Protecting your food processing facility from dust explosions

The Imperial Sugar dust explosion of 2008 was a tragic reminder of the potential for common food processing ingredients to cause unneeded loss of life and property in a food processing plant. And while it is not feasible to ditch dusty ingredients like sugar, flour and cornstarch in most food processes, processors should be aware of the danger that particular ingredients create and formulate a plan to keep their workers and plants safe.

Common ingredients that create dust hazards

Whether you are using baking powder as an ingredient or packaging raw sugar for sale, handling particulate solids creates hazards. Before minimizing the risks that those hazards pose, food processors need to know what ingredients have the potential to create dust explosions:

Animal feed
Baking ingredients (baking soda, baking powder)
Cocoa
Coffee (roasted, ground and soluble)
DDGs (distillers dried grains)
Flour
Nut dust
Nutritional powders
Pollen
Powdered flavorings
Powdered milk
Soybean (processed)
Starches
Sugar

Keep in mind, this is not an exhaustive list of every ingredient that could pose a dust explosion threat. Metal shavings, plastic shavings and sawdust are just a few nonfood materials that can also create massive explosions in high enough concentrations.

The explosive potential is not in the flammability of the materials themselves — it is in the high surface area of the dust particles.

While wood is flammable, it takes a few minutes and some kindling to light up a log, which could then take hours to burn to ash, depending on its size. A grain of sawdust from the same log, however, takes a small amount of heat or a little static shock to ignite. Once it is on fire, it flashes to ash in an instant.

Since the burn happens on the surface of the material, which is exposed to oxygen, the higher the surface area, the higher its explosive potential. In an enclosed space where dust particles accumulate, a single ignited particle could cause a chain reaction that leads to a percussive explosion with the potential to crumble concrete floors and rip doors off their hinges.

Identify and control sources of dust

To put dust control measures in place, processors need to figure out where the hotspots in their facility are located.

Wherever there is mechanical transfer (like a conveyor belt, as we saw in the 2008 Imperial Sugar incident) or pneumatic (pressure conveyors) transfer of powder ingredients or finished products, there is a risk of dust building up, especially near line connections and dispensers. Make sure these systems are designed to handle the amount of material flowing through them to avoid internal accumulation and potential blockages.

Where powder ingredients are added by hand, there is also a risk of airborne dust particles escaping to nearby surfaces.

As dust gets into the air from transfer and production processes, it accumulates on top of equipment, rafters, silos and storage bins.

A dust collection system should be in place to remove airborne particles before they have the chance to settle on surfaces in the plant. The system should be calibrated for the correct volume and particulate size to prevent clogs in the dust collector. The filter material should also be specifically selected for the ingredient running through it.

The location of dust collectors is also paramount to the safety of the plant and personnel. Vacuum hoods and point source vacuums should be placed in areas where material is added, transferred or packed — where loose particles will most likely escape.

Also, the dust collection system should be configured to release any built-up or vented dust outside the process area in the event of a system failure.

Check equipment NEC hazard ratings

According to the National Electrical Code (NEC), Class 2, Division 1 hazards are areas where combustible dust is present under normal operating conditions, while Class 2, Division 2 hazards are defined as areas where combustible dust is not present under normal operating conditions.

A Class 2, Division 1 space could be the area where sugar is transferred into an open container or the storage silo where it is kept. A Class 2, Division 2 space could be the area where a pneumatic transfer tube carrying cocoa powder runs through — where a leak or rupture could lead to hazardous levels of dust.

Electrical equipment used in the vicinity of these spaces should be rated to operate under these conditions.

On a recent bakery project Stellar worked on, the dough mixers had a warning label stating devices plugged in within a 10-foot radius around the mixers must be rated Class 2, Division 2. Stellar designed the space to keep lighting fixtures and other easily moved devices that were not Class 2, Division 2 outside the danger zone to save costs. Generally, equipment rated for more hazardous conditions is more expensive than nonhazard rated versions.

Keep good housekeeping habits

Even if you make every effort to capture and control dust in your food plant, particles are bound to escape over time and eventually build up on equipment in processing areas. Good housekeeping measures are the only way to keep this accumulation at bay.

Educate workers in the processing area about dust hazards and the best ways to handle particulate ingredients during production. Make sure safety and cleanliness is part of the workforce’s culture — employees will appreciate the measures you take to keep them safe by enforcing high standards on the job.

