Dust Explosions in the Pulp and Paper Industry

7/29/2019 Dust Explosions in the Pulp and Paper Industry

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Dust Explosions in the Pulp and Paper Industry

Timothy J. Myers

Exponent, Inc.

ABSTRACT

Recent catastrophic dust explosions have caused an increased focus on dust hazards by government agencies such as

the U.S. Chemical Safety Hazard and Investigation Board (CSB). Investigation of these explosions has revealed that

many facilities, inspectors, and enforcement agencies have limited knowledge of dust explosion hazards. Materials

present in the pulp and paper industry, including wood and paper dust, can represent significant dust explosion

hazards. This paper describes the history of dust explosions in the pulp and paper industry, reviews existingregulations, standards, and practices for the prevention and mitigation of dust explosions, and discusses increased

regulatory and enforcement efforts that may occur.

INTRODUCTION

Several catastrophic dust explosions have recently occurred outside of the pulp and paper industry. Five of theseincidents are summarized in Table I and have caused 22 fatalities, an even greater number of injuries, and significant

property damage. Preliminary data released by the U.S. Chemical Safety Hazard and Investigation Board (CSB) at aJune 22, 2005 public hearing identified approximately 200 dust explosions that have occurred since 1985 that

resulted in approximately 100 fatalities and 600 injuries.

Table I: Recent Catastrophic Dust Explosions

Year Facility State Dust Fatalities

1999 Gray Iron Casting Foundry Massachusetts Phenolic Resin 3

2002 Rubber Recycling Facility Mississippi Scrap Tire Grindings 5

2003 Rubber Drug Delivery Products North Carolina Polyethylene Dust 6

2003 Fiberglass Insulation

Manufacturer

Kentucky Phenolic Resin 7

2003 Automotive Wheel Foundry Indiana Aluminum Dust 1

An explosion in 1785 at a flour warehouse in Turin, Italy is frequently cited as the first reported dust explosion. Therecent incidents in Table I, demonstrate that catastrophic dust explosions continue to occur in a variety of industries

over 200 years later. Because of the attention received by these recent incidents, it is expected that many industries,

including the pulp and paper industry, will see a greater focus on identification and mitigation of dust explosion

hazards. Materials present in the pulp and paper industry including paper and wood dust can represent dust

explosion hazards. Fortunately, current standards and guidelines from the NFPA and other organizations provideguidance to prevent and mitigate dust explosion hazards. The recent focus on dust explosions may cause changes to

local and federal regulations. There will likely be a concurrent increase in emphasis on identifying and mitigating

dust explosion hazards by inspectors from various public and private agencies, such as OSHA, local fire

departments, and insurance companies. Increased awareness and educational programs on dust explosion hazardsare also expected.

FINDINGS FROM RECENT INVESTIGATIONS

The CSB completed investigations of the North Carolina [1] and Kentucky [2] explosions listed in Table I and is

currently investigating the Indiana incident. Additionally, in response to these recent incidents, the CSB launched a

nationwide study to determine the scope of the problem and recommend new safety measures for facilities thathandle combustible powders. The CSBs findings from these investigations include:

Facilities did not fully comply with recognized guidelines and standards for the prevention and mitigationof dust explosions.

Inspectors from major insurance companies and government agencies who had visited the facilities prior tothe explosions did not recognize the dust explosion hazards at these facilities.


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OSHA regulations related to dust explosion hazards are limited to specific industry regulations andclassification of electrical equipment and forklifts for areas containing combustible dusts. (Note: OSHAregulations specific to the pulp and paper industry is described later in this paper)

OSHA has not adopted a comprehensive standard for the prevention and mitigation of dust explosions suchas NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing,

Processing, and Handling of Combustible Particulate Solids.

The CSB is not a regulatory authority and cannot issue citations, however it can and does make recommendations to

other government agencies, trade organizations, standards organizations, and private and public companies.Recommendations from these investigations have included:

Training inspectors from insurance companies and government agencies to recognize dust explosionhazards.

Incorporating standards such as NFPA 654 into local code requirements. Creating outreach programs to educate industries about dust explosion hazards.

