In today’s episode of the Dust Safety Science podcast, we go over an incident update for an explosion at a bicycle parts factory in Fuxing, Taiwan.
This explosion was reported in our incident database on November 17, 2022. We knew that metal dust was involved, it occurred near the dust collection area, and three employees were seriously injured – two of them with second- and third-degree burns. The facility was described as very dusty, and the area impacted by the explosion was quite small. According to the early reports, it was about two square metres wide.
What Did the Government Report Say?
We reached out to local contacts in Taiwan to learn more and eventually received a one-page government report. It contained four sections: Summary, Cause, Prevention Measures and Business Impact.
Under Summary and Cause, there are some interesting details. This may have been an explosion in a simple enclosureless dust collector connected directly to a stationary wheel sander or wheel wire brush grinder. It appears that the system was typically used to sand or polish aluminum tubes at this bicycle manufacturing facility.
On the day when the explosion happened, they switched to grinding iron pipes. The report also suggests that grinding the ferrous iron allowed sparks to enter this dust collection system and ignite an aluminum dust cloud in the system, causing the deflagration.
Government Recommendations
The government report contained some recommendations.
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- Using wet dust collection for highly active and reactive metals.
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- Not allowing the same dust collection system to be used for grinding of different metals.
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- Creating management of change process for switching from one type of operation to another. A change from grinding aluminum tubing to grinding iron pipe would require management change evaluation.
The report offers some takeaways that we didn’t originally have. First, we now know what the base material was. Previously, it was said to involve metal dust, but now we know that aluminum was involved, and switching from grinding iron pipes may have played a role in what happened. These iron pipes may have provided the ignition source for the explosion that injured these three workers.
Concern #1: No Restriction on Collected Materials
Our team looked at NFPA 484 to see how it might apply to this scenario, and a few things stand out. Section 13.2 .3.5 says “Dust collection systems shall not be used to collect incompatible materials or other materials that might react with the conveyed metal dust or particles.”
Another statement indicates that “the collection of any other than metal the system was designed to collect is prohibited.” This was a system designed to collect aluminum, and NFPA 484 would therefore prohibit using it to collect iron.
The third statement under this restriction is that if other metals are to be collected, the modified process shall first be reviewed under management of change to ensure that the requirements of this chapter are maintained when you’re moving to those other materials.
Concern #2: Enclosureless or Integrated Filter Systems
Just from the photos, it’s hard to determine what the exact make and model of the system was. It does appear to be sort of a small enclosureless dust collector. These systems are explicitly (at least the dry type) explicitly prohibited in NFPA 484.
Section 13.2 .4.4.4.2 states that “enclosureless dry type air material separators shall be prohibited.” Another section says that self-contained dry air material separators, downdraft benches and environmental control boosts with integral filter media in the wall shall be prohibited unless complying with other stated requirements. At least within 484, enclosureless dust collection systems or these dry dust collection systems are explicitly prohibited.
Concern #3: Potential Ignition Sources
First, we are going to address the ignition source mentioned in this government report. Then we’ll talk about other types of ignition sources that may have been involved but weren’t investigated yet.
In NFPA 484 13.2 .3.6.7, it says that dust collection systems that remove material from operations that generate sparks, hot metals or similar ignition sources under normal operating conditions shall utilize a wet type air material separator unless protected from explosion, fire and sparks and isolated to prevent the propagation of flame and pressure between interconnected equipment and upstream work areas in accordance with NFPA 68 and NFPA 69. It goes on to say in the Appendix for that same statement that examples of spark-producing dust sources include but are not limited to metal grinding, polishing and cutting and sawing.
In this case, the concern is that if you have potential ignition sources that are getting sucked into a dust collection system or potentially sucked in due to dust collection system, then it needs to be a wet material or a wet-type air material separator, unless you’re providing protection for fires and explosions and isolation in this type of system. According to the incident reports that we have, neither of these were followed.
Potential for Thermite Reactions
In section 17.1. 3, which is the section on legacy metals in NFPA 484 (legacy metals are aluminum, magnesium, titanium, zirconium and a couple of other ones that they list in the standard), it says that caution shall be exercised in mixing of fines or molten metal with metal oxides like iron oxide or rust, which is what you find on on this type of pipe.
The section states that thermite reactions are extremely exothermic, and are possible between a metal and any metal oxide lower in electromotive series, which includes iron oxide, especially at elevated temperatures.
Conclusion
There isn’t a lot of information in this one-page government report. We believe that they are going to release a more detailed report. When this happens, we can review it in depth and see what lessons can be learned for the future.
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Dust Safety Share
Incidents:
Coal Dust Explosion at Railroad Facility Damages Nearby Properties
Standards
NFPA 44
NFPA 484
NFPA 68
NFPA 69.
Documents
Government Report
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