Uncover Process Risks With a Dust Hazards Analysis

Dust incidents are a significant industry safety problem. For those working in the process industries, we have known about combustible dust hazards for decades. The coal mining sector conducted much of the earliest research on dust hazards, so there has been a wealth of information available for a very long time, but many facilities are still unaware of the dangers.

Part of the issue is that the majority of explosible dust is not historically considered hazardous in the same way as a flammable or toxic chemical; therefore, combustible dust does not get a lot of attention. Many organizations did not believe they were handling hazardous material, even if it contained dust. Facilities would say, “We're just handling flour, sugar, plastic, so that is not hazardous.”

Bottom line is, if your company works with a material that is organic, then it is most likely to be explosive. For example, metals such as aluminum and magnesium, biosolids, paper, dried blood, rubber, fertilizer, etc., are flammable or explosible.

Learnings From Incidents

Companies often fail to act despite compliance standards requirements and multiple small incidents, but it is important to remember that ignorance does not exclude liability.

Catastrophic Dust Explosion and Fire

On December 11, 1995, an explosion and fire at an industrial complex in Methuen, Massachusetts, injured 37 people and destroyed much of the facility. The fire took over twelve hours to bring under control.

They manufactured synthetic imitation fleece fabric primarily made from recycled plastic bottles and petroleum. According to OSHA incident investigators [1], the explosion was caused by an electrical spark that ignited a combustible nylon fiber dust cloud in the hopper room at the beginning of a production line. The hopper room is where the nylon fibers are applied to the cloth backing.

Prior to the 1995 explosion, managers and staff at Malden Mills did not generally understand that nylon fibers were an explosion hazard, despite reports of earlier events at the same facility indicating that the fibers were ignited by static electricity [2].

Fatal Ignition of a Wood Dust Cloud

On May 11, 2004, a dust cloud ignited at a manufacturing facility in France when two technicians were trying to put out a smoldering fire below a hydraulic press with a dry powder extinguisher [3]. As a result, one technician died and the other suffered severe burns. Production was shut down for 10 days, resulting in severe operating losses.

At the time of the incident, a 10-15 cm (4–6 inches) layer of wood dust was present. The dust layer had started to burn when the temperature climbed above 200° C. The manufacturer used the press to produce particle board by applying high pressure and heat to wood shavings/fibers mixed with resin, generating wood dust. Based on experience, it was observed that beyond a temperature of 165° C, dust particles in the vicinity ignited.

Prior combustible dust incidents were deemed of no major importance by the company and thus not reported to the French regulatory authorities. After the fatal fire, the manufacturer took steps to mitigate the risks at their source, including adequate personnel training.

What is an Explosion?

Stage 1 - Deflagration

Deflagration or fire is the propagation of a combustion zone at a speed less than the speed of sound in the unreacted medium. When we go from deflagration to detonation, we are now faster than the speed of sound. Once you get to the speed of detonation, you cannot do anything to stop it, so we need to stop it before it gets to a deflagration.

Stage 2 - Explosion

An explosion is the bursting or rupture of an enclosure or a container due to the development of internal pressure from deflagration. The container could be a piece of equipment, a room, or even the building itself.

Secondary explosions can be far more destructive than primary explosions. When you have a small explosion in, say, a 55-gallon drum, which would probably not even have explosion protection on it, what that does is shake that accumulated dust that is sitting on that 55-gallon drum on the floor around it. It also sends fire out with that shaking, causing a secondary explosion. That is when the true hazard comes.

What is a Hazard?

A hazard is defined as a chemical or physical condition that has the potential for causing harm to people, property, or the environment. These are examples of scenarios that have the potential to cause problems:

• A vessel containing a hazardous chemical
• A cylinder of toxic gas
• A tank of flammable liquid
• A vessel where combustible dust is mixed
• A drum of hazardous water
• A rotating piece of equipment

The process industries deal with all types of hazards. Hazards can lead to different types of events. How we handle those events is how we prevent hazards.

