Nicholas Licht Design Engineer Dust Explosion Fundamentals

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 combustible dust incidents in the US from 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: Note: Coal mines & grain handling facilities excluded from study (Ref. U.S. Chemical Safety Board Report No H-1)

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

Dust Explosion Pentagon

Dust Explosion by Equipment Type Equipment Type% of Incidents Dust Collector52 Impact Equipment17 Silos & Bins13 Dryers & Ovens9 Processing Equipment6 Conveyor3 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 (P max ) – The maximum pressure developed in a contained deflagration of an optimum mixture Deflagration Index (K st ) -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 StandardIndustryEdition NFPA 652AllNew NFPA 654All – General Industry Document2013 NFPA 61Food/Agricultural2013 NFPA 664Wood2012 NFPA 484Metal2012 NFPA 655Sulfur2012

NFPA Dust Standards How-to Documents StandardPurposeEdition NFPA 68Explosion Venting2013 NFPA 69Suppression/Isolation/Containment/Inerting2014 NFPA 77Static Hazards2014 NFPA 70National Electric Code2014 NFPA 499Practical Electric Classification2013

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? P max P red P stat 0.1 bar

Mitigation - Venting 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 (K st ) Vessel Volume Vessel Strength – Reduced Pressure (P red ) Vessel Geometry – (L/D Ratio) – Filter Bag/Cartridges Factors that Impact Venting Initial Pressure (+/-) Explosion Vent – Mass Index (M) – Burst Pressure (P stat ) – Burst Design Hinged/Translating

Mitigation – Suppression 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 (P red ) Vessel Geometry – (L/D Ratio) – Filter Bag/Cartridges Factors that Impact Suppression Initial Pressure (+/-) Material (K st ) Activation Pressure (P stat )

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 6.) Containment 7.) Inerting 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 Prevention

Dust Collectors

Hierarchy of Equipment Use 6.) Containment 7.) Inerting 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 Prevention

Dust Collectors

Hierarchy of Equipment Use 6.) Containment 7.) Inerting 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 Prevention

Dust Collectors

Hierarchy of Equipment Use 6.) Containment 7.) Inerting 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 Prevention

Dust Collectors

Hierarchy of Equipment Use 6.) Containment 7.) Inerting 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 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, U.S. Chemical Safety Board, 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”