U.K Combustible Dust Fire with Metal Dust

“The fire was on the mezzanine floor in a hopper containing metal dust"
www.miltonkeynes.co.uk

OSHA needs to look at DSEAR and ATEX and include ComDust in the universe of potentially explosive atmospheres in the rulemaking process, which also includes flammable liquids, gases, vapors, and mists. Can't continue like the present situation in the USA with ComDust as a separate entity. Until then, the US Fire Administration will continue to ignore the fire and explosion hazards of ComDust with deficient incident reporting in the National Fire Incident Reporting System NFIRS 5.0

Combustible Dust Laboratory Testing Primer

Potential combustible dust fires and explosions in the manufacturing, non-manufacturing, and utility sectors is a global problem. Across international borders the occupational safety regulatory standards for addressing combustible dust fire and explosion hazards varies. In contrast, the laboratory equipment in evaluating the hazard for ignition sensitivity and explosion severity is uniform with minor differences in methodology. For example, the 20 liter sphere is utilized worldwide in obtaining vital information on the maximum pressure and deflagration index (Kst) of combustible dust.

An excellent depiction of a dust explosion shown in the high speed video, shot at 600 frames per second, with 1 gram of custard powder dispersed in a glass tube past a hot coil ignition source. The glass tube has a volume of 1.2 litres, providing an explosive dust concentration of approximately 830 g/m3. Notice how the explosion pressure wave drives the dust ahead of it and out of the tube and debris from the explosion - mostly pieces of unburnt powder - continue to fall for some time afterwards. The second video sequence shows the same quantity of custard powder being ignited, but viewed from above. Note the thin plastic film held across the tube opening that acts as an explosion relief vent.

The catastrophic Imperial Sugar Refinery dust explosion in 2008 reminded global stakeholders how devastating industrial dust explosions can be. Measuring the explosive properties of the material being handled is, of course, the essential first step to understanding the hazard. Michael Ward of Explosion Hazard Testing in the U.K. has written an educational and very useful guide to explain combustible dust testing and what the lab results tell us in terms of explosion prevention and protection options.

The main points that the guide discusses:

• UK statistics for fire and explosion

• What a dust explosion is and the terminology involved

• What laboratory tests are available and how they are conducted

• What they tell us about the fire and explosive properties of the material

• What tests are considered mandatory under U.K. and and EU legislation

The dust testing guide can be downloaded for free here

OSHA Ventilation Standard Revise for Combustible Dust

Reviewing the recent OSHA Combustible Dust NEP status report (Figure 6) illustrates that 90% of the citations for combustible dust arose from OSHA General Industry Standards. Approximately 10% of the citations were General Duty Clause citations where a majority of examples were for ventilation such as ductwork, dust collectors, and other aspects of the dust collection system used in ventilation. (pages 7-10 of 12 page .pdf)

The current OSHA General Industry Ventilation Standard 29 CFR 1910. 94 includes elements that address dust hazards in abrasive blasting, grinding, polishing, and buffing operations. Problem is, the Ventilation Standard originates more from an industrial hygiene viewpoint, where attention is directed towards respiratory hazards such as silica sand inhaled during blasting operations. What about combustible dust fire and explosion hazards from inadequate ventilation throughout the manufacturing sector?

Local Exhaust Ventilation
A key aspect in the fire triangle in reducing the possibility of a combustible dust fire or explosion is to remove the combustible dust fuel load. Good housekeeping alone will not completely remove the dust fuel load in most manufacturing processes, so dilution ventilation or local exhaust ventilation (LEV) must be utilized. Local exhaust ventilation (LEV) is the most effective in reducing explosive combustible dust concentrations.

Local exhaust ventilation (LEV) includes four major components: exhaust hood, ductwork, fan/ motor, and dust collector. The system must be properly designed and maintained so as to prevent and mitigate possible combustible dust related fires and explosions. Many of the combustible dust related fires occur or progress into the ventilation system. So it is extremely important that spark detection/flame suppression, abort gates, and explosion ventilation be incorporated in the industrial ventilation system.

General Industry Standards
The OSHA General Industry Ventilation Standard 1910.94(a)(2)(iii), does note that for abrasive blasting, the principles set forth in the National Fire Protection Association Explosion Venting Guide, NFPA 68-1954 be adhered to. What about other manufacturing processes where flammable or explosive dust mixtures may be present? There is a disconnect in many other General Industry Standards in not addressing combustible dust hazards such as in Hazard Communication, Housekeeping, and PPE. It's odd that Powered Industrial Trucks and Hazardous (Classified) Locations General Industry Standards address combustible dust, yet the majority of other General Industry Standards do not.

A proposed separate combustible dust standard does not address the antiquated OSHA General Industry Standards where many of the standards are from an industrial hygiene standpoint that fails to comprehensively address fire and explosion hazards concerning occupational safety. The Ventilation Standards in the maritime, construction, and general industry is an excellent example of this weakness.

For example, ventilation fire hazards in spray finishing are addressed in regards to solvent vapor there is the requirement 1910.94(c)(6)(ii) to dilute solvent vapor to at least 25 percent of the lower explosive limit of the solvent being sprayed. What about minimum explosive concentrations (MEC)/lower explosive limit (LEL) for combustible dust that is captured in the industrial ventilation system that are also possible fire and explosion hazards thoughout the manufacturing sector?

Potentially Explosive Atmosphere
Until OSHA recognizes that combustible dust is a potentially explosive atmosphere like in the above example for solvent vapors there will be a weakness in the Ventilation Standards that is mostly directed towards industrial hygiene. An excellent example where our international trading partners do understand that combustible dust poses an explosive atmosphere like flammable vapors, gases, and mists is the U.K DSEAR and EU ATEX Directives

OSHA cannot continue to address Industrial Ventilation as the most important engineering controls solely from an industrial hygiene standpoint. Industrial safety is just as important and must be on the flip side of the coin. The OSHA Salt Lake Technical Center(SLTC), which edited the informative and educational OSHA Ventilation Health and Safety Topics page should know better. Especially when SLTC is conducting all the testing for combustible dust ignition sensitivity and explosion severity.

U.S. Bureau of Mines
Over two decades ago Martin Marietta Laboratories and Marcom Associates, Inc. under contract from the U.S. Bureau of Mines (USBM closed in 1995 and transferred to NIOSH in 1996), prepared an excellent 220 page document, "Dust Control Handbook For Mineral Processing." The educational content was mostly centered on respiratory hazards concerning industrial hygiene in the mineral processing industry.

Many of the excellent chapters are applicable to the design and maintenance of industrial ventilation so as to minimize combustible dust fire hazards. In addition to the resource being located on the OSHA Safety and Health Topic Silica, Crystalline pages it should be cross-referenced on the OSHA Safety and Health Topic Ventilation Additional Information page.

Conclusion
In conclusion from reviewing the OSHA Combustible Dust NEP status report it appears that too much emphasis is being directed toward the General Duty Clause. Especially when over 30 percent of the report provides examples of General Duty Clause combustible dust citations where a majority of these citations are for industrial ventilation issues. What the ComDust NEP status report failed to emphasize, was the 90% of citations arose from General Industry Standards. Powered Industrial Trucks was not even included in Figure 7 of the report. Many of these antiquated General Industry Standards have not come to terms with combustible dust fire and explosion hazards from an industrial safety standpoint.

A separate combustible dust standard will provide many with a warm and fuzzy feeling but does not address an alternative regulatory approach in revising the current General Industry Standards so as to comprehensively come to terms with the 21st century occupational safety fire and explosion hazards in the workplace.

Resources
Designing Dust Collection Systems by Gary Q. Johnson-Workplace Exposure Solutions