Limiting Oxygen Concentration (LOC) Test

What Is a Limiting Oxygen Concentration(LOC) Test?

The Limiting Oxygen Concentration (LOC) for combustible dust is the minimum oxygen level in air at which a dust explosion or combustion cannot be sustained, even with an ignition source or sufficient fuel. It defines the lower boundary below which a dust-air mixture cannot support combustion or explosion.

Testing Principle and Methodology

• A sample of the dust is dispersed in a 20L Sphere, which is pressurized with a compressed air–inert air mixture using partial pressures.
• A 2.5 kJ chemical ignitor is activated to attempt ignition.
• ASTM recommends the sample have a particle size of at least 95% less than 75 microns and moisture content below 5%.

In some unique cases where the material does not segregate during normal operation, we test the sample as received. If you’re unsure how to prepare your sample, contact Prime Process Safety Center for guidance.

To determine the LOC, we vary the oxygen concentration around the dust’s most easily ignitable concentration (typically based on the Kst/Pmax value). We gradually replace oxygen with nitrogen to reduce flammability. The LOC is reached when the pressure ratio in the chamber drops below 2.0.

Typical Dust Explosion Graph for LOC determination in a 20L Sphere

Applicable Standard

The LOC test follows ASTM E2931, Standard Test Method for Limiting Oxygen (Oxidant) Concentration of Combustible Dust Clouds, and BS EN 14034 Part 4.

Data Interpretation

Testers determine the LOC based on the pressure ratio in the chamber. If the pressure ratio reaches 2.0 or higher, or if Pmax exceeds 0.5 barG, the test confirms ignition. The lowest oxygen level that no longer supports ignition defines the LOC.

Engineers use LOC test results to design nitrogen inerting systems that maintain safe oxygen levels during processing. Understanding the LOC is crucial for:

• Fire and Explosion Prevention
• Risk Assessment and Hazard Analysis
• Safety Protocol Development
• Process and Equipment Design
• Regulatory Compliance
• Incident Prevention and Worker Safety
• Emergency Preparedness

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Any questions or concerns? To learn more about our services, please call +1 (346) 462-3838 /+1 (346) 462-3816 or email info@primeprocesssafety.com.

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When Do You Perform A Limiting Oxygen Concentration(LOC) Test?

LOC testing is essential in settings where flammable materials, including combustible dusts, are present. It is particularly important when inerting is used to prevent explosions. LOC testing should also be performed during:

• New material introductions
• Regulatory compliance checks
• Incident reviews

Regular LOC assessments help ensure workplace safety and prevent dust-related fire or explosion hazards.

Why Choose Prime Process Safety Center

Prime Process Safety Center is a trusted leader in process safety testing with experienced laboratory personnel. Our mission is to provide accurate, reliable, and defensible data that meets both industry and regulatory standards.

• Our team is highly experienced in conducting LOC tests.
• We use advanced explosibility testing equipment to ensure precision.
• Strict protocols and quality control ensure consistent results.
• We interpret your test results and provide meaningful recommendations for your application or research.

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