In today’s episode, we will be providing an update on the 2022 grain dryer explosion in Singapore as part of our ongoing incident update series. These shorter episodes aim to collect more information on incidents from our incident database. Our team reaches out to local authorities, fire marshals, fire departments, and other investigators to gather crucial information about incidents, allowing us to improve our ability to identify the causes of losses and enhance our response, preparation, and understanding of combustible dust incidents over time.
A preliminary investigation concluded that the dryer contained an ignition source and an accidental leak occurred due to a flaw in the explosion-proof device, resulting in a worker being burned. Although there may be some translation challenges in a report we received, it appears that the leak was caused by ineffective deflagration venting.
Our research team conducted an in-depth investigation and obtained the Workplace Safety & Health Council of Singapore’s Serious Accident & Incident Report, which includes valuable photos of the incident. The report features a closed-circuit camera recording of the flash fire as it happened and provides detailed information on what occurred and caused injury to the worker.
According to the photos, the site layout featured a circular dryer located in a moderately congested area, with a small cyclone and conveying systems nearby. A steel grating and a walking platform were situated above the dryer. The dryer was designed to heat spent grains and remove moisture, but during handling and moving, the grains generated smaller particles which were heated, creating a combustible dust cloud in the confined space of the dryer. The report suggests that this dust cloud ignited and caused the explosion.
The investigation into the ignition source revealed that spade blades were installed inside the dryer to convey and elevate the spent grains for drying. These blades were secured using lifting shackles that were not properly maintained, causing them to become loose and allowing foreign objects to enter the dryer. The report includes a photo showing one of the four-inch lifting shackles with signs of charring, indicating that it played a role in the ignition. It was hypothesized that the four materials found in the dryer could generate sparks or heat when knocked against the inner walls, serving as the ignition source for the explosion.
One key question that arose was about explosion protection. The report recommends that dust handling equipment with relief vents be safely designed to vent energy in case of a dust explosion. The vent dimensions must be adequately sized to withstand the maximum force expected during an explosion. From the photos, it appears that there was a rectangular slot vent with a large aspect ratio at the top of the dryer. The vent was ducted out of the dryer, made a 90-degree turn, and appeared to be ducted away from the catwalk and platform area above the dryer. The ducting had the same aspect ratio and made an almost 90-degree turn before going straight up around the platform area.
The photos indicate a possible rupture in the ducting emerging from the dryer, close to where the vent panel would be. It’s uncertain if there was a vent on the ducting that released or if the ducting ruptured. The design was inadequate, as it vented directly into the platform’s plates on the underside and up into the grating on the sides. The report text also supports this by stating that the relief vent “blasts it open.”
The slot vent area combined with the long, thin duct and turn was insufficient to vent the deflagration away from the platform and grating above the dryer. The report shows a bright CCTV image of the deflagration, but the employee’s location is indiscernible. The report also presents the dryer grating and platform image, but it’s unclear if it was taken just before the deflagration.
Once again, the location of the employee during the deflagration cannot be determined from the available image. Although there may be someone visible on the platform, it is difficult to confirm. The deflagration itself originates from the top of the vent duct, situated on the upper front face of the dryer. It appears to travel vertically upwards through the grating around the platform, as evidenced by the images provided. Additionally, due to the steel plate directly above the release point, the deflagration also spreads out to the sides. It is unclear whether the employee was standing on the platform or any of the grating during the incident.
It’s possible that the employee was standing off to the side or front of the dryer as the fireball engulfed the area. However, it’s a bit unusual that they only suffered an elbow burn injury from the dust deflagration. It’s possible that they were using their arm to shield themselves and were at an unfortunate distance that caused their arm to be burned. Another possibility is that molten material landed on their arm during the incident.
Several investigations have been conducted on the subject, including an academic research paper titled “Burns Due to Grain Dust Explosions,” published by Russell Baldwin and EJ Law in Volume 12, Issue number nine, pages 767 to 771 of the Journal of Trauma in 1980. The paper analyzed multiple grain dust explosions and found that the hands and face were the most frequently burned areas, with shoulders, chests, and thighs being affected in more severe cases. However, the fact that the employee in this incident only suffered burns on their elbow is peculiar and does not provide much insight into what occurred. It is possible that the employee was on the catwalk and that the grating only burned in one area or that the elbow burns were caused by some form of shielding.
In conclusion, it is uncertain whether personal protective equipment could have prevented this incident due to the limited information available.
Conclusion
This concludes our update on the grain dryer explosion. While initial information was scarce, we were able to gather details on the site layout and identify improper ducting as a possible factor in the incident. The area consisted of a congested circular dryer with a steel grating and walking platform above it. The ignition source may have been loose supports inside the dryer that became heated, causing sparks or heating during operation.
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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
Dust Explosion at Singapore Grain Facility Leaves One Worker Burned
Reports
WSH Alert
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