During a June 22, 2005 CSB public hearing on combustible dust fire and explosions hazards, the CSB Board askedpanelists if they believed OSHA should create comprehensive regulations for the prevention and mitigation of dust

explosions, or incorporate appropriate National Fire Protection Association (NFPA) standards and guidelines by

reference. A possible outcome of the current CSB investigation of dust explosion hazards could berecommendations to OSHA to incorporate by reference the current NFPA standards and guidelines for the

prevention and mitigation of dust explosions.

DUST EXPLOSIONS IN THE PULP AND PAPER INDUSTRY

History of Dust Explosions in the Pulp and Paper Industry

In the 1970s and 1980s, several authors described recent dust explosions that occurred in the pulp and paper

industry and the fire and explosion hazards of paper dust[3,4,5,6]. These studies indicated that although it is oftenthought that paper dust is only mildly explosive, its dust explosion characteristics are similar to many dusts that are

commonly accepted to be dust explosion hazards, such as coal, flour, and grain dusts. It is difficult to ascertain the

total number of dust explosions that occur in the pulp and paper industry each year as studies have shown that mostdust explosions are not reported and there are few centralized databases of reported dust explosions [7]. It is clearhowever, that the fact that paper dust is thought of as mildly explosive has resulted in a lack of recognition of the

real hazard Figure 1 provides data from three databases tabulating the most common materials involved in historicalindustrial dust explosions.


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0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

Coal Metals Other/Unknown Paper/Pulp Plastics Wood

Dust Type

Pe

rcentofExplosionsin

Each

Data

base

U.S. Facilities 1900 to 1956 - NFPA Database

F.R.Germany Facilities 1965 to 1980 - Jeske and Beck Database

Facilities Insured by FM Global 1985 to 1995 - FM Global Database

Figure 1: Types of dust involved in dust explosions identified in three databases. NFPA (546 explosions), and

Jeske and Beck (269 explosions), FM Global (150 explosions), databases [8,9, and 10]. Incidents involving

food and feed documented in the NFPA and German databases were not included in this figure.

Pulp and paper dust was involved in approximately 1.6 to 4% of the reported dust explosions in the databases shownin Figure 1. While this may seem like a relatively small number, it is likely that many smaller paper dust fires and

explosions that do not cause significant damage or injury to workers go unreported to insurance companies and local

fire departments. Wood dust is the most common fuel in two of the three databases and the second most commonfuel in the third database, involved in approximately 30 to 40% of dust explosions. The frequency of dust

explosions involving wood dust is important for the pulp and paper industry, given that many pulp and paper

manufacturers also produce wood products and that wood is the raw material for the pulping processes, and is used

as a fuel in power boilers.

Characteristics of Dusts Present in the Pulp and Paper Industry

A complete description of various test methods used to characterize the explosion hazards of dust is beyond the

scope of this paper. A survey of ASTM testing methods useful for characterizing the ignition and explosioncharacteristics of dusts was recently published [11]. However, it is useful to compare some dust explosion

characteristics of dusts that may be present in the pulp and paper industry to the characteristics of other dusts that

may be more commonly known as explosion hazards.

In Table II, three dust explosion characteristics are tabulated for examples of dust that may be present in pulp and

paper mills, and dusts that may be more commonly known as dust explosion hazards to the general public or safetyprofessionals. The maximum explosion over pressure is the maximum rise in pressure that will occur when a dust is

dispersed in air and ignited in a closed vessel. The Kst is a volume-normalized rate of pressure rise in this same test

and is independent of vessel volume for sufficiently large vessels. These two values provide an indication of the


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expected severity of an explosion with a specific dust. Larger values of the maximum overpressure and Kst

represent a greater explosion severity. It should be noted, that these maximum overpressures are not typically

reached in industrial explosions because the walls of most buildings will fail at much lower pressures, venting the

explosion. The dust cloud ignition temperature is the temperature at which a dust cloud will ignite without an

ignition source, similar to the autoignition temperature of a gas or vapor.

