Combustible Dust in Grain Handling Facilities29 CFR 1910.272

This material was produced under a grant (SH22284SH1) from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does the mention of trade names, commercial products, or organization imply endorsement by the U.S. Government.

Overview of Combustible Dustin the GrainIndustry

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Overview of Combustible Dust in Industry

2. Identify the basic considerations used in a facility hazard analysis for dust; and,

3. Describe the prevention and mitigation techniques used in control of the combustible dust hazard.

Unit ObjectivesAt the conclusion of this unit

you will be able to::1. Describe several recent

dust explosions and the dust deflagration process;

“Combustible Dust in Industry. . .” - OSHA Safety and Health Information Bulletin (SHIB 07-31-2005) (download at http://www.osha.gov/dts/shib/index.html )NFPA 654

This presentation is based on

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Background

The U.S. Chemical Safety and Accident Investigation Board (CSB) and OSHA have identified these explosions as representative of a national safety problem.

This section describes and examines a series of horrific dust explosions that have occurred recently.

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US Chemical Safety Board– Found a pattern

of catastrophic dust explosions

– Recommended that OSHA take action

– MSDS sheets often fail to provide dust explosion information

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Experience in the Grain Handling Industry

In the late 1970s grain dust explosions left 59 people dead and 49 injured.

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Experience in the Grain Handling Industry

In 1987, OSHA promulgated the Grain Handling Facilities standard (29 CFR 1910.272) still in effect

Imperial Sugar CompanyPort Wentworth GA Explosion and FireFebruary 7, 200814 Deaths and Numerous serious injuries

U.S. DEPARTMENT OF LABOR Occupational Safety and Health Administration

DIRECTIVE NUMBER: CPL 03-00-008EFFECTIVE DATE: March 11, 2008

SUBJECT: Combustible Dust National Emphasis Program

This allows increase enforcement activities

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Combustible Dust ExplosionsPractice Quiz

1. A combustible dust explosion or deflagration may occur when combustible dust, an ignition

source, air or other oxidant, ______________ are present.

A. Dispersion of the dustB. ConfinementC. A and B aboveD. None of the above

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Combustible Dust ExplosionsPractice Quiz

1. A combustible dust explosion or deflagration may occur when combustible dust, an ignition

source, air or other oxidant, ______________ are present.A. Dispersion of the dust

B. ConfinementC. A and B aboveD. None of the above

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With confinement there is an explosion

Dust Explosion Requirements

• Dust is combustible.• It must be dispersed in air or another oxidant in a

concentration at or above the minimum explosible concentration (MEC).

• There is an ignition source, such as – an electrostatic discharge, – spark, – glowing ember, – hot surface, – friction heat, or – a flame

that can ignite the dispersed combustible mixture

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Combustible Dust ExplosionsPractice Quiz

2. A combustible dust explosion in a piece of equipment or area where dust has accumulated:A. May shake loose more accumulated dust

B. Damage a containment systemC. Cause one or more destructive secondary

explosionsD. All of the above

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Combustible Dust ExplosionsPractice Quiz

2. A combustible dust explosion in a piece of equipment or area where dust has accumulated:A. May shake loose more accumulated dust

B. Damage a containment systemC. Cause one or more destructive secondary

explosionsD. All of the above

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Some event disturbs the settled dust into a cloud

Dust cloud is ignited and explodes

Dust Explosion in a Work Area

Dust settles on flat surfaces

Dust

Adapted from CSB

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Dust Explosions

– damage a containment system (such as a duct, vessel, or collector).

• The additional dust dispersed into the air may cause one or more secondary explosions.

• These can be far more destructive than a primary explosion.

An initial (primary) explosion in• processing equipment or in an

area where fugitive dust has accumulated:– may shake loose more

accumulated dust; or,

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Time, msec. (Timing of actual events may vary)

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

Primary deflagration inside process equipment

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Shock wave causedby primary deflagration

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

20Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

Shock waves reflected by surfaces within the building cause accumulated dust to go into suspension

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

Dust clouds thrown in the air by the shock waves

22Time, msec.

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

Primary deflagration breaks out of the equipment enclosure - creating a source of ignition

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

Secondary deflagration ignited

24Time, msec.0 25 50 75 100 125 150 175 200 225 250 300 325

Secondary deflagration is propagated through the dust clouds

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

Secondary deflagration bursts from the building

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

Collapsed building with remaining fires

Adapted from OSHA diagrams prepared byJohn M. Cholin, P.E., FSFPE, J.M. Cholin Consultants, Inc.