Evaluate the Hazards at Your Facility

If there is a potential to cause an explosion, a thorough Dust Hazard Analysis (DHA) should be conducted by a qualified, experienced person. A DHA study will highlight risks associated with dust and provide recommendations, including:

• Development of a program that helps in understanding the dusts and its testing
• Development of mechanisms that prevent the formation of dust layers near working areas
• Understanding if the dust storage is capable of handling all the dust produced
• Developing new mechanisms to mitigate the risk of dust explosion if the existing mechanism is not sufficient
• Reducing the ignition source around the working areas
• Making sure that the devices have continuous grounding or bonding
• Developing a holistic program to mitigate any potential scenario that may arise from the combustible dusts, etc.

Poor DHA recommendations often stem from ignoring the Hierarchy of Controls, focusing only on PPE rather than eliminating dust, and failing to prioritize actions based on risk. Effective DHAs require specific dust testing per NFPA guidelines and must address both ignition sources and explosion propagation.

Table 1 - Examples of poorly written recommendations

Questions & Answers on DHAs

Q. Does the NFPA have any requirements for how long companies have to implement changes recommended based on the DHA?

A. There are no recommendations as to the timeline of the action items. If I were going to look at it as though I am doing a revalidation in 5 years, I would want – it just says you need to do a plan as soon as possible – so if you have a plan in place and you are taking steps to accomplish some of those action items and you have them, say, on a capitol budget, and that sort of stuff, then I think that would be appropriate but there is no specific timeline that I have seen.

Q. Is a separate DHA required or recommended if you already have site PHAs in place?

A. As long as the PHA evaluated the dust hazard, that should suffice. PHAs are generally more comprehensive than what’s required for a DHA. I would stress the caveat is that the PHA looked at the dust characterization data, it looked at the safe operating ranges and considered fire flash and fire explosion hazard, then it’s the same analysis.

Q. When is a DHA recommended to be performed for a new plant of a new technology?

A. If you are asking about when in the design steps, I would say similar to when you would apply a PHA, once the detailed design is done but before the equipment has been ordered. Because if changes need to be made, you want to do that before you order the equipment.

Q. For HAZOP style DHA is there a standard list of guide words or deviations?

A. We would just use the standard ones for hi flow, low flow, high pressure, low pressure, and temperature. There might be some individual ones for things like batch operations and such but we already have those in our standard list of guide words so we don’t use anything out of the ordinary when doing a HAZOP for a dust then we would for a standard DHA.

Q. Where would I find a list of potential “What if” questions for an agricultural DHA?

A. Process Safety Office^® PSMPro™ software by our exclusive partner ioMosaic does have a list of questions for agricultural DHA, and then I would also point you towards some of the CCPS books. I don’t know if they have specific ones on agriculture, but they would have Dust Hazard Analysis checklists. The CCPS Guidelines for Combustible Dust Hazard Analysis, Publisher, Wiley (2017), has some checklists in there.

We Can Help

ioKinetic can help you meet OSHA’s process safety management regulation for PSM-covered processes, EPA Risk Management Program (RMP) Standard, NFPA 654, and other NFPA regulations hands-on or remotely. We offer a package Dust Hazard Analysis (DHA) that includes test plan development, testing and data analysis, and interpretation. Call us at 1-844-ioKinetic or send us a note to speak to an expert regarding your PHA/DHA needs.

References

[1] OSHA. "No 27074 Ignition of a wood dust cloud in a production unit." Occupational Safety and Health Administration, 11 Dec. 1995, www.osha.gov/ords/imis/accidentsearch.accident_detail?id=655530.

[2] CSB. "Combustible Dust Hazard Study." U.S. Chemical Safety and Hazard Investigation Board, Nov. 2006, www.csb.gov/assets/1/20/dust_final_report_website_11-17-06.pdf.

[3] BARPI. "No 27074 Ignition of a wood dust cloud in a production unit." ARIA, Apr. 2008, www.aria.developpement-durable.gouv.fr/wp-content/files_mf/FD_27074_AllouvilleBellefosse_2004_ang.pdf.