Combustible dust hazards are common in industry and have gained additional exposure due to the OSHA Combustible Dust National Emphasis Program (NEP) which was re-issued as a result of the fatal accident at Imperial Sugar. Fauske & Associates, LLC (FAI) offers a wide range of services related to Dust Hazards Analysis (DHA) characterizing, preventing and mitigating combustible dust explosion and fire hazards. These services include combustible dust testing, onsite assessments, OSHA and NFPA compliance assistance, audit preparation, training, ignition source evaluation and vent sizing calculations.
Our process safety professionals have served clients in a variety of industries including metal processing, wood/paper products, agriculture, food products, textiles, plastics, pharmaceuticals and many others.
Explosion Severity Test - (KSt ,PMax and dP/dtMax)
Minimum Ignition Energy - (MIE)
Minimum Explosible Concentration - (MEC)
Minimum Autoignition Temperature of a Dust Cloud - (MIT)
Hot Surface Ignition Temperature of Dust Layers - (LIT)
Limiting Oxygen Concentration - (LOC)
Testing is completed on-site in our state of the art dust testing facility per ISO 17025 guidelines.
Very often, when performing dust and explosibility testing quotes for customers, we are asked what exactly a Go/No-Go test is? While we offer a list of testing services to determine the deflagration hazards of dust samples per ASTM (American Society of Testing and Materials), OSHA (Occupational Health & Safety Administration, NFPA (National Fire Protection Agency) and UN (United Nations), knowing what this basic test is can go a long way for tackling your safety needs.
In order to "screen" for the possibility of dust explosibility in your facility, we perform a Go/No-Go Screening Test. Based on ASTM E1226, "Standard Test Method for Explosibility of Dust Clouds", this test is an abbreviated set explosion severity method with three dust concentrations to determine if the sample is explosible. This test is generally performed with samples tested "as received" or sieved with a 40 mesh (420μm) screen and using one 5-kJ chemical igniter as the ignition source. [>100 grams (~¼ lb) of sample less than 420μm required]
In a previous post: "How To Collect and Ship Combustible Dust Samples For Testing", we discussed the simple steps for getting your samples to a lab for testing. See below for our chart that discusses the outcomes for your dust tested. If your test sample is a "Yes, it explodes" then further tests can be run to determine how quickly and how severe the explosion will be (KSt/Pmax Test), followed by testing what concentration of dust in the air will cause a risk of explosion (MEC Test). Next, another test can determine if a spark will cause an explosion (MIE) test.
But, what if your Go/No-Go test result is a "no"? Well, we next look at what temperature it will take make your dust layer ignite. To find the Minimum Autoignition Temperature (MIT) of a dust cloud in the air, the MIT tests the minimum temperature that would cause your dust cloud to ignite. Next, is the LIT Test, which determines the hot-surface ignition temperature of dust layer. Finally, a Burn Rate test is conducted to determine how quickly the dust material will burn.
All of these tests start with the Go/No-Go Test. A comprehensive DHA or Process Hazards Analysis (PHA) can apply your test results to real world scenarios at your facility. Better to know wha t you are dealing with so you can plan safely! In addition, if you have a dust collector and aren't sure what to do next, read: "Combustible Dust Made Easy".
Here are some other tests run for dust explosibility screening:
Unless otherwise instructed, dust testing is performed on the sample as it is received (“as received”) from your facility as mentioned earlier. It may be screened to less than 420 μm (40 mesh) – OSHA’s and NFPA’s demarcation of a “dust” – to facilitate dispersion into a dust cloud. Particle size may vary widely depending on the sample.
Furthermore, please note that per ASTM recommendations (and some NPFA requirements); samples should be tested at a particle size less than 75 μm and less than 5% moisture. Please note that testing materials in a method not complying with the ASTM/EU recommendations may produce explosion severity and explosion sensitivity data that is not considered conservative enough for explosion mitigation design.
FAI combustible dust experts can visit your facility to evaluate your receiving, storage, use, processing and disposal of all “powder” materials. They will evaluate existing dust management programs, handling practices, equipment, fire/explosion suppression systems, warning devices and onsite extinguishing capabilities. Possibilities for fugitive dust control will also be identified where appropriate. FAI can provide the following services:
NFPA and OSHA NEP Combustible Dust Compliance
Identifying the electrostatic characteristics of a material is an important step when evaluating the hazards associated with a process, especially for those that handle materials that exhibit low ignition energies.Charge separation and accumulation are inherent problems resulting from industrial operations that handle powders of low conductivity. This charge separation and accumulation is a product of the friction and impact between particles that occurs during the movement of granular material during a variety of typical process operations.To identify potential static electrical hazards of a material, it is important to evaluate the level of charge separation and accumulation that occurs during transport, the resistivity of the material and how quickly any accumulated charge can be dissipated.