Table II: Dust explosion characteristics of various materials used in the pulp and paper industry and selected

reference materials. (Data from Eckhoff [12])

Dust Median Particle

Size

(m)

Maximum Explosion

Overpressure (bar-g)

Kst value

(bar-m/s)

Dust Cloud Ignition

Temperature

(C)

Dusts that May be Present in Pulp and Paper Mills

Cellulose Dust 51 9.3 66 500

Paper Pulp Dust 29 9.8 168

Paper Tissue Dust 54 8.6 52 540

Lignin Dust 18 8.7 208 470

Organic Dyestuff


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other industry specific standards. As an example, this standard would apply to pulp and paper mills where pulp,

paper, and other fibers and dusts may be present.

These standards provide guidance in the following areas:

Housekeeping

Employee training, inspection, and maintenance Management of change Building construction Segregation, separation, or detachment of dust handling and processing areas Control of ignition sources (friction, bearings, equipment, electrical equipment, static electricity, open flames

and sparks, heating systems, hot surfaces, industrial trucks, powder-actuated tools)

Explosion venting Equipment explosion protection Equipment isolation Bulk storage Material transfer systems (duct systems, bucket elevators, conveyors, fans or blowers) Size reduction operations Particle size separation Mixers and blenders Dryers Dust collection equipment Fire protection

NFPA 654 places a specific emphasis on housekeeping, employee training, inspection, maintenance, control of

ignition sources, and management of change. Those sections of the standard apply retroactively to existing

facilities. Additional NFPA standards provide guidance in specific areas of explosion prevention and mitigation andmany of these are referenced within NFPA 654 and 655. These include:

NFPA 68 Guide for Venting of Deflagrations NFPA 69 Standard on Explosion Prevention Systems NFPA 70National Electric Code NFPA 499Recommended Practice for the Classification of Combustible Dusts and of Hazardous

(Classified) Locations for Electrical Installations in Chemical Process Areas

NFPA 505 Fire Safety Standard for Powered Industrial Trucks Including Type Designations, Areas of Use,Conversions, Maintenance, and Operation

FM Global data sheets. An industrial insurer, FM Global, publishes data sheets that include guidelines for the

prevention of dust explosions and guidelines for specific processes in the pulp and paper industry that may involve

dust explosion hazards. These include:

7-4 Paper Machines And Pulp Dryers 7-10 Wood Processing And Woodworking Facilities 7-17Explosion Protection Systems 7-57 Pulp and Paper Mills 7-73Dust Collectors and Collection Systems 7-76 Prevention And Mitigation Of Combustible Dust Explosions And Fire 7-102/12-29 Yankee Dryers

General Guidance

The general approach for preventing dust explosions is similar to that used to prevent explosions of fuel gases orflammable and combustible liquid vapors in air: preventing the simultaneous occurrence of fuel, oxygen and an

ignition source in the same location. The dust concentration in air required to fuel a dust explosion is typically on


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the order of 100 grams/m3, orders of magnitude greater than concentrations that are typically considered to be

breathing hazards for most materials. As a general rule of thumb, the dust concentrations in air required to fuel a

dust explosion restrict visibility to less than 1 or 2 meters. During normal operating conditions, the concentrations

of dust required to fuel a dust explosion are typically only found within process equipment and not in the occupied

portions of facilities.

A significant difference between leaks of flammable gases and fugitive dust from process equipment exists. When a

small amount of gas or vapor leaks from a process vessel, it is diluted by air with time and distance, quicklyreducing the concentrations to below the lower flammability limit and reducing the hazard. Conversely, fugitive

dust will eventually settle on surfaces in a facility actually resulting in concentrations much higher than the original

dust cloud released from the equipment. These dust accumulations can be dispersed at a later time, creating dust

clouds of sufficient concentration to fuel a dust explosion.

Dust explosions that occur outside of process equipment are often caused by dispersion and ignition of dust

accumulations within the facility. Many catastrophic dust explosions actually consist of a chain of explosions with

an initial small explosion or other event dispersing dust accumulations within the facility, which then allow theexplosion to propagate throughout the facility. Dust accumulations in rafters and other elevated areas in a building

can represent a significant quantity of material. Sections of NFPA 654 describe that accumulation of dust as small

as 0.8 mm (1/32) can represent a dust explosion hazard. Because of this, it is critical to minimize releases of dustfrom process equipment into a facility and to provide dust collection systems where material is transferred between

equipment. Aggressive housekeeping programs are required to continually remove dust accumulations before theyreach hazardous levels.