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Dust Explosion Hazard

“. . .any industrial process that reduces a combustible material and some normally noncombustible materials – to a finely divided state – presents a potential for a serious fire or explosion.”

(NFPA’s Industrial Fire Hazards Handbook)

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Combustible Dust Explosions

In the past section, we discussed a series of horrific dust explosions that have occurred recently. • Common causes were

identified• How the explosions

occurred was outlined• The factors needed to

produce an explosion and the explosion process were discussed in detail.

Dust

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Particles

• In this section, particles that participate in an explosion process are discussed.

• Their characteristics are identified.

• How they form in an industrial process is outlined. Grain Dust Particles

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ParticlesPractice Quiz

1. Regarding combustible dust particles – grinding and polishing waste:

A. Hazard decreases as particle size increases.B. Hazard increases as particle size decreases.C. They produce no hazard.D. None of the above.

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ParticlesPractice Quiz

1. Regarding combustible dust particles – grinding and polishing waste:

A. Hazard decreases as particle size increases.B. Hazard increases as particle size decreases.C. They produce no hazard.D. None of the above.

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Combustible Particulate Solid

• Dusts• Fines• Fibers• Flakes• Chips• Chunks• Mixtures of any of the above

Any combustible solid material composed of distinct particles or pieces, regardless of size, shape or chemical composition

Includes

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Combustible Dust

• Dusts are just a small fraction of combustible particulate solids

• The term combustible dust does NOT encompass all hazardous particulates

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 of shape

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Particles

Size– Pellets > 2mm diameter – Granules 0.42mm - 2mm– Dust particles < 0.42mm (420

ųm)

Hazard increases as particle size decreases – Larger surface area for combustion – Fine particles may have a larger role

in dust cloud ignition and explosion propagation

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Particles

Dusts may occur in the process stream and cause a hazard, regardless of starting particle size of the material

may break into

or

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Facility Dust Hazard Assessment

In this section, the various components of a facility dust hazard assessment are discussed.

Several factors are identified as critical to the assessment:– Facility hazard analysis to

identify the potential for dust explosions

– Measures to prevent dust explosions

– Measures to mitigate the damage of dust explosions

– Training—for both prevention and mitigation

Hazard Analysis Couch

Dust

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Facility Hazard Analysis Components

Carefully identify:• Materials that can be combustible

when finely divided; • Processes which use, consume, or

produce combustible dusts;• Equipment in which dust may be

concentrated;• 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.

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Determine Applicable Standards

Identify and follow the applicable federal, state, and local laws and regulations. Some commonly applicable mandatory requirements– OSHA General Duty Clause and

Standards– The International Code Council’s

International Fire Code®– NFPA’s Uniform Fire Code®.

29 CFR 1910

– Local building codes frequently adopt NFPA dust standards by reference

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See Explosives regulations

Dust Combustibility – One Element of the Dust Explosion Pentagon

The primary factor in an analysis of these hazards is whether the dust is in fact combustible.

Determine if a dust cloud will:– Detonate– Deflagrate– Present a fire hazard– Or will Not burn or

ignite

Testing may be necessary

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See Explosives regulations

Dust Combustibility

A detonation is a combustion event that burns faster than the speed of sound:

• Not common in industry; • Not generally the problem in

an industrial dust explosion.A deflagration is a combustion

event that burns slower than the speed of sound:

• A pushing force; • The mechanism of destruction in most

combustible dust explosions.

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Dust Combustibility

Combustible dust per NFPA 654• Prior to 2006 - “Any finely divided solid material

that is 420 microns or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosion hazard when dispersed and ignited in air.”

• 2006 Edition – 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.

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Dust Combustibility vs. Health Effects

0

2.5 ug/m3 15 mg/m3

15 g/m3 1200 g/m3

Explosible Range

IHRange

Concentration 1000X

43What is wrong here?

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Other Hazard Analysis Considerations

A thorough analysis will consider all possible scenarios in which dust can be disbursed, – The normal process and – Potential failure modes

Where dust is concentrated:In equipment such as dust collectors, a

combustible mixture could be present whenever the equipment is operating.

