Combustible Dust Hazards and Control

Wes Hofmann

Safety Engineer

OSHA - St. Louis Area Office

Sept. 2008

Why are we here??

To prevent and/or reduce the following:

Catastrophic Combustible Dust Incidents

Malden Mills

Methuen, MA

December 11, 1995

37 Injured

Nylon Fiber

Combustible Dust Explosions History

Firefighting efforts following the explosion at Malden Mills (Methuen, Massachusetts, December 11, 1995).

Combustible Dust Explosions History

Jahn Foundry

Springfield, MA

February 26, 1999

3 dead9 Injured

Phenolic resin dust

Combustible Dust Explosions History

• Ford River Rouge: • Secondary • Coal Dust Explosion• February 1, 1999• Killed 6 workers and

injured 36

Combustible Dust Explosions History

May 16, 2002Rouse PolymericsVicksburg, MS5 dead, 7 injuredRubber Dust

Combustible Dust Explosions History

• January 29, 2003 - West Pharmaceutical Services, Kinston, NC– 6 deaths, dozens of

injuries– Facility produced rubber

stoppers and other products for medical use

– Plastic powder accumulated above suspended ceiling ignited

West Pharmaceutical facility destroyed by polyethylene dust

Combustible Dust Explosions History

• February 20, 2003 • CTA Acoustics • Corbin, KY

– 7 Workers died– Facility produced

fiberglass insulation for automotive industry

– Resin accumulated in production area and was ignited

Combustible Dust Explosions History

• October 29, 2003• Hayes Lemmerz

Manufacturing Plant– Two severely

burned (one of the victims died)

– Accumulated aluminum dust

– Facility manufactured cast aluminum automotive wheels

Chemical Safety Board (CSB) Report Notes

• Notes from the CSB - US Dust Incidents 1980 to 2005*:

- “Dust incidents are a significant industry safety problem”

- On average “10 dust explosions per year”

- Nearly 5 fatalities and 29 injuries per year

- The annual rate is increasing

Dust Incidents, Injuries, Fatalities 1980-2005 [CSB Report]

FatalitiesInjuriesIncidents

Inju

ries

/ F

atal

itie

s

Inci

den

ts

Chemical Safety Board (CSB) Report Notes

• Notes from the CSB - US Dust Incidents 1980 to 2005*:

- 281 incidents recorded

- 119 fatalities

- 718 injuries

- 14 fatalities in three incidents in 2003.

Chemical Safety Board (CSB) Report Notes

• Notes from the CSB - US Dust Incidents 1980 to 2005*:

*CSB Investigative Report: Combustible Dust Hazard Study Nov. 9, 2006 (Database excluded grain, coal, transportation and non-manufacturing).

Types of Combustible Dusts

• Metal dust such as aluminum and magnesium

• Wood dust• Coal and other carbon dusts.• Plastic dust• Biosolids• Organic dust such as sugar,

paper, soap, and dried blood.• Certain textile materials• Candy, sugar, spice, flour, grain• Rubber• Fertilizer

Industries: Dust Explosion Hazards

Industries with potential dust explosion hazards:• Agriculture• Chemical • Textile • Forest and furniture products • Metal Processing • Paper products • Pharmaceuticals • Recycling operations (metal, paper, and plastic recycling

operations.)• Food

Fire Triangle - Dust Explosion Pentagon

FIRE TRIANGLE: DUST EXPLOSION PENTAGON:

Combustible Dust Oxygen in Air

Ignition Source (Heat)

Dispersion Confinement

Explosion

(Fuel)

Combustible Dust Explosion Pentagon: Five Elements – ALL Necessary

1. Combustible Dust (Fuel)

2. Oxygen in Air

3. Ignition Source

4. Dispersion

5. Confinement

1. Combustible Dust (Fuel)

2. Oxygen in Air

5. Confinement

3. Ignition Source

4. Dispersion

Explosion

IMPORTANTNO DUST EXPLOSION OCCURS

if one or more elements are missing

Element 1: Combustible Dust

Agricultural Products such as:• Corn Starch, Dry Milk, Sugar,

Wood Flour, Powered MilkAgricultural Dusts such as:• Cocoa Powder, Hops (malted),

Rice Flour, Wheat grain dustCarbonaceous Dusts such as: • Petroleum Coke, Pine Soot,

Bituminous Coal, Wood Charcoal.

