Combustability determination for walnut hulling and shelling facility dusts

Authors: Whitelock, Derek; Tumuluru, Jaya Shankar; Armijo, Carlos

Submitted to: Journal of Agricultural Safety and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2025
Publication Date: 8/4/2025
Citation: Whitelock, D.P., Tumuluru, J., Armijo, C.B. 2025. Combustability determination for walnut hulling and shelling facility dusts. Journal of Agricultural Safety and Health. 31(3):165-172. doi: 10.13031/jash.16193.
DOI: https://doi.org/10.13031/jash.16193

Interpretive Summary: Fires and/or explosions at agricultural facilities have been an issue across the world. While some agricultural industries like sugar and grain handling facilities have had issues with fires or explosions and have been subject to regulations on dusts for many years, many other agricultural processors have had no issues with dust fires or explosions. It may be surprising to hear that walnut dust is designated as combustible by the U.S. Occupational Safety and Health Administration and some local governments, and insurance companies have attempted to apply that designation to dust at walnut huller and sheller facilities. Facilities that generate potentially combustible dusts must abide by National Fire Protection Association standards that require expensive sprinkler systems and approved dust control systems (costing $100,000 to over $1 million dollars in some cases) and may have difficulties obtaining approval for building permits and insurance coverage. At the request of the Western Agricultural Processors Association, ARS researchers in Las Cruces, New Mexico, conducted tests to determine the combustibility of dust from walnut hulling and shelling facilities. These tests showed that walnut dusts were not combustible and therefore not an explosion hazard. These results should enable the industry to keep walnut huller and sheller dusts from being classed as combustible and help clear the way for construction of new walnut processing plants and save the industry many thousands of dollars for needless fire and explosion suppression hardware and practices.

Technical Abstract: Fires and explosions at agricultural facilities have been an issue across the world. While some agricultural industries like sugar and grain handling facilities have had issues with fires or explosions and have been subject to regulations on dusts for many years, many other agricultural processors have not. The U.S. Occupational Safety and Health Administration (OSHA) lists walnut dust as combustible. Some local governments and insurance companies have attempted to apply that designation to dust at walnut huller and sheller facilities. Facilities that generate potentially combustible dusts must abide by National Fire Protection Association standards that require expensive sprinkler systems and approved dust control systems and may have difficulties obtaining approval for building permits and insurance coverage. Tests following United Nations Manual of Tests and Criteria, Part III, Subsection 33.2.1, Test N.1, “Test Method for Flammable Solids” were conducted to determine the combustibility of dust samples collected at walnut hulling and shelling facilities in California. According to these tests following the UN method, the walnut huller and sheller dusts were not flammable solids and therefore should not be considered combustible dusts.