Hazards Analysis, Code Compliance & Procedure Development

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Laboratory testing to quantify dust explosion and reactivity hazards

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Design emergency pressure relief systems to mitigate the consequences of unwanted chemical reactivity and account for two-phase flow using the right tools and methods

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Properly size pressure relief vents to protect your processes from dust, vapor, and gas explosions

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Pressure relief sizing is just the first step and it is critical to safety handle the effluent discharge from an overpressure event

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Safe storage or processing requires an understanding of the possible hazards associated with sensitivity to variations in temperature


Classification of hazardous materials subject to shipping and storage regulations

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Develop critical safety data for inclusion in SDS documents


Model transport of airborne virus aerosols to guide safe operations and ventilation upgrades


Model transport of contamination for source term and leak path factor analysis

Fire Analysis

Model transport of heat and smoke for fire analysis

Flammable or Toxic Gas

transport of flammable or toxic gas during a process upset

OSS consulting, adiabatic & reaction calorimetry and consulting

Onsite safety studies can help identify explosibility and chemical reaction hazards so that appropriate testing, simulations, or calculations are identified to support safe scale up

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Engineering and testing to support safe plant operations and develop solutions to problems in heat transfer, fluid flow, electric power systems

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Testing to support safe design of batteries and electrical power backup facilities particularly to satisfy UL9540a ed.4

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Testing and consulting on the explosion risks associated with devices and processes which use or produce hydrogen

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Safety analysis for packaging, transport, and storage of spent nuclear fuel

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Our Nuclear Services Group is recognized for comprehensive evaluations to help commercial nuclear power plants operate efficiently and stay compliant.

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Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions

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Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions

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Testing and modeling services to support resolution of emergent safety issues at a power plant

Adiabatic Safety Calorimeters (ARSST and VSP2)

Low thermal inertial adiabatic calorimeters specially designed to provide directly scalable data that are critical to safe process design

Other Lab Equipment and Parts for the DSC/ARC/ARSST/VSP2 Calorimeters

Products and equipment for the process safety or process development laboratory


Software for emergency relief system design to ensure safe processing of reactive chemicals, including consideration of two-phase flow and runaway chemical reactions


Facility modeling software mechanistically tracks transport of heat, gasses, vapors, and aerosols for safety analysis of multi-room facilities


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Recent Posts

Combustible Dust Basics, Part 3: What is Overdriving?

Posted by The Fauske Team on 04.09.14

20 Liter ChamberThis article is the final in a three part series following, "Combustible Dust Basics, Part 2: What Testing Do I Need?"

The “Explosion Severity Test” is a standard dust test used to quantity the maximum pressure of a dust cloud explosion (Pmax) and the speed of the pressure rise (KSt). The test is generally conducted in a 20L sphere (pictured at top) because it is directly scalable to the 1m3 sphere (pictured at bottom), which is the original instrument used to test combustible dust. The 20L sphere is a practical substitute for the 1m3 chamber, as it requires significantly less sample to conduct the test. On the other hand, the 1m3 sphere  is considered to be the “gold standard” for dust testing, and it is useful for providing data whenever the results from the 20L tests raise questions about the explosive characteristics of a dust.

1m3 sphere

Per Ashok Dastidar, PhD, MBA, Vice President, Dust & Flammability Testing and Consulting Services at Fauske & Associates, LLC (FAI): "The 20L chamber has become the modern workhorse of dust cloud explosibility testing. Explosibility testing in these chambers are performed per ASTM E1226, E1515 and E2931 as well as the EN 14034 methods. Units worldwide provide valuable data to help create dust explosion hazard mitigation strategies in various process industries ranging from agriculture, wood working, pharmaceutical, plastics, fine chemical as well as metal working.

The relatively small size of the 20L sphere results in two limitations," continues Dastidar. "The first is 'overdriving'. Overdriving occurs when the powerful ignition source used to conduct experiments in the 20L chamber preheats the test material and burns the dust cloud under study without really generating a propagating flame. The second limitation is 'underdriving' – where the walls of the 20L chamber abstract heat from the dust cloud explosion and thereby partially quenching the intensity of the deflagration. Both of these phenomena degrade the test data and thus impede the establishment of adequate explosion hazard mitigation. Though the vast majority of dusts and powders are not affected by these phenomena – there are still a few that are."

The solution to both these issues is to perform the relevant tests in a large vessel such as the 1m3. Because of the size and geometry of the 1m3 vessel, it is not as susceptible to overdriving or underdriving. The following blog explores the history of the overdriving issue as well as the methodological response designed to solve overdriving concerns.

Studies going back to 1992 conclude that false positives can occur due to overdriving. False positives may result because materials that will not self-propagate a deflagration will burn due to the overdriving of the large pyrotechnic igniters in the small vessel. It was found that testing in a 20L vessel indicated that a dust was explosible even though the dust was not explosible in a larger 1m3 vessel or in full scale mine tests.  However, strong ignitors may produce overly conservative data in a 20L chamber, and that further tests in a 1m3 chamber would be necessary for a "more realistic hazard determination,” and that “the final determination should be made in a larger system, such as a 1m3chamber”.

A more recent 2007 paper by Proust compared testing results in a modern 20L vessel (consistent with the ASTM E1226) and a 1m3 vessel and again found that overdriving caused false positives in the 20L vessel. The paper found that some dusts with KSt values as high as 65 bar-m/s in the 20L vessel were not actually explosible when tested in a 1m3 vessel and concluded that “a significant proportion of dusts (5 over 21) explode, although weakly, in the 20L sphere and not at all in the 1m3 vessel. From the present analysis, a dust with KSt of 45 bar m/s in the 20L sphere may not explode in the 1m3 chamber.” As a general rule, dusts with a Kst under 50 bar m/s are candidate for clarification testing in the 1m3 chamber.

The ASTM E1226-10 Standard Test Method for Explosibility of Dust Clouds also describes that overdriving can occur in the 20L vessel and recommends testing in a larger chamber such as a 1m3 chamber to determine if a dust is actually explosible. NFPA 68 – 2007 Standard on Explosion Protection by Deflagration Venting also describes that overdriving can occur in the 20L vessel and states, “It can be impossible to unequivocally determine whether a dust is noncombustible in the case of small vessels [e.g., the 20 L (0.02 ft3) vessel]. The ideal solution is to use large (10 kJ) igniters in larger [1m3 (35 ft3)] vessels." Given that the same standard (ASTM E1226-10) governs the performance of dust testing in the 1m3 and 20L chambers, there is no reason not to perform a 1m3 test to ensure that the data is correct.

For more information on your dust testing questions or needs, contact Jeff Griffin at griffin@fauske.com or 630-887-5278. www.fauske.com 

Common Questions Regarding Dust Sample  Collection, Preparation, and Testing



Topics: Combustible Dust, kst, explosion severity test, combustible hazard, dust test, pmax, overdriving


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