Other locations to consider are those where dust can settle, both – in occupied areas and – in hidden concealed spaces.

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Prevention and Mitigation

• Prevention– Dust control– Ignition control

• Mitigation– Damage control

Training must be carried out for both Prevention and Mitigation

After the hazard analysis is completed, one or more of the following may be applied:

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Prevention –Dust Control

NFPA 654 - contains comprehensive guidance

Some recommendations:• Minimize the escape of dust

from process equipment or ventilation systems

• Use dust collection systems

• Utilize surfaces that minimize dust accumulation and facilitate cleaning

Spots are not raindrops

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?

NFPA 654 – guidance

• Provide access to all hidden areas to permit inspection

• Inspect for dust residues in open and hidden areas, at regular intervals

• Clean dust residues at regular intervals

Dust Control

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Dust Control

NFPA 654• Use cleaning methods

that do not generate dust clouds;

• Only use vacuum cleaners approved for dust collection;

HAZ LOC

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Dust Control

NFPA 654• Locate relief valves away

from dust hazard areas; and • Develop and implement a

hazardous dust– inspection, – testing, – housekeeping, and – control program (Written, and specifying

frequency and methods).

Dust

Clean

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Prevention – Ignition Control

NFPA 654 • Use appropriate

electrical equipment and wiring methods;

• Control static electricity, including bonding of equipment to ground;

• Control smoking, open flames, and sparks;

No!

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Ignition Control

• Separate heating systems from dusts;

• Proper use of cartridge-activated tools; and

• Adequately maintain equipment.

Hot work permit____________________________________

Grinder

Kaboom!

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Ignition ControlOther ignition

sourcesOSHA 29 CFR

1910.178 (c) regulates powered industrial trucks in dust areas Class I & II

Group D & G

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Intermediate bulk containers (IBC) –Manual dumping of

particulate matter directly into a vessel from an IBC is not permitted •Where the vessel contains a flammable mixture of gases or vapors

•Where displacement could cause a flammable atmosphere external to the vessel NFPA 654 (9.3.3)

Vessel With

Flammablemixture

Dust

Ignition Control

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Ignition Control

Intermediate bulk containers (IBC) Manual additions into a vessel containing flammable vapors through an open port or man-way are permitted in 50 lb. batches or less NFPA 654 (9.3.3)

< 50 lbs.

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Mitigation - Damage Control

• Separation of the hazard (isolate with distance);

• Segregation of the hazard (isolate with a barrier);

• Deflagration venting

• Spark and ember detection

• Explosion suppression

• Dilution with non-combustible dust

• Venting through a listed dust retention and flame arresting device

• Oxidant concentration reduction

Methods of controlling and reducing severity of an explosion

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Damage Control

NFPA 654 (10)

• Sprinkler systems; and

• The use of other specialized suppression systems.

Specialized Agents• Gaseous agents• Dry chemicals• Water spray or mist• Others

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Hazardous vertical surface accumulation

Employees need to be trained

• To recognize and prevent hazards associated with combustible dust

• In taking preventative action; and/or

• How to alert management

Training – For Both Prevention and Damage Control

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TrainingEmployees need to know • The safe work practices applicable to

their job tasks • The overall plant programs for dust

control and ignition source control• Emergency proceduresTraining must be• Before they start work• Periodically to refresh their knowledge• When reassigned • When hazards or processes change

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Training

Management’s Responsibility• Comply with the Hazard Communication Standard• Have a qualified team conduct a facility analysis (or have

one done by qualified outside persons) prior to the introduction of a hazard and

• Develop a prevention and protection/mitigation scheme tailored to the operation.

List of Chemicals

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Training

Supervisors and managers should be aware of and support the plant dust and ignition control programs.

Their training should include • identifying how they can

encourage the reporting of unsafe practices and

• facilitate abatement actions.

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Facility Dust Hazard Assessment

Gentle sweeping

only

In this section, the various components of a facility dust hazard assessment were discussed.

Several factors were identified as critical to the analysis:– Facility hazard analysis to identify

the potential for dust explosions– Measures to prevent dust

explosions– Measures to mitigate the damage of

dust explosions– Training—for both prevention and

mitigation

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Necessary training for dust explosion prevention was discussed in this section.

Training needs were identified for:– Employees– Supervisors– Managers.

