Nicholas LichtDesign 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 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 Dusts Examples

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

How Does Mitigation Work?

UnventedVented

Time

Pres

sure

Pmax

Pred

Pstat 0.1 bar

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

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

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

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

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

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, 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”