- Food dusts were found in 23% of combustible dust incidents. For causing problems, food is second only to wood dusts, which were found in 24% of incidents.
- The food products industry has the most combustible dust incidents, being responsible for 24% of all incidents across all industries. This time, the race isn’t even close -- wood products comes in second place at 15%.
NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
Current edition: 2013 Next edition: 2017 NFPA 61 is the main food industry-specific standard for combustible dusts. It applies to three types of food manufacturing facilities:- All facilities that handle or process dry agricultural bulk materials, their by-products, or dusts including grains, oilseeds, agricultural seeds, legumes, sugar, flour, spices, and feeds.
- All facilities that manufacture and handle starch.
- Seed preparation and meal-handling systems of oilseed processing plants that are not already covered by NFPA 36: Standard for Solvent Extraction Plants.
Examples of facilities covered by NFPA 61:
- Bakeries
- Flour mills
- Wet and dry corn milling
- Dry milk products
- Cereal processing
- Snack food processing
- Chocolate processing
- Sugar refining and processing
NFPA 61 housekeeping guidance
The sections of NFPA that apply specifically to housekeeping are in Chapter 10: Dust Control. NFPA 61 requires food manufacturers to control airborne combustible dusts generated from all processes, equipment, and material transfer points. The dust must be removed concurrently with operations. The following list summarizes the main requirements.- Dust removal: Vacuuming is the preferred method of removing dust, particularly in hazardous locations (see NFPA 70: National Electrical Code). Since compressed air causes dust to become airborne, it can be used only after shutting down all machinery and ensuring all ignition sources are under control.
- Dust emissions: To prevent dust from escaping from processing equipment into the surrounding environment, NFPA 61 recommends control measures including suppressants, venting systems, and air aspiration.
- Dust collection: Dust collection systems and all of their components must be made of noncombustible materials. If a dust collection system shuts down, its related machinery must shut down as well.
- Centralized vacuum systems: Centralized vacuum systems require static-conducive cleaning tools and static-dissipative hoses. The air-material separator must provide filtration and be fitted with a system for explosion prevention.
- Documentation: Food manufacturers are required to have a documented housekeeping program that specifies both the method and the frequency of cleaning.
NFPA 70: National Electrical Code
Current edition: 2014 Next edition: 2017 NFPA 70 is the National Electrical Code (NEC). The NEC covers everything related to the installation of electrical equipment across all industries and all types of buildings. This code is in force in all 50 states. Food manufacturers need to be aware of two main sections of NFPA 70 because they apply to housekeeping.Combustible dust definition
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.” 500 microns is about 0.02 inches. This just goes to illustrate how even very tiny specks can lead to huge problems if they’re allowed to accumulate.Hazardous locations
The NEC defines different classes of hazardous (classified) and non-hazardous locations. These classes determine not just the wiring of buildings, but also the equipment and housekeeping procedures that can be used in different areas of facilities. For example, NFPA 61 specifies that portable vacuum cleaners should be used for dust removal in Class II, Group G, Division 1 locations. What does that mean? Hazard classes are determined by the type of fire risk they present:- Class I locations are hazardous because of flammable or combustible gases and vapors.
- Class II locations are hazardous because of combustible dust.
- Class III locations are hazardous because of easily ignitable fibers or combustible flyings.
- Group E locations contain metal dusts.
- Group F locations contain carbonaceous dusts.
- Group G locations contain all other combustible dusts, including those from flour, grain, wood, plastic, and chemicals.
- Division 1 locations have enough combustible dust in the air under normal operating conditions to pose a risk of fire or explosion.
- Division 2 locations don’t normally have enough combustible dust to cause a problem (though abnormal conditions may increase the safety risk).
