Combustible Dust

OrThings that go BOOM in the night

Warren Silverman MD

• In 1999, a primary explosion of natural gas in an idle power boiler followed by a secondary explosion of disturbed coal dust in the facility caused six fatalities and fourteen serious injuries in a Michigan electrical power generation facility. (See Safety and Health Information Bulletin: Potential for Natural Gas and Coal Dust Explosions in Electrical Power Generating Facilities.)

• In May 2002, an explosion occurred at Rouse Polymerics International, Inc., a rubber fabricating plant, in Vicksburg, Mississippi, which injured eleven employees, five of whom later died of severe burns. The explosion occurred when highly combustible rubber dust that had been allowed to accumulate ignited.

• On January 29, 2003, an explosion and fire destroyed the West Pharmaceutical Services plant in Kinston, North Carolina, causing six deaths, dozens of injuries, and hundreds of job losses. The facility produced rubber stoppers and other products for medical use. The fuel for the explosion was a fine plastic powder, which accumulated above a suspended ceiling over a manufacturing area at the plant and ignited.

• On February 20, 2003, an explosion and fire damaged the CTA Acoustics manufacturing plant in Corbin, Kentucky, fatally injuring seven employees. The facility produced fiberglass insulation for the automotive industry. The resin involved was a phenolic binder used in producing fiberglass mats.

• On the evening of October 29, 2003, a series of explosions severely burned three employees, one fatally, and caused property damage to the Hayes Lemmerz manufacturing plant in Huntington, Indiana. One of the severely burned men subsequently died. The Hayes Lemmerz plant manufactures cast aluminum automotive wheels, and the explosions were fueled by accumulated aluminum dust, a combustible byproduct of the wheel production process.

What are we talking about?Some terms used:

• Combustible– capable of igniting and burning

• Deflagration– combustion that propagates through a gas or

along the surface of an explosive at a rapid rate driven by the transfer of heat

– Subsonic ( propagates slower than the speed of sound)

– No additional heat source is needed to cause reaction to continue

Definitions: Combustible Dust

• A particulate (solid) which is a fire or deflagration hazard when it is airborne in air or other oxidizing medium over a range of concentrations regardless of particle size or shape

• Usually refers to, but is no restricted to particles 420μm or smaller (can pass through a US #40 standard sieve

• Usually, the finer the dust particles, the more explosive

• Different dusts of the same chemical material will have different ignitability and explosibility characteristics,– variables include particle size, shape, and moisture

content. – Additionally, these variables can change while the

material is passing through process equipment

– 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 pressures that could result in an explosion.

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

– Dust-ignitionproof. 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 suspensions of a specified dust on or in the vicinity of the enclosure.

– Dusttight. Enclosures constructed so that dust will not enter under specified test conditions.

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

– Minimum Explosible Concentration (MEC). The minimum concentration of combustible dust suspended in air, measured in mass per unit volume that will support a deflagration

The following criteria must be met before a deflagration can occur:

– The dust has to be combustible.

– The dust has to be dispersed in air or another oxidant, and the concentration of this dispersed dust is 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 that is at or above the MEC.

the following criteria must be met before an explosion can occur:

• The above criteria for deflagration must be present.

• The combustible mixture is dispersed within a confined enclosure (and the confined enclosure does not contain sufficient deflagration venting capacity to safely release the pressures) such as a vessel, storage bin, ductwork, room or building. It must be noted that a small deflagration can disturb and suspend the combustible dust, which could then serve as the fuel for a secondary (and often more damaging) deflagration or explosion.

Danger signs

• Plant History of Fires: The plant has a history of fires involving combustible dusts.

• Material Safety Data Sheets (MSDS): The MSDS may indicate that a particular dust is combustible and can cause explosions, deflagrations, or other fires. However, do not use MSDSs as a sole source of information because this information is often excluded from MSDSs.

• Dust Accumulations: 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. The 5% factor should not be used if the floor area exceeds 20,000 ft2, in which case a 1,000 ft2 layer of dust is the upper limit.

• Accumulations on overhead beams, joists, ducts, the tops of equipment, and other surfaces should be included when determining the dust coverage area. Even vertical surfaces should be included if the dust is adhering to them.

