Starch
Years ago a paper mill I worked at handled starch with a vac conveying system, transporting from a railcar thru bag shaker and via screw conveyor to storage bin.
Other systems, too, for bulk starch and clay transport, but I will focus on the vacc starch system.
The mill observed required grounding and explosion-proof equipment where needed, but still had an explosion, resulting in the injury of two persons. One required brief hospitalization, as I remember.
The problem?
When a system was stopped before purging (on purpose or equipt failure), there was often some backflow of material from the line to the unloading area, resulting in a brief cloud of dust.
In the explosion case, the dust cloud drifted through a door to the adjacent outside area where a maintenance worker was cutting/welding. The "explosion" fortunately was a "flash" in a relatively open area where pressure buildup was not possible.
The mill now has warning lights to alert workers of starch being unloaded in the area, explosion avoidance training, and workers need to check for current/planned/potential unplanned dusty work conditions as part of the hotwork permit process.
No problems since. ■
Dust Explosions
Brian,
Your description of the incident sounds like a case of poor system design and management. These sorts of things should not happen if proper procedures are followed, especially when doing hot work.
I have investigated dust explosions (in a sanding system at an MDF plant). Spark extinguishing systems and venting systems were installed but did not react quickly enough because of poor maintenance. Serious damage to the baghouse structure was avoided because adequate venting area was provided. The filter bags were a total loss but the system was put back into operation quickly.
Good design is not enough. Education and training needs to be maintained to avoid complacency.
Michael Reid. ■
Re: Dust Explosions
I would agree that without any doubt maintenance and management of the installation would be key-factors for keeping the installations as well protected as they are designed for. Explosion protection starts with a mind-set, where all personel throughout the organization will need to have an understanding of the risks and implemented protection strategy.
Indeed keeping the designed measures up in good and acceptable levels of working shape is a challenge. Also explosion protection measures shal be selected such that they will likely not be effected by lack of maintenance. Or they require minimal maintenance. ■
Re: Dust Explosions
You might want to check on accidents in the coal mining and power industry. Following our observations, there is at least once a year a major coal dust explosion and fire on the north american continent and in europe each, causing major equipment and production losses, and in some cases human injuries.
Usually spilled coal dust fines are ignited by for example conveyor rollings (idlers) that have become too hot. Background cause is often a missing total dust management /engineering from the start. Direct causes are often missing dust suppression, wrong conveyor design, lacking cleaning and maintenance. ■
Re: Dust Explosions
Another example: Again, back in the 60's and before "my time" but appropriate for the subject: I was told by an old-timer (now retired, at least). A corn starch processing plant in Cedar Rapids, Iowa had a major dust explosion in the 60's resulting in catastrophic loss of life and physical assest. Again, this was related to starch conveying. I do not remember the cause, but I believe six were killed. The initial explosion was small, but due to poor housekeeping, it kicked up a secondary dust could and a huge secondary explosion. It impressed on me that this is serious stuff. It's almost more imprtant to keep the area clean to keep the possibility of secondary (tertiary) explosions remote.
I suspect that there are many more explosions in agricultural grain silos than all industrial accidents put together.
Brian ■
Dust Explosions
Dust explosions as you mentioned ara a part of life in grain elevators , some years ago in the powder and bulck show in chicago, a speacker adressed the point extensively, In some cases voltage builds up in the belt conveyors , a spark jumps to grownd at the head pulley trough the dust cloud and aprimary small explosion occurs , the bang shakes the dust from the structural parts and you have a secondaru explosion , as the dust / air mixture increases the explosion can be bigger and so on untill no mre airborne dust can be found.
I heard some corn elevators were using corn oil as dust supressing agent.
I have handled pirophoric materials in belts and pneumatic conveyors and dust explosions some times can be eliminated or at least can be reduced, trough design to a point where the equipment hardly notices the event, in some cases , product diversion and overflows are required to avoid contaminating the storage with ignited particles. The gates though need to be carefully designed,
If you can, contact PT Karakatoa Steel in INdonesia for references.
Marco ■
Re: Dust Explosions
I worked for years for Baghouse.com, and many of our clients before we came to work with them, had experienced dust explosions caused in large part because improper maintenance procedures, and general lack of regard for the danger that this kind of situation can present.
I recently authored an article on the subject on QFilter.com: http://www.qfilter.com/res/Dust-Expl...hem/detail/136
During my research I found several examples of real life incidents, that lead to loss of life, large amounts of property damage. You might find the article interesting... ■
Dust explosions
Dust explosion hazards are "frequent", but may be a phenomena that may be exagerated. I would like to invite those that have actually experienced a suspect dust explosion in a dust or bulk handling installation or equipment to share his/her experiences. What was the possible cause of the explosion ? Were any explosion preventive or protective measures in use? How effective were they ? What can be learned from the experience of few, for many others ? ■