Probability of Occurrence

A recent dust explosion at a wood pellet mill in Germany drives home the point that global collaboration concerning combustible dust fires and explosion hazards in the workplace must be a central theme in managing the risk. Without the knowledge of probability of occurrence, a comprehensive process hazard analysis cannot be developed. The problem is in obtaining the incident data. Solely relying on news accounts will not provide global coverage. Especially when all global ComDust incidents are not reported as such.

A good start would be for the Sub-Committee of Experts on the Globally Harmonized System of Classification and Labelling of Chemicals to network with their prospective local professional associations, trade organizations, and governmental agencies. A network would enable stakeholders to share incident data, which could assist in managing the risk.

The recent OSHA ComDust ANPRM is an excellent example in obtaining an understanding of probability of occurrence, where in Table 1, national industries were listed that had previous combustible dust related fires and explosions. On an international perspective many manufacturing processes have similar process situations and process conditions. So just because a ComDust incident has not yet happened in one geographic region does not mean it will not happen in another global region with a similar manufacturing process.

A good example, are recent combustible dust explosions in Germany wood pellet mill and the earlier sugar silo explosion. Global manufacturers have similiar processes, which also includes the United States. OSHA in addition to acquiring information on probability of occurrence in the USA, which was illustrated in Table 1 of the combustible dust ANPRM, should also be aware of the global perspective. This global proactive situational awareness will assist all stakeholders in the proposed combustible dust rulemaking.

Combustible Dust Hazards Lacking in Safety Data Sheets

In the global workplace, identifying and evaluating the risk from combustible dust related fires and explosions supposedly begin with the information provided on Safety Data or Material Safety Data Sheets (SDS/MSDS). These essential documents provide essential hazard identification, information on ingredients, first aid measures, fire-fighting procedures, handling and storage information, exposure controls/personnel protection, physical and chemical properties, etc.

Yet vital combustible dust physical characteristics of ignition sensitivity and explosion severity is lacking in a majority SDS’s. So how do stakeholders manage the risk in the workplace if important fire and explosion data is lacking?

Physical Fire and Explosion Hazards
An important development in hazard communication amongst international trading partners is the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (GHS). This system provides a universal method of communicating the potential health and physical hazards that chemicals pose in the workplace, during transportation, or consumer usage of chemical products. Yet unfortunately, harmonization in communicating the physical and chemical hazards of combustible dust is also deficient in the newly implemented United Nations GHS.

Additionally a major problem arises with materials that are not chemicals, such as wood, paper, food, etc that are not included in the GHS Safety Data Sheet hazard communication protocol. How are the physical hazards of potential combustible dust related fire and explosions suppose to be communicated to the workplace from these non-chemical substances? The problem is intensified with the requirement that the raw product manufacturer or importer must provide the physical property data in the initial preparation of the SDS.

Life-cycle Hazard Awareness
This is great at the initial stage of a raw product’s lifecycle. But what about later on in the life-cycle when a product manufacturer utilizes the raw product in the production process? The production process handles the combustible particulate solid and generates combustible dust in operations such as cutting, grinding, polishing, crushing, conveying, mixing, sifting or screening of materials.

Now all of a sudden the physical properties have changed from a raw bulk product with a minimal hazard to a substance that provides a potentially explosive atmosphere under the right conditions. All that is needed for a dust explosion in addition to the basic fire triangle is a rendezvous with confinement and suspension .Understanding the parameters to initiate a combustible dust flash fire or dust explosion is where the SDS should come into the picture in managing the fire and explosion risk, but unfortunately does not.

Global Harmonization Deficiency
Back in April 2009, the USA Occupational Health and Safety Administration (OSHA) submitted a working document to the United Nations Committee of Experts on the Transport of Dangerous Goods on the Globally Harmonized System of Classification and Labeling of Chemicals. The document requested that the Sub-Committee of Experts on the Globally Harmonized System of Classification and Labelling form a conference committee in developing classification criteria for combustible dusts in the Safety Data Sheets.

Currently GHS recognizes combustible dust is a hazard by identifying dust in the SDS. Solely identifying is not sufficient enough. The global workplace needs additional information such as guidance in fire-fighting measures, exposure controls/personnel protection, handling/storage, physical and chemical properties, etc.

Explosive Atmospheres
Additionally combustible dust needs to be classified like flammable liquids and gases, which also can present an explosive atmosphere in the global workplace. In the EU, the ATEX Directives (Appareils destinés à être utilisés en ATmosphères EXplosibles) already recognizes the explosive nature of combustible dust that have the same explosive severity as vapor cloud explosions. Yet communicating the risk amongst international trading partners is another story through the GHS Safety Data Sheets.

In the United States recognition of the fire and explosion hazards from combustible dust that have the potential of an explosive atmosphere is not on the same level of awareness as the ATEX Directives in the EU. Currently in the USA, there is no occupational health and safety regulation that specifically references combustible dust in the industrial setting. In contrast there is an OSHA Grain Facility Standard that was implemented back in the 1980’s that addresses combustible dust hazards in grain mills, feed mills, etc.

Rulemaking Process
Following the catastrophic 2008 Imperial Sugar Refinery dust explosion in Port Wentworth, Georgia OSHA began taking enhanced measures in addressing combustible dust in the manufacturing workplace. Currently OSHA is in a general industry combustible dust rulemaking process. An undisclosed source says that OSHA will announce next week in the Federal Register the Advanced Notice of Proposed Rulemaking (ANPRM) where stakeholders can comment in the development of the proposed general industry regulation.

On another front, concerning hazard communication, OSHA is proposing to modify its existing Hazard Communication Standard (HCS) that includes Materiel Safety Data Sheets to conform with the United Nations’ (UN) Globally Harmonized System of Classification and Labelling of Chemicals (GHS). Two weeks ago OSHA issued its proposed rule in the Federal Register concerning harmonization of its current Hazardous Communication System with GHS and will seek comments from stakeholders for a ninety day period.

In addition to proposing to the United Nations committee that combustible dust be classified in the GHS Safety Data Sheets its also seeking comments from stakeholders in the USA whether the interim coverage of combustible dust as an unclassified hazard in the GHS SDS is sufficient in communicating the risk throughout the workplace. Hopefully stakeholders will provide OSHA with a plethora of comments on this very complex issue of combustible dust related fires and explosion in the industrial workplace.

Conclusion
Presently all global manufacturing facilities are at risk with the deficient ignition sensitivity and explosion severity information not included in the Safety Data and Material Data Sheets. The only alternative in properly managing the risk proactively would be for plant owners and managers to have their combustible dust tested for minimum ignition temperature (MIT), minimum ignition energy (MIE), minimum explosive concentration (MEC), explosion severity, volume resistivity, etc. Solely relying on physical fire and explosion hazard data in the SDS or MSDS that the raw product manufacturer or importer provided at the top of the lifecycle is an accident waiting to happen.

Resources

Classification and Labeling of Chemicals (GHS).

Working Document ComDust GHS

ATEX directive
Hazard Communication Guidance ComDust
OSHA HazCom Proposed Rule GHS