NFPA 61 or NFPA 68: Combustible Dust Explosion Protection
REMBE Inc. Sales Engineer Payton Ball shares insights on NFPA 61 and NFPA 68 and how the standards can help address combustible dust hazards.
September 3, 2020
Payton Ball, BSME, Sales Engineer, REMBE Inc.
Let’s say you are a Project Engineer for a pet food production facility. You’ve recently hired a consultant to conduct a Dust Hazard Analysis (DHA), according to NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, rev. 2020 (NFPA 61) & NFPA 652, Standard on the Fundamentals of Combustible Dust, rev.2019 (NFPA 652). You are now tasked with the responsibility of implementing several DHA recommendations, one of which is to implement explosion protection on your plant’s bucket elevators in compliance with the NFPA standards.
Bucket elevators provide you a means to transport large volumes of product via belt/chain efficiently and to higher elevations than typically practical with pneumatic or open belt conveying. These systems in your plant are essential, and transport everything from whole grains, to processed additives and ingredients. Your challenge is to correctly interpret and apply the applicable NFPA standards. While your facility falls under the NFPA 61 umbrella for food processing facilities, NFPA 68, Standard on Explosion Protection by Deflagration Venting, rev. 2018 (NFPA 68), the standard for deflagration venting, may also apply.
Many questions arise in food processing facilities with respect to bucket elevator explosion protection. Prescriptive methods of explosion protection for bucket elevators can be found in both NFPA 68 and NFPA 61 Standards. NFPA 68 lays out parameters for the protection of all hazardous dusts, while the methodology in NFPA 61 is specifically for grain handling. In many cases the specific commodity NFPA standards refer to the other core combustible dust standards.
Determining the applicable standard to use for bucket elevator protection is rather simple! It starts and stops with the definition of “bulk raw grain”. In NFPA 61-20 3.3.6, bulk raw grain is defined as “Grain materials, such as cereal grains, oilseeds, and legumes, that have not undergone processing or size reduction”. The key characteristic here is regarding processing, and size reduction. We look further in the NFPA Standard 61 to find two primary divisions for bucket elevator legs: