammable cloud. Courtesy: Camfil FarrAPCTen-year retrospective
An explosion at the West Pharmaceutical facility in Kingston, N.C., in January 2003 killed six workers and injured 38 others, including two firefighters. The culprit was inadequate control of dust hazards at the plant. Just a month later, in February 2003, another explosion and fire damaged the CTA Acoustics manufacturing plant in Corbin, Ky., fatally injuring seven workers. Investigators found that resin dust, accumulated in a production area, was likely ignited by flames from a malfunctioning oven, triggering the explosion.

Probably the most famous combustible dust explosion in the past decade—and the one that re-focused the national spotlight on this issue—was the February 2008 accident at the Imperial Sugar Company’s Wentworth, Ga., refinery. A dust cloud explosion triggered a fatal blast and fire that killed 13 workers and injured 42 others, generating a storm of media attention and government scrutiny.

These are not the only fatal explosions to occur in U.S. manufacturing plants, though they are the three deadliest to be investigated. More recently, in December 2010, two brothers lost their lives in a chemical explosion at the New Cumberland, W.Va., plant of AL Solutions. And during 2011, three deadly fires and explosions occurred at a Hoeganaes Corp. plant in Gallatin, Tenn. Investigators found that accumulations of fine iron powder in the facility led to the explosions.
About 5 ms later, the dust ignites and the vent is opened. Courtesy: Camfil Farr APCIn the U.S. alone between 1980 and 2005, the Chemical Safety Board reported 281 explosions caused by ignited combustible dust. These explosions resulted in 199 fatalities and 718 injuries. Combustible dust explosions over the past 10 years in U.S. plants are blamed for well over 100 fatalities and hundreds more injuries. Sadly, experts believe that all of these accidents were preventable if the companies involved had followed best practices for fire and explosion protection such as the methodologies described in this article.

Explosion protection solutions
There are two general categories of equipment used to comply with NFPA standards for the explosion protection of dust collection systems: passive and active. Passive systems react to the event, while active systems detect and react prior to or during the event. The goal of a passive system is to control an explosion so as to keep employees safe and minimize equipment damage in the plant. An active system, by contrast, can prevent an explosion from occurring. An active system involves much more costly technology and typically requires recertification every three months.

Passive devices
Almost immediately the flame is extended away from the dust collector and into a safe area. Courtesy: Camfil Farr APC
Explosion venting: Designed to be the “weak” link of the dust collector vessel, an explosion vent opens when predetermined pressures are reached inside the collector, allowing the excess pressure and flame front to exit to a safe area. It is designed to minimize damage to the collector and prevent it from blowing up in the event of a deflagration, thereby reducing the safety hazard.

Flameless venting: Designed to install over a standard explosion vent, a flameless vent extinguishes the flame front exiting the vented area, not allowing it to exit the device. This allows conventional venting to be accomplished indoors where it could otherwise endanger personnel and/or ignite secondary explosions.

Passive float valve: Designed to be installed in the outlet ducting of a dust collection system, this valve utilizes a mechanical barrier to isolate pressure and flame fronts caused by the explosion from propagating further through the ducting. The mechanical barrier reacts within milliseconds and is closed by the pressure of the explosion.

Back draft damper: A mechanical back draft damper is positioned in the inlet ducting. It utilizes a mechanical barrier that is held open by the process air and is slammed shut by the pressure forces of the explosion. When closed, this barrier isolates pressure and flame fronts from being able to propagate further up the process stream.

The smoke and dust quickly clear. the entire event took just 150 ms. Courtesy: Camfil Farr APCFlame front diverters: These devices divert the flame front to the atmosphere and away from the downstream piping. Typically, these devices are used between two different vessels equipped with their own explosion protection systems. The flame front diverter is used to eliminate “flame jet ignition” between the two vessels that could overpower the protection systems installed.