Additionally, designing and installing a central vacuum system in your facility makes it easy for operators and sanitation workers to regularly vacuum hard-to-reach areas like corners, rafters and the tops of storage bins without having to drag around bulky cleaning equipment.

A central vacuum system makes it easy for spills to be quickly cleaned on the production floor while minimizing the risk of a traditional floor vacuum malfunctioning and possibly spilling even more dust in your plant.

Instilling knowledge, cleanliness and safety in your workforce while providing employees with the tools to keep them safe will protect your employees, business and brand.

Jon Phillips has more than 16 years of experience in electrical design and construction of commercial, institutional and industrial buildings. His responsibilities include development of electrical documentation for schematic and detailed design, cost studies and interfacing with other engineering disciplines to integrate electrical power, fire alarm system, control, instrumentation and data/voice communication system requirements.

Gerry Golomka has more than 42 years of engineering, maintenance and operations experience in the food manufacturing industry. His responsibilities include organizing and directing process design, packaging and automation requirements for food and beverage manufacturing facilities. Golomka oversees initial development of critical project criteria and budgets, food safety, technical requirements of equipment, proper execution of construction documents, equipment installation and commissioning.

Stellar

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3 must-have PSM elements to prevent dust explosions and other disasters

By Richard Boyd, Stellar

Process safety management (PSM) is the OSHA standard that mandates companies to identify, evaluate and control potentially hazardous activities, chemicals and components used in their processes.

While PSM audits are performed every three years, you should periodically perform self-audits to protect your facility from punitive measures from OSHA and, more importantly, to protect your employees from potentially catastrophic events that could lead to loss of life or property.

However, this is not a guide on performing self-audits. Instead, we will walk through a few PSM elements that you should pay special attention to while performing self-audits.

Management of change

When any ingredient, material, piece of equipment or operating procedure within a process changes, the effect of that change must be evaluated for any impacts on the health and safety of employees. The management of change (MOC) protocol should begin when the change is contemplated.
If new ingredients/materials are used in a process, the existing equipment that the ingredients come into contact with must be capable of handling the ingredients/materials without malfunction.
If production speed increases, line equipment must be checked to ensure it can handle the increased capacity, increased volume and higher rates of wear and tear.

Mechanical integrity

Process equipment must be designed and configured to handle the materials, production capacity and the volume involved in a given process.
Equipment should be in good operating condition and not in disrepair (e.g., leaking, chaffing, corroded or clogged).
Lack of mechanical integrity inspections and testing can lead to equipment malfunction and/or failure, leading to loss of production time, increased equipment repair or replacement costs, and/or problems in adjacent equipment and/or processes.

Emergency planning and procedures

Employees should be routinely educated and drilled on emergency procedures, including proper procedures, evacuation routes, emergency exits and the location of emergency equipment.

A cautionary tale: 2008 Imperial Sugar plant explosion

In February 2008, a dust explosion killed 14 employees and injured 36 others at the Imperial Sugar refinery in Savannah, Georgia. A combination of improper MOC, lack of mechanical integrity and insufficient emergency planning led to the tragic, but avoidable, explosion.

Management of change

Imperial Sugar modified conveyor lines used to move sugar through the plant by enclosing the conveyor to protect from contamination; however, the enclosure did not have a dust collection system.
Had plant management followed proper MOC protocol, the enclosure’s dust levels would have been measured and found to be at dangerous levels, prompting the addition of a dust collection system.

Mechanical integrity

The overhead chutes used to deliver sugar to the conveyor line from storage silos would occasionally clog with clumps of sugar, leading to conveyor blockages that sent sugar spilling onto the floor and high concentrations of sugar dust into the air inside the conveyor enclosure.
When concentrated sugar dust came in contact with an ignition source, which the U.S. Chemical Safety Board (UCSB) believes was an overheated bearing, it caused a percussive explosion that crumbled floors and knocked down walls, largely destroying the facility’s packing buildings.

Emergency planning and response

Evacuation drills had not been performed, so employees were not familiar with the safest exit routes in the event of an emergency.
The explosion knocked out power and many of the emergency lights within the plant, so workers trying to escape the ensuing fires had to find their way out of a maze of dark rooms and hallways.

By keeping a keen eye on these key PSM elements, you can protect your employees from a deadly mishap like the Imperial Sugar explosion while insulating your business from massive financial setbacks and years of bad PR.

Richard Boyd has over 23 years of experience in industrial refrigeration and has served as the project manager for the “Stellar Safety and Compliance” team where he manages all phases of process safety management. He conducts audits of the PSM and risk management programs for numerous facilities.