– Likely areas of dust accumulations within a plant are:

»structural members »conduit and pipe racks »cable trays »floors »above ceiling »on and around equipment (leaks around

dust collectors and ductwork.)

Fire / Explosion hazard areas

• Class I : Liquids or vapors

• Class II : Combustible Dusts

• Class III : Fibers or Flyings (often not suspended)

• Petroleum refineries, and gasoline storage and dispensing areas; • Dry cleaning plants where vapors from cleaning fluids can be

present; • Spray finishing areas; • Aircraft hangars and fuel servicing areas; and • Utility gas plants, and operations involving storage and handling

of liquified petroleum gas or natural gas.

• Grain elevators; • Flour and feed mills; • Plants that manufacture, use or store magnesium or aluminum

powders; • Producers of plastics, medicines and fireworks; • Producers of starch or candies; • Spice-grinding plants, sugar plants and cocoa plants; and • Coal preparation plants and other carbon handling or processing

areas.

• Textile mills, cotton gins; • Cotton seed mills, flax processing plants; and • Plants that shape, pulverize or cut wood and create sawdust or

flyings.

Class II Dusts

• Division 1:– Ignitable quantities of dust

normally are or may be in suspension, or conductive dust may be present

• Division 2:– Dust not normally

suspended in an ignitable concentration (but may accidentally exist). Dust layers are present.

E: Metal dusts (conductive,* and explosive)

F: Carbon dusts (some are conductive,* and all are explosive)

G: Flour, starch, grain, combustible plastic or chemical dust (explosive)

Class II locations. Class II locations are those that are

hazardous because of the presence of combustible dust.– 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.

Group F. Atmospheres containing combustible carbonaceous dusts that have more than 8 percent total entrapped volatiles or 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.

Types of Dust

• Organic– Sugar, Flour, Paper, Soap,

Dried Blood

• Wood– All varieties including

sawdust

• Metal– Aluminum, Magnesium

• Plastic Dust (additives)• Carbon Dust : Coal

Elements of Disaster

• Fuel – Combustible Dust• Ignition Source

– Friction, Heat ( conductive, convection), electrical sparks, static electric spark, heat generating activities (grinding , welding), Smoldering

• Oxygen or other oxidizing agent• Dust Dispersion causing a cloud at or above the

Minimal Explosible Concentration (MEC)• Confinement of the dust cloud

– Dust Collectors, Process Machinery

KstThe deflagration index of a dust cloud

Dust explosion class*

Kst (bar.m/s)* Characteristic* Typical material**

St 0 0 No explosion Silica

St 1 >0 and ≤ 200 Weak explosion Powdered milk, charcoal, sulfur, sugar and zinc

St 2 >200 and ≤ 300 Strong explosion Cellulose, wood flour, and poly methyl acrylate

St 3 >300 Very strong explosion

Anthraquinone, aluminum, and magnesium

Common Dusts Micron Kst ValueActivated Carbon 18 44

Aluminum Grit 41 100

Aluminum Powder 22 400

Asphalt 29 117

Barley Grain Dust 51 240

Brown Coal 41 123

Charcoal 29 117

Cotton 44 24

Magnesium 28 508

Methyl Cellulose 37 209

Milk Powder 165 90

Paper Tissue Dust 54 52

Pectin 59 162

Polyurethane 3 156

Rice Starch 18 190

Silicon 10 126

Soap 65 111

Soy Bean Flour 20 110

Sulphur 20 151

Tobacco 49 12

Toner 23 145

Wood Dust 43 102

Combustible Dust Testing

• NFPA 68 stipulates that if a dust sample is available, it must be tested.

• The standard further states that it is the responsibility of the end-user (i.e., the plant or safety engineer) to commission the required testing and report on results

Dust Testing

• Obtain dust sample and send to lab• Screening test – Inert vs. explosive• If Inert - stop• If combustible:

– Kst (defined as the deflagration index of a dust cloud, or rate of pressure rise)

– Pmax (the maximum pressure in a contained explosion). – Costs will range from around $600 for screening only to

about $1,400 for the standard battery of ASTM explosibility tests if needed

Places to collect dust samples• "High spaces" such as roof beams, open web beams, tops of pipes

and ductwork, and other horizontal surfaces located as high in the overhead as possible. Note: These are the preferred locations; however, if a means of safe access is not available, sample(s) should not be collected.

