On February 7, 2008, a huge explosion and fire at the Imperial Sugar refinery northwest of Savannah, Georgia, caused 14 deaths and injured 38 others, some with serious and life-threatening burns. Massive accumulations of combustible sugar dust throughout the packaging building fueled the explosion.
Later, an investigation by the U.S. Chemical Safety Board revealed Imperial Sugar could have prevented the tragedy. The report attributes the fire to “poor equipment design, poor maintenance and poor housekeeping” and stressed the company might have prevented the incident if it hadn’t let dust build up.
Though the Imperial Sugar tragedy led to standards for combustible dust concerns, data compiled annually since 2016 shows fire prevention efforts have some distance to go.
Dust Safety Science’s “2020 Combustible Dust Report” reveals that of the 26 incidents in 2020, 50.2% occurred in the food products/processing industry.
This research highlights that food is a prime culprit in combustible dust fires and explosions. In fact, food materials caused 48% of the incidents, second only to wood dusts, which contributed to 27.6% of the events.
Clearly, the food industry is more susceptible than other industries to combustible dust fires and explosions. The most obvious sources of dust in these facilities include flour, grains, proteins, spices, sugar and teas. But OSHA’s Combustible Dust poster also lists less common items like tomatoes, lemon pulp, and carrots.
Following NFPA codes and standards can mitigate risks for combustible dust fires and explosions. Knowing and understanding these standards and adhering to what they require are necessary for every foods processing operation.
NFPA 61 is a food-industry specific standard that applies to three types of food processing facilities:
- Those that receive, handle, process, dry, blend, use, mill, package, store or ship dry agricultural seeds, legumes, sugar, flour, spices, feeds, dry dairy/food powders and other related materials.
- Plants that manufacturer and handle starch.
- Seed preparation and metal handling systems of oilseed processing plants not covered by NFPA 36.
The standard effects a host of facilities, including bakeries or flour mills, sugar refining and processing facilities, cereal and snack food processing plants, chocolate producers, wet and dry corn mills, and dry milk product facilities.
NFPA released a new edition of NFPA 61 in 2020. The changes aligned NFPA 61 with NFPA 652 when possible and extended the deadline for completing a dust hazard analysis (DHA) for existing processes and facility compartments to Jan. 1, 2022.
It also revised surface resistivity requirements for conveyor belts, lag belts, and lagging, and added a statement to exclude air-material separators with a dirty side volume of less than 0.2 m3 (8 ft3) from explosion protection requirements. The revision also includes sections on spray dryer systems, mixers and blenders, and work activities that present an ignition source.
This document helps food manufacturers control airborne combustible dusts. It mandates dust removal as work commences. These efforts may include:
- Dust removal processes such as vacuuming,
- Dust emissions capture that prevents dust from escaping from processing equipment via control measures that include suppressants, venting systems, and air aspiration.
- Dust collection systems on machinery.
- Centralized vacuuming systems that use static-conducive cleaning tools and static-dissipative hoses.
NFPA 61 also requires food manufacturers to maintain a documented housekeeping program that specifies how and when cleaning will take place.
Fire professionals also known NFPA 70 as the “National Electric Code.” NFPA calls this code the “benchmark for safe electrical design, installation and inspection to protect people and property from electrical hazards.”
Two sections of NFPA 70 apply to housekeeping: the combustible dust definition and hazardous locations section.
NFPA 70 defines combustible dust as “dust particles that are 500 microns or smaller and present a fire or explosion hazard when dispersed and ignited in air.”
It also defines different classes of hazardous (classified) and non-hazardous locations. These classifications determine the wiring, equipment and housekeeping procedures allowed in different areas of a facility.
The code classifies locations as:
- Class I: Locations with flammable or combustible gases and vapors.
- Class II: Locations made hazardous by combustible dust.
- Class III: Locations filled with easily ignitable fibers and combustible flyings.
Note: Class II also divides the type of dust into categories: Group E locations contain metal dusts, Group F areas contain carbonaceous dust, and Group G hazards include flour, grain, wood, plastic and chemical dusts.
NFPA 70 then puts each class into two categories. Division 1 locations have dust in high enough concentrations that they require control measures, while Division 2 locations don’t contain enough dust to cause a problem.
NFPA 652 introduced new requirements not included in commodity-specific standards. The standard manages combustible dust fires and explosions across industries, processes and dust types.
This code applies to all facilities and operations that deal with combustible dust and fills gaps in commodity-specific standards. While it’s best to follow the most specific requirement available, if your industry lacks a specific requirement, follow NFPA 652.
This standard requires companies to test dust, then perform a DHA to identify and evaluate potential fire, flash fire, and explosion hazards in the facility. They must then create a plan to manage hazards and train employees affected by identified hazards.
NFPA 652 requires cleaning methods that match potential risk and reduce the possibility of creating a combustible dust cloud. It’s preferable to vacuum up dust. But NFPA 652 also permits sweeping or water wash-down when vacuuming isn’t possible.
NFPA 68 applies to food manufacturing operations and details requirements for deflagration venting, including the devices and systems that vent combustion gases and pressures. Its goal is to protect against explosions caused by internal heat and pressures.
This standard helps facility operators calculate vent size in areas with dust hazards present. It also includes sections on deflagration venting, installing and maintaining vent enclosures, testing combustible dusts, and the characteristics of combustible dusts.
This standard covers explosion prevention when venting isn’t possible.
While NFPA 68 covers explosion protection by deflagration venting, NFPA 69 prevents and mitigates explosions by:
- Inerting systems
- Oxygen concentration reduction
- Combustible concentration reduction
- Spark detection and extinguishment
- Explosion suppression
- Explosion isolation
- Detonation arresters
- Pressure containment
NFPA standards exist to protect food processing facilities from tragedy, but companies must apply them. It begins with assessing a facility’s fire protection plan then shoring up identified weaknesses and talking to employees about their role in fire prevention. A strong safety culture provides the best fire protection around.