Training

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Guidelines and Standards

The Dusty BIG 10 from NFPA 61 . . .Agricultural and Food Processing . . .68 . . . Venting of Deflagrations69 . . . Explosion Prevention Systems70 . . . National Electrical Code, Articles 500, 502, 50391 . . . Exhaust Systems for Air Conveying . . .484 . . .Combustible Metals499 . . . Classification of Combustible Dusts and of

Hazardous (Classified) Locations . . .654 . . .Manufacturing, Processing, and Handling of

Combustible Particulate Solids655 . . . Sulfur Fires and Explosions664 . . .Wood Processing and Woodworking Facilities

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Housekeeping Citations and Violations

– Depths presenting explosion, deflagration or other fire hazards.

– Not small amounts in isolated spots

– Representative measure-ments at several locations

– Submit sample to lab

29 CFR 1910.22 (a) Housekeeping. (1) All places of employment, passageways … and

service rooms shall be kept clean… (2) The floor of every workroom shall be maintained in a

clean…condition.”

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OSHA NEP on Housekeeping

• NFPA 654 and FM Global Data Sheet 7-76 are referenced.

• Clean immediately whenever a dust layer of 1/32-inch thickness accumulates– over a surface area of at least

5% of the floor area of the facility or any given room,

– Not to exceed 1,000 ft2

Sampling coal dust

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Include:– Overhead beams, joists,

ducts,– The tops of equipment,

and other surfaces – Even vertical surfaces if

they are dusty

OSHA NEP on Housekeeping

Rough calculations may show – surface area of bar joists is approximately 5% of the

floor area and– the equivalent surface area for steel beams can be as

high as 10%.

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OSHA NEP on Housekeeping

An idealized approach based on • Uniformity of the dust layer • Bulk density of 75 lb/ ft3, • Dust concentration of 0.35oz/ ft3, and • Dust cloud height of 10 ft.

25 Ft40 Ft

10 Ft5% of 20,000 ft2

building

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Additional Citations and Violations

Egress violations 29 CFR 1910.33-37

Where a absence of safe, convenient access to exits and exit routes is noted

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Additional Citations and Violations

Fire protection violations 29 CFR 1910.156 (fire brigades) and

1910.157 (portable fire extinguishers) where violations of these standards are found.

Where company policy requires designated employees to use fire extinguishers and others to evacuate, there are mandates for– An emergency evacuation plan,

meeting 29 CFR 1910.38 and– A fire prevention plan meeting the

requirements of 29 CFR 1910.39.

You have the right to:A safe and healthful workplace Know about hazardous chemicals Information about injuries and illnesses in your

workplace Complain or request hazard correction from

employer

Employee Rights and Responsibilities

You have the right to:TrainingAccess to Hazard exposure and medical

recordsFile a complaint with OSHAParticipate in an OSHA inspectionBe free from retaliation for exercising

safety and health rights

Employee Rights and Responsibilities

OSHA website: www.osha.gov and OSHA offices: Call or Write (800-321-OSHA)

Compliance Assistance Specialists in the area offices National Institute for Occupational Safety and Health

(NIOSH) – OSHA’s sister agencyOSHA Training Institute Education CentersDoctors, nurses, other health care providersPublic librariesOther local, community-based resources

Employee Rights and Responsibilities

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Review of Combustible Dust in Industry

2. Identify the basic considerations used in a facility hazard analysis for dust; and,

3. Describe the prevention and mitigation techniques used in control of the combustible dust hazard.

Unit Objectives

1. Describe several recent dust explosions and the dust deflagration process;

Agriculture Exemption

Enforcement Guidance for Small Farming OperationsThe Appropriations Act exempts small farming operations from enforcement of

all rules, regulations, standards or orders under the Occupational Safety and Health Act. A farming operation is exempt from all OSHA activities if it:

• Employs 10 or fewer employees currently and at all times during the last 12 months; and

• Has not had an active temporary labor camp during the proceeding 12 months.

Note: Family members of farm employers are not counted when determining the number of employees.

– Important to check with your state OSHA since there are 25 states that match or exceed this OSHA Instruction

Source: OSHA Instruction CPL 02-00-051

Disclaimers

• This material was produced under a grant (SH22284SH1) from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does the mention of trade names, commercial products, or organization imply endorsement by the U.S. Government.