Understanding NEC for Grain and Feed Locations

Understanding NEC for Grain and Feed Locations

Every day we deal with unique hazards in the industries we serve, especially in feed mills and grain storage facilities. Construction of large feed mills and grain elevators were the norm of the 70s, increasing annual production drastically. Since then, technology has played a critical role in the growth of the feed and grain industry, paving the way for increased safety measures, throughput, compliance, and automation.

In this article we’re going to review:

  • What is NFPA and NEC
  • NFPA Hazardous Location Classification and Examples
  • Types of Ignition Sources
  • Solutions on how to Reduce Risks of Explosions

When selecting an electrical design-build contractor for a facility upgrade or new build, it is important to review their qualifications and capabilities, as well as industry experience they bring to the project. Hiring an electrical contractor with feed, grain, and National Fire Protection Agency (NFPA) knowledge is a game changer. 

Understanding NFPA and NEC

As Principal on the NFPA 70 Code-Making Panel 14, emphasis on chapter 5 special occupancies and hazardous locations (articles 500-516), I’m reminded daily the importance of understanding code and ensuring our work is compliant.

Classifications

NFPA 70 National Electrical Code (NEC) is used when designing and installing electrical systems to ensure code compliant installations and designs. Chapter 5 covers special occupancies such as grain elevators and feed mills. Hazardous locations are broken down into three different classifications and the wiring methods and equipment types used in these areas are also covered in articles 501, 502, 503:

    • Class 1 Gas and vapors
    • Class 2 Dust
    • Class 3 Fibers

Groups

From there, locations are then broken down by groups, which are defined by the type of hazardous material found in the area. It is important to note specific materials are designated to the specific type of group. Electrical components are rated for specific groups under the Class and Division, so it is important to know what the group designation is and assure your installation materials match the group that exists in the environment you are installing in.

    • A – Acetylene
    • B – Flammable gas with MESG less than or equal to .45MM
    • C – Flammable gas with MESG greater than .45MM and less than .75MM
    • D – Flammable gas with MESG greater .75MM
    • E – Metal dust
    • F – Carbon black/coal dust
    • G – Grains, starches, flour, wood dusts

Divisions

And finally, facilities are then broken down by divisions, the probability of hazardous materials in quantities sufficient to produce an explosion if ignited being present during normal and abnormal operating conditions. The goal is to be classified as a Class 2, Division 2 facility.

    • Division 1: Hazardous gas/vapor/dust present during normal operating conditions
    • Division 2: Hazardous gas/vapor/dust not likely present during normal operating conditions

Hazardous Location Classification and Examples

CLASS GROUP DIVISION EXAMPLE
1 B 1 Gases exist under normal conditions; gases exist due to faulty operations. 
1 B 2 Gases or liquids can only be released by rupture or breakdown; failure of ventilation equipment. 
2 G 1 High concentration of dust is present during normal conditions (explosive levels)
2 G 2 Normal conditions do not present high levels of combustible dust to be explosive. 

Types of Ignition Sources

The fire triangle consists of the most basic ingredients to create fire (heat, fuel, and oxygen). Taking the fire triangle a step further with the inclusion of confinement and dispersion, you now have the Dust Explosion Pentagon. The combination of these elements can be disastrous for a facility. By simply removing just one element from the dust explosion pentagon, you can reduce the risk for explosion. 

The amount of wheat or starch dust to create an explosion is about 30 grams per cubic meter. These concentrations can exist inside of grain handling equipment and on bid decks or receiving pits without dust collection.

Standard ignition sources include:

  • Motors
  • Control devices
  • Light fixtures and receptacles
  • Powered industrial equipment such as conveyors, legs and fans.

Solutions on how to Reduce Risks of Explosions

As stated above, the goal of all facilities with hazardous locations is to reduce situations that house all the components to create an explosion present at the same time. Through proper facility design and protection techniques, explosions in hazardous locations can be prevented. Some of the common protection techniques include:

  • Installing hazard monitoring (HazMon) on all powered industrial equipment and have it commissioned and tested annually.
  • Designing projects with safety in mind (reference NFPA 654)
  • Conducting a Dust Hazard Analysis (DHA) to identify the potential for fire/explosion associated with dust in a facility.
  • Installing dust collection and explosion suppression systems.
  • Preventative maintenance through good housekeeping to prevent dust accumulation.

Putting safety first is something we take serious at Knobelsdorff. Working with a knowledgeable partner and taking the time to strategically plan and upgrade or new facility will save you in the long run.

Let’s get to work.