Objectives
• Brief Overview of CV Technology• History of Dust Explosions• Recent Events• Dust Explosion Basics• Codes and Standards• Methods of Protection
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 ExplosionsFebruary 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 Dust Events in US: 1980-2005
Food Products24%
Lumber & Wood15%
Chemical Manufacturing12%Primary Metal Industries
8%
Rubber & Plastic
Products8%
Electric Services
8%
Other7%
Fabricated Metal
Products7%
Equipment Manufactur-
ing7%
Furniture & Fixtures4%
Distribution of Dust Events by Industry
Food23%
Wood24%Metal
20%
Plastic14%
Coal8%
Inorganic4%
Other7%
Distribution of Dust Events by Material Type
Note: Coal mines & grain handling facilities excluded from study(Ref. U.S. Chemical Safety Board Report No. 2006-H-1)
Dust Explosion Concept
Log Kindling Dust
-Burns slowly-Difficult to ignite
-Burns quickly-Easier to ignite
-Burns very fast-Easily ignited
Dust Explosion PentagonIgnition Source
Suspended Cloud
Oxygen Explosive
Dust
Confined Area Dust
Explosion Pentagon
Dust Explosion by Equipment Type
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 andMitigation 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
Mitigation - VentingVenting:• 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
– Reduced Pressure (Pred)
• Vessel Geometry – (L/D Ratio)– Filter Bag/Cartridges
Factors that Impact Venting
• Initial Pressure (+/-)• Explosion Vent
– Mass Index (M)– Burst Pressure (Pstat)– 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 (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
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
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
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
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
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”
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, 3rd edition, R.K. Eckhoff, Elsevier, 2003
• Factory Mutual Loss Prevention Data 7-76, “Prevention and Mitigation of Combustible Dust Explosions and Fires”