Active devices
Chemical isolation: Designed to react within milliseconds of detecting an explosion, a chemical suppression system can be installed in either inlet or outlet ducting. Typical components include explosion pressure detector(s), flame detector, and a control panel. This system creates a chemical barrier that suppresses the explosion within the ducting, reduces the propagation of flame through the ducting, and minimizes pressure increase within connected process equipment.

Chemical suppression: Whereas chemical isolation is used to detect and suppress explosions within the ducting, chemical suppression protects the dust collector itself. It is often used, together with isolation, when it is not possible to safely vent an explosion or where the dust is harmful or toxic. The system detects an explosion hazard within milliseconds and releases a chemical agent to extinguish the flame before an explosion can occur.

Fast acting valve: Designed to close within milliseconds of detecting an explosion, the valve installs in either inlet or outlet ducting. It creates a mechanical barrier within the ducting that effectively isolates pressure and flame fronts from either direction, preventing them from propagating further through the process.

High-speed abort gate: The gate is installed in the inlet and /or outlet ducting of a dust collection system and is used to divert possible ignition hazards from entering the collector, preventing a possible explosion from occurring and preventing flame and burning debris from entering the facility through the return air system. A mechanical barrier diverts process air to a safe location. Abort gates are activated by a spark detection system located far enough upstream to allow time for the gate to activate.

When planning explosion protection, don’t overlook additional devices and materials that can help reduce fire risk within the dust collection system. For spark-generating applications, a range of features and technologies is available, from flame-retardant and carbon anti-conductive filter media to spark arrestors in the form of drop-out boxes, perforated screens, or cyclone devices installed at the collector inlet. Fire sprinkler systems may also be required with some installations.

A dust collector that uses vertically mounted filter cartridges can also reduce fire and explosion risks. With horizontally mounted cartridges, dust becomes trapped in the pleats in the upper third of the filters. This trapped dust can burn even if the filter media is fire retardant. Horizontal cartridges are also exposed to all of the dust entering the collector, coarse and fine. This leads to premature failure from abrasion and leaks. These leaks can go unnoticed for quite some time while fine combustible dust is blown into your facility. Vertically mounted filters use baffle systems to segregate much of the dust into the hopper, which reduces the load on the filters and helps eliminate these problems.

Avoid pitfalls
A variety of situations can place a facility at risk, but there are some common denominators. The ones we have most commonly encountered in our field experience are:

Complacency about maintaining the status quo: “I’ve been here for years and we’ve never had a problem” is an all-too common refrain. This mind-set stems in part from a common misconception that the facility’s dust is not explosive because it has not had an event, when in fact the opposite may be true. In some cases, it may take years for dust to accumulate to explosive levels as seen in the CTA Acoustics event.
To understand the risks, let’s review the five elements that comprise what is known as the “dust explosion pentagon”:
  • Combustible dust
  • An ignition source
  • Oxygen in the air
  • Dispersion of the dust in sufficient concentration to be explosive
  • Containment of the dust cloud within a confined or semi-confined vessel or area.
All five of these elements may exist in an industrial facility, but all must be present at the same time for an explosion to occur. If there is no containment, it is still possible for a flash fire to erupt if elements 1-4 are present simultaneously.

In a closed vessel such as a cartridge dust collection system, an explosion typically begins when an ignition source enters the dust collector. This ignition source can come from many things and in most cases is never identified. When a pulse cleaning event occurs, a suspended cloud of combustible dust is present in high concentration within the collector.

Though some incidents involve a single explosion, it is more common for a series of deflagrations to occur. The initial explosion can dislodge ignitable dust hidden on overhead surfaces or other areas over a large area and trigger secondary explosions that can be ignited from the initial explosion or from other ignition sources. It is these secondary explosions that have historically caused the majority of injuries and damage to property.

How do you know if your facility is at risk? Even if there has never been a problem before, this is no guarantee of future safety. The level of hazard can change from day to day and even from moment to moment—whether due to the introduction of a new process, a temporary lapse in housekeeping, or a static electricity discharge caused by improper grounding. It takes ongoing vigilance and management of change to identify conditions in your plant that might cause a potential safety problem.

