Dust Explosion Fundamentals Nicholas Licht Design Engineer Objectives

Dust Explosion Fundamentals Nicholas Licht Design Engineer

Objectives • • • Brief Overview of CV Technology History of Dust Explosions Recent Events Dust Explosion Basics Codes and Standards Methods of Protection

Headquarters & Manufacturing in Jupiter, Florida

History of Dust Explosions • First recorded dust explosion occurred in Turin, Italy back in 1785 • 281 combustible dust incidents in the US from 1980 -2005 • Resulted in 119 deaths and 718 injuries

Consequences of Dust Explosions February 2008: Imperial Sugar-Savannah, GA • Caused by a overheated bearing • 14 people killed • Over 40 injured • Resulting OSHA fines totaled $8. 7 million • Rebuild cost of $200 million

Combustible Dusts Examples

Combustible Dust Events in US: 1980 -2005 Distribution of Dust Events by Industry Furniture & Equipment Manufacturing Fabricated 7% Metal Products 7% Fixtures 4% Other 7% Rubber & Plastic Products 8% Inorganic 4% Food Products 24% Lumber & Wood 15% Electric Services 8% Primary Metal Industries 8% Distribution of Dust Events by Material Type Other 7% Coal 8% Food 23% Plastic 14% Metal 20% Chemical Manufacturing 12% & grain handling facilities excluded from study Note: Coal mines (Ref. U. S. Chemical Safety Board Report No. 2006 -H-1) Wood 24%

Dust Explosion Concept Log -Burns slowly -Difficult to ignite Kindling Dust -Burns quickly -Easier to ignite -Burns very fast -Easily ignited

Dust Explosion Pentagon Ignition Source Confined Area Explosive Dust Explosion Pentagon Suspended Cloud Oxygen

Dust Explosion by Equipment Type % of Incidents Dust Collector 52 Impact Equipment 17 Silos & Bins 13 Dryers & Ovens 9 Processing Equipment 6 Conveyor 3 Source: FM Global Property Loss Prevention Data Sheet 7 -76, “Prevention and Mitigation of Combustible Dust Explosion and Fire”, May 2008

Dust Explosion Terminology • Maximum Pressure (Pmax) – The maximum pressure developed in a contained deflagration of an optimum mixture • Deflagration Index (Kst) -The deflagration index of a dust cloud – Index value related to the rate of pressure rise over time

Dust Explosion Terminology Secondary Explosions: • Occur when deflagrations propagate from one vessel to another through connecting piping/equipment • Secondary explosion are often what causes the greatest amount of damage • Pressure piling will occur increasing deflagrations into detonations • Explosion isolation equipment used to prevent this from occurring

NFPA Dust Standards • Keyway Documents Standard Industry Edition NFPA 652 All New NFPA 654 All – General Industry Document 2013 NFPA 61 Food/Agricultural 2013 NFPA 664 Wood 2012 NFPA 484 Metal 2012 NFPA 655 Sulfur 2012

NFPA Dust Standards • How-to Documents Standard Purpose Edition NFPA 68 Explosion Venting 2013 NFPA 69 Suppression/Isolation/Containment/Inerting 2014 NFPA 77 Static Hazards 2014 NFPA 70 National Electric Code 2014 NFPA 499 Practical Electric Classification 2013

Protection Techniques Prevention or Mitigation • Prevention: eliminate the potential for an explosion • Mitigation: accept that an explosion may occur and institute engineered measures that eliminate the potential for injury and/or damage – Mitigation is a damage limiting technique

How Does Mitigation Work? Pressure Pmax Unvented Vented Pred Pstat 0. 1 bar Time

Mitigation - Venting: • Rupture panels to relieve pressure preventing a vessel failure • Amount of vent area needed is determined using NFPA 68 equations • Explosion vent need to exhaust into a safe area or a quenching device

Mitigation - Venting Factors that Impact Venting • Material (Kst) • Vessel Volume • Vessel Strength • Initial Pressure (+/-) • Explosion Vent – Reduced Pressure (Pred) • Vessel Geometry – (L/D Ratio) – Filter Bag/Cartridges – Mass Index (M) – Burst Pressure (Pstat) – Burst Design • Hinged/Translating

Mitigation – Suppression: • Detect a deflagration at early stage and quench the event with chemical suppressant • Cannon/bottle consist of pressurized gas and suppressant chemical • System triggers by pressure or optical sensor • Higher maintenance requirements

Mitigation – Suppression Factors that Impact Suppression • Vessel Volume • Vessel Strength – Reduced Pressure (Pred) • Vessel Geometry – (L/D Ratio) – Filter Bag/Cartridges Factors that Impact Suppression • Initial Pressure (+/-) • Material (Kst) • Activation Pressure (Pstat)

Isolation

Isolation: • Must be used to prevent propagation of an event in one vessel to interconnected equipment • Usually always needed in conjunction with venting or suppression

Hierarchy of Equipment Use 1. ) Free venting a vessel outdoors 2. ) Free venting a vessel indoors next to an exterior wall using a duct 3. ) Free venting a vessel indoors next to an exterior roof using a duct 4. ) Flameless venting 5. ) Active Suppression 6. ) Containment 7. ) Inerting Prevention

Dust Collectors

Dust Collectors

Hierarchy of Equipment Use 1. ) Free venting a vessel outdoors 2. ) Free venting a vessel indoors next to an exterior wall using a duct 3. ) Free venting a vessel indoors next to an exterior roof using a duct 4. ) Flameless venting 5. ) Active Suppression 6. ) Containment 7. ) Inerting Prevention

Dust Collectors

Dust Collectors

Hierarchy of Equipment Use 1. ) Free venting a vessel outdoors 2. ) Free venting a vessel indoors next to an exterior wall using a duct 3. ) Free venting a vessel indoors next to an exterior roof using a duct 4. ) Flameless venting 5. ) Active Suppression 6. ) Containment 7. ) Inerting Prevention

Dust Collectors

Dust Collectors

Hierarchy of Equipment Use 1. ) Free venting a vessel outdoors 2. ) Free venting a vessel indoors next to an exterior wall using a duct 3. ) Free venting a vessel indoors next to an exterior roof using a duct 4. ) Flameless venting 5. ) Active Suppression 6. ) Containment 7. ) Inerting Prevention

Dust Collectors

Dust Collectors

Hierarchy of Equipment Use 1. ) Free venting a vessel outdoors 2. ) Free venting a vessel indoors next to an exterior wall using a duct 3. ) Free venting a vessel indoors next to an exterior roof using a duct 4. ) Flameless venting 5. ) Active Suppression 6. ) Containment 7. ) Inerting Prevention

Concluding Remarks • No two dust explosions are the same. – No uniform dust laws like there are for gases • Standards are evolving • The dust explosion hazard exists – Be aware of the “I’ve never had a dust explosion before”

Questions?

References • NFPA-654, “Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids” • NFPA-68, “Standard on Explosion Protection by Deflagration Venting” • NFPA-69, “Standard on Explosion Prevention Systems” • OSHA Website, http: //www. osha. gov/ • U. S. Chemical Safety Board, http: //www. chemsafety. gov/ • Dust Explosions in the Process Industries, 3 rd edition, R. K. Eckhoff, Elsevier, 2003 • Factory Mutual Loss Prevention Data 7 -76, “Prevention and Mitigation of Combustible Dust Explosions and Fires”