Grain Handling – Dust Explosion Hazards Paul Schlumper Georgia Tech Research Institute 404-407-6797 Dust Explosion Requirements Fuel Ignition Dispersion Confinement Adapted from CSB Oxygen Dust explosion in a work area Dust Dust settles on flat surfaces Some event disturbs the settled dust into a cloud Adapted from CSB Dust cloud is ignited and explodes Dust explosions An initial (primary) explosion in • processing equipment or in an area where fugitive dust has accumulated • may shake loose more accumulated dust, or • 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 Particles and Powders Size • Pellets > 2mm diameter • Granules 0.42mm and 2mm, and • dust particles < 0.42mm (420μm) Hazard increases as particle size decreases • larger surface area for combustion • Fine particle may have a larger role in dust cloud ignition and explosion propagation. Facility Analysis Components Carefully identify: • 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. Facility Analysis Components Identify and follow the applicable federal, state, and local laws and regulations. Some commonly applicable mandatory requirements 29 CFR 1910 • OSHA General Duty Clause and Standards • The International Code Council’s International Fire Code® • NFPA’s Uniform Fire Code®. – Local building codes frequently adopt NFPA dust standards by reference Dust Combustibility The primary factor in an assessment 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 See Explosives regulations 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. Agricultural Dust per NFPA 61 • Any finely divided solid agricultural material 420 microns or smaller in diameter that presents a fire or explosion hazard when dispersed and ignited in air.” Dust Combustibility *25 watt light bulb probably can not be seen through ten feet of a combustible dust mixture What bulb ? 2 meters 40 g/m3 concentration of comb. dust suspended in air 25 watts Glass Glass What is wrong here? Electrical classification • OSHA Electrical standard (29 CFR Part 1910 Subpart S) • NFPA 70, the National Electrical Code®. • NFPA 499, . . . Classification of Combustible Dusts and of Hazardous (classified) Locations for Electrical Installations in Chemical Process Areas. Electrical Equipment Class Division Division Group II 1 2 E F G CPL 03-00-008 – National Emphasis Program “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.” NOTE: 1910.272 stipulates 1/8 inch for Grain Dust Dust Control NFPA 654 - contains comprehensive guidance Some of its recommendations: 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; Spots are not raindrops Dust Control 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 NFPA 654 – guidance • Use cleaning methods that do not generate dust clouds, if ignition sources are present; • Only use vacuum cleaners approved for dust collection; HAZ LOC Classified Electrical Ignition Control NFPA 654, identifies comprehensive guidance • Use appropriate electrical equipment and wiring methods; • Control static electricity, including bonding of equipment to ground; • Control smoking, open flames, sparks; No! Yes! Ignition Control NFPA 654 - guidance • Control mechanical sparks and friction; • Use separator devices to remove foreign materials capable of igniting combustibles from process materials; • Separate heated surfaces from dusts; Non - Magnetic rotating drum Magnetic Core Ignition Control Hot work permit NFPA 654 - guidance • Separate heating systems from dusts; _________ _________ _________ _________ • Proper use and type of industrial trucks; • Proper use of cartridge activated tools; and • Adequately maintain equipment. Kaboom! Grinder Ignition Control Other ignition sources Use appropriate Class II Electrical equipment and wiring methods where required OSHA 29 CFR 1910.178 (c) regulates powered industrial trucks in dust areas Coal handling operations must comply with OSHA 29 CFR 1910.269 Class I & II Group D & G Training Employees need to be trained • To recognize and prevent hazards associated with combustible dust • In taking preventative action, and/or • How to alert management. Hazardous vertical surface accumulation Training Management 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 scheme tailored to the operation. List of Chemicals NFPA Standards – Dust Hazards 61 Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities 68 Deflagration Venting Systems 69 Explosion Prevention Systems 70 National Electric Code 77 Static Electricity 85 Boiler and Combustion Systems 86 Ovens and Furnaces 91 Exhaust Systems NFPA Standards Electrical & Systems 484 Combustible Metals Includes Magnesium, Titanium, Zirconium, Aluminum, Tantalum and other reactive metals 499 Classification of Combustible Dust 654 manufacturing, Processing