Failure to conduct a hazard analysis (also called a risk evaluation): This is probably the biggest oversight that we see. The NFPA states that a hazard analysis is needed to assess risk and determine the required level of fire and explosion protection. The analysis can be conducted internally or by an independent consultant, but either way the authority having jurisdiction will ultimately review and approve the findings.

When it comes to explosion protection, the first step in a hazard analysis is to determine if your dust is explosive. Most commercial test laboratories offer a low-cost test to establish whether a dust sample is combustible. If the test is positive, then the explosive index (Kst) and the maximum pressure rise (Pmax) of the dust should be determined by ASTM E 1226-10, Standard Test Method for Explosibility of Dust Clouds.

Your dust collection equipment supplier needs the Kst and Pmax values in order to correctly size explosion venting or suppression systems. Failure to provide this information will increase your costs, since the supplier will use worst-case estimates of the Kst and Pmax values or may even refuse to provide the equipment. The liability to the manufacturer and to the equipment purchaser is too high to ignore the life safety objectives.

The fact is, any dust above 0 Kst is now considered to be explosive, and the majority of dusts fall into this category. If OSHA determines that even a very low Kst dust is present in a facility with no explosion protection in place, a citation will result. This is one of the biggest changes to occur with the reintroduction of the OSHA NEP in 2008.

Shopping for price over quality: Every plant engineer is acquainted with the benefits of basing purchasing decisions on life-cycle cost—sometimes called “total cost of ownership”—over choosing equipment with the lowest price tag. A dust collector is no exception. A well-designed dust collection system can pay for itself rapidly in energy and maintenance savings, costing far less to operate than a unit with a low initial price. A high-quality, heavy-duty collector can also offer a less obvious advantage in the event of a combustible dust problem.

As documented both in full-scale testing and field experience, in the event that a dust explosion occurs in the collector, a low-end model will more than likely require total replacement. A collector made of thicker-gauge metal with higher vessel strength, however, will survive an explosion and can often continue in service with only the explosion vent and filter cartridges needing to be replaced.

Use of noncompliant devices: A close cousin to the “price versus quality” issue involves the use of noncompliant or uncertified explosion protection devices. As an example, sometimes products, such as back flap dampers, may be reverse-engineered by suppliers that do not have any expertise in explosion protection or have chosen not to perform the required testing to satisfy the standards and/or the performance-based provisions. No testing exists to prove that the device will comply with current standards. If an OSHA inspector finds this situation in the field, the plant will have to replace the device and may be subject to a fine. Worse yet, if a combustible dust problem should occur, there is no guarantee that the device will perform as expected.

It is also worth noting that there is no such thing as an “NFPA-approved” device. A supplier may correctly state that a device “carries CE and ATEX certifications” or is “manufactured in accordance with NFPA standards,” but test data must be available to support these claims. Such a device might cost more than its noncompliant counterpart, but in the long run it can save money, headaches, and even lives.

Housekeeping deficiencies: In its October 2011 update on the Combustible Dust NEP, OSHA reported that one common violation encountered during inspections involved “hazardous levels of dust accumulation in the workplaces due to poor housekeeping practices.” In the authors’ experience, as a rule of thumb, if an OSHA inspector can run his finger across a dusty surface or see a footprint, that is considered a citable condition. Even diligent cleanup of floors and work surfaces is not sufficient if more elevated areas are neglected: Dust accumulation on rafters and other horizontal overhead surfaces or on top of machinery is a frequent culprit. Also, the NFPA recently tightened its definition of hazardous surface dust (in NFPA 654), defining it as any dust layer of 1/64 in. (0.4 mm) or greater, compared to a previous limit of 1/32 in. (0.8 mm) of dust.

When it comes to the dust collector, a simple but important housekeeping requirement is to change filters when airflow through the system reaches a differential pressure limit as prescribed by the manufacturer or when the pressure drop across the collector is negatively affecting the ability of the dust collection system to capture the dust, thus allowing it to escape into the facility.