In the event that a dust explosion occurs, other elements of the standards are designed to reduce the amount of

damage caused by the explosion. These measures include using damage limiting construction of buildings and

pressure relief vents or blow-out panels on buildings and process vessels to vent pressures before they cause

buildings to collapse or process equipment to rupture.

CURRENT REGULATORY STATUS

The NFPA is not a regulatory agency, and as such, the NFPA codes described above do not become regulationsunless they are incorporated into regulations by an authority having jurisdiction or AHJ. AHJs can be local, state, or

federal government organizations or agencies. In this section, we describe the routes through which these standards

may become regulations in various jurisdictions

Building Codes

Original construction of facility. Building codes adopted by local or state governments vary throughout the United

States. Increasingly, these building codes are incorporating the entire National Fire Code (NFC) of the NFPA byreference. The NFC consists of all NFPA standards including applicable standards for the prevention and mitigation

of dust explosions. Generally, building codes require newly constructed facilities to be built to the standards in

effect at the time of building design or construction. In many jurisdictions older facilities are grandfathered and areonly required to follow the codes in effect at the time of construction of the facility, unless some portions of the

codes apply retroactively. Significant modifications to a building may require compliance with current standards.

The threshold in the degree of modification that requires compliance with current standards is often clearly defined.

Typically, building code officials will only be involved in the initial construction of the building and modifications

to the building if building permits are obtained.

Review of current operation of facility. In many jurisdictions, local and state fire marshals are responsible for

periodic inspection of a facility to ensure that the facility continues to comply with applicable regulations after its

initial construction.

OSHA Regulations

Direct OSHA regulations. There are two primary OSHA regulations related to dust explosion hazards in general

industry. The first is section 29 CFR 1910.178 which specifies the allowable types of industrial trucks or forklifts


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that may be used in environments with Class II combustible dusts or Class III combustible fibers. This section of

the OSHA regulations is based on an historical version of NFPA 505 Fire Safety Standard for Powered Industrial

Trucks Including Type Designations, Areas of Use, Conversions, Maintenance, and Operation. Similarly section 29

CFR 1910.307 specifies the requirements for electrical equipment that may be used in environments with Class II

dust or Class III fibers. This section of the OSHA regulations is based on an historical version of NFPA 70NationalElectric Code.

Standards incorporated by reference for the pulp and paper industry. Section 29 CFR 1910.261 providesadditional regulations specific to the pulp, paper, and paperboard mills. This section incorporates two dust

explosion standards by reference, using their ANSI designations from the late 1960s. The first standard, ANSI

Z12.12-1968, refers to NFPA 655, which is currently titled Standard for Prevention of Sulfur Fires and Explosions.

The inclusion of this standard likely dates back to a time when sulfite mills and sulfur-burners were more commonin the pulp and paper industry. The one section of 29 CFR 1910.261 that uses the expression dust explosion refers

to sulfur burners and sulfur-burner houses. The second standard incorporated by reference, ANSI Z33.1-1961,

corresponds to NFPA 91, which at the time was titledInstallation of Blower and Exhaust Systems for Dust, Stock,

and Vapor Removal or Conveying. Currently, NFPA 91 is titled Standard for Exhaust Systems for Air Conveying ofVapors, Gases, Mists, andNoncombustible Particulate Solids (emphasis added) and portions of the standard dealing

with combustible particulate solids has been incorporated into NFPA 654 Standard for the Prevention of Fire and

Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.

General duty clause. The general duty clause, section 5(a)(1) of the Occupational Safety and Health Act, statesthat each employer shall furnish to each of his employees employment and a place of employment which are free

from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.This clause is used to cite employers when a specific OSHA regulation does not exist for the alleged safety

violation. A search of an OSHA database of general duty clause citations including the words dust and

explosion identified over 200 citations between 1995 and 2004 [14]. The actual number of facilities cited is

somewhat lower as many of these citations are multiple citations to a single facility. It is possible that some citations

related to dust explosions are not included in this database or this search.


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0

5

10

15

20

25

30

35

40

45

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Year

Citations

Figure 2: OSHA general duty clause citations containing both the terms dust and explosion by year.