• Equipment and floors where dust has accumulated.

• The interior (i.e., bins and/or bags) of a dust collector.

• Within ductwork.

Tests run

• Percent through 40 mesh• Percent moisture content• Percent combustible material• Percent combustible dust• Metal dusts will include resistivity• Minimum explosive concentration (MEC)• Minimum ignition energy (MIE)• Class II test• Sample weight• Maximum normalized rate of pressure rise (dP/dt) – Kst Test• Minimum ignition temperature

The following information may be gathered during the course of the inspection:

• Explosion prevention and mitigation controls such as – the isolation or segregation of dust-generating processes, – building damage-limiting construction, – explosion venting for dust-processing areas; – process equipment relief process isolation and – explosion suppression

• The dimensions of the room as well as the areas of the dust accumulations of greater than 1/32-inch depth.

• The design information on the dust collection systems, along with – model numbers and serial numbers (located on the side of the equipment along with the

manufacturer and phone numbers).

– Size (volume) of dust collectors (Note: Dust collectors are referred to as "air-material separators" in NFPA 654).

– Warning signs or alerts on the equipment referencing combustible dust.

– Any sources of ignition in the area, such as welding, fork truck traffic, etc.

– Information on whether the electrical equipment in the area is designed for use in a hazardous (classified) location.

• Note: Do not open electrical boxes or disconnect electrical cords. Opening them could cause an electrical arc, especially in an area with metal dust.)

• Even if you believe your dust is inert, it should be tested since materials (ie: glue on paper, some coating applied, etc) may change the combustible nature of the material

• If your dust is found to be even slightly combustible, you will be required to use explosion venting equipment on your dust collector

• The specific results of the explosibility testing will enable your dust collection supplier to determine whether you can use a standard explosion vent; or whether the vent size, ducting and related components will need to be specially calculated and modified to ensure compliance.

• Equipment must meet NFPA guidelines

Dust Control (NFPA 654)

• Minimize the escape of dust from process equipment or ventilation systems;

• Use dust collection systems and filters; • Utilize surfaces that minimize dust accumulation and

facilitate cleaning; • 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

• Use cleaning methods that do not generate dust clouds, if ignition sources are present;

• Only use vacuum cleaners approved for dust collection;

• Locate relief valves away from dust hazard areas; and

• Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in writing with established frequency and methods).

• The OSHA ventilation standard, 29 CFR 1910.94, contains ventilation requirements for certain types of operations (such as abrasives, blasting, grinding, or buffing) which involve dusts, including combustible dusts.

• 29 CFR 1910.22(a)(1) requires employers to keep work places and other areas clean, which includes the removal of dust accumulations

• Immediate cleaning is warranted 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.

• The 5% factor should not be used if the floor area exceeds 20,000 cubic foot, in which case a 1,000 cubic foot layer of dust is the upper limit.

• Accumulations on overhead beams, joists, ducts, the tops of equipment, and other surfaces should be included when determining the dust coverage area. Even vertical surfaces should be included if the dust is adhering to them.

• 1/32 inch is about the thickness of a paper clip

Areas to look for dust

• structural members• conduit and pipe racks• cable trays• floors• above ceiling• on and around equipment (leaks around dust

collectors and ductwork.)

Ignition Control

• Use appropriate electrical equipment and wiring methods;

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

• Control smoking, open flames, and sparks; • Control mechanical sparks and friction; • Use separator devices to remove foreign materials

capable of igniting combustibles from process materials;

• .

• Separate heated surfaces from dusts; • Separate heating systems from dusts; • Proper use and type of industrial trucks; • Proper use of cartridge activated tools; and • Adequately maintain all the above equipment

Electrical Wiring

• When a dust hazard area is identified, special Class II wiring methods and equipment (such as "dust ignition-proof" and "dust-tight") must be used as required by 29 CFR 1910.307 and as detailed in NFPA 70 Article 500.

• Do not confuse Class II equipment with Class I explosion-proof equipment, as Class II addresses dust hazards, while Class I addresses gas, vapor and liquid hazards.