Chemical Dusts such as:• Lactose, Sulfur, Calcium

Acetate, Methyl-CellulosePlastic Dusts such as:• Phenolic Resin,

(poly)Propylene, (poly)Vinyl Chloride, Melamine Resin

Metal Dusts such as:• Aluminum, Magnesium, Zinc,

Bronze

Fuel Source: Combustible Dust

Elements 1, 2, and 3 are part of the Fire Triangle

Element 2: Oxygen in Air

• The Oxygen content in air is all that is necessary to support an explosion.

Elements 1, 2, and 3 are part of the Fire Triangle

Element 3: Ignition Source

Can be Electrical • Static• Lighting or • Generated

Can be Mechanical• Match/lighter• Spark

Elements 1, 2, and 3 are part of the Fire Triangle

Element 4: Dispersion

Dispersion in the right concentration• Dust needs to be dispersed in the air

NOTE:

Elements 1, 2, 3, and 4 will cause a deflagration

Element 5: ConfinementExplosion

• Confinement can be provided by process equipment, ducting, piping, dust collection equipment, and the building (itself).

All 5 Elements = EXPLOSIONExplosion

Propagation of a Dust Explosion:2 Stages

Deflagration

Propagation of a Combustion Zone at a speed that is less than the speed of sound in the unreacted medium.

ExplosionThe bursting or rupture of an

enclosure or a container due to the development of internal pressure from deflagration.

(Remembering: The container could be the building structure itself.)

Secondary Explosions

As this animation illustrates, secondary explosions can be far more destructive than primary explosions due to the increased quantity and concentration of dispersed combustible dust.

The “Typical” Explosion Event

ProcessEquipment

InitialInternal Deflagration

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

Latent Dust throughout the facility

The “Typical” Explosion Event

ProcessEquipment

InitialInternal Deflagration

Shock Waves

Time, msec.

0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

ProcessEquipment

InitialInternal Deflagration

Elastic ReboundShock Waves

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

ProcessEquipment

InitialInternal Deflagration

Dust clouds causedby Elastic Rebound

The “Typical” Explosion Event

ProcessEquipment

Containment Failure from InitialDeflagration

Dust Clouds Causedby Elastic Rebound

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

ProcessEquipment

Secondary DeflagrationInitiated

Dust Clouds Causedby Elastic Rebound

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

ProcessEquipment

Secondary DeflagrationPropagates through Interior

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

ProcessEquipment

Secondary DeflagrationVents from Structure

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

The “Typical” Explosion Event

Secondary DeflagrationCauses Collapse and Residual Fires

Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

Diagrams Courtesy of John M. Cholin, P.E., FSFPE, J.M. Cholin Consultants, Inc.

Definitions and Terminology What is Combustible Dust?

NFPA’s, NEP, & General Info.: • Definitions• Data (Particle size)• Electrical• Explosion Event• General Information

Definitions and Terminology What is Combustible Dust?

NFPA 654 (2006) Definitions• Combustible dust. A combustible particulate solid that

presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape.

• Combustible Particulate Solid. Any combustible solid material composed of distinct particles or pieces, regardless of size, shape, or chemical composition.

• Hybrid Mixture. A mixture of a flammable gas with either a combustible dust or a combustible mist.

Definitions and Terminology What is Combustible Dust?

NFPA 69 (2002), and 499 (2004) Definitions– Combustible Dust. Any finely divided solid material 420

microns or less in diameter (i.e., material passing through a U.S. No. 40 Standard Sieve) that presents a fire or explosion hazard when dispersed

• 1 micron (µ) = 1.0 x 10-6 m  = 1.0 x 10-4 cm = 1.0 x 10-3 mm •  420 µ = 420 x 10-4 cm = .042 cm = 0.4mm • A typical paper thickness is approximately 0.1mm

Particle Size of Common Materials

Common Material Size (microns)

Table salt 100

White granulated sugar 450 - 600

Sand 50+

Talcum (baby) powder 10

Mold spores 10 – 30

Human hair 40 - 300

Flour 1 - 100

Source: Filtercorp International Ltd.

