Brief review of dust explosion test methodologies peaks and pi8alls

Transcription

1 Brief review of dust explosion test ethodologies peaks and pi8alls Ashok Ghose Dastidar, PhD MBA Vice President, Dust & Flaability Testing and Consulting Services Fauske & Associates, LLC.

2 Dr. Ashok Ghose Dastidar, Ph.D., MBA B.Sc. Cheistry MBA Saint Mary s University Master of Applied Science Ph.D. Cheical Engineering 23 years of experience in the field of dust & gas/vapor explosions and cobustion Safety Consulting Engineers, Inc Fauske & Associates, LLC Meber of AIChE Chairperson of the ASTM E27.05 Subcoittee on Dust Explosion Test Methods On NFPA Technical Coittees for: 654, 61, 664, 484, 91 and 655 On Editorial Advisory Board of Powder/Bulk Solids On Editorial Board of Journal of Loss Prevention in the Process Industries

3 Dust Explosions in Industrial Systes 3

4 Dust Fires & Explosions Like all fires, a dust fire occurs when fuel (the cobustible dust) is exposed to heat (an ignition source) in the presence of oxygen (air) Reoving any one of these eleents of the classic fire triangle eliinates the possibility of a fire 4

5 Dust Fires & Explosions (continued) Dust explosions require the presence of two additional eleents dust dispersion and confineent Suspended dust burns ore rapidly and confineent allows for pressure buildup; reoval of either the suspension or the confineent eleents prevents an explosion, although a fire ay still occur 5

6 Introduction Dust explosions are a serious hazard in process industries - Loss of land, labor and capital Current state (key findings fro U.S. Cheical Safety & Hazards Investigations Board (USCSB) report) At least 281 cobustible dust fires and explosions occurred in general industry between 1980 and 2005, which - Caused at least 119 fatalities and 718 injuries in the United States - Occurred in a wide range of industries and involved any types of cobustible dusts - Currently NO national standard for worker protection; OSHA has 29CFR (1987) 6

7 Recent Major Dust Explosions January West Pharaceuticals Services Kinston, North Carolina Fine plastic dust - 6 fatalities any injured February 2003 CTA Acoustics Corbin, Kentucky fiberglass binder dust 1 fatality several injured October 2003 Heyes Leerz Huntington, Indiana Aluinu Dust 1 fatality several injured February 2008 Iperial Sugar Port Wentworth, Georgia Sugar dust 14 Fatalities 38 Injured 7

8 Introduction (continued) Consensus standards, developed by the NFPA, that provide detailed guidance for preventing and itigating dust fires and explosions are widely considered to be effective, however: - These standards are voluntary, unless adopted as part of a fire code by a state or local jurisdiction and have not been adopted in any states and local jurisdictions, or have been odified - NFPA standards are part of the International Fire Code and Unifor Fire Code - Also, soe regions have adopted NFPA 1: FIRE CODE see Chapter 40 - These codes are also Recognized And Generally Accepted Good Engineering Practices (REGEGAP) 8

9 NFPA Dust Hazard Standards NFPA publishes 6 occupancy standards that are focused on dust explosion hazards - NFPA 652 NFPA 654 NFPA 61 NFPA 664 NFPA 484 NFPA 655 NFPA publishes 7 design standards referenced in the 6 occupancy standards - NFPA 68 - NFPA 69 - NFPA 91 - NFPA 13 - NFPA 15 - NFPA 72 - NFPA 70 NEC NFPA 499 NFPA 77 9

10 Fraework NFPA 652 NFPA 68, 69, 70 etc. ASTM NFPA 61 NFPA 484 NFPA 664 NFPA

11 Testing Methods 11

12 NFPA Recoended Tests Screening Tests P ax & K St MEC LOC MIE MIT LIT NFPA 61 NFPA 654 NFPA 652 NFPA 664 NFPA

13 Screening Tests Is My Material Cobustible? Two ain tests - Deterination of Cobustibility UN Test N.1 (4.1) Test Method for Readily Cobustible Solids Identifies if the aterial presents a fire hazard - Deterination of Explosibility ASTM E1226 Go/No Go Methodology ASTM E1515 Miniu Explosible Concentration 13

14 Cobustibility Screening Test Duration of ignition source can influence cobustibility - Metals and nonetals have different flaedwell ties - What about ixtures? Saples could elt and pose a pool fire hazard - Not reflected in the ethod 14

15 Electric Arc versus Pyrotechnic Igniter Source: Fauske & Associates, LLC Electric Arc can ignite etals Source: Fauske & Associates, LLC Pyrotechnic Igniter ay not ignite soe etals 15

16 Explosibility Screening Test 16

17 Explosion Severity (P ax & K St ) ASTM E1226 Deterined in a 20-L or 1-³ chaber Indication of the severity of an explosion Data used in the design of explosion protection devices - P ax = axiu pressure - K St = (dp/dt) ax V ⅓ - The higher the nuber the ore severe the dust deflagration will be If an enclosure is constructed to withstand this pressure failure, explosion venting or suppression is not required New addition of Go/No Go explosibility screening test 17

