Approaches to Economical Combustible Dust Explosion Protection: A Study of Spray Dryer Processes by Johannes Lottermann, Senior Consultant, Explosion Protection, Head of Projects and Expansion, REMBE Safety +_Control
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CHEMICAL ENGINEERING (www.che.com)
From the first line of defense to the last, explosion prevention and protection firms are upping their game to preserve yours
Following the devastating explosion at the Imperial Sugar Co.’s Georgia factory that killed 14 people, injured many more employees and leveled the facility in February 2008, it was determined by the U.S. Occupational Safety and Health Admin. (OSHA; www.osha.gov) officials and the U.S. Chemical Safety Board (CSB; both Washington, D.C.; www.csb.gov) that the catastrophe could have been prevented had the manufacturer taken available steps to reduce the presence of sugar dust in its facility.
As a result of these findings, the U.S. regulatory climate turned a watchful eye toward combustible dust in the workplace, culminating in the announcement by new OSHA Chairman George Miller that a new standard on combustible dust is to be expected in the near future as part of the agency’s Reissued Combustible Dust National Emphasis Program (see box below). This announcement, combined with the current increase in OSHA inspections with regard to combustible dust in targeted industries, has spurred a lot of interest in explosion prevention and protection equipment in the chemical manufacturing industry, which is third behind the wood and food industries on OSHA’s list of targets.
Venting versus suppression
There are pros and cons to each type of system. “We see many advantages of venting over suppression systems,” says Gerd Mayer, President of REMBE, INC. (Charlotte, NC; www.rembe.us), which offers both types of equipment. “Suppression systems are subject to a lot of faults and if you don’t actually have an explosion situation and the suppression system is emptied, a facility can be knocked out of production for several days because everything, not just the dust collector, will have to be cleaned as the agent spreads all over the processing line. If you’re in a food, chemical or pharmaceutical plant, you don’t want suppression agents in your product.”
Figure 3. The Q-Rohr-3 guarantees
indoor venting without any flames or dust
propagation, allowing protection for
equipment that is hard to access or free
standing in the process area.
Also, there are high maintenance costs associated with suppression systems, says Mayer. NFPA 69 explains that a suppression system should be checked a minimum of four times a year because the agent-containing bottles can lose pressure, which would result in faulty or no activation during an event.
Following the events at Imperial Sugar, OSHA immediately reissued its Combustible Dust National Emphasis Program. The executive summary, quoted below from the Reissued OSHA Directive CPL-03-00-008, explains how the agency plans to handle its inspections and what industries and materials will likely be targeted.
OSHA is reissuing the directive on the Combustible Dust National Emphasis Program to increase its enforcement activities and to focus on specific industry groups that have experienced either frequent combustible dust incidents or combustible dust incidents with catastrophic consequences. OSHA initiated its previous Combustible Dust National Emphasis Program on October 18, 2007. As a result of a recent catastrophic accident involving a combustible dust explosion at a sugar refinery, OSHA has decided to intensify its focus on this hazard. The Agency will increase its activities in outreach, training, the creation and dissemination of guidance and educational materials and cooperative ventures with stakeholders, as well as enhancing its enforcement activities through this amendment to the National Emphasis Program (NEP).
The purpose of this NEP is to inspect facilities that generate or handle combustible dusts that pose a deflagration or other fire hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape; deflagrations can lead to explosions. Combustible dusts are often either organic or metal dusts that are finely ground into very small particles, fibers, fines, chips, chunks, flakes, or a small mixture of these. Types of dusts include, but are not limited to: metal dust, such as aluminum and magnesium; wood dust; plastic dust; biosolids; organic dust, such as sugar, paper, soap and dried blood; and dusts from certain textiles. Some industries that handle combustible dusts include: agriculture, chemicals, textiles, forest and furniture products, wastewater treatment, metal processing, paper products, pharmaceuticals and recycling operations (metal, paper, and plastic).
In situations where the facility being inspected is not a grain handling facility, the laboratory results indicate that the dust is combustible, and the combustible dust accumulations not contained within dust control systems or other containers, such as storage bins, are extensive enough to pose a deflagration, explosion, or other fire hazard, then citations under 29 CFR 1910.22 (housekeeping) or, where appropriate, 29 CFR 1910.176(c) (housekeeping in storage areas) may generally be issued. Combustible dusts found in grain handling facilities are covered by 29 CFR 1910.272.
For workplaces not covered by 1910.272, but where combustible dust hazards exist within dust control systems or other containers, citations under section 5(a)(1) of the OSH Act (the General Duty Clause) may generally be issued for deflagration, other fire, or explosion hazards. National Fire Protection Association (NFPA) standards (listed in Appendix A of this directive) should be consulted to obtain evidence of hazard recognition and feasible abatement methods. Other standards are applicable to the combustible dust hazard. For example, if the workplace has a Class II location, then citations under 29 CFR 1910.307 may be issued to those employers having electrical equipment not meeting the standards requirements.
Combustible Dust Explosions
“If a dust cloud (diffused fuel) is ignited within a confined or semi-confined vessel, area or building, it burns very rapidly and may explode. The safety of employees is threatened by the ensuing fires, additional explosions, flying debris and collapsing building components.” 
If you can eliminate the possibility of ignition sources, combustible dust or oxygen with 100% certainty, you can eliminate the possibility of Combustible Dust Explosions.
As a practical matter, you can take steps to reduce potential sources of ignition of combustible dust, but can you really say with 100% certainty that all ignition sources are eliminated all of the time, given the “human factor”? And you can never eliminate the fuel or combustible dust, since this is the process media that is being produced. Likewise, it is cost prohibitive, in most situations, to remove oxygen from the equation.
So, you need to protect against the possibility of a Combustible Dust Explosion and its effects:
Your first step in preventing a Combustible Dust Explosion is eliminating the possibility of possible potential sources of ignition, including: 
The human factor turns potential ignition sources into real ignition sources and can lead to dust explosions!
 “Combustible Dust in Industry: Preventing and Mitigating the Effects of Fire and Explosions”, OSHA Safety and Health Information Bulletin, SHIB 07-31-2005
 EN 1127-1; NFPA 654.
Four Steps You Can Take Toward a Safer Combustible Dust Explosion Protection Process
There are 4 steps you can take to safeguard your facility against combustible dust and explosions:
Step 1 Combustible Dust Explosion Prevention. To the extent possible:
Avoid the occurrence of an explosion
Avoid effective ignition sources
Step 2 Explosion Protection – Limit the Dangerous Consequences of an Explosion
Step 3 Organizational Measures
Step 4 Building Precautions
Awareness and education is the key. That’s why, in addition to providing superior quality explosion prevention and protection equipment, REMBE® has actively engaged companies, industry associations, regulatory bodies and thought leaders, as partners, to increase awareness and education. REMBE® has developed and maintained close working relationships with OSHA, NFPA and ATEX, among other regulatory and governing bodies, continuously sponsoring and participating in educational awareness programs to promote safety practices in manufacturing facilities.
For More Information
There are a number of organizations and services available to assist with developing training, maintenance and other programs that will help you manage your ongoing risk, including:
Regulations and Standards:
For more information about combustible dust explosions, generally: