combustible wood dust safety 2015 nfpa 644
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Combustible Dust Safety
John NewquistDraft 8 2 2015
History of Dust ExplosionsFirst recorded dust explosion occurred in Turin, Italy back in 1785
281 combustible dust incidents in the US from 1980-2005
Resulted in 119 deaths and 718 injuries
Accidents in Industry caused by Combustible Dusts
For example, combustible sugar dust was the fuel for a massive explosion and fire that occurred Feb. 7, 2008, at the Imperial Sugar Co. plant in Port Wentworth, GA., resulting in 13 deaths and hospitalization of 40 more workers, some of whom received severe burns. Below is an illustration of the facility after the explosion.
Accidents in North Carolina caused by Combustible Dusts
Above: Courtesy U.S. Chemical Safety Investigation BoardAbove: Aerial View of explosion and fire that occurred on Jan 29, 2003, at West Pharmaceutical Services plant in Kinston, N.C
What Materials Can Form a Combustible Dust?A combustible dust explosion hazard may exist in a variety of industries, including: food (e.g., candy, sugar, spice, starch, flour, feed), grain, tobacco, plastics, wood, paper, pulp, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals (e.g., aluminum, chromium, iron, magnesium, and zinc), and fossil fuel power generation.
Above: Courtesy U.S. Chemical Safety Investigation Board, November 2003, fatal accident at an automotive parts plant explosion in the U.S. that involved aluminum dust that originated near an aluminum chip melting furnace.
Combustible Dust Events in US: 1980-2005Note: Coal mines & grain handling facilities excluded from study(Ref. U.S. Chemical Safety Board Report No. 2006-H-1)
Dust Explosion by Equipment TypeEquipment Type% of IncidentsDust Collector52Impact Equipment17Silos & Bins13Dryers & Ovens9Processing Equipment6Conveyor3
Source: FM Global Property Loss Prevention Data Sheet 7-76, Prevention andMitigation of Combustible Dust Explosion and Fire, May 2008
NFPA Dust StandardsKeyway Documents
StandardIndustryEditionNFPA 652AllNewNFPA 654All General Industry Document2013NFPA 61Food/Agricultural 2013NFPA 664Wood 2012NFPA 484Metal2012NFPA 655Sulfur2012
NFPA Dust StandardsHow-to DocumentsStandardPurposeEditionNFPA 68Explosion Venting2013NFPA 69Suppression/Isolation/Containment/Inerting2014NFPA 77Static Hazards2014NFPA 70National Electric Code 2014NFPA 499Practical Electric Classification2013
April 2014Corrigan TXFour people remain hospitalized, three in critical condition, after an explosion and fire at a Polk County plywood mill a) dust collector bags impeded the venting area of the dust collector deflagration vents. b) explosion vents releasing in the dust collector without taking measure to protect employees from the fireball pathc) dust collector vented and the deflagration traveled upstream to the sander. d) responding to a fire within the sander dust collection system without the main blower remaining in operation. e) responding to a fire within the sander dust collection system without a choke between the sander dust collector and silo leading to the briquetter.
Chemical Safety BoardFrom 2008 to 2012, The CSB board documented, 50 combustible dust accidents that led to 29 fatalities and 161 injuries.
Objectives)Identify the NFPA 654/664 Standards applicable to your dust issues.Identify three OSHA Standards cited in COMDUST NEPIdentify three questions that a plant would be asked in an OSHA COMDUST NEP inspection.
OSHAOSHA has regularly stated that NFPA standards that have not been specifically incorporated into OSHA standards or adopted by state or local jurisdictions should be considered by companies as guidance. At the same time, however, the NEP Compliance Directive instructs OSHA inspectors to consult the NFPA standards to obtain evidence of hazard recognition and feasible abatement methods to support a citation under the GDC. Consequently, companies should consult NFPAs when evaluating and mitigating potential combustible dust hazards at their facilities.
The Long and Winding Road
History of HazardsOSHA InspectionsIssuesCitationsTrends
Trend 1 Rare Events but Still OccurringTwo British Columbia sawmills - 2012Four dead and 52 injuredFines of up to $652,000These were wood dust explosions
Trend 2 OSHA NEP continuesCombustible Dust National Emphasis Program (NEP) revised March 2008CSB issues recommendations in 2005
Advanced Notice of Proposed Rulemaking (ANPRM) published October 2009Expert panel met May 2011
Possible Ignition SourcesPossible ignition sources include:Open flames and sparks (welding, industrial grinding and cutting, matches, etc.)Hot Surfaces (dryers, bearings, heaters, etc.)Heat from Mechanical ImpactsElectrical Discharges (switch and outlet activation)Electrostatic Discharges (static electricity)Smoldering or burning dustSmoking materials (cigarettes, lighters, cigars, etc.)
OSHA InspectionsOver 1000 COMDUST NEP inspections since 2008High Violations per inspections (Over 6.0/inspection)
Triggers are: Complaint or referral Media reports of fires and explosionsInspection Targeting List
~150-300 inspections in 2014
Sample Accident Jan 2009The laminate panels pass on a conveyor underneath a curing UV light. A panel jammed up underneath the UV light. The panel heated up to the point where itcharred, smoldered and eventually caught fire. The charred pieces were sucked up into the local exhaust system, where they ignited the dust collector located outside the plant. The dust collector blew up, sending a shock wave back into/through the plant.
Several overhead doors were blown off, and one of thesestruck 4 employees, injuring them.
19The company makeslaminated panels. After manufacture, the panels pass on a conveyor underneath a UV light. The heat from the UV light cures the glue in the panels.
But, this morning, a panel jammed up underneath the UV light. After a while, the panel heated up to the point where itcharred, smoldered and eventually caught fire. The charred wood were sucked up into the local exhaust system, where they ignited the dust collector located outside the plant. The dust collector blew up, sending a shock wave back into/through the plant. Several overhead doors were blown off, and one of thesestruck 4 employees, injuring them. Only one person is still in the hospital (kept for observationbecause ofblowto head).
COMDUST NEP Plant history of firesEmployers Dust Management SystemMSDSsDust AccumulationDust CollectorsVentilation SpecificationsOne liter of dust sampledPhotosInterviews Employees, Employers
Sample OSHA QuestionsWhat is the Plants Housekeeping program? Is there dust accumulation of 1/32 inch thick?Dust collectors located inside of buildings? Explosion relief venting distributed over the exterior walls of buildings and enclosures?
NFPA 654 Layer Depth Criterion Method 6.1.3Hazard is present if dust 1/32 inches thick covers 5% of room or building area up to 20,000 ft2 Up to 1000 ft2 in a building 20,000 ft2 or larger
100 feet200 feet20,000 sq. ft. Building5% or 1000 sq. ft.
40 feet50 ft1000 sq. ft. Building or Room5% or 50 sq. ft.200feet
200 feet40,000 sq. ft. Building1000sq. ft.22
The main point of the Layer Depth Criterion Method is that it indicates an amount of dust that presents a hazard. If a layer of dust with a bulk density of 75 lb/ft3 covers up to 5% of the area in rooms or buildings up to 20,000 ft2 a hazard is present. For rooms or buildings 20,000 ft2 or larger 1000 ft2 covered by dust presents a hazard. This is applied in an area of any size, for example: - In a 1000 ft2 building or room, only 50 ft2 of dust would be permitted. - In a 40,000 ft2 only 1000 ft2 of dust would be permitted, etc.
How much dust is too much?Fugitive dust outside equipment Permitted thickness NFPA 654Particulate Solids1/32 inch at 75 lbs/ft3 , adjusted for other bulk densitiesNFPA 664Wood1/8 inch assumes 20 lbs/ft3 bulk densityNFPA 484MetalsNo accumulation clean dailyNFPA 61Food +AgricultureRemove along with operations references NFPA 654OSHA GrainGrain Handling1/8 inch program and priority areas listedOSHA NEPGeneral Industry1/32 inch Refers to NFPA 654 and FM Data Sheet 7-76
Adapted from: Application of NFPA 654 . . . Samuel A. Rogers, Process Safety, 3 - 2012 23
NFPA 664 for wood and wood products permits 1/8 inch of dust. This is a layer roughly four times as thick for a dust that is roughly 20 lbs/ft3 or one fourth the density. The OSHA grain standard, 29 CFR 1910.272, also permits a layer 1/8 inch deep. The standard also requires a housekeeping program listing priority cleaning areas. Agricultural dusts are often approximately 40 lbs/ ft3 only half the 75 lbs/ft ft3 criterion, not one fourth the density.23
Sample OSHA QuestionsDoes the facility have isolation devices to prevent deflagration propagation between pieces of equipment connected by ductwork? Does the facility have an ignition control program, such as grounding and bonding?
Fire through a duct is bad
Sample OSHA QuestionsAre Vacuum cleaners used in dusty areas and approved for the hazard classification?Are separator devices to remove foreign materials used? Can tramp metal ignite combustible dusts in the dust collection systems?
Check the label for Class II
Sample OSHA QuestionsIs the exhaust from the dust collectors recycled? Does the dust collector system have spark detection and explosion/deflagration suppression systems?
Sample OSHA QuestionsAre ducts design