Key points
Since the earliest days when people began to store and handle grain in bulk quantities, fires and explosions have been a hazard. Almost any organic material is combustible as a dust, and this includes almost all food products.
The National Fire Protection Association (NFPA) has issued standards for handling combustible dust in general, and for handling food and agricultural dust specifically.
The industry has made great improvements in raising awareness and improving safety procedures, and the NFPA has led the way in setting standards for combustible dust handling and fire prevention.
Combustible dust hazards
Most food industry dust is combustible. The National Fire Protection Association (NFPA) has several standards that relate to the food processing industry and to combustible dust.
Food processing materials that can cause fires or explosions include flour, sugar, spices, powdered drink mixes including coffee and tea, whey powder and powdered milk, dust from shelling or processing nuts, and corn or rice starch.
While the Occupational Safety and Health Administration (OSHA) has dust control standards that relate specifically to certain types of agricultural dust, there is no general combustible dust regulation for all industries or materials.
The food processing industry has a history of combustible dust incidents, including the well-known Imperial Sugar explosion in 2008. Sugar dust had accumulated throughout the facility, and when ignition occurred in a storage building and adjacent silos, the explosion caused numerous other explosions throughout the facility.
The secondary explosions, caused by accumulated dust disturbed by the blast, caused even more damage. 14 people died and 40 were injured. OSHA fined the company over $8 million dollars, noting that the owners should have been aware of the hazards in the facility, including accumulated dust and lack of employee training. The company also settled over 40 lawsuits from injured employees and families.
To prevent these kinds of devastating combustible dust incidents, NFPA 61, the Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, addresses the specifics of fires and explosions in this industry.
More recently, NFPA 652, the Standard on the Fundamentals of Combustible Dust, has introduced new recommendations that apply across all industries that handle combustible dust. NFPA 61, along with other industry-specific standards, are now being adjusted to align as closely as possible with NFPA 652.
NFPA 652 and dust hazard analysis
As of September 2020, all facilities with dust present are required to have performed a dust hazard analysis. This must be documented, and during an inspection OSHA can request this document and verify it. This process starts with an analysis of the dust itself, but it also involves inspecting all equipment and areas of the facility for potential hazards and documenting the plans to address them.
Dust can be collected and sent to a testing facility. The test results will establish whether the dust is combustible and other information, such as the force it can exert in an explosion and the temperature needed to ignite it. When companies are installing a dust collection system, this type of dust test may be requested to help the company decide what types of fire and explosion safety features to install on the system.
NFPA 652 details the areas of a facility that require a dust hazard analysis, and what to look for. Any area where combustible dust is transported, accidentally or as part of the manufacturing process, must be examined.
This also includes ductwork or other ways that a fire could travel from one process area to another. Fugitive dust that escapes into other parts of the building, even hidden or unnoticed areas, must be identified. Dust explosions have occurred when dust accumulated unnoticed in spaces such as above drop ceilings or inside access spaces.
For every area or process identified as a potential dust hazard, the potential for fire or explosion must be assessed. If there is oxygen and an ignition source available in the presence of combustible dust, there is a risk of fire. If these two factors exist and the dust is also suspended in the air, or could become suspended in air, conditions exist for a deflagration or explosion.
Once these hazards are identified, they must be documented, and a plan for addressing the hazard must be put into place. One very important strategy is basic housekeeping, which means cleaning up all fugitive dust immediately before it can start to build up.
Since many food processing facilities require a high level of hygiene anyway, housekeeping is likely to be part of the regular process. However, some areas can be overlooked, and some processes generate so much dust that basic housekeeping measures will not keep it under control.
Some types of industries use water to keep dust from igniting and to keep it from becoming airborne. This many not be an option in the food processing industry, since the combustible material may be a process ingredient that needs to stay dry.
Using compressed air to blow away accumulated dust is not an acceptable method of removal, since causing dust to become airborne creates a higher explosion risk.
Dust collection systems are a recommended strategy for controlling combustible dust. In the food process industry, there are multiple options for types of dust collection systems, but all of them will need to meet the same basic safety standards laid out by NFPA 652 for this type of equipment.