NFPA 652: Standard on the Fundamentals of Combustible Dust
Current edition: 2016 Next edition: 2019 NFPA 652 is a brand new standard that covers the requirements for managing combustible dust fires and explosions across industries, processes, and dust types. It was created to clear up confusion between the five industry-specific combustible dust standards:- NFPA 61: Agricultural and food processing facilities (see above)
- NFPA 484: Combustible metals
- NFPA 664: Wood processing and woodworking facilities
- NFPA 654: General manufacturing/other industries (e.g., plastics, pharmaceuticals; see below)
- NFPA 655: Sulfur
Relationship between NFPA 61 and NFPA 652
With more than one standard in place, it can be difficult to know which one to follow. The table below shows which standard food manufacturers should consider primary in cases conflicts may exist.Conflict | Standard to Be Applied |
Where a requirement in NFPA 61 differs from the requirement in NFPA 652... | NFPA 61 |
Where a requirement in NFPA 61 prohibits a requirement in NFPA 652... | NFPA 61 |
Where NFPA 61 neither prohibits or provides a requirement... | NFPA 652 |
Where a conflict exists between a general requirement and a specific requirement... | NFPA 652 - Specific |
What’s new for food manufacturers in NFPA 652?
The biggest change NFPA 652 brings to the table is that it requires a Dust Hazards Analysis, or DHA, which NFPA defines like this: “A systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility.” According to this new requirement, the owner or operator of any facility where combustible exists is responsible for conducting a DHA to identify the hazards, create a plan for managing the hazards, and providing training for anyone affected by the hazards. Here are the key points you need to know about NFPA 652 and the DHA:- NFPA 652 is retroactive. An insurance company, government inspector, state fire marshal, or other authority having jurisdiction (AHJ) can apply any portion of the standard if there’s an unacceptable degree of risk.
- A dust test is required. Before you can perform a hazards analysis, you must first test your dust to determine whether it’s combustible or explosible. The absence of a previous combustible dust incident is not sufficient to show that a particulate is not combustible or explosible.
- There are no industry exceptions or automatic grandfathering. DHAs must be completed for all processes and facilities by September, 2018, which is three years after the standard went into effect.
- Documentation is required. Test results as well as historical and published data must be kept on file at all times.
NFPA 652 housekeeping guidance
NFPA 652 provides specific guidance about housekeeping and vacuum cleaning.- Similar to NFPA 61, this standard specifies that the cleaning method must match the potential risk. In particular, NFPA 652 requires cleaning methods to reduce the potential for creating a combustible dust cloud.
- Vacuuming is the preferred method of cleaning.
- Sweeping/water washdown is only permitted where vacuuming is not practical.
- Blowdown is only permitted when the methods mentioned above have already been used.
NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
Current edition: 2013 Next edition: 2017 NFPA 654 is a general standard for dealing with combustible dust. It doesn’t specifically address food manufacturing environments. In fact, NFPA 654 is primarily directed toward the chemical processing industry. However, as it is a general manufacturing standard, many in the food industry have historically turned to it for guidance, particularly before NFPA 652 went into effect. This is likely to change. At least in terms of housekeeping, the guidelines in this standard are nearly identical to those in NFPA 652. So, for now, food manufacturers probably don’t need to be too concerned with NFPA 654. Instead, concentrate on making sure your facilities and processes comply with NFPA 61 and NFPA 652.NFPA 68: Standard on Explosion Protection by Deflagration Venting
Current edition: 2013 Next edition: 2017 These last few standards don’t specifically discuss housekeeping, but they do apply to food manufacturing. NFPA 68 provides requirements for deflagration venting, which includes the devices and systems that vent combustion gases and pressures. The goal is to protect buildings against explosions due to internal heat and pressure. The following sections provide information related to combustible dusts:- Section 6.2.2 provides a formula for calculating vent size in an area where dust is a hazard.
- Chapter 8 is devoted to deflagration venting for dusts and hybrid mixtures.
- Chapter 11 details installation and maintenance requirements of vent enclosures.
- Annex C discusses a procedure for testing combustible dusts.
- Annex F provides characteristics of combustible dusts including several common agricultural dusts.
NFPA 69: Standard on Explosion Prevention Systems
Current edition: 2014 Next edition: 2019 NFPA 69 covers explosion prevention where venting isn’t possible. It focuses on the following methods:- Control of oxidant concentration
- Control of combustible concentration
- Predeflagration detection and control of ignition sources
- Explosion suppression
- Active isolation
- Passive isolation
- Deflagration pressure containment
- Passive explosion suppression