Damage Control

• Separation of the hazard (isolate with distance); • Segregation of the hazard (isolate with a barrier); • Deflagration venting of a building, room, or area; • Pressure relief venting for equipment; • Provision of spark/ember detection and extinguishing

systems; • Explosion protection systems (also refer to NFPA 69,

Standard on Explosion Prevention Systems); • Sprinkler systems; and • The use of other specialized suppression systems.

Training

• Workers are the first line of defense in preventing and mitigating fires and explosions.

• The people closest to the source of the hazard should be trained to recognize and prevent hazards associated with combustible dust in the plant, – they can be instrumental in recognizing unsafe conditions – taking preventative action – and/or alerting management.

• Employers with hazardous chemicals (including combustible dusts) in their workplaces are required to comply with 29 CFR 1910.1200, the Hazard Communication standard.

Documents of Interest• a. NFPA 654, Standard for the Prevention of Fires and Dust• Explosions from the Manufacturing, Processing, and Handling of• Combustible Particulate Solids.• b. NFPA 484, Standard for Combustible Metals, Metal Powders, and• Metal Dusts.• c. NFPA 664, Standard for the Prevention of Fires and Explosions in• Wood Processing and Woodworking Facilities.• c. NFPA 68, Guide for Venting of Deflagrations.• d. NFPA 85: Boiler and Combustion Systems Hazards Code• e. NFPA 69, Standard on Explosion Prevention Systems.• f. NFPA 499, Recommended Practice for the Classification of• Combustible Dusts and of Hazardous (Classified) Locations for• Electrical Installations in Chemical Process Areas.• g. FM Global Safety Data pamphlet FM 7-76

Applicable OSHA Standards• 1910.22 Housekeeping• 1910.36 Design and Construction

for Exit Routes• 1910.37 Safeguards and Features

for Exit Routes• 1910.38 Emergency Action Plans• 1910.39 Fire Prevention Plans• 1910.94 Ventilation• 1910.132 Personal Protective

Equipment• 1910.145 Specifications for

Accident Prevention Signs and Tags

• 1910.146 Permit-Required Confined Space

• 1910.157 Fire Extinguishers• 1910.165 Employee Alarm

Systems• 1910.176 Material handling• 1910.178 Powered Industrial

Trucks• 1910.26 Electrical Power

Generation• 1910.272 Grain Handling Facilities• 1910.307 Hazardous Locations• 1910.1200 Hazard

Communication

General Duty Clause

• Must have a feasible means to abate the hazard in order for OSHA to cite the General Duty Clause

• Compliance Officers are allowed to use the NFPA standards as evidence of feasible means of abatement– NFPA standards can also be used for evidence of

industry recognition of the hazard

NFPA Publications Relevant to Combustible Dust Hazard Controls

NFPA Number Title Current Edition61 Standard for the Prevention of Fires and Dust Explosions in

Agricultural and Food Processing Facilities2008

68 Guide for Venting of Deflagrations 2007

69 Standard on Explosion Prevention Systems 2008

70 National Electrical Code 2008

77 Recommended Practice on Static Electricity 2007

85 Boiler and Combustion Systems Hazards Code 2007

86 Standard for Ovens and Furnaces 2007

91 Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids

2004

484 Standard for Combustible Metals 2006

499 Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas

2008

654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

2006

655 Standard for Prevention of Sulfur Fires and Explosions 2007

664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

2007

• http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=3830– • Old Directive Number: CPL 03-00-008 – • Title: Combustible Dust National Emphasis

Program (Reissued) – • Information Date: 03/11/2008

Other Dusts

Three Primary Categories

• Respirable Dust • Inhalable Dust • Total Dust

Respirable Dust

• respirable particles Mass fraction of dust (particles) that penetrates to the unciliated airways of the lung (the alveolar region).

• Note: This fraction is represented by a cumulative log-normal curve having a median aerodynamic diameter of 4 µm, standard deviation 2 µm

• Inhalable Dust– The EPA describes inhalable dust as that size fraction of dust

which enters the body, but is trapped in the nose, throat, and upper respiratory tract. The median aerodynamic diameter of this dust is about 10 µm.