Note: A single employer received 36 citations in 1996.

Over 100 of these general duty clause citations specifically reference NFPA standards that could have been followed

to mitigate dust explosion hazards. Some of the more frequently referenced standards relevant to the pulp and paperindustry and the number of citations in which they were referenced are listed in Table III.

Table III: NFPA standards related to dust explosions that are relevant to the pulp and paper industry and

frequently referenced in OSHA general duty clause citations. Data for the period of 1995 to 2004.

Standard Title Number of Citations

Referencing Standard

NFPA 68 Guide for Venting of Deflagrations 10

NFPA 69 Standard on Explosion Prevention Systems 11

NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the

Manufacturing, Processing, and Handling of Combustible Particulate Solids

26

NFPA 664 Standard of Fires and Explosions in Wood Processing and Woodworking

Facilities

24

The data in Table III demonstrates that OSHA considers NFPA standards for the prevention and mitigation of dust

fires and explosions such as NFPA 654 and NFPA 664 to be good engineering practice that should be followed by

industry even though they are not specifically referenced in the OSHA regulations. However, both OSHA

inspectors and industrial health and safety professionals likely have a lower awareness of these standards than theywould have if they were formally incorporated into OSHA standards.


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POTENTIAL FUTURE REGULATORY AND ENFORCEMENT CHANGES

It is likely that state and local building codes that do not currently incorporate NFPA standards for the prevention

and mitigation of dust explosions will be modified to incorporate these standards. It is also possible that in the

future, OSHA may add specific regulations related to dust explosions in general industry, or more likely incorporateexisting NFPA codes. However, currently OSHA may not be inclined to create additional regulations. In another

recent CSB investigation, the CSB recommended that OSHA broaden the Process Safety Management (PSM)

regulation to include reactive chemical hazards. In response to the CSB recommendation, OSHA appeared reluctantto modify the regulation and is instead focusing on creating greater awareness to the reactive chemical hazard and

using the general duty clause where significant hazards exist [15].

Thus, the immediate impact of these recent catastrophic dust explosions may not be in changes to regulations, but

instead to greater awareness of inspectors and more aggressive enforcement of current regulations and NFPA

standards as a good engineering practice under the general duty clause. At the recent June 22, 2005 CSB public

hearing on combustible dust fire and explosions hazards, officials from two states where recent catastrophic dust

explosions occurred, described their greatly increased efforts to educate their inspectors to recognize dust explosionhazards and increased inspection of facilities likely to have dust explosion hazards.

CONCLUSIONS

Several catastrophic dust explosions have recently occurred outside of the pulp and paper industry. Because of theattention received by these recent incidents, it is expected that many industries, including the pulp and paper

industry, will see a greater focus on dust explosion hazards. Materials present in the pulp and paper industry

including paper and wood dust can constitute dust explosion hazards. Fortunately, existing NFPA standards andguidelines provide guidance to prevent and mitigate dust explosion hazards. These standards and guidelines are

being increasingly incorporated into state and local building codes. In the future, OSHA may incorporate these

standards or elements of these standards into regulations. However, the more immediate impact will likely be

increased awareness of government and insurance inspectors to dust explosion hazards when they inspect industrialfacilities.

References

1. U.S. Chemical Safety Hazard Investigation Board, Investigation Report: Dust Explosion, West Pharmaceutical

Services, Inc., Kinston, North Carolina, January 29, 2003, Report No. 2003-07-I-NC, September 2004,http://www.csb.gov/completed_investigations/docs/CSB_WestReport.pdf

2. U.S. Chemical Safety Hazard Investigation Board, Investigation Report: Combustible Dust Fire and Explosions,

CTA Acoustics, Inc. Corbin, Kentucky, February 20, 2003, Report No. 2003-09-I-KY, February 2005,

http://www.csb.gov/completed_investigations/docs/CSBFinalReportCTA.pdf3. Boyle, G.M., Dust Explosion Hazards in the Paper Industry, Paper Technology, 11(1), pp. 35-40 (1970).

4. Cocks, R. E., Recognition and Control of Dust Explosion Conditions, proceedings from the 1978 TAPPI

Engineering Conference, San Francisco, California.