Some long-life cartridge filters available today can operate for two years or even longer between change-outs; but for heavy dust-loading applications, filter replacement might be considerably more frequent. Also, use of a listed portable vacuum helps keep the surrounding area free of spilled dust and surface dust. Use of compressed air to control dust is permitted only under certain conditions because it can increase the hazard by creating a combustible dust cloud.

Another housekeeping misstep is storing dust in the dust collector’s hopper. The hopper should be equipped with a device that discharges the dust into a separate drum or storage container after it is pulsed off the filters during the cleaning process. Equally important, this storage container must be emptied regularly, or dust can back up into the hopper. Dust sitting in a hopper creates a potential fire or explosion risk, and may also affect performance of the dust collection system. This will lead to loss of airflow, which will reduce conveying velocities, allowing build-up of dust in the ducting and emissions of dust at the process hoods.

Misconceptions about “open” style dust collectors: There is a fairly widespread misconception that open-type dust collection systems, such as those incorporated into downdraft tables and booths, are not a hazard. While these collectors admittedly differ from traditional dust collectors in that they do not take the form of a tightly contained vessel, at least four of the five ingredients of the explosion pentagon may still be present: combustible dust, an ignition source, oxygen, and dispersion of the dust in sufficient concentration to pose a hazard. Thus, there is still a risk of flash fire directed by a pressure front—a potentially fatal risk, given that workers are in close proximity in these environments. If you are using an open-type dust collector, you must still test and evaluate the combustibility of the dust and equip the area with fire and/or explosion protection equipment as required.

The mistake of over-engineering: The problems and pitfalls described thus far involve not doing enough in one way or another. But sometimes plant engineers err on the side of doing too much—the error of over-specification, which results in explosion protection solutions that may be needlessly expensive and time-consuming to maintain and monitor.

The NFPA uses relatively conservative textbook calculations in its standards for explosion protection equipment, and justifiably so. However, the NFPA also allows real-world destructive test data to be used in place of its own standard calculations, provided the dust collection supplier can provide adequate data to prove that the collection system is designed to meet a specific set of criteria for a given situation. The use of real-world destructive test data is thus a permissible and sometimes overlooked strategy.

An example is actual explosion testing of a dust collector to show that it will stand up to anticipated pressure conditions, instead of using the reduced pressure calculations in NFPA 68. By combining field testing and full-scale dust collection laboratory test apparatus to prove certain assumptions, this approach might allow you to install longer duct lengths in a given application; to use a single explosion vent where multiple vents might otherwise have been needed; or even to use explosion venting in place of a more costly chemical suppression system. Find out if your dust collection supplier can provide real-world test data to assist in a strategy that may help you to avoid over-engineering and save on equipment costs without compromising safety.

There is no universal agreement about the best way to tackle the combustible dust problem. Some concur with the CSB position that OSHA needs to accelerate efforts to produce and enforce its own standard, citing a long-standing precedent with the grain industry.
Explosions in grain bins used to be one of the biggest safety problems in the U.S. In 1987, following a series of deadly explosions, OSHA promulgated a Grain Handling Facilities Standard that remains in effect today. This standard has yielded major improvements in combustible dust safety in these facilities.

According to OSHA, “The lessons learned in the grain industry can be applied to other industries producing, generating, or using combustible dust.”

Others argue that more stringent and perhaps consolidated dust standards from the NPFA, diligently enforced by OSHA and local authorities, would be preferable to a separate OSHA standard. What everyone does seem to acknowledge is that more drastic action is necessary to prevent combustible dust tragedies from continuing to occur.

Until such action is mandated, a certain degree of self-regulation is called for. Every plant engineer can choose to be part of the problem or part of the solution. By following the guidelines in this article, and securing the help of engineering consultants and equipment suppliers with a proven track record in combustible dust applications and performance-based solutions, you can minimize risk factors and maximize combustible dust safety in your facility.