• Total Dust– Total dust includes all airborne particles, regardless of their

size or composition.

The Health Effects• Dust composition

- Chemical - Mineralogical

• Dust concentration - On a weight basis: milligrams of dust per cubic meter of air (mg/m3) - On a quantity basis: million particles per cubic foot of air (mppcf)

• Particle size and shape - The particulate size distribution within the respirable range - Fiberous or spherical

• Exposure time

Applicable OSHA Standards• General Industry (29 CFR 1910) 1910 Subpart G, Occupational health and

environmental controls – 1910.94, Ventilation

• 1910 Subpart Z, Toxic and hazardous substances – 1910.1000, Air contaminants

• Table Z-1, Limits for air contaminants • Table Z-3, Mineral dusts

• Shipyard Employment (29 CFR 1915) 1915 Subpart C, Surface preparation and preservation

– 1915.34, Mechanical paint removers • 1915 Subpart Z, Toxic and hazardous substances

– 1915.1000, Air contaminants • Construction Industry (29 CFR 1926) 1926 Subpart D, Occupational health and

environmental controls – 1926.55, Gases, vapors, fumes, dusts, and mists

• Appendix A Gases, vapors, fumes, dusts, and mists

– 1926.57, Ventilation

Pneumoconiosis• Coal workers lung(also known as "black lung" or anthracosis) -• Asbestosis • Silicosis (also known as "grinder's disease") – silica • Bauxite fibrosis - bauxite • Berylliosis – beryllium • Siderosis – iron • Byssinosis – cotton • Silicosiderosis - mixed dust containing silica and iron• Labrador Lung (found in miners in Labrador , Canada) - mixed dust

containing iron, silica and anthophyllite, a type of asbestos• Popcorn workers lung disease – Diacetyl emissions and airborne

dust from butter flavorings used in microwave popcorn production

Airborne Fungal Dusts

• Histoplasmosis• Other animal or plant based

species– Psitticosis– Coccidiomycosis– Fungal agents in wood

processing,sawmills

Hypersensitivity Pneumonitis

Type[7] Specific antigen Exposure

Bird fancier's lungAlso called bird breeder's lung,pigeon breeder's lung, and poultry worker's Lung.

Avian proteinsFeathers and bird droppings [8]

Farmer's lung

•The moldsThermophilic actinomycetes[8]

•Aspergillus species•Saccharopolyspora rectivirgula, and•Micropolyspora faeni

Moldy hay

Crack lung Crack cocaine Heavy crack smoking

Bagassosis Thermophilic actinomycetes[8]

Moldy bagasse (pressed sugarcane)

Malt worker's lung Aspergillus clavatus[8] Moldy barley

Maple bark disease Cryptostroma corticale[8] Moldy maple bark

Miller's lung Sitophilus granarius (wheat weevil)[8] Dust-contaminated grain[8]

Humidifier lung

•The bacteriaT. candidus•Bacillus subtilis•B. cereus, and Klebsiella oxytoca;•Thermophilic actinomycetes[8]

the fungi•Aureobasidium pullulans;[8]

and the amoebae•Naegleria gruberi,•Acanthamoeba polyhaga, and•Acanthamoeba castellani.

Mist generated by a machine from standing water

Mushroom worker's lung Thermophilic actinomycetes Mushroom compost

Compost lung Aspergillus Compost

Peat moss worker's lung Caused by Monocillium sp. and Penicillium citreonigrum Peat moss

Suberosis Penicillum frequentans Moldy cork dust

Japanese summer house HP Trichosporon cutaneum Damp wood and mats

Cheese-washer's lung Penicillum casei[8] or P.roqueforti Cheese casings

Metalworking fluids HP Nontuberculous Mycobacteria.

Mist from metalworking fluids.

Hot tub lung Mycobacterium avium complex Mist from hot tubs.

Mollusc shell HP Aquatic animal proteins Mollusc shell dust.

Isocyanate HP TDI, HDI, and MDI Paints, resins, and polyurethane foams.

TMA HPchemical worker's lung[8] Trimellitic anhydride[8] Plastics, resins, and

paints.Berylliosis Beryllium Electronics industry

Wine-grower's lung Botrytis cinerea mold Moldy grapes