5. Staples, F.J., Pulp Air Suspension Drier Causes and Prevention of Fires and Explosions, Transactions of the

Institution of Professional Engineers New Zealand, Electrical/Mechanical/Chemical Engineering Section, 12(1), pp.51-56 (1985).

6. Grandmaison, E.W., Review of the Explosion Hazard of Pulp and Paper Dust, proceedings from the 1986

TAPPI Engineering Conference, Atlanta, Georgia.

7. Guidelines for Safe Handling of Powders and Bulk Solids, Center for Chemical Process Safety, AmericanInstitute of Chemical Engineers, Page 6-7, (2005).

8. National Fire Protection Association, Report of Important Dust Explosions: a Record of Dust Explosions in the

United States and Canada since 1860, 1957.9. Beck, H., Schadenalyse von Staubexplosionen, Staub-Reinhalt. Luft, 42 pp. 118-123(1982) as reported in

Eckhoff, R.K., Dust Explosions in the Process Industries, Third Edition, pp. 22-25 (2003).

10. FM Global, Property Loss Prevention Data Sheet 7-76, Prevention and Mitigation of Combustible Dust

Explosions and Fire, Revised January 2001.11. L.G. Britton, et al., The Role of ASTM E27 Methods in Hazard Assessment Part II: Flammability and

Ignitability, Process Safety Progress, Volume 24(1), pp. 12-28, (2005).


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12. Eckhoff, R.K., Dust Explosions in the Process Industries, Third Edition, pp. 686-699 (2003).

13. NFPA Inc. One Battery March Park Quincy, Massachusetts, 02269.14. OSHA General Duty Standard Search, http://www.osha.gov/pls/imis/generalsearch.html.

15. Letter from John L. Henshaw, Assistant Secretary for Occupational Safety and Health to Carolyn W. Merritt,

Chairman of the U.S. Chemical Safety Hazard and Investigation Board, November 13, 2003.


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Dust Explosions in the

Pulp and Paper Industry

Dust Explosions in theDust Explosions in the

Pulp and Paper IndustryPulp and Paper IndustryTim MyersTim MyersExponent Failure Analysis AssociatesExponent Failure Analysis Associates

21 Strathmore Road21 Strathmore Road

Natick, Massachusetts 01760Natick, Massachusetts 01760

[email protected]@exponent.com

OutlineOutlineOutline

Recent catastrophic dust explosions inRecent catastrophic dust explosions inother industriesother industries

Basic elements of dust explosionsBasic elements of dust explosions

Characteristics of dusts present in theCharacteristics of dusts present in thepulp and paper industrypulp and paper industry

Methods for preventing and mitigatingMethods for preventing and mitigatingdust explosionsdust explosions

Possible regulatory and enforcementPossible regulatory and enforcementchangeschanges

Recent catastrophic dust explosionsRecent catastrophic dust explosionsRecent catastrophic dust explosions


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Recent catastrophic dust explosionsRecent catastrophic dust explosionsRecent catastrophic dust explosions

Year Facility State Dust Fatalities

1999 Gray Iron

CastingFoundry

Massachusetts Phenolic

Resin

3

2002 Rubber

Recycling

Facility

Mississippi Scrap Tire

Grindings

5

2003 Rubber Drug

Delivery

Products

North

Carolina

Polyethylene

Dust

6

2003 Fiberglass

Insulation

Manufacturer

Kentucky Phenolic

Resin

7

2003 Automotive

Wheel Foundry

Indiana Aluminum

Dust

1

CSB findings and recommendationsfrom recent dust explosionsCSB findings and recommendationsCSB findings and recommendationsfrom recent dust explosionsfrom recent dust explosions

FindingsFindings

Facilities did not fully comply with recognized guidelines andFacilities did not fully comply with recognized guidelines andstandards.standards.

Insurance and government inspectors did not recognize dustInsurance and government inspectors did not recognize dustexplosion hazards.explosion hazards.

OSHA has limited regulations related to dust explosionOSHA has limited regulations related to dust explosionhazards and has not adopted a comprehensive standard forhazards and has not adopted a comprehensive standard forthe prevention and mitigation of dust explosions.the prevention and mitigation of dust explosions.