Supine has held numerous positions with Camfil Farr APC including research and development manager, technical director, and currently plant manager. Walters, a registered professional engineer with 30 years’ experience in air pollution control and dust collection systems, is a senior engineer with the company. The authors can be reached at 800-479-6801 or 870-933-8048; e-mail filterman(at) website

Monday, June 4, 2012

Combustible Dust: Rely on Best Practices

From by Jonathan A. Jacobi of UL PureSafety, a great article on relying on best engineering practices, regardless of changing regulations.  We have always relied on best prescriptive and engineered design practices for fire and explosion prevention and protection, system design, and have relied on FM Global Data Sheets and other insurers input, NFPA and other Standards as well as practical experience from the best minds available to aspire to industry best practices for our customers and clients. Read on...

Combustible Dust Management Training: Rely on Best Practices, Not Shifting Regulatory Winds :: POWER Magazine : 

None of you reading this magazine needs an article—or new governmental regulations—to tell you that flash fires and explosions involving coal dust can cause catastrophic incidents, fatalities, facility damage, and financial consequences. One of the most tragic incidents occurred at a Michigan power plant in 1999. Six people were killed and 38 were injured when natural gas from a boiler exploded, setting off secondary explosions caused by disturbed coal dust. In the past decade, managing combustible dust hazards to prevent such tragedies has received increased attention from companies, industry groups, insurers, and regulators. (See “Coping with Coal Dust,” in the March 2012 issue or the archives at

A turning point was the 2006 U.S. Chemical Safety Board (CSB) report identifying 281 combustible dust incidents between 1980 and 2005 that caused 119 fatalities and 718 injuries. That sparked efforts to enhance standards and ramp up enforcement, and those efforts intensified after a 2008 combustible dust explosion killed 14 people and injured 38 at an Imperial Sugar refinery in Georgia (Figure 5).

 5. The dangers of combustible dust. The 2008 dust explosion at the Imperial Sugar Refinery in Georgia, shown here, focused increased national attention on issues surrounding combustible dust. Source: Chemical Safety Board

Recently, on the fourth anniversary of that tragedy, CSB Chairman Rafael Moure-Eraso stated that “safety recommendations that followed from our investigation of this accident will go far in saving lives. I am pleased to report that on this accident anniversary all but one of our recommendations have been successfully adopted.”

The unfulfilled recommendation? That the U.S. Occupational Safety and Health Administration (OSHA) create a new “comprehensive standard to reduce or eliminate hazards from fire and explosion from combustible powders and dust.”

Seeking a Comprehensive Combustible Dust Standard

The quest for a “comprehensive standard” has taken the industry down a long and winding road, inspiring countless debates and some confusion. After OSHA spent years laying the groundwork for such a standard, while pursuing a vigorous Combustible Dust National Emphasis Program (NEP), it is somewhat baffling that the agency recently shifted its combustible dust rulemaking initiative from “active” to the ambiguous “long-term actions” status (Figure 6).

6. An explosive situation. Fire and explosion can occur where coal is handled, processed, and used. This is one reason why electric power plants are included in OSHA’s National Emphasis Program. Source: UL PureSafety

Regardless of the meaning of that shift, even without a new standard, OSHA has found plenty of regulations to cite and has made the energy industry a priority for related inspections. Beyond the obvious need to protect your workers, facilities, and bottom line, there are solid reasons not to take a “wait and see” approach that relies on new standards.
OSHA has cited facilities based on 17 existing standards in the NEP, including those involving electrical installations, housekeeping, hazard labeling, personal protective equipment hazard assessment, and the “General Duty” clause.

According to Sanji Kanth, senior safety engineer with OSHA’s enforcement directorate, from the launching of the program through October 2011 there were 2,600 inspections related to the NEP, resulting in more than 12,000 violations (approximately 8,500 classified as “serious,” “willful,” or “repeat”) and total civil penalties exceeding $24 million.

Companies may be held civilly liable in the absence of a federal standard, because consensus standards exist, including stringent state-run OSHA, local, and organization-specific requirements, as well as those defined by insurance risk managers, fire safety enforcement officers, and others.

