In this episode of the DustSafetyScience Podcast, we go over a case study involving a 2013 metal dust explosion in a 3D printing application.
3D printing and its use of combustible plastics and metal dust is a really important topic because it’s a rapidly growing industry. It was discussed in Episode #33 with Jason Reason, who talked about explosion and fire safety in 3D printing applications. Glenn Saraduke also referenced it in Episode #58.
Unfortunately, there appears to be a low level of awareness of the potential hazards involved with 3D printing. The common assumption is that everything is inerted, so why worry about explosion hazards? In this episode, we are revisiting the issue with a 2013 case study that left one worker with third-degree burns. In the process we also discuss:
- The incident background
- Five takeaways from the OSHA report
- Four points to consider for the future
Overview of the Powderpart, Inc. Explosion
The metal dust explosion occurred on November 5th, 2013, at Powderpart Inc. in Woburn, Massachusetts. According to a May 2014 OSHA news release, one worker, who was alone in the facility at the time, received third-degree burns. There was at least one 3D printer on-site that used combustible metal powder.
The release stated that the company, which faced $64,600 in penalties, failed to do the following:
- Eliminate known sources of potential ignition
- Follow equipment manufacturing guidelines
- Notify the local fire department about the workplace presence of hazardous materials
- Locate employee workstations in a place that was free from flammable powder and deflagration hazards.
In addition to the fire and explosion danger, OSHA identified serious hazards that included:
- The use of unapproved electrical equipment
- Electrical equipment and wiring that was unsuitable for hazardous locations
- Failure to train employees on chemical hazards and safeguards
- Failure to supply employees with all necessary protective clothing, equipment and training
- No documented respiratory protection program
- Failure to post danger tags on potentially explosive areas
Jeffrey Erskine, OSHA’s area director for Middlesex and Essex counties, said, “The fire and explosion hazards when working with titanium and aluminum are established, particularly when the materials are in powder form. Just as it’s easier to start a campfire with kindling than with logs, it’s easier for a metal fire to start when you’re working with metal powder that is as fine as confectioner’s sugar.”
In other words, any facility working with these materials should be expected to know about the danger involved.
Robert Hooper, OSHA’s acting regional administrator for the New England area, stated, “Establishments that use metal powders in this new technology need to scrutinize their processes and take steps to prevent and protect their employees from fire and explosion hazards that arise with these materials. The market for 3-D printed parts made from titanium and aluminum alloys includes the automotive, aerospace, defense, medical, dental and jewelry industries. Basic safety measures must be incorporated into this 21st-century technology, so that it can grow without harming the employees who are building this new industry.”
Powderpart Inc. received one willful violation of $14,000 for its failure to have Class D metal fire extinguishers in the facility, despite the need for them when titanium and aluminum were being processed. It also received nine serious violations totalling over $50,000 for the remaining hazards.
Five Takeaways from the OSHA Report
Reading through the citations, we compiled the following five takeaways.
1. The employer did not provide any ignition source control to the injured employee
Inspectors found that the sole worker was cleaning and working with the 3D printing machinery while the powder bed was open and had access to flammable oxygen levels. They also found that there weren’t controls in place, such as electrostatic discharge cables or mats.
Back in Episode #58, Glenn Saraduke talked about how critical safety is when the powder bed is open because oxygen concentration reduction has been lost. The material is no longer being inerted, so you have to be extremely careful about ignition sources and have controls in place.
2. The employer failed to provide a reliable oxidant inerting system
The OSHA report mentions that there were insufficient controls and instrumentation on the inerting system. The facility used oxygen sensors inside the system, but they didn’t have any instrumentation to monitor the argon gas.
The objective is to maintain the operation outside the flammable region. Instrumentation should have redundancy depending on the criticality of the operation. Two ways to accomplish this are:
- Providing the argon supply tank with a load cell
- Providing the argon supply tank with a reliable level sensor
The Powderpart Inc. facility did have an oxygen sensor, but that’s not enough. Under NFPA 69, the gas being used needs to be monitored and the system must be redundant.
3. The employer failed to follow equipment instructions for maintenance and cleaning
The facility had a dry dust collection system that was not emptied daily or even monthly. The citation report also stated that:
- The wet separators were not cleaned each time a different material was handled, so residual metal dust could potentially cause a thermite reaction and ignite.
- The facility did not ensure that liquid levels were maintained in the wet separator.
4. The facility layout was faulty
The report noted that a dry dust collector was located indoors and that the reverse pulse filter created a dust cloud during operation. An employee workbench was also located near a sieving station, although it contained stored powder and an unrated shop vac.
5. Fire response was faulty
There were no Class D fire extinguishers on site and no mechanism to disconnect the water sprinkler system. When water comes into contact with burning aluminum or titanium, it can create hydrogen gas and cause a hydrogen explosion.
Powderpart Inc. also failed to notify the fire department that they were using these water-reactive titanium and aluminum powders. If unsuspecting firefighters had come in and sprayed water on the flames, it could have caused a devastating explosion.
This happened during a magnesium dust fire in Eaton Rapids, Michigan, in 2018. A magnesium scrap pile caught fire and the sprinklers went off, causing a series of explosions. Workers were thrown into door jambs, resulting in serious injuries.
So what really happened on November 5th, 2013? Unfortunately, we don’t know the answer, but one line in the OSHA citation stated that the employer’s use of a water sprinkler system, coupled with its preexisting failure to disclose the presence of water-reactive titanium and aluminum alloy powders to the Woburn Fire Department, created a hydrogen explosion hazard to which its employee was exposed when a combustible dust metal fire and explosion occurred.
Four Points to Consider for the Future
Below are four main points that should be considered for safety in 3D printing and related applications.
1. Oxygen reduction or inerting systems are critical safety equipment and training is essential
It’s fine to have an inerting system in place, but what happens when you remove it to open up a 3D printer? You need ignition source control and fire-resistant clothing for workers due to the high hazard risk. During non-normal operations, is there a reliable way of measuring inerting system activity? Do employees understand the risk?
2. You need to understand what can happen when mixing water with reactive materials
The explosions are very severe and rapid. If you have materials that are mixing in dust collectors or dust vacuums, can it cause a thermite reaction? You need to understand these materials and how they react.
3. You need to involve your local fire department
If you handle water-reactive metals, you need to advise your local fire department so they know how to respond should a fire occur.
4. Understanding ignition control is essential
As we stated earlier, many people believe that in an inerted application, there is no hazard. It’s not true. The hazard is there, there is just an ignition control in place to protect you from it. If that control is removed during normal operation, other hazard controls need to be in place.
Conclusion
The Powderpart Inc. explosion illustrates many of the misconceptions about combustible metal dust hazards in 3D printing applications. Although these incidents are tragic, we can only hope that they create enough awareness to reduce the risk of repeat incidents.
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
The resources mentioned in this episode are listed below.
DustSafetyScience
Combustible Dust Incident Database
DustSafetyScience Podcast
Questions from the Community
2020 Digital Dust Safety Conference
Standards
NFPA 69
News Releases
OSHA News Release
Reports
OSHA Violation Details
Previous Episodes
DSS058: Firefighter Education in Combustible Dust Incident Response with Glen Saraduke
DSS033: Explosion and Fire Safety in 3D Printing Applications with Jason Reason
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DSS071: Case Study – Metal Dust Explosion in a 3D Printing Application in 2013