Dust collection systems for dust management
The best way to control the accumulation of fugitive dust in the food processing facility is to install a dust collection system. There are many options for these types of systems, but considering the combustibility of food production dust, all will require NFPA recommended safety features.
While the number of fires and explosions in the food processing and agricultural industries have remained steady for many years, the number of injuries and fatalities has decreased considerably. In part, this is due to safer dust collection systems. In many recent situations, a fire has been confined to the dust collector and not able to spread back into the building.
Baghouses are a popular option in many areas of food processing. These dust collectors filter out dust using long cloth bags. The bags may be kept clean by a fan or by compressed air pulsing. Baghouses are efficient for most materials, but not for extremely small dust particles.
They also tend to be very large, because many bags are needed to create enough surface area for filtration. Baghouses continue to be very popular in the food processing and agricultural industries, especially where the dust is not extremely fine. Although bags are very durable, removing and replacing them can be a very messy and time-consuming task.
Another option for dust collection systems is a cartridge collector. These use pleated cartridges that are kept clean with pulses of compressed air. The cartridges have a much higher surface area than bags, so the dust collector can be smaller.
Another advantage of the cartridge collectors is that the filters are much easier to remove and replace than bags in a baghouse. Cartridge collectors can also achieve a higher level of filtration for very small particles.
NFPA 652 recommends several fire and explosion safety features with a dust collection system. First, the airflow in the system must be high enough to keep all dust moving through the system and not accumulating in the ductwork. This means that it is not safe to make modifications to the system without checking to make sure the airflow isn’t compromised.
All types of dust collectors need to have appropriate explosion venting that will direct the force of an explosion in a safe direction and prevent dangerous pressure inside the collector.
If standard explosion venting through panels can’t be achieved because the collector is located inside a building, the system will require either a flameless explosion vent or a chemical suppression system.
An explosion isolation valve is a safety device that is mechanically triggered by the force of an explosion. When it closes, it prevents the explosion and fire from traveling any farther. Spark traps and abort gates are both designed to prevent fires from occurring in the dust collector.
A spark trap is a passive prevention device that extinguishes sparks before they can reach the collector. An abort gate is attached to a sensor that registers the presence of flame or sparks.
The sensor will cause the abort gate to slam closed and safely vent the hazard. Chemical extinguisher systems are also available. When triggered, they use chemicals to rapidly extinguish a fire.
Design of dust collection systems
Dust collection systems for food processing are usually source capture systems, which means they will have a hood located at the point where dust needs to be collected. The most typical setup is one or more dust collectors with ductwork leading to the hoods and fans large enough to maintain airflow to all the capture points.
Occasionally, some part of the process may be in an area that’s difficult to access with ductwork or so far away from the system that maintaining airflow is a problem. In this situation, a small cartridge dust collector can be placed directly at the capture point.
These small and compact systems can be located on conveyors and other food process equipment. The only requirement is that they have access to power for running the fan and compressed air for pulse cleaning.
The most important aspect of a dust collection system is that it does not allow any significant amount of dust to escape or accumulate in the facility. A dust hazard analysis will help identify all the possible locations where dust needs to be controlled.
It should also be noted that a dust collection system will not address dust that has already accumulated in the facility. Cleaning up dust accumulation should follow NFPA 652 recommendations, which means avoiding any method that causes the dust to become airborne. Vacuum systems can be used if they meet NFPA standards.
Achieving safety and compliance
The NFPA standards are always geared toward preventing damage, injury, and loss of life. Compliance with their standards will create a safer work environment. Because the food processing industry makes up a large percentage of overall combustible dust accidents, following these standards is especially important.
Improved safety features have helped prevent accumulation of dust in food processing facilities. They have also improved the ability to control potential explosions and contain them safely within the dust collector. However, fugitive dust that escapes during the process can still accumulate and ignite if problems in the dust collections system aren’t addressed.
A dust hazard analysis will help identify any dust problems that exist before putting in a new dust collection system, or problems with the current system.
Addressing these problems as soon as possible helps keep dust under control in the facility, greatly reducing the risk of a fire or explosion.
By making the dust hazard analysis a thorough, documented process, companies will be able to present safety inspectors with evidence that they are proactive in handling dust control.