18 20-L Siwek Test Chaber Source: Fauske & Associates, LLC 10 kj ignition source 18

19 Pressure-Tie Data Fro an Experient Pressure is plotted as the ordinate Tie is plotted as the abscissa The peak of the pressuretie plot is the highest pressure generated in the explosion for the test The rising slope of the pressure-tie plot is the rate of pressure rise for the test 19

20 Explosion Paraeters as a Function of Dust Concentration Peak explosion data plotted as a function of dust concentration Rate of pressure rise data plotted as a function of dust concentration The highest point is the P ax The highest point is the (dp/dt) ax In this graph for niacin, the P ax is 7.9 bar(g) at 500 g/³ In this graph for Niacin, the (dp/ dt) ax is 930 bar/s 20

21 Overdriving the Explosion Can occur in: - E1226 [P ax & K St ] - E1515 [MEC] - E2931[LOC] Burning of the dust in the igniter flae Igniter flae preheats cloud Exacerbate explosion severity and potential 20-L Test Chaber 21

22 Underdriving the Explosion Can occur in: - E1226 [P ax & K St ] - E1515 [MEC] - E2931[LOC] Vessel wall cools the flae Diinished explosion severity and potential 20-L Test Chaber 22

23 Ignition Source for Explosion Severity Test 23

24 Spherical 1-³ Chaber Original ISO test vessel - 20-L developed to replicate results ~ 1000 Liters Uses 10-kJ ignition source However; - Uses large quantities of saple - Cubersoe and unwieldy to operate Source: Fauske & Associates, LLC 24

25 These Phenoena Not Possible In The 1 ³ Chaber 25

26 Data Interpretation Tips Identify what apparatus is being used. - 20L Vessel has potential for under-driving & over-driving - Bureau of Mines Chaber only adequate for deterining if a aterial is explosible If over-driving is suspected consider 1 3 Challenge Test - Low K St <50 bar-/s - Low P ax <3 bar 26

27 Miniu Autoignition Teperature of a Dust Cloud (MIT) ASTM E1491 Measures the sensitivity to hot surfaces and environents - Hot surfaces in dryers, bearings and echanical parts - Maxiu exposure teperature Materials that do not ignite with ignition source ay autoignite Source: Fauske & Associates, LLC 27

28 Miniu Ignition Energy (MIE) ASTM E2019 Predicts the ease and likelihood of ignition of a dispersed dust cloud MIE of a flaable dust is the iniu spark energy needed to ignite an ideal concentration under lab conditions - A capacitive discharge spark is used for this test - Test can be run with or without inductance - Copared to typical electrostatic ignition sources - Exact ethod not always indicated ay lead to overly conservative strategy 28

29 Miniu Ignition Energy (MIE) ASTM E2019 (continued) 29

30 Miniu Ignition Energy Test 30

31 Miniu Ignition Energy (MIE) ASTM E2019 (continued) Exaples: sugar (powdered) 30 J, paper dust J, aluinu 50 J, agnesiu 40 J MIE (J) Recoended Precaution per BS Low sensitivity to ignition; ground plant below this level 100 Consider grounding personnel below this level 25 The ajority of ignition incidents occur below this level 10 1 High sensitivity to ignition. Consider restrictions on the use of high resistivity non-conductors below this level Extreely sensitive to ignition at this level. Handling operations should be such that they iniize the possibility of suspending the powder in air.; dissipate or discourage charge operations 31

32 Miniu Autoignition Teperature of a Dust Cloud (MIT) ASTM E 1491 Measures the sensitivity to hot surfaces and environents - Hot surfaces in dryers, bearings and echanical parts - Friction spark ignition with MIE data - Maxiu exposure teperature 32

33 Autoignition Teperature of a Dust Layer (LIT) ASTM E2021 Sensitivity to ignition on hot surfaces - Other side roo teperature Longer exposure tie (1-2 hr) - LIT is typically lower than MIT Soe aterials elt before reacting - Not a true iniu since layer thickness affects results 33

34 Layer Ignition Test MIT values can be affected by oven geoetry - horizontal vs vertical LIT can be affected by layer thickness vs 5 34

35 Practical Use of MIT and LIT Data Can be used to deterine axiu allowable surface teperatures of equipent. - Organic dusts that ay dehydrate or carbonize Maxiu surface teperature ust not exceed the lower of either the ignition teperature (MIT/LIT) or 165 C Maxiu Teperature Teperature Class C F (T Code) T T T2A T2B T2C T2D T T3A T3B T3C T T4A T T6 35

36 Dust Explosion & Fire Characteristics Variables effecting output - Dust properties (type, size and exposed surface area) - Nature of oxidative atosphere (sensitivity to oxygen or other oxidizer) - Dispersion echaniss (lofting of powder light or fine powders stay lofted) - Type / agnitude & location of ignition (low energy ignition or self ignition fine powder) - Nature of confineent (volue, yield strength and initial pressure) 36

37 The End 37