Increase of Surface Area

• Finer the particle > surface area = more explosive a dust is likely to be

• Dust made up of particle sizes from fine to coarse; fines play a more prominent role in explosion

• Presence of dusts should be anticipated in the process stream-regardless of starting particle size

Definitions and Terminology

• Class II Locations– Locations that are hazardous because of the presence of

combustible dust.

• The following are Class II locations where the combustible dust atmospheres are present:– Group E. Atmospheres containing combustible metal dusts,

including• aluminum, magnesium, and their commercial alloys, and other

combustible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment.

Definitions and Terminology

– Group F. Atmospheres containing combustible carbonaceous dusts that have more than 8 percent total entrapped volatiles as per ASTM D 3175 *, OR• Those that have been sensitized by other materials so that they

present an explosion hazard• Coal, carbon black, charcoal, and coke dusts are examples of

carbonaceous dusts.

– Group G. Atmospheres containing other combustible dusts, including• flour, grain, wood flour, plastic and chemicals.

• ASTM D 3175: Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke (used for coal and coke dusts)

Definitions and Terminology Deflagration Vs. Explosion

• Deflagration: Propagation of a combustion zone at a velocity that is less than the speed of sound in the unreacted medium.

• Detonation: Propagation of a combustion zone at a velocity that is greater than the speed of sound in the unreacted medium.

• Explosion: The bursting or rupture of an enclosure or a container due to the development of internal pressure from deflagration.

Explosion

Deflagration

Detonation

Employer’s Responsibilities

• Facility Components Analysis• Assess Workplace Conditions• Prevention Methods (Electrical)• Control Methods• Corrective Actions• Facility Changes• Employee Training

Facility Components Analysis

• Materials that can be combustible when finely divided;

• Processes which use, consume, or produce combustible dusts;

• Open areas where combustible dusts may build up;• Hidden areas where combustible dusts may

accumulate;• Means by which dust may be dispersed in the air;

and,• Potential ignition sources.

Assess Workplace Conditions

Determine if any of the Combustible Dust are Produced or Processed, if so:

- All areas of the facility need to be checked for any locations where there are dust deposits.

- Sample the dust to identify the type of material it is and to determine if it is combustible.

- Check high areas above false ceiling, on ledges, top of beams, top of joists and on the top of and around any process equipment.

Prevention Methods forExplosions by Electrical Equipment

Dust-Ignition Proof • Equipment enclosed in a

manner that excludes dusts and does not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspension of a specified dust on or in the vicinity of the enclosure.

Dust Tight• Enclosures constructed

so that dust will not enter under specified test conditions

Control Methods

Deflagration Isolation• A method employing

equipment and procedures that interrupts the propagation of a deflagration of a flame front, past a predetermined point.

Deflagration Suppression• The technique of

detecting and arresting combustion in a confined space while the combustion is still in its incipient stage, thus preventing the development of pressure that could result in an explosion.

Corrective Actions

If combustible dust conditions are found, corrective action is needed. Such action(s) should include but are not limited to:

- Repair of any leaks in process equipment.

- Establishment of Housekeeping Plan and Schedule to control dust present out side of process equipment.

Determine Facility Changes

Determine if:- Flame Detectors are needed on Process

Equipment.- Fire Extinguisher operated by Flame Detectors

are needed on Process Equipment.- Blow Out Venting is needed on Process

Equipment.- Any present or new Blow Out Venting needs to

be vent to the outside of the building

Possible Facility Changes or Method Controls

Screw Conveyor Chokes

Possible Facility Changes or Method Controls

Screw Conveyor Chokes

Possible Facility Changes or Method Controls

Rotary Valves

Possible Facility Changes or Method Controls

Flame Front Diversion

Possible Facility Changes or Method Controls

Mechanical Isolation

Possible Facility Changes or Method Controls

Chemical Isolation

Employee Training and Operational Changes

Employee Training• Necessary Training of

Employees on handling Combustible Dust Hazards.

• Retraining of Present Employee.

• Establish Training Program for New Employees.

Operational Changes• Establish a reporting

system for employees to report dust accumulation conditions that are occurring.