Industry and public awareness of these hazards remains high due to media attention; even minor shortcomings could damage brand reputation, worker morale, and productivity—as well as expose your company to whistleblowing complaints and liability claims.
Additionally, OSHA’s March 2012 revisions to its Hazard Communication Standard included combustible dust in the definition of “hazardous chemicals”—one more indicator of OSHA’s intent to increase regulation and enforcement.

But here’s the point to remember: Combustible coal dust is not an area where any company should wait for regulators to issue clarifications. If you stay current with existing best practices, you will stay ahead of regulators and prevent your company from becoming a tragic example cited in future reports arguing for stricter regulations.

Industry Best Practices Are the Best Way Forward

The power generation industry as a whole is exemplary in promoting, defining, and following safety best practices. That includes managing coal dust hazards. The National Fire Protection Association (NFPA) regulations, particularly NFPA 654, are widely adopted, and organizations such as the Powder River Basin Coal Users’ Group (PRBCUG) have brought stakeholders together to develop and share best practices that exceed regulatory guidelines. The industry’s shared knowledge is also evident in the many prior articles written by members of the PRBCUG that have appeared in POWER, such as “Proactive Strategies for Dealing with Combustible Dust” (May 2011) and “A Burning Concern: Combustible Dust” (May 2010).

Still, one area of hazard management sometimes gets underestimated: training. That’s understandable, because mechanical solutions and smartly engineered processes sit atop the hierarchy of dust control measures. Developing these solutions comes naturally to many industry professionals, whereas learning effectiveness, behavior modification, and culture change may feel like learning a foreign language.

However, all controls rely to some extent on people. People design and operate the material-handling and dust collection equipment and are responsible for the maintenance and housekeeping that determine whether equipment and systems work as intended. Inadequate equipment maintenance and housekeeping were among the causative factors of the Imperial Sugar explosion, according to the CSB’s investigative findings. Consequently, training was included in the CSB’s post-incident recommendations for both Imperial and its property insurer, Zurich Services Corp.

Training Is Critical for a Proactive Program

Physical and mechanical aspects of a comprehensive combustible dust management program are thoroughly discussed in articles such as those mentioned earlier, so in this article I will highlight three areas where training and safety culture have an impact: inspections, maintaining equipment, and housekeeping. Consider these contributing factors behind the worst combustible dust incidents over the past 15 years:
  • Workers and managers were unaware of dust explosion hazards or failed to recognize the serious nature of dust explosion hazards.
  • Procedures and training to eliminate or control combustible dust hazards were inadequate.
  • Warning events were accepted as normal, and their causes were not identified and resolved.
  • Process changes were made without adequately reviewing them for the introduction and addition of new potential hazards.
To be sure, other contributing factors included equipment, facility design, and so on; the point is that to be comprehensive and proactive, your combustible dust management program must address the human variables as well.

Hazard and risk assessments performed by safety professionals are important. However, it’s equally important that management, supervisors, and frontline workers are trained to spot hazards on a daily basis. Training can ensure accurate, ongoing recognition of the following:
  • Areas where combustible dusts accumulate.
  • Processes and activities that cause dust to become airborne.
  • Potential ignition sources.
Training and periodic retraining to refresh knowledge and cover any hazard or process changes can also ensure that management and employees will share an accurate perception of risks and will work effectively together to implement and improve controls.

Don’t Wait for Regulators—Or Incidents

Despite increased attention and regulatory enforcement, the CSB has recorded 70 new incidents since 2006. Such incidents are too costly, in both human and business terms, to accept any goal other than zero for your company. Regardless of what regulators do or don’t do in the future, commit to proactively ensuring that your facilities follow the best practices established by the NFPA and PRBCUG. Evaluate all aspects of your program, including whether your people are being adequately trained to take combustible dust threats seriously and avert them.

—Contributed by Jonathan A. Jacobi (, a senior environmental, health, and safety consultant at UL PureSafety. Jacobi is a certified safety professional (CSP), construction health and safety technician (CHST), and OSHA-authorized outreach trainer for construction and general industry.