and Handling of Combustible Particulate Solids 655 Sulfur 664 Wood and more 1910.272 – Grain Handling Facilities (Promulgated in March 1988) • • • • • • • • (a) – Scope (b) – Application (c) – Definitions (d) – Emergency Action Plan (e) – Training (f) – Hot Work Permit (g) – Entry Into Grain Storage Structures (h) – Entry Into Flat Storage Structures • • • • • • • • • (i) – Contractors (j) – Housekeeping (k) – Grate Openings (l) – Filter Collectors (m) – Preventive Maintenance (n) - Grain Stream Processing Equipment (o) – Emergency Escape (p) – Continuous-Flow Bulk Raw Grain Dryers (q) – Inside Bucket Elevators Application of Standard Sections (a) – (n) Apply to all grain handling operations, such as elevators, mills, etc. Sections (o) – (q) Apply to grain elevator operations only. Hot Work Permit • Hot Work Permits • • • • Written Authorized by Employer’s Representative Meet requirements of 1910.252(a) Kept on file until completion of operations • Exceptions • Authorizing agent is present • Authorized welding shop • Authorized hot work area – outside of grain facility Contractor Information • Fire Hazards • Explosion Hazards • Safety Rules of the Facility • Emergency Action Plan Housekeeping • Housekeeping Program • Written • Establish Frequency and Methods to Reduce Accumulations: • • • • Ledges Floors Equipment Other Exposed Surfaces • Priority Housekeeping Areas, including at least the following: • Floor areas within 35 feet (10.7 m) of inside bucket elevators; • Floors of enclosed areas containing grinding equipment; • Floors of enclosed areas containing grain dryers located inside the facility. • Important: Fugitive grain dust accumulations exceeding 1/8 inch shall be removed immediately from priority housekeeping areas. Housekeeping Housekeeping • Compressed Air can be used for cleaning IF: • Machinery in area shut-down • All other potential ignition sources shut-down and/or removed. Housekeeping Housekeeping Dust Collection Systems • Fabric Dust Filter Collectors • • • • Pressure drop monitoring device Located outside of facility, OR Protected by an Explosion Suppression System, OR Protected by Fire-Resistant Construction Preventive Maintenance • Equipment: • • • • Dryers Grain Stream Processing Equip. Dust Collection Equipment Bucket Elevators • Preventative Maintenance • Regularly scheduled inspections • Mechanical • Safety Control Equipment • 1910.272(m)(1) The employer shall implement preventive maintenance procedures consisting of: • Lubrication and other appropriate maintenance • Prompt correction of: • Malfunctioning dust collection systems • Inside bucket elevator failures: • Overheated bearings and/or slipping/misaligned belts • Certified Inspection Record • LOTO Grain Stream Processing Equipment • Grain stream processing equipment shall be equipped with an effective means of removing ferrous material from the incoming grain stream. Continuous-Flow Bulk Raw Grain Dryers • All direct-heat grain dryers shall be equipped with automatic controls that: – Will shut-off the fuel supply in case of power or flame failure or interruption of air movement through the exhaust fan; and, – Will stop the grain from being fed into the dryer if excessive temperature occurs in the exhaust of the drying section. • Direct-heat grain dryers installed after March 30, 1988 shall be: – Located outside the grain elevator; or – Located in an area inside the grain elevator protected by a fire or explosion suppression system; or – Located in an area inside the grain elevator which is separated from other areas of the facility by construction having at least a one hour fire-resistance rating Inside Bucket Elevators • Bucket elevators shall not be jogged to free a choked leg. • Belts and lagging shall be conductive • < 300 Megaohms electrical resistance rating • Bucket elevators shall have a means of access to: • Head pulley area • Boot area Inside Bucket Elevators •Bearing are to be mounted external to leg casing Bearing monitoring device is required Belt monitoring Motion detection device – to indicate choking condition Belt alignment device Hazard Monitoring Devices Sample Motion Probe Located on Tail Shaft of Bucket Elevator Hazard Monitoring Devices Bearing Temperature Monitoring Sample Display Internal Hot Bearing Sensor Installed Through Grease Fitting Hazard Monitoring Devices Belt Alignment Monitoring NFPA 61 – Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities 1-Administration 2-Referenced Publications 3-Definitions 4-Construction Requirements 5-Ventilation and Venting 6-Explosion Prevention, Relief, and Venting 7-Equipment 8-Dryers 9-Heat Transfer Operations 10-Dust Control 11-Pneumatic Conveying 12-Building Fire Protection 13-Supplemental Requirements QUESTIONS?