RecommendationsRecommendations

Train inspectors to recognize dust explosion hazards.Train inspectors to recognize dust explosion hazards.

Incorporate dust explosion standards into local codeIncorporate dust explosion standards into local coderequirements.requirements.

Create outreach programs to educate industries about dustCreate outreach programs to educate industries about dustexplosion hazards.explosion hazards.

Effect of particle size on combustion rateEffect of particle size on combustion rateEffect of particle size on combustion rate

After Eckhoff, Dust Explosions in the Process Industries (2003)


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Elements of a Dust ExplosionElements of a Dust ExplosionElements of a Dust Explosion

Combustible dustCombustible dust

Small particle sizeSmall particle size OxidizableOxidizable

Oxidizer (typicallyOxidizer (typicallyair)air)

Ignition sourceIgnition source

Dispersion of dustDispersion of dust

ConfinementConfinement

Paper dust explosion demonstrationPaper dust explosion demonstrationPaper dust explosion demonstration

Materials frequently involved in dustexplosionsMaterials frequently involved in dustMaterials frequently involved in dustexplosionsexplosions

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

Coal Metals Other Paper/Pulp Plastics Wood

Dust Type

PercentofExplos

ions

U.S. Facilities 1900 to 1956 - NFPA Database

F.R.Germany Facilities 1965 to 1980 - Jeske and Beck Database

Facilities Insured by FM Global 1985 to 1995 - FM Global Database


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Explosion characteristics of dustsExplosion characteristics of dustsExplosion characteristics of dusts

Dust MedianParticle Size

(m)

Maximum ExplosionOverpressure (bar-g)

Kst value(bar-m/s)

Dust CloudIgnition

Temperature (C)

Dusts that May be Present in Pulp and Paper MillsCellulose Dust 51 9.3 66 500

Paper Pulp Dust 29 9.8 168

Paper Tissue Dust 54 8.6 52 540

Lignin Dust 18 8.7 208 470

Organic Dyestuff


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PreventionPreventionPrevention

Limiting the simultaneous occurrence of dust,Limiting the simultaneous occurrence of dust,oxidizer, and an ignition source will prevent aoxidizer, and an ignition source will prevent a

dust explosion.dust explosion. Dust suspension (MEC ~ 10 to 500 grams/mDust suspension (MEC ~ 10 to 500 grams/m33))

Orders of magnitude greater than breathingOrders of magnitude greater than breathingexposure limitsexposure limits

Reduces visibility to 1 to 2 metersReduces visibility to 1 to 2 meters

Oxygen (LOC ~ 5 to 15%)Oxygen (LOC ~ 5 to 15%)

Vessels can beVessels can be inertedinerted to below LOCto below LOC

Ignition SourcesIgnition Sources

Hot work, open flames, sparks, hot surfacesHot work, open flames, sparks, hot surfaces

Hazard of dust accumulationsHazard of dust accumulationsHazard of dust accumulations

Dust layers as thin as 1/32 (0.8 mm) can represent anDust layers as thin as 1/32 (0.8 mm) can represent anexplosion hazard when dispersed.explosion hazard when dispersed.

Initial explosions can disperse dust accumulationsInitial explosions can disperse dust accumulationscausing secondary explosions. Secondary explosionscausing secondary explosions. Secondary explosionscan cause small initial events to become catastrophic.can cause small initial events to become catastrophic.

Dust accumulations on elevated surfaces and withinDust accumulations on elevated surfaces and withinduct work can be especially hazardous.duct work can be especially hazardous.

Minimizing dust accumulationsMinimizing dust accumulationsMinimizing dust accumulations

Minimize escape of dust from equipment.Minimize escape of dust from equipment. Operate equipment at negative pressure.Operate equipment at negative pressure.

Maintain equipment seals.Maintain equipment seals.

Use dust collection systems in dustUse dust collection systems in dust

generation areas.generation areas. Frequent housekeeping to remove dustFrequent housekeeping to remove dust

accumulations before they reach hazardousaccumulations before they reach hazardouslevels.levels. Avoid vigorous sweeping, air hoses, and otherAvoid vigorous sweeping, air hoses, and other

methods that produce dust clouds.methods that produce dust clouds.

