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Managing Combustible Dust in Manufacturing - My Experience in
Ontario
Paul Bozek, PEng CIH ROH
RT 215 Managing and Regulating Combustible Dust
Outline• Definition of “Combustible” Dusts• Typical hazardous processes• Typical controls and Issues (examples)• Regulatory Requirements/Guidelines and
Programs to manage the risk
Manufacturing Sites Type Typical Combustible DustsFood and Beverage Sugar, Cocoa, Flours,
Starch, hops, grains Pharmaceuticals Actives, fillers/additivesPlastics Polymer powders and
granulesRecycling/E-waste handling
many
Not a comprehensive list, just example industries
Definition of “Combustible Dust” [Pmax x (dP/dt)max]2
Explosion Severity = ------------------------------(>0.5) [Pmax x (dP/dt)max]1
[MIT x MIE x MEC]1
Ignition Sensitivity = -------------------------------(>0.2) [MIT x MIE x MEC]2
1 = Pitt Coal 2 = Subject Dust
Definition of “Combustible Dust”– “…..presents risk of fire or deflagration hazard
when suspended in air….
– Definition used to include, “<420 microns”
– Good Aspects• Not “normally present” suspended in occupied
workspaces• Min Explosive Conc. often 1000x OEL
Definition of “Combustible Dust”Problems: (in Hazard Identification)
– Parameters are size dependent!• “as is” testing vs “sieve <420 microns”
– Full testing is expensive ($3,000+)• Testing for KST alone gives only (dp/dt)max
– Moisture content, fat content affect results
– MSDS’s often silent or misleading• “as is” product may be too large to be combustible but may contain fines
that are combustible
Typical “Settled Dust” Hazards
Re-suspended Dust hazard – requires Electrical “Hazardous Location” (Class 2 Division 1 or 2).
“Settled Dust” Hazard Control
Positive press?
Maintenance
Ignition Controls
Documented Cleaning Schedule
Typical Hazardous Processes(Explosions Inside Equipment)–Silo and Container Filling–Pneumatic conveying–“Air Material Separators”• Dust Collectors• Cyclones
–Size reduction processes (eg grinding)–Sieving, Blending–Drying (eg fluidized bed)
Control: Explosion Venting
Vents may be needed in ducts or piping
Fireball hazard – Size? Where?
Alternately, “suppression”
Dust Collector :Explosion Vent - Locations
Vent duct to outdoors
“Flameless” Vent
Dust Collector – Air Discharge Location?
Directly Outside or
Inside + secondary filter + “Hazloc”
Electrical “Hazardous Locations”Drawing stamped by P.Eng
Elec equipment specs meet “Hazloc” classification?
Installation inspected by Electrical Authority?
Lift trucks rated for Hazloc?
Issues: Static Bonding OK?
Issues: Plastic Containers/Liners
Size matters – static can build-up on containers or in bulk powders during transfer
Combustible Dust Policy/Programs
–Identify, Assess Risk, Control• Recognizing its’ presence historically a problem
– Scope of Program Requirements• OH&S Act, Fire Codes, many best practice guides (NFPA)
– Change Management• A good time to review compliance/conformance• In Ontario, “Pre-Start H&S Review” requirements have
triggered good project-based reviews
Ontario: “Pre-Start H&S Review” Report Requirements – Legally required when new or modified processes• “process involves a risk of ignition or explosion that
creates a condition of imminent hazard to a person’s health or safety”• “use of a dust collector involves a risk of ignition or
explosion”
– Guidelines from Ministry and PEO for P.Eng• Scope of report goes well beyond strict compliance• Includes NFPA 68, 69, 499, 505 & ACGIH Ind Vent.
Thank You! – Acknowledgement:
Paul Bozek, PEng CIH ROH [email protected]
RT 215 Managing and Regulating Combustible Dust