Combustible DustEnforcement

per National Office Stats:

Richard Fairfax, CIH

Director

Enforcement Programs

November 1, 2007 – June 30, 2008(8 mos. Period)

Inspections Conducted

258

68

0

50

100

150

200

250

300

350

400

Federal 18(b) State

326 Total Inspections

Total Violations Issued

746

441

0

100

200

300

400

500

600

700

800

900

Federal 18(b) State

1,187 Total Violations

% Total Violations Cited As Serious

74%

28%

0%

20%

40%

60%

80%

100%

Federal 18(b) State

% Total Violations Cited As S,W,R,FTA, Unclass

75%

30%

0%

20%

40%

60%

80%

100%

Federal 18(b) State

Avg. Number Violations Issued Per Initial Inspection

6

7.8

0123456789

10

Federal 18(b) State

Avg. Penalty Per Serious Violation

$850$764

$0

$200

$400

$600

$800

$1,000

Federal 18(b) State

% Inspections In-Compliance(Insps W/O Violations & Closed)

12% 9%

0%

20%

40%

60%

80%

100%

Federal 18(b) State

Combustible Dust Violations

• (5)(a)(1) Violations – 29• Housekeeping Violations – 42• Electrical Violations – 14

Typical 5(a)(1) Violations

1. Baghouse dust collectors (at several facilities) were located inside a building without proper explosion protection systems, such as explosion venting or explosion suppression systems.

2. Deflagration isolation systems were not provided to prevent deflagration propagation from dust collectors to other parts of the plant.

3. The rooms with excessive dust accumulations were not equipped with explosion relief venting distributed over the exterior walls and roofs of the buildings.

Typical 5(a)(1) Violations

4. The horizontal surfaces such as beams, ledges and screw conveyors at elevated surfaces were not minimized to prevent accumulation of dust on surfaces.

5. Air from the dust collector was recycled through ductwork back into the work area. This was found at several facilities.

6. Legs of bucket elevators were not equipped with explosion relief venting.

Typical 5(a)(1) Violations

7. Explosion vent on bucket elevator(s) were directed into work areas and not vented to a safe, outside location away from platforms, means of egress, or other potentially occupied areas.

8. Equipment (such as grinders and shakers) were not maintained to ensure that they were dust tight, thus combustible dust would leak into the surrounding area.

9. Pulvirizers were not provided with explosion venting or deflagration suppression systems.

Typical 5(a)(1) Violations

10. Ductwork from the dust collection system to other areas of the plant were not constructed of metal.

11. Employees were using electric grinder(s) on a duct entering a baghouse style dust collector without a hot work permit system.

12. Open flames from a propane heater for comfort heating were in an area where agricultural products were ground.

Other Primary Applicable OSHA Standards

1910.22 General – Housekeeping

1910.307 Electrical Hazardous (Classified) Locations

1910.178 Powered Industrial Trucks

1910.263 Bakery Equipment

1910.265 Sawmills

1910.272 Grain Handling

Housekeeping: Possibility of Secondary Explosion?

Dust Layer Thickness Guidelines

1/8” in grain standard

Rule of thumb in NFPA 654

1/32” over 5% of area – Floor area max. 20,000 SFFloor area exceeds 20,000 SF – 1,000 SF Upper Limit for dustThese facts are an idealized approach (Reference Annex D – NFPA 654)

1/32” approximately equals the thickness of a typical paper clip.

Dust Layer Thickness Guidelines

Rough calculations show that the available surface of bar joists is approximately 5% of the floor area;

The equivalent surface for steel beams can be as high as 10%.

OSHA Contact Information:

NEED TECHNICAL and/or

SAMPLING INFORMATION:

The following personnelmay be of assistance:

OSHA Contact Information:

TECHNICAL INFORMATION:

Sanji Kanth – OSHA National Office

200 Constitution Ave. NW

Room 3119

Washington, DC 20210

(202) 693-1850

OSHA Contact Information:

OSHA SAMPLING INFORMATION:

Jon Rima – Salt Lake Technical Center

8660 S. Sandy Parkway

Sandy, Utah 84070

(801) 233-4966

That’s All Folks!!

Thank You For Your Time!!