Materials we refer to here include all types of flammable hazards including combustible dust/dust hazards, flammable liquid, flammable gas and flammable vapors. The prevention of dust explosions and other fire hazards are are the basis of comprehensive process safety management programs. Necessary combustible dust testing, liquid flammability
Streaming current is defined as the current generated from the flow of charged materials. The level of streaming current generated depends upon the static electricity characteristics of the material and the nature of the process. Unfortunately, there is no relationship between the streaming current in powders and that of liquids (1). In these instances, experimental determinations must be made to identify ignition hazards that may result from charge accumulation during process operations. From these types of
1 R.A. Mancini, “The Use (and Misuse) of Bonding for Control of Static Ignition Hazards, “Plant/Operations Progress (Jan.1998) 7(1): 24.
To identify the streaming current and charge accumulation of a material, Fauske & Associates, LLC (FAI) provides a Powder Chargeability test. The test procedure involves pouring a known amount of material down an inclined section of pipe. The powder then exits the pipe, falling into a Faraday cup. During the test, the charge that accumulates in the Faraday cup is measured using a coulomb meter and the flow rate
of the powder is recorded on a mass per time basis. This data can then be used to approximate the charge density of a material.
To further classify the powder, it is necessary to evaluate the resistivity of the material. This is done per ASTM D257. The resistivity of a powder is governed by the particle size, level of surface contamination and packing density of the material and often is quite different than the resistivity of the material in its pure solid form. Powders with high resistivities typically lose their charge very slowly, even when the process equipment is properly grounded. In some instances, this can translate to poor heat dissipation and can lead to potential fires (2). More importantly, improper handling of materials with both high and low resistivity can create hazardous scenarios. Insufficient grounding and bonding of process equipment can lead to high levels of charge accumulation. At some point, a threshold is reached and charge breakdown occurs resulting in
At FAI, we follow ASTM D257 to evaluate the volume and surface resistivity of a material. The volume resistivity can be determined by measuring the electrical resistance between opposite faces of a volume of powder. The volume resistivity of the material, commonly expressed in ohm-meter, can then be used to classify the material as either a conductive, dissipative or insulative. Likewise, the surface resistivity can be characterized by slightly modifying the test procedure. The units for surface resistivity are ohms per square. The square refers to any square geometry of a material, whether it be a square meter, square foot or square centimeter. The ranges used to characterize a material based on these parameters are shown below.
Results from a resistivity test conducted on a Pittsburgh pulverized coal sample using this method are shown below.
Another important electrostatic characteristic is the charge relaxation time of powders. This property varies greatly amongst different materials and is hard to estimate even if the dielectric constant of the material is approximated because it does not follow the hyperbolic trend found in liquids. The proper method to evaluate the charge decay time of a specific powder is to directly measure it. Once an understanding of the time required for a charge to relax for a given powder is gained, process parameters such as
At FAI, a JCI 155 Charge Decay Test Unit is used to measure the charge decay of powders. This piece of equipment is programmed to apply a
From the tests conducted on Pittsburgh pulverized coal, it can be seen that the material is very resistive in powder form. Processing this material will likely result in charge accumulation and could reach conditions that result in a hazardous static electricity discharge. However, by utilizing this data, it is possible to minimize this risk by implementing proper grounding and bonding of process equipment. The data also provides clues on how to adjust process parameters to reduce charge
Gaining an understanding of the electrostatic characteristics of a particular material can greatly assist in the assessment and mitigation of fire and explosion hazards in the process environment. For additional information on assessing electrostatic hazards, please contact FAI at email@example.com or 630-887-5223.
Pratt, Thomas H. Electrostatic Ignitions of Fires and Explosions. New
Britton, Laurence G. Avoiding Static Ignition Hazards in Chemical Operations
Our team is happy to help train your staff in the understanding of technical issues, process safety programs or audits, regulations and more. We perform process safety audits as part of a comprehensive hazards analysis and can work with you to make sure your staff is supplied with skills training needs in many ways including:
Level I - Gap Analysis
Level II - training & consulting
Level III - Program Development and Implementation
Partial List of Services Offered:
• Reviews and upgrades of all your safety process systems and regulatory requirements
• VPP Consulting
• Audits, reviews, and upgrades of all your Operating, Safety, and Maintenance Procedures
• Training program evaluations for both completeness and effectiveness (from technical skills to professional development) and upgrades where
• Reviews and upgrades of your program elements such as Employee Participation and Process Safety Information for effectiveness and completeness
• Work process effectiveness evaluations and upgrades
• Overall organizational development (e.g., motivation, work processes)
• Stress reduction
• Evaluations of the effectiveness of communication
We design, custom develop and deliver any site specific training materials needed by your organization. Our Consultants, Engineers and Technical Specialists are available to deliver the classroom, lab or on-the-job training your staff needs. In addition, we will assist with the identification and procurement of commercially available training materials where available.