Grain elevators and silos handle more particles and contend with more dust every day than the typical food processing facility will contend with in a lifetime, so it’s no surprise that grain dust tops the list of causes in 164 North American fire and explosion incidents in the 2017 Combustible Dust Incident Report.
Not far behind, however, are events at food processing facilities. Pistachios, oregano, fishmeal and pet food are among the fuels implicated in the continent’s dust explosions.
The report was created by Chris Cloney, principal of DustEx Research Ltd. (www.dustsafetyscience.com), Halifax, Nova Scotia. “We don’t have any system to measure our improvement in preventing and containing explosions,” says Cloney (who recently completed doctoral work in combustible dust) in explaining why he created the report in 2016. He also wants to create better communications between key stakeholders — food processors, safety professionals, regulators and researchers — to ensure affordable safety solutions.
Comprehensive reporting of industrial explosions and fires hasn’t existed, although a Canadian review of dust explosions from 1980-2005 found an average of 10 events per year. The average over the final five years was 22, and Cloney’s research suggests there were 33 events in 2016 and 32 last year.
Dust collectors were the leading equipment classification in 2017’s events -- no surprise, since they combine four of the five factors necessary for an explosion. “The only thing you’re missing is an ignition source,” says Cloney, and hot metal, static electricity or even a faulty filter bag can supply it.
A dust collector was pinpointed as the cause of an explosion July 27, 2017, at the Stanfield, Ore., plant of 3D Idapro Solutions, a processor of carrots and potatoes used in pet foods. One person was injured. The most deadly 2017 event occurred May 31, when atmospheric corn dust exploded at Didion Milling in Cambria, Wis., killing five and injuring 14. The company is appealing the $1.8 million fine levied by OSHA, which cited 19 safety violations at the mill.
Dust collectors are adjunct components to a pneumatic conveying system, removing atmospheric dust as a safeguard to the kind of secondary explosion that devastated the Imperial Sugar refinery in Port Wentworth, Ga., a decade ago, killing 14 workers and injuring scores.
Many manufacturers rely on shop vacuums to control airborne dust, according to David Kennedy, business development manager at Belleville, N.J.-based Vac-U-Max (www.vac-u-max.com), but those machines are inadequate. A plant manager may swallow hard when quoted the price of a combustible dust vacuum, he allows, adding, “Compliance is expensive, noncompliance is more expensive.”
Vac-U-Max recently certified its compressed air-powered combustible dust vacuums under ATEX, the European standard that all European powder-transfer equipment must meet. Major U.S. manufacturers also are ATEX-compliant, although Kennedy points out that OSHA guidelines require certification by a nationally recognized testing lab, a technicality that Vac-U-Max met by contracting with Intertek labs in Cortland, N.Y., for its certification.
The FSMA factor
Controlling or eliminating processes that carry cross-contamination risk has led many food manufacturers to install bulk-handling systems to remove operator handling. With enforcement of the preventive controls rules of the Food Safety Modernization Act, the conversion rate is accelerating, Kennedy reports. “FSMA also has had a big impact on equipment design, with more and more of our equipment designed for disassembly and easy cleaning,” he adds.
Food processors typically start with a transport system for a discrete process and build from there, observes Nick Hayes, president of Volkmann Inc. (www.volkmannusa.com), Bristol, Pa. That means integrating Volkmann’s dense-phase vacuum conveyors with other manufacturers’ equipment at multiple points, complicating the explosion-prevention calculus.
Hayes takes pride in the inherent safety of Volkmann’s systems, which were re-engineered to be explosion-resistant down to 1 millijoule (less than 3,000ths of a calorie) of ignition energy, down from 3 millijoules. For end-users, safety is assumed, however, and their expectations revolve around performance. They’re happy to leave Newton’s laws of motion and the finer points of physics to vendors; they simply want materials transported as quickly, efficiently and damage-free as possible.
That becomes particularly challenging when multiple materials are being transported. Powdered lemonade is an example: The lemon flavoring particles are considerably smaller than the sugar particles, making segregation a concern. “Segregation is a critical issue with pharmaceuticals,” Hayes points out, but it’s also important to food processors that put a premium on product consistency.
“How powders are handled in vacuum conveying varies tremendously,” he continues. “Test it, test it, test it is the golden rule. If you want to be sure you have a system that works, test it in conditions as close to the conditions in your own plant as possible.”
Monitoring day-to-day performance may require an advanced control system. On that score, Bethlehem, Pa.-based Flexicon Corp. (www.flexicon.com) believes its open software gives food manufacturers the flexibility to operate the on-board PLC and HMI for a basic conveyor independently or integrated with a plant-wide controls network.
“The programs created by Flexicon are not password protected,” points out David Boger, vice president-global business development & marketing. “The customer can modify these programs as needed. The customer can program the equipment, too, if they’d like.”
A wide range of sensors provides feedback for control points in the system, and remote monitoring and adjustment of the equipment while in operation is possible, Boger adds.
All of which is important if orders are to be filled and throughput goals are to be reached. Still, manufacturers ignore the safety factors in powder and bulk material transfer at their own risk. In an era of increasing specialization, knowing where to turn for expert advice in a particular area is a challenge, Cloney concedes, but meeting the challenge is essential if human life and the facility itself are valued.
“Proper housekeeping will negate the need for many safety measures,” he concludes, adding, “Contacting safety professionals early on can be beneficial.”