Do not neglect elevated surfaces or other difficultDo not neglect elevated surfaces or other difficultto reach areas.to reach areas.


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Eliminating ignition sourcesEliminating ignition sourcesEliminating ignition sources

Areas with combustible dust may be classifiedAreas with combustible dust may be classifiedas Class II or III Division 1 or 2 by OSHA andas Class II or III Division 1 or 2 by OSHA and

the National Electric Code (NEC).the National Electric Code (NEC). Classified electrical equipment should be used.Classified electrical equipment should be used.

Classified industrial trucks (fork lifts) should beClassified industrial trucks (fork lifts) should beused.used.

Eliminate other ignition sourcesEliminate other ignition sources

Sparks (friction, electrical, static electricity)Sparks (friction, electrical, static electricity)

Hot surfacesHot surfaces

Hot workHot work

Open flamesOpen flames

Mitigation of dust explosionsMitigation of dust explosionsMitigation of dust explosions

Damage limiting construction of buildingsDamage limiting construction of buildings

Strong building frameStrong building frame

Lightweight non load bearing walls or ventsLightweight non load bearing walls or vents

Explosion venting on equipment and buildingsExplosion venting on equipment and buildings

Fast acting detection and suppressionFast acting detection and suppressionequipment in vesselsequipment in vessels

Isolation devices between equipmentIsolation devices between equipment

Chokes, rotary valves, fast acting valves, flameChokes, rotary valves, fast acting valves, flamefront divertersfront diverters

Regulatory and enforcement issuesRegulatory and enforcement issuesRegulatory and enforcement issues

Many current building codes incorporate NFPA dustMany current building codes incorporate NFPA dustexplosion standards.explosion standards.

Older facilities may be based on building codes that did notOlder facilities may be based on building codes that did notadopt these NFPA standards.adopt these NFPA standards.

OSHA has not formally incorporated comprehensiveOSHA has not formally incorporated comprehensivedust explosion standards.dust explosion standards.

OSHA does cite facilities for not complying with NFPAOSHA does cite facilities for not complying with NFPAstandards asstandards as goodgood engineeringengineering practicepractice..

Current focus on dust explosions is likely to increaseCurrent focus on dust explosions is likely to increaseenforcement efforts.enforcement efforts.

Government agencies may add reference to NFPAGovernment agencies may add reference to NFPAstandards in regulations.standards in regulations.


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OSHA dust explosion citationsOSHA dust explosion citationsOSHA dust explosion citations

0

5

10

15

20

25

30

35

40

45

19 95 1 996 1 99 7 199 8 1 99 9 2 000 20 01 20 02 20 03 20 04

Year

GeneralDutyClauseCitation

s

Standards referenced in citationsStandards referenced in citationsStandards referenced in citations

Standard Title Citations

Referencing

Standard

NFPA 68 Guide for Venting of Deflagrations 10

NFPA 69 Standard on Explosion Prevention

Systems

11

NFPA 654 Standard for the Prevention of Fireand Dust Explosions from the

Manufacturing, Processing, andHandling of Combustible

Particulate Solids

26

NFPA 664 Standard of Fires and Explosions in

Wood Processing andWoodworking Facilities

24

ConclusionsConclusionsConclusions

Several recent catastrophic dust explosions haveSeveral recent catastrophic dust explosions haveincreased focus on dust explosions by governmentincreased focus on dust explosions by governmentagencies.agencies.

Dusts present in the pulp and paper industry canDusts present in the pulp and paper industry canrepresent dust fire and explosion hazards.represent dust fire and explosion hazards.

Existing standards and codes provide guidance forExisting standards and codes provide guidance forpreventing and mitigating dust explosions.preventing and mitigating dust explosions.

Facilities in the pulp and paper industry are likely toFacilities in the pulp and paper industry are likely tosee increased emphasis on dust fires and explosionssee increased emphasis on dust fires and explosionsby insurance and government inspectors.by insurance and government inspectors.

Although NFPA standards are not formallyAlthough NFPA standards are not formallyincorporated in all jurisdictions, they are recognizedincorporated in all jurisdictions, they are recognizedas good engineering practice by OSHA.as good engineering practice by OSHA.

Documents

Dust Explosions in the Pulp and Paper Industry