Chilworth provides safety services to industry to help PREVENT dust explosions and PROTECT against their effects. Industrial dust explosions occur frequently. They cause loss of life, injury, plant damage, loss of production, litigation and adverse publicity. Industries at risk include: chemical, fine chemical, pharmaceutical, foods, petrochemical, plastics, metal, paints and other processing industries.
A wide range of laboratory tests are available to determine the ignition sensitivity and explosion severity of the material and quantify the risk associated with the process. This helps determine the necessary precautions to take to prevent a dust explosion.
Independent professional advice
Our consultant engineers provide independent consulting advice on explosion prevention and impartial guidance on choice and design of explosion protection systems (relief venting, containment, suppression, use of inert gas, isolation techniques, etc.)
We can offer a TOTAL SAFETY PACKAGE to help
Dust Explosion Tests
Kst and Pmax Values -Measure of explosion severity. Used in relief vent sizing and design of explosion suppression and containment systems.
Limiting Oxygen Concentration (LOC) – Measure of the oxygen concentration below which an explosion will not occur. Used in designing inerting systems.
Minimum Ignition Energy – Measure of sensitivity to ignition by electrostatic discharge
Minimum Ignition Temperature – Measure of sensitivity to ignition by hot surfaces, friction sparks, and electrical equipment
Resistivity, Conductivity, and Chargeability – Measure of ignition risks
Explosibility Screening Test – Go / No Go Test
The explosibility screening test determines whether a powder or dust will explode when exposed to an ignition source when in the form of a dust cloud. The test results in a material being classified as either Type Go — explosible — or Type No Go — non-explosible. Thus, the test is also known as the Go / No Go Test.
Chilworth performs explosibility screening testing first using the Modified Hartmann Tube apparatus. The apparatus consists of a 1.2-liter vertical tube mounted onto a dust dispersion system. Powder or dust samples of various sizes are dispersed in the tube and attempts are made to ignite the resultant dust cloud by 10 J constant arc ignition source. If the material fails to ignite in the Modified Hartmann Tube apparatus, A/B testing is continued in the 20-litre sphere apparatus. Powder or dust samples of various sizes are dispersed inside the sphere and are exposed to a 10 kJ ignition source (chemical igniters).
Minimum Ignition Energy Test – Dust Cloud
The minimum ignition energy (MIE) test determines the lowest spark energy capable of igniting a sample when dispersed in the form of a dust cloud. The test is used primarily to assess the potential vulnerability of powders and dusts to electrostatic discharges, but is also relevant to frictional sparks.
Chilworth performs MIE testing in accordance with American Society for Testing and Materials (ASTM) E2019, British Standard 5958, 1991 and European Standard: IEC 1241-2-3: 1994 using the Modified Hartmann Tube apparatus. Powder or dust samples of various sizes are dispersed in a 1.2-liter vertical tube and attempts are made to ignite the resultant dust cloud with discrete capacitive sparks of known energy.
Minimum Ignition Energy – Dust Layer
The minimum ignition energy (MIE) of a dust layer is determined by placing a dust layer sample on a ground metal plate and approaching the surface of the sample from above using a spherical electrode. The electrode is connected to a capacitor bank and high voltage power source and is capable of delivering electrostatic discharges of known energy to the powder sample. Trials are performed for varying discharge energies and layer depths until the MIE of the dust layer sample has been determined.
Minimum Ignition Temperature Test – Dust Cloud
The minimum ignition temperature (MIT) test determines the lowest surface temperature capable of igniting a powder or dust dispersed in the form of a dust cloud. The MIT is an important factor in evaluating the ignition sensitivity of powders and dusts and is relevant for defining the maximum operating temperature for electrical and mechanical equipment used in dusty environments.
MIT testing is performed using the Godbert-Greenwald Furnace in accordance with ASTM E1491 and as described by the U.S. Bureau of Mines in ROI 5624 and by the Institute of Chemical Engineers (UK) in their publication, “Guide to Dust Explosion Prevention and Protection – Part 2″ (1988) and the European Standard 1241-2-1: 1994. Powder or dust samples of various sizes are dispersed into the furnace and the minimum wall temperature capable of igniting the dust cloud is determined.
Minimum Ignition Temperature Test – Dust Layer
The MIT-Layer test determines the lowest surface temperature capable of igniting a powder or dust when in the form of a five (5) millimeter (mm) or 12.7 millimeter (mm) (other depths may be used) layer. The MIT of a dust layer is used together with the MIT of a dust cloud to define the maximum operating temperature for electrical and mechanical equipment used in dusty environments.
MIT-Layer testing is performed in accordance with ASTM E2021 and a method described in International Electrotechnical Commission (IEC) Document 31H (1982). The test involves heating a circular layer sample 5 mm thick and 100 mm in diameter on a hot plate at constant temperature for 30 minutes. The temperature of the sample layer and the hot plate are monitored and the minimum surface temperature capable of igniting the powder or dust layer is determined.
Minimum Explosible Concentration Test
The minimum explosible concentration (MEC) test determines the smallest concentration of material in air that can give rise to flame propagation upon ignition when in the form of a dust cloud. The test involves dispersing powder or dust samples in a vessel and attempting to ignite the resulting dust cloud with an energetic ignition source. Trials are repeated for decreasing sample sizes until the MEC is determined.
MEC test is performed using the 20-Liter Sphere apparatus in accordance with International Standards Organization (ISO) method 6184/1 or ASTM E1515.
Limiting Oxygen Concentration Test
The limiting oxygen concentration (LOC) determines the minimum concentration of oxygen (displaced by nitrogen) capable of supporting combustion. An atmosphere having an oxygen concentration below the LOC is not capable of supporting combustion and thus cannot support a dust explosion. The LOC test is used to study explosion prevention or severity reduction involving the use of inert gases and to set oxygen concentration alarms or interlocks in inerted plant and vessels.
LOC testing can be performed using the 20-Liter Sphere apparatus. Powder or dust samples of various sizes are dispersed in the vessel and attempts are made to ignite the resulting dust cloud with an energetic ignition source. Trials are repeated for decreasing oxygen concentrations until the LOC is determined. Notably, no consensus test method presently exists for determination of LOC.
Explosion Severity Test (Maximum Explosion Pressure, Kst)
Chilworth performs explosion severity testing using the 20-Liter Sphere apparatus. A powder or dust sample is dispersed within the sphere, ignited by chemical igniters, and the pressure of the resulting explosion is measured. The sample size is varied to determine the optimal dust cloud concentration. The maximum pressure and rate of pressure rise are measured and used to determine the Kst value and St hazard class of the material. These data can be used for the purpose of designing dust explosion protection measures and equipment.
Explosion severity testing is performed in accordance with American Society for Testing and Materials (ASTM) Method E 1226, National Fire Protection Association (NFPA) Standard 68 (1994), German Society of Engineers (VDI) Method 3673 (1995), and International Standards Organization